So I always see mention of this, but I've never run across a detailed discussion of it. What does it take to 'increase gross weight' on a homebuilt? What reasons have people done this? What's the good, the bad, and the ugly about it? Is there a good reason NOT to give yourself a few extra pounds when getting all the paperwork done with the FAA (even if you're never planning on using it)?
Van's Air Force
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Increasing Gross Weight
- Thread starter zsadecki
- Start date
I'm just a lurker, but what I've been told is you can set the gross weight at whatever limit you want (within reason of course). However, as I understand the process, you just have to flight test it during phase I...so be careful what you ask for. 
I know of one guy who basically did what you're talking about. He has a limit a couple hundred pounds more than what Van's recommends. He rarely fly?s at the weight...and when he does, he realizes it's a 'different' airplane and the G-limits/stall speeds/sink rates/maneuvering speed/etc/etc are all different.
There was a pretty good discussion about this on the Lancair group (LML) (http://www.lancair.net/) about six months ago...didn't follow it intently, but what I did read was interesting.
Hope this helps.
-Jim
o=\o
I know of one guy who basically did what you're talking about. He has a limit a couple hundred pounds more than what Van's recommends. He rarely fly?s at the weight...and when he does, he realizes it's a 'different' airplane and the G-limits/stall speeds/sink rates/maneuvering speed/etc/etc are all different.
There was a pretty good discussion about this on the Lancair group (LML) (http://www.lancair.net/) about six months ago...didn't follow it intently, but what I did read was interesting.
Hope this helps.
-Jim
o=\o
Rosie
Well Known Member
zsadecki said:
I believe I know one answer you are looking for Zach...I fly an RV-6A for which I set the gross weight at 1800 lbs. Van's recommended gross weight is 1650 lbs.
When the aircraft was inspected by the FAA (2 reps no less), I presented in the Weight & Balance data (of which they kept a copy) 15 different weight scenarios including:
Gross Weight C.G (1800 lbs)
Most AFT C.G. (Gross Weight at T/O, fly to Min. Fuel)
Typical Pilot/Passenger, No Baggage
Most Forward C.G. (Heavy Pilot Wt., Full Fuel)
Most Forward C.G. (Std Pilot Wt., Full Fuel)
Etc, Etc...
For each scenario, I showed that the aircraft remained WITHIN CG.
Here's the calculation for my worst case scenario, Gross Weight CG (1800 lbs):
........................................Weight x Arm = Moment
Aircraft Empty Weight..........1138.......67.64.....76969.25
Fuel (37 gallons)..................222........70.00.... 15540.00
Pilot..................................195....... 87.40.....17043.00
Passenger..........................185........ 87.40....16169.00
Baggage.............................60......... 117.00...7020.00
...........................TOTAL...1800 lbs...............132741.25
C.G. = Moment/Weight = 73.75 inches aft of the datum
Aircraft is WITHIN CG limits
The above calculation, was computed using my weight and another MALE friend's weight, not Victoria's weight
As you can see, in a real world scenario, it would be very easy to exceed Van's recommended gross weight of 1650 lbs even though the plane will fly well within the acceptable CG range at 1800 lbs.
Now, here's the reasoning behind the 1800 lb gross weight that I (you the manufacturer) set for the gross weight;
I set the gross weight at 1800 lbs so that I will not 'bust' an FAA ramp check for being OVER GROSS WEIGHT! Oh yes, we DO get ramp-checked here in the SoCAL area but that's another story!
For every flight I make, I never worry about being over gross weight or out of CG since I know well what it takes to be out-of-limits.
What does it take to 'increase gross weight' on a homebuilt? It takes you convincing the FAA that it's safe for your aircraft!
I hope this helps answer your question
Rosie
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Thanks, Rosie... That was pretty much the answer I was looking for and expecting. I had noticed on Checkoway's weight and balance database that many people had gross listed higher than the 'recommended gross'. It made perfect sense to me why you would do that, staying legal for most any loading scenario (a.k.a. leaving room for the occasional trip with bubba and his suitcase full of canvas clothes). I figured as long as you did proper flight planning with weight and balance and didn't do any 6g turns in turbulence with bubba along for the ride, you wouldn't be comprimising your safety and there's no reason not to give yourself a high gross limit... And I'm glad to hear that there isn't any extra red tape to handle just because you're over the kit manufacturer's recommended limit!
I am now in the process of doing a recurrent airworthiness certification to increase the gross weight of an aircraft (not an RV). Basically you must provide data to show that the new gross weight is reasonable. For an RV you can take the aerobatic gross weight and extrapolate the numbers from 6 Gs to 4.4 Gs (utility catagory stds). On the RV-6 for example this comes out to about 1850 lbs. max. On the RV-6 you will find that the aft CG limit is the determining factor as you will usually hit the aft CG limit before getting to a high gross weight. Other factors are the design landing loads of the landing gear system. In other words; Yes you can change gross weight on an amateur-built aircraft, but you can't just pick a number out of the air.
Mel DAR
Mel DAR
Rick6a
Well Known Member
zsadecki said:
I just received the airworthiness certificate on my unpainted 1098 lb. RV-6A. For paperwork purposes, I set the gross weight at 1900 lbs. The veteran DAR made his own computations and went over my W&B calculations and determined that aft CG *could* be exceeded past a weight of 1815 lbs.or so. In any case, he was not adverse to accepting the 1900 lb. gross weight. I view this (rightly or wrongly) as cheap insurance against the possibility of being issued a violation for exceeding GW during some unexpected ramp check.
Rick Galati RV-6A "Darla"
robertahegy
Moderator/Tech Counselor
A good load of baggage, even under 100 lbs, and some not too hefty pilot and pax will get you very aft in the CG. Most typically set up RVs will be around 80 inches for the EWCG. Mine is 79.33 with a C/S prop, 0-360, and average equipment. My RV-7A weighed in at 1117 and I certified it for 1800. Adding a load of baggage and two average size people already gets the CG pretty near aft limits. As fuel burns off, the CG continues to go aft.
Is the biggest reason for increasing the gross to accomodate larger passengers and more baggage? If so, then everything added into those areas moves the CG aft. Counterbalance to offset these increases sure seems counterproductive. And if you are running with a light weight fixed pitch prop?
WOW!! You won't have any trouble at all keeping a nose wheel off the ground.
Roberta
Is the biggest reason for increasing the gross to accomodate larger passengers and more baggage? If so, then everything added into those areas moves the CG aft. Counterbalance to offset these increases sure seems counterproductive. And if you are running with a light weight fixed pitch prop?
WOW!! You won't have any trouble at all keeping a nose wheel off the ground.
Roberta
redbeardmark
Well Known Member
Cee-Gee
This is a very good point. The CG does move aft(in my 8A) as fuel is burned off. You might be just inside the CG limit at takeoff, but later in flight you will be aft of the CG limit.
After weighing your aircraft and before presenting your aircraft to the inspector, run through the numbers and see what is reasonable and safe for your particular aircraft. "Doing the math" is an extremely important part of prepping for the inspector and for each flight.
"Travel light... and freeze at night."
robertahegy said:
This is a very good point. The CG does move aft(in my 8A) as fuel is burned off. You might be just inside the CG limit at takeoff, but later in flight you will be aft of the CG limit.
After weighing your aircraft and before presenting your aircraft to the inspector, run through the numbers and see what is reasonable and safe for your particular aircraft. "Doing the math" is an extremely important part of prepping for the inspector and for each flight.
"Travel light... and freeze at night."
Rick6a said:
So what's this really supposed to mean, considering the last few comments about aft CG? Does the 'real' CG envelope have a sloping line near the aft/heavy corner? How do you determine this? Van's calls out contants and does not mention any change with weight. Maybe this is venturing into dangerous territory, but does the builder also get to specify C.G. limits as well? If so, could we modify the W&B envelope to allow for more aft CG at higher weights? Is this something that can be fairly easily determined, or am I gonna have to make a call to my aeronautical engineer friends from college?
robertahegy
Moderator/Tech Counselor
The CG limits are determined by the design of the aircraft. Where the wings and control surfaces are placed has to be balanced for stable flight. Regardless of the weight of an airplane, the CG limits have to be maintained for stable flight. So it is entirely concievable to increase your gross weight and not be able to utilize this increase if doing so violates the CG limits. Laws of physics will prevail. That is why it is so important to calculate your W&B under all possible conditions during the entire flight, hence, what happens to the CG as fuel is burned off. If you take off with full fuel and land with tanks near empty, you will move the CG aft. If you took off near the aft limits, when you land, you could be seriously aft.
Van's gives you these limits for their particular planes. Your EWCG establishes how various loading moves the CG forward or aft. Your arms for any given loading must be such that the CG limits are maintained. This is all very basic math in determining your W&B.
Roberta
Van's gives you these limits for their particular planes. Your EWCG establishes how various loading moves the CG forward or aft. Your arms for any given loading must be such that the CG limits are maintained. This is all very basic math in determining your W&B.
Roberta
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pierre smith
Well Known Member
Determining gross weight
Mornin' everybody. We just 'plugged' in our RV6A wings and it won't be long now
How do I go about getting a higher gross weight listed for my airplane? I've read a story or two here but do I fly it at increasingly heavier weights and document that, or do I also have to weigh the airplane and calculate the CG to back up the flights?
My ag airplane has a published gross weight and also a restricted gross weight, much higher. Someone mentioned being ramp checked and being within a higher gross weight. Info please,
Pierre
RV6A 180HP Catto 3 blade....soon....
Mornin' everybody. We just 'plugged' in our RV6A wings and it won't be long now
How do I go about getting a higher gross weight listed for my airplane? I've read a story or two here but do I fly it at increasingly heavier weights and document that, or do I also have to weigh the airplane and calculate the CG to back up the flights?
My ag airplane has a published gross weight and also a restricted gross weight, much higher. Someone mentioned being ramp checked and being within a higher gross weight. Info please,
Pierre
RV6A 180HP Catto 3 blade....soon....
gmcjetpilot
Well Known Member
How Fat can you get it.
Just kidding, but I was a structural engineer for Boeing, so I do have respect for airframe strength and loads. My comment about what ever you want is not too far off . You can write down the limits you want as the manufacture, even if it is more than Van's spec. However I also have a lot of respect for Van and his limits. They are there for a reason, a margin of safety.
With that said, to answer your question, 1800 lbs (heavy) max gross is not unreasonable for a RV-6, but with some caveats, cautions, disclaimers, explanations and limitations. Since you are the manufacture you can write down what you want, within reason, not that I think it is a good idea or saying you should do it. However here is what to consider.
Higher gross means you are affecting:
strength,
controllability and
performance.
As far as strength from Van's spec's you have an aerobatic airframe (+6/-3Gs) at 1375 lbs. If you look at the standard FAR 23 normal/utility load factor +4.4/-2 Gs, you could ratio up the aerobatic gross to determine the a "normal" gross.
1375 lbs X 6G/4.4G = 1875 lbs. (17% above standard 1600 lb gross)
The FAA allows aircraft in Alaska to exceed gross by 15%, FAR 91.323(b)(2). Why or How can they do that? They are waiving or reducing the margin of safety built into the structure. When you are increasing the gross over Van's spec you are reducing the margin of safety. You must recognize this and respect it. That means flying more conservatively. Remember you are sacrificing structural margin for more payload weight, but done with intelligence the extra risk is small if done with caution. Also what about landing weight? Those 5x5 tires are small and the model "A" nose tire is real small. I would be careful about taking off a soft field with fwd CG and heavy weights.
The other parts of the equation is control and performance. As a pro-pilot you know the difference between having the hopper full and empty.
As far as control never exceed Van's CG limit. Period. In fact stay well with in the CG and not near the limits at the "extend" gross would be advised. Also when you fly avoid the corners of the speed, performance and maneuver envelope. Also in turbulence it would be advised to fly at or below Vno, 180 mph (structural cruise). Consider reducing Vno by 1 mph for every 20 lbs over 1600 lbs gross.
As far as performance the RV has excess performance and can stand more weight, however you are correct you should document calculations or flight test results of at least the following parameters at the new gross: Stall speed, take-off/landing distance, climb rate, cruise speed/fuel burn and best glide speed. The RV is great but a RV-6 fixed pitch, high/hot airfield at gross is going to suck wind, so don't over estimate the capabilities either.
The Key is to build a light RV. The lighter the plane the better it performs, the more efficient and the better it handles.
A side note: I have only talked to max gross for normal flying, not aerobatic gross. That is the problem of building a heavy RV, you end up with a solo only aerobatic plane. Of course some justify flying above the "designed" weight by saying I will fly "light aerobatics". That is cool, since all typical aerobatics can be done at 3-3.5 Gs if you know what you are doing. However you can easily screw up and go right to 6 Gs if you are not careful or know what you are doing. A RV is an OK aerobatic plane but builds speed fast. Be careful. As I said build you RV light, especially if you want to do dual aerobatics.
Regards George (Former structures engineer for Boeing)
Great question, get this, put down what ever you want!pierre smith said:
Just kidding, but I was a structural engineer for Boeing, so I do have respect for airframe strength and loads. My comment about what ever you want is not too far off . You can write down the limits you want as the manufacture, even if it is more than Van's spec. However I also have a lot of respect for Van and his limits. They are there for a reason, a margin of safety.With that said, to answer your question, 1800 lbs (heavy) max gross is not unreasonable for a RV-6, but with some caveats, cautions, disclaimers, explanations and limitations. Since you are the manufacture you can write down what you want, within reason, not that I think it is a good idea or saying you should do it. However here is what to consider.
Higher gross means you are affecting:
strength,
controllability and
performance.
As far as strength from Van's spec's you have an aerobatic airframe (+6/-3Gs) at 1375 lbs. If you look at the standard FAR 23 normal/utility load factor +4.4/-2 Gs, you could ratio up the aerobatic gross to determine the a "normal" gross.
1375 lbs X 6G/4.4G = 1875 lbs. (17% above standard 1600 lb gross)
The FAA allows aircraft in Alaska to exceed gross by 15%, FAR 91.323(b)(2). Why or How can they do that? They are waiving or reducing the margin of safety built into the structure. When you are increasing the gross over Van's spec you are reducing the margin of safety. You must recognize this and respect it. That means flying more conservatively. Remember you are sacrificing structural margin for more payload weight, but done with intelligence the extra risk is small if done with caution. Also what about landing weight? Those 5x5 tires are small and the model "A" nose tire is real small. I would be careful about taking off a soft field with fwd CG and heavy weights.
The other parts of the equation is control and performance. As a pro-pilot you know the difference between having the hopper full and empty.
As far as control never exceed Van's CG limit. Period. In fact stay well with in the CG and not near the limits at the "extend" gross would be advised. Also when you fly avoid the corners of the speed, performance and maneuver envelope. Also in turbulence it would be advised to fly at or below Vno, 180 mph (structural cruise). Consider reducing Vno by 1 mph for every 20 lbs over 1600 lbs gross.
As far as performance the RV has excess performance and can stand more weight, however you are correct you should document calculations or flight test results of at least the following parameters at the new gross: Stall speed, take-off/landing distance, climb rate, cruise speed/fuel burn and best glide speed. The RV is great but a RV-6 fixed pitch, high/hot airfield at gross is going to suck wind, so don't over estimate the capabilities either.
The Key is to build a light RV. The lighter the plane the better it performs, the more efficient and the better it handles.
A side note: I have only talked to max gross for normal flying, not aerobatic gross. That is the problem of building a heavy RV, you end up with a solo only aerobatic plane. Of course some justify flying above the "designed" weight by saying I will fly "light aerobatics". That is cool, since all typical aerobatics can be done at 3-3.5 Gs if you know what you are doing. However you can easily screw up and go right to 6 Gs if you are not careful or know what you are doing. A RV is an OK aerobatic plane but builds speed fast. Be careful. As I said build you RV light, especially if you want to do dual aerobatics.
Regards George (Former structures engineer for Boeing)
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pierre smith
Well Known Member
Gross weights
Thanks so much George........pretty much what I expected. Since it's experimental, do I assume that categories don't apply, such as Utility/Normal, etc? The added few pounds you calculated ..1875 vs 1600 would do exactly what I need......two 175 pounders (not often) full fuel and that leaves 138# for suitcases...wonderful. That'll keep me in what amounts to the utility category but on a long trip and fuel burned off, I'll be landing under 1600#, Van's spec numbers! Great answer and a ramp check would be passed too.
Pierre
Thanks so much George........pretty much what I expected. Since it's experimental, do I assume that categories don't apply, such as Utility/Normal, etc? The added few pounds you calculated ..1875 vs 1600 would do exactly what I need......two 175 pounders (not often) full fuel and that leaves 138# for suitcases...wonderful. That'll keep me in what amounts to the utility category but on a long trip and fuel burned off, I'll be landing under 1600#, Van's spec numbers! Great answer and a ramp check would be passed too.
Pierre
briand
Well Known Member
Gross Weight More than Vans Specs?
I did a search being sure that there must have been a discussion on this topic in the past but couldn't find anytyhing.
I have seen a few RV's with a max. of 1900# even though Vans says 1800. Maybe someone (who knows how) can set up a poll.
Why do some believe theirs should be higher?
I did a search being sure that there must have been a discussion on this topic in the past but couldn't find anytyhing.
I have seen a few RV's with a max. of 1900# even though Vans says 1800. Maybe someone (who knows how) can set up a poll.
Why do some believe theirs should be higher?
Article in October issue of RV Builders Hotline
There was an interesting article on this in the October issue of RV Builders Hotline. It could be found Here:
http://home.comcast.net/~rvnewsletter/
There was an interesting article on this in the October issue of RV Builders Hotline. It could be found Here:
http://home.comcast.net/~rvnewsletter/
gmcjetpilot
Well Known Member
Higher Gross Weight and Added Fuel Revisited, by Van
Here is the article:
Two RVator issues back, I discussed the issue of modifying RVs by adding tanks and increasing the gross weight. I asked for comments, specifically reasons why builders felt qualified or justified in setting higher limits than Van's published. I got the, some of which I hadn't bargained on. They were not at all complimentary! Here are some of them, either direct quotes or generalized. I have taken the liberty to add yet more comments of my own (Unlike the Internet chat sites, I can have the last word here.)
Several persons indicated their reason for specifying a higher gross was to make sure they would not be in violation should they be a "few pounds " over factory gross the next time they are "ramp checked" by the FAA.
When was the last time that you were ramp checked for gross weight compliance? We checked the FAA dregs pertaining to ramp checks and weight compliance is not a check item!
Van's staff member said that I could list any gross weight number that I wanted.
(He said COULD, not SHOULD. ) Let's clarify the Van's aircraft position. Yes, according to FAA rules, the builder of a homebuilt airplane can specify any gross weight he chooses. While the FAA allows this freedom, Van's does not endorse any arbitrary increase in operation limitations, be it weight, speed, or G load. It is our hope that builders will respect our design expertise and testing experience for setting the limits of their individual RVs. In a certified aircraft, the pilot CAN operate in excess of the certificated (factory) gross weight, but because of FAA regulations, he MAY not do so. In a homebuilt, the pilot both CAN and MAY exceed factory limits -- giving him the freedom to be as wise or as stupid as he chooses.
Some readers found a contradiction in our position against arbitrarily adding fuel tanks and then featuring RVs which had been altered for long range "round the world flights" and the like. One respondent noticed that there were aftermarket tanks on display at the Van's booth at a major fly-in show, which could be interpreted as an endorsement.
I agree that showcasing such aircraft does seem to contradict our precautions about exceeding limits. But, as Jon Johanson and others with long-range RVs will be quick to point out, Van's never encouraged or endorsed their efforts. Rather, we cautioned them about possible consequences. I'm sure that they would also be quick to point out the extreme caution they exercised when operating so far outside the factory limits. These over-gross operations were special cases, not routine as implied by most of the 'elevated gross" homebuilts. We have in the past permitted after-market products to be displayed as courtesy, not as endorsement. We're more caution now, courtesy be damned.
Several respondents stated that they had calculated G-load strength of their airplanes based on a ratio of standard category weight relative to aerobatic gross weight to arrive a higher gross weight.
For primary structural considerations, this is basically valid, but it does not take into consideration possibly safety issues related to higher stall speed, landing gear loads etc. Just because the wing won't break because of the higher gross weight doesn't mean that other bad things can't happen.
Some find it desirable to file and fly IFR in conditions which permit VFR and need added fuel to meet IFR minimums. Example is summertime in the Eastern USA when visibility or ceilings restrict VFR to low altitudes where it is hot, humid, and bumpy.
I can't argue with the logic of that. However, that logic does not override structural, aeroelastic, and handling considerations caused by overloading or redistribution of loading.
Most of the "reasons" given involve some sort of rationalization or denial, of the limits of the airplane. They essentially say "I want to satisfy some insurance or regulatory requirement, therefore it is OK to alter factory limits." The inescapable truth is that there are consequences for any alterations of aircraft limits. these consequences may be minor or major depending on the nature and degree of that alterations. Minor consequences will probably not result in serious safety compromises during normal flight operations. But, because there are inescapable consequences which reduce the margin of safety of the aircraft, however slightly, these consequences can become serious when operating under abnormal conditions. If you are certain that you will never find yourself in abnormal conditions, congratulations! You're better than I am.
Let me repeat another primary concern about altering limits, specifically higher gross weights. that is, the effect is has on the subsequent owners and pilots of the airplane. Several builders commented that they exercised special caution when flying at elevated gross weights. That's fine, but airplanes change hands all the time and the new owner/pilot may not be as knowledgeable and accept the "penciled in" elevated gross as normal. Also, new builders may assume that since "everyone else is increasing their gross weight, then it must be OK, so I might as well do it too."
If "a little knowledge is dangerous," then NO KNOWLEDGE even more dangerous.
Here is the article:
Two RVator issues back, I discussed the issue of modifying RVs by adding tanks and increasing the gross weight. I asked for comments, specifically reasons why builders felt qualified or justified in setting higher limits than Van's published. I got the, some of which I hadn't bargained on. They were not at all complimentary! Here are some of them, either direct quotes or generalized. I have taken the liberty to add yet more comments of my own (Unlike the Internet chat sites, I can have the last word here.)
Several persons indicated their reason for specifying a higher gross was to make sure they would not be in violation should they be a "few pounds " over factory gross the next time they are "ramp checked" by the FAA.
When was the last time that you were ramp checked for gross weight compliance? We checked the FAA dregs pertaining to ramp checks and weight compliance is not a check item!
Van's staff member said that I could list any gross weight number that I wanted.
(He said COULD, not SHOULD. ) Let's clarify the Van's aircraft position. Yes, according to FAA rules, the builder of a homebuilt airplane can specify any gross weight he chooses. While the FAA allows this freedom, Van's does not endorse any arbitrary increase in operation limitations, be it weight, speed, or G load. It is our hope that builders will respect our design expertise and testing experience for setting the limits of their individual RVs. In a certified aircraft, the pilot CAN operate in excess of the certificated (factory) gross weight, but because of FAA regulations, he MAY not do so. In a homebuilt, the pilot both CAN and MAY exceed factory limits -- giving him the freedom to be as wise or as stupid as he chooses.
Some readers found a contradiction in our position against arbitrarily adding fuel tanks and then featuring RVs which had been altered for long range "round the world flights" and the like. One respondent noticed that there were aftermarket tanks on display at the Van's booth at a major fly-in show, which could be interpreted as an endorsement.
I agree that showcasing such aircraft does seem to contradict our precautions about exceeding limits. But, as Jon Johanson and others with long-range RVs will be quick to point out, Van's never encouraged or endorsed their efforts. Rather, we cautioned them about possible consequences. I'm sure that they would also be quick to point out the extreme caution they exercised when operating so far outside the factory limits. These over-gross operations were special cases, not routine as implied by most of the 'elevated gross" homebuilts. We have in the past permitted after-market products to be displayed as courtesy, not as endorsement. We're more caution now, courtesy be damned.
Several respondents stated that they had calculated G-load strength of their airplanes based on a ratio of standard category weight relative to aerobatic gross weight to arrive a higher gross weight.
For primary structural considerations, this is basically valid, but it does not take into consideration possibly safety issues related to higher stall speed, landing gear loads etc. Just because the wing won't break because of the higher gross weight doesn't mean that other bad things can't happen.
Some find it desirable to file and fly IFR in conditions which permit VFR and need added fuel to meet IFR minimums. Example is summertime in the Eastern USA when visibility or ceilings restrict VFR to low altitudes where it is hot, humid, and bumpy.
I can't argue with the logic of that. However, that logic does not override structural, aeroelastic, and handling considerations caused by overloading or redistribution of loading.
Most of the "reasons" given involve some sort of rationalization or denial, of the limits of the airplane. They essentially say "I want to satisfy some insurance or regulatory requirement, therefore it is OK to alter factory limits." The inescapable truth is that there are consequences for any alterations of aircraft limits. these consequences may be minor or major depending on the nature and degree of that alterations. Minor consequences will probably not result in serious safety compromises during normal flight operations. But, because there are inescapable consequences which reduce the margin of safety of the aircraft, however slightly, these consequences can become serious when operating under abnormal conditions. If you are certain that you will never find yourself in abnormal conditions, congratulations! You're better than I am.
Let me repeat another primary concern about altering limits, specifically higher gross weights. that is, the effect is has on the subsequent owners and pilots of the airplane. Several builders commented that they exercised special caution when flying at elevated gross weights. That's fine, but airplanes change hands all the time and the new owner/pilot may not be as knowledgeable and accept the "penciled in" elevated gross as normal. Also, new builders may assume that since "everyone else is increasing their gross weight, then it must be OK, so I might as well do it too."
If "a little knowledge is dangerous," then NO KNOWLEDGE even more dangerous.
Well said George.
Still, I would like to know how large the design margins are (in the 9A). My kids and I are all bigger/heavier (over 6'4") than the average human size Van used (180 lbs) for his calculations. It would be nice to know how safe 2 x 240 lbs people, a load of fuel, and a reasonable amt of overnight luggage really are, or are not.
Am I wrong thinking that slightly longer distances and higher speed allowances (or more power) for takeoff/landing, and maybe slightly slower cruise speeds, in rough air, are the only real factors that must be accounted for?
Still, I would like to know how large the design margins are (in the 9A). My kids and I are all bigger/heavier (over 6'4") than the average human size Van used (180 lbs) for his calculations. It would be nice to know how safe 2 x 240 lbs people, a load of fuel, and a reasonable amt of overnight luggage really are, or are not.
Am I wrong thinking that slightly longer distances and higher speed allowances (or more power) for takeoff/landing, and maybe slightly slower cruise speeds, in rough air, are the only real factors that must be accounted for?
gmcjetpilot
Well Known Member
Yea but
I hear you but I think vans point is the subtle aspect of flying smoothly, landing smoothly, not flying heavy on a gusty day, so on and so on..... rationalization, I promise to fly XYZ to mitigate the extra weight. Van is saying does the new owner REALLY understand all the implications of the extra weight?n468ac said:
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mgomez
Well Known Member
cobra said:Well said George.
Still, I would like to know how large the design margins are (in the 9A). My kids and I are all bigger/heavier (over 6'4") than the average human size Van used (180 lbs) for his calculations. It would be nice to know how safe 2 x 240 lbs people, a load of fuel, and a reasonable amt of overnight luggage really are, or are not.
Am I wrong thinking that slightly longer distances and higher speed allowances (or more power) for takeoff/landing, and maybe slightly slower cruise speeds, in rough air, are the only real factors that must be accounted for?
If your empty weight comes out to 1100 lbs, you'll be able to carry your 480 lbs of meat, 20 gal of gas, and 50 lbs of luggage and stay below the recommended 1750 lbs MGTOW. 20 gallons is good for 2 hours with reserve...not bad in a 150 kt airplane. This is assuming you are in the CG envelope, of course.
The issues with higher-than-recommended weights are more subtle than most people think, and that's why Van's is trying to encourage us to stick with what they designed for. Here are a couple:
- Gust margin...that's why small, slow, lightly wing-loaded airplanes aren't designed for (say) 2.5 gs, even though it would save on structural weight...it's too easy for them to get overstressed by a gust. By flying above the design MGTOW, you're effectively turning your 4.4 g airplane into a < 4.4 g airplane.
- Climb performance takes a big hit at higher weights, at a more-than-linear rate. Adding 10% to the weight gives you a ~15% hit in ROC.
- It's hard to "land more gently" consistently. The gear was designed for a particular weight, and exceeding it reduces the margin.
- As I alluded to above, we also need to keep the CG location in mind, not just the weight. How big a problem this is depends on where we add the higher-than-recommended weight.
Yeah, I'd like to know the design margins too. I'd also like to have the complete FEA model and the CAD files and the static load test results, but that's their proprietary data and if I were in their shoes I wouldn't share it either.
I think the two biggest problems one will have flying heavy are landing softly and flying a tail heavy airplane. The gear is designed for a specific load. If you increase the load and land hard you could collapse the gear. As the plane burns fuel the tail will get heavier and much more sensitive. Aft CG planes become even more dynamically unstable as the CG shifts even further back. Control movements will have to be well controlled. You certainly don't want to pull back quickly. Many plane crashes have happened in the past 10 years from tail heavy planes. I think one not too many years ago was a USair commuter plane flying out of Charlotte. My plane that I am building will more than likely be over the recommended weight. But my CG will not be any different than the factory RV-10. I am using a heavier engine than the IO-540 but I added another battery and moved equipment into the back. If you plan on doing alot of aft cg flying, I would start by putting as much equipment up front as possible and I would practice flying with somebody who is experienced in it. It's not fun especially in IMC.
N916K
Well Known Member
To the people that are raising the gross weight of their airplanes, I would be concerned about the moment arm you are using for your baggage compartment. If you used the Vans number instead of calculating it when you did your weight and balance, you may want to redo your weight and balance. The Vans moment arm for the baggage compartment is very far forward.
I did quite a few tests when calculating the weight and balance of my airplane. When I placed a case of oil against the back of the baggage compartment I got a moment arm of 136 inches. That is quite a big longer than the Vans number of 122 inches for an RV9.
Just something to think about.
I did quite a few tests when calculating the weight and balance of my airplane. When I placed a case of oil against the back of the baggage compartment I got a moment arm of 136 inches. That is quite a big longer than the Vans number of 122 inches for an RV9.
Just something to think about.
Kevin Horton
Well Known Member
Actually, that should be "Well said Van.", as George simply quoted the RVator article that Van wrote.cobra said:
I see nothing wrong with using a gross weight higher than Van recommends, as long as you understand that the laws of physics still apply. Wanting the wing and landing gear to be strong enough for a higher weight does not make it so.
If the weight is increased, and you want the same level of safety as at Van's recommended weight, then you need to operate the aircraft differently. Reduce the g limit. Stay off rough strips. Slow way down if the conditions are turbulent, etc.
Kevin Horton
Well Known Member
Manoeuvring speed provides protection to the structure against the effects of overload, by ensuring that the wing stalls before the limit loads are reached. If we have an aircraft that is designed to handle 6g at a weight of 1500 lb, for example, then the wing is designed to be capable of a load of 9000 lb. The faster we go, the more lift the wing can produce at the stall, and at some speed it can just produce 9000 lb - this is the manoeuvring speed if we only consider the wing. If the aircraft was lighter, and we were at the same speed as above, we could still pull to the stall - the g would be higher, but the wing could still only produce 9000 lb of lift, so it would be OK.mlw450802 said:
But, manoeuvring speed also protects other things, like engine mounts. The load on the engine mounts varies as the engine weight times the g. If the weight is decreased, manoeuvring speed decreases, to ensure that the g does not exceed the limit value.
So, if we decrease the weight below the design value, manoeuvring speed decreases, to protect the engine mount, and other similar items. But, if we increase the weight above the design value, we cannot increase manoeuvring speed, as that would subject the wing to higher loads.
Kevin Horton
Well Known Member
Yes, this is true, and this will reduce the load on things like the engine mount.mlw450802 said:
Aerobatic gross weight..
After reading the article in Kitplanes on the RV-8, I have a question. The article makes a reference to the early kits as having a max aerobatic weight of 1550, and later that was increased to 1600 lbs. with the "later model wings". How are the later model wings defined? I bought a wing kit from another builder, and it was shipped back in 2001 I believe. The man I bought it from said it was one of the first -7 wing kits shipped, and somewhere on the paperwork I remember seeing something to lead me to belive it was the 10th -7 wing kit shipped. Now, the -8 was in production prior to the -7, true?
It's all pre-punched, and the only thing I've seen that's different is 1 drawing, the ailerons, and the only physical change was in the nose rib piece where the iron pipe counterweight attaches. I think I should have the "later" wing. I know I should call Vans, and will at some point, but it's early and I'm here at the comp thinking of it now.
Thanks...
After reading the article in Kitplanes on the RV-8, I have a question. The article makes a reference to the early kits as having a max aerobatic weight of 1550, and later that was increased to 1600 lbs. with the "later model wings". How are the later model wings defined? I bought a wing kit from another builder, and it was shipped back in 2001 I believe. The man I bought it from said it was one of the first -7 wing kits shipped, and somewhere on the paperwork I remember seeing something to lead me to belive it was the 10th -7 wing kit shipped. Now, the -8 was in production prior to the -7, true?
It's all pre-punched, and the only thing I've seen that's different is 1 drawing, the ailerons, and the only physical change was in the nose rib piece where the iron pipe counterweight attaches. I think I should have the "later" wing. I know I should call Vans, and will at some point, but it's early and I'm here at the comp thinking of it now
.Thanks...
N814P
Member
Gross weight question
Well, I finished my SportAir RV Assembly class - drilled out many rivets (y'know, just to practice) and I'm back home reading my May '09 issue of KitPlanes, with my tail kit ready to start. On page 12 it was discussing Larry Simpson's performance with his Subaru engine and regarding the weight increase of the engine it says...
"To compensate for the weight of engine package - and, to be fair to the Subaru, the additional systems required aft of the firewall to support this electric-only powerplant - Simpson increased his 7A's maximum gross weight to 1950 pounds, up 150 pounds from Vans recommendations..."
Uh... how did he increase the gross weight? Isn't that pretty much fixed by design and structural strength? Can (and why would) a builder arbitrarily increase the "maximum gross weight" of his aircraft, just because he wants to? The whole thing seemed like a safety issue, but I'm no engineer. I thought I bring up the issue.
(no, I do not want to start an alternate engine discussion/debate - I just want to discuss the gross weight issue)
Thanks!!
Well, I finished my SportAir RV Assembly class - drilled out many rivets (y'know, just to practice) and I'm back home reading my May '09 issue of KitPlanes, with my tail kit ready to start. On page 12 it was discussing Larry Simpson's performance with his Subaru engine and regarding the weight increase of the engine it says...
"To compensate for the weight of engine package - and, to be fair to the Subaru, the additional systems required aft of the firewall to support this electric-only powerplant - Simpson increased his 7A's maximum gross weight to 1950 pounds, up 150 pounds from Vans recommendations..."
Uh... how did he increase the gross weight? Isn't that pretty much fixed by design and structural strength? Can (and why would) a builder arbitrarily increase the "maximum gross weight" of his aircraft, just because he wants to? The whole thing seemed like a safety issue, but I'm no engineer. I thought I bring up the issue.
(no, I do not want to start an alternate engine discussion/debate - I just want to discuss the gross weight issue)
Thanks!!
N941WR
Legacy Member
Ralph,
Since Larry is the manufacture of the plane and not Van's, he set the GW any where he wants. Of course he will have to test fly the plane at those weights.
Check Dan C's W&B web page, http://www.rvproject.com/wab/, and you will see a lot of RV's with expanded GW's.
Since Larry is the manufacture of the plane and not Van's, he set the GW any where he wants. Of course he will have to test fly the plane at those weights.
Check Dan C's W&B web page, http://www.rvproject.com/wab/, and you will see a lot of RV's with expanded GW's.
pierre smith
Well Known Member
Hi Ralph......
......If you'll do a search, you'll see this subject covered thoroughly. However,
if he sets the gross higher, then the G limits also come down with a little math. Instead of a 6G airplane at gross, he may now have a 4G airplane. Furthermore, depending on exactly where that weight is, the spin characteristics at those weights may be dangerous...maybe not.
Regards,
......If you'll do a search, you'll see this subject covered thoroughly. However,
if he sets the gross higher, then the G limits also come down with a little math. Instead of a 6G airplane at gross, he may now have a 4G airplane. Furthermore, depending on exactly where that weight is, the spin characteristics at those weights may be dangerous...maybe not.
Regards,
Just to clarify...an RV model that is approved for aerobatics is good for 6 G's at a specified aerobatic gross weight, not the normal gross weight.
The specified aerobatic gross weight (good for 6 G's) for an RV-7(A) is 1550 lbs, not the normal gross weight of 1800 lbs.
No RV model is a 6 G airplane at (normal) gross weight.
L.Adamson
Well Known Member
My 6A's gross weight is set a 1850 lbs. I've seen as high as 1950 & 2000.
Van's weights were set very conservantly back in those days. Heavier constant speed props were not even the norm. The airframe of the 6 is so strong, that it's the landing gear that's more of a limiting factor. However, the gear is along the lines of newer designs which have higher gross weights. The sixes wing structure is like a battle tank, and none have failed that I know of.
Those of us that have been around these planes for 15 years or so, know that the six is capable of much higher gross weights than the figures of 1600 & 1650. Surprisingly, even at 1850 the six is more nimble and sporty on the controls than some of the lighter new designs.
Bottom line, is that the builder sets the weight. The inspector may want to know that the aircraft is capable of this weight. But in the case of the sixes, there are many hundreds flying that prove the figures. You'll find few sixes that are set at those 1600 lb. figures. If you want more info, google this, or search here or the Matronics forums. There is a lot of info.
L.Adamson --- RV6A
Van's weights were set very conservantly back in those days. Heavier constant speed props were not even the norm. The airframe of the 6 is so strong, that it's the landing gear that's more of a limiting factor. However, the gear is along the lines of newer designs which have higher gross weights. The sixes wing structure is like a battle tank, and none have failed that I know of.
Those of us that have been around these planes for 15 years or so, know that the six is capable of much higher gross weights than the figures of 1600 & 1650. Surprisingly, even at 1850 the six is more nimble and sporty on the controls than some of the lighter new designs.
Bottom line, is that the builder sets the weight. The inspector may want to know that the aircraft is capable of this weight. But in the case of the sixes, there are many hundreds flying that prove the figures. You'll find few sixes that are set at those 1600 lb. figures. If you want more info, google this, or search here or the Matronics forums. There is a lot of info.
L.Adamson --- RV6A
Chris, we'll talk about this too. In brief, you need to import at Van's recommended Gross, no more, no less. After it's imported and flying, you can apply to Transport Canada to have it increased. Near as I can tell it will require a new climb test, and possibly a new flight test period (and possibly abbreviated to 5 hours).
I plan to attempt this on mine too, and have run a bunch of numbers to support the change. It should be acceptable to up to a normal category gross of 1800lb, and even support the request with some engineering if TC asks for it.
In brief, you need to import at Van's recommended Gross, no more, no less. After it's imported and flying, you can apply to Transport Canada to have it increased. Near as I can tell it will require a new climb test, and possibly a new flight test period (and possibly abbreviated to 5 hours).I plan to attempt this on mine too, and have run a bunch of numbers to support the change. It should be acceptable to up to a normal category gross of 1800lb, and even support the request with some engineering if TC asks for it.
Flying Scotsman
Well Known Member
Reading all of this, it sure seems to me that there's no systematic approach to setting max gross weight benig put forth. I see a lot of numbers thrown out (1800, 1900, 1950, 2000, etc.), and some excellent discussions of CG limits, and some talk about Va ranges, etc. But the numbers just seem arbitrary. What's special about Van's figures + 100 pounds?
So let's imagine you've got a brand new plane, from a brand new design, that you developed all by yourself, and there is no Van's to give you a number from which to start.
How would you determine the correct max GW?
If you know that, then couldn't you do the same for an RV? No more "Van's + 100*x" to choose an arbitrary max....
(BTW, I'm a bit confused about the "you have to test fly at max GW"...I'm sure you do, but what are you testing *for*? That it will fly? What do you do if it doesn't? That you can recover from stalls? What are you supposed to do if it doesn't? That is...*what* are you supposed to test *for*?)
So let's imagine you've got a brand new plane, from a brand new design, that you developed all by yourself, and there is no Van's to give you a number from which to start.
How would you determine the correct max GW?
If you know that, then couldn't you do the same for an RV? No more "Van's + 100*x" to choose an arbitrary max....
(BTW, I'm a bit confused about the "you have to test fly at max GW"...I'm sure you do, but what are you testing *for*? That it will fly? What do you do if it doesn't?
That you can recover from stalls? What are you supposed to do if it doesn't? That is...*what* are you supposed to test *for*?)
Andy Hill
Well Known Member
You/it would have been designed to a Max GW value structurally e.g. wing spars v required Load Factor(s), Gear Legs v requirements - which may be "best practice" or as set by specification / legislation.
i.e. GW would typically come first, before design and not v-v. Flight Testing might, of course, reveal design deficiencies that require GW to be lowered. Flight Testing, by itself, I cannot see "raising GW" (?) unless it was a aerodynamic requirement limiting the GW e.g. a max stall speed.
Andy
Warning, Will Robinson, Warning!!!!
Gross weight is what the structure is sized for and performance is calculated at. I work in advanced design at a major aircraft company and gross weight is everything in the design process. It dictates everything from loads, to maneuverability, to range, to cost.
I typically stay out of threads like this do to the flaming of those that do not agree but, it is my duty as a sworn aeronautical engineer to mention that people should not be so cavalier about setting higher gross weights then the aircraft was designed to. I cuts down margins. In 99.9% of the time it will not be a factor but that one chance in a million that extra margin may save your bacon. As pilot you can not control every factor during a flight so may not have the ability to compensate for the higher gross weight flying characteristics. I agree we are all the manufacturer of our aircraft and we can build it the way we want but, we are not the designer. In the real world of aircraft design/build the manufacturer only builds what the designer analyzed.
This concludes my warning.
Gross weight is what the structure is sized for and performance is calculated at. I work in advanced design at a major aircraft company and gross weight is everything in the design process. It dictates everything from loads, to maneuverability, to range, to cost.
I typically stay out of threads like this do to the flaming of those that do not agree but, it is my duty as a sworn aeronautical engineer to mention that people should not be so cavalier about setting higher gross weights then the aircraft was designed to. I cuts down margins. In 99.9% of the time it will not be a factor but that one chance in a million that extra margin may save your bacon. As pilot you can not control every factor during a flight so may not have the ability to compensate for the higher gross weight flying characteristics. I agree we are all the manufacturer of our aircraft and we can build it the way we want but, we are not the designer. In the real world of aircraft design/build the manufacturer only builds what the designer analyzed.
This concludes my warning.
Van who?
I've seen pictures of wing loading tests with the sand bags & all.
This is a static load test. I wonder how they interpret this in the dynamic realm.
I'm sure there's alot more to the analysis.
Although I'm just an electrical engineer, I know enough to know that I don't know much about aircraft structures and I've certainly have not done any testing.
When it comes to setting the gross weight or engine recommendations, I'm going to defer to some guy in Oregon named Van. What the heck could HE possibly know....?
As others have said. "if you want a faster or heavier plane, build something else..."
Just my $0.02.
Dave
-9A FWF kit
N514R
I've seen pictures of wing loading tests with the sand bags & all.
This is a static load test. I wonder how they interpret this in the dynamic realm.
I'm sure there's alot more to the analysis.
Although I'm just an electrical engineer, I know enough to know that I don't know much about aircraft structures and I've certainly have not done any testing.
When it comes to setting the gross weight or engine recommendations, I'm going to defer to some guy in Oregon named Van. What the heck could HE possibly know....?
As others have said. "if you want a faster or heavier plane, build something else..."
Just my $0.02.
Dave
-9A FWF kit
N514R
L.Adamson
Well Known Member
But sometimes...............it might not be so cavalier. Maybe we know more about it than some. End of subject...
edit: that didn't sound quite right. It's not me personally deciding I know more. It's just a case of knowing additional information.
L.Adamson --- RV6A
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I, too, was trained as an aeronautical engineer. I even did some work for a local DAR, re-(or maybe reverse-) engineering part of a deHavilland Beaver to add a mod that somebody was interested in. The Beaver is an excellent example of an airplane that today flies *regularly* well beyond it's original design gross weight.;406417 said:
But keeping the discussion in the RV-space, compare the RV-6A and the RV-6. Why does the -6A get another 50 lb of gross? Because the nosewheel generates that lift? Of course not. The limitation in gross is clearly in the landing gear, and the FAR part 23 requirements for landing gear loading at time of landing. So operating a -6 at 1650 lb gross is clearly just as safe as a -6A, *once the plane is off the ground*. And, of course,
provided you're within CG limits (same on both planes).
So there's 50 lb of extra weight that could be applied, without even getting into the math, but assuming you set a max Landing weight for your -6 of 1600lb. I wouldn't even contact Vans to confirm that this is a safe choice, it falls into the category of the "blindingly obvious."
It's when you start looking at the loadings in the Utility and Aerobatic category that things become a little more confusing though. Remember, these aircraft have a gross weight set at the Utility category limit of +4.4G. If the plane is flown within the Normal category limit of +3.8G (like most light aircraft), there's no reason they couldn't carry the same weight. If you do run the math here, you end up with a gross at Normal limits around 1850 lb.
What needs to be considered is where the extra 200 lb would go on the airframe. And as is quoted above, you need to keep in mind that your margins have been significantly reduced as well. Flying a 200mph airplane into unexpected wind shear it may be very easy to get over 3.8G before you could slow it down. I know I hit wind shear in my -6 bringing it back from Idaho, and registered 2.2G on the meter, at 140mph indicated... I slowed down when I started seeing 50mph tailwinds.
I haven't finished running all the numbers to make myself comfortable that a gross weight increase is possible or prudent. When I do, and if everything meets FAR part 23 requirements when I have, i'll publish it and hopefully everyone can benefit from it. If not, i'll live with the Van imposed limit, and eat a few less burgers and a few more salads and keep my weight down...
"once the plane is off the ground"
but what if you take-off and need to make an immediate landing and are now 50# above the designed landing gear limits? Can you land safely? Probably, but are your margins reduced? Absolutely. I'm also a trained Aero engineer as well as a test pilot and know with certainty there is no end to the rationalizations pilots/builders will make when they want to alter the planes they build and fly. Some if not most are NOT based upon analysis. Are we sure the RV series was designed to Part 23 standards? Where they required to be? What if those margins have already been reduced during the design process? I wouldn't approach GW increases without KNOWING those answers first. Having done increased gross weight testing in a fully instrumented Naval aircraft with hundreds of engineers on the team I still found myself on the wrong side of a handling qualities cliff with the houses getting big really fast so I'll warn you to be very cautious and not so cavalier about this. I will increase my useful load, which is really what we are talking about here, by carefully managing the stuff I put into it, staying in top physical condition, and making sure if bubba wants to fly with me, he has to meet my aircraft limits, not the other way around. Just my opinion..to each his own.
but what if you take-off and need to make an immediate landing and are now 50# above the designed landing gear limits? Can you land safely? Probably, but are your margins reduced? Absolutely. I'm also a trained Aero engineer as well as a test pilot and know with certainty there is no end to the rationalizations pilots/builders will make when they want to alter the planes they build and fly. Some if not most are NOT based upon analysis. Are we sure the RV series was designed to Part 23 standards? Where they required to be? What if those margins have already been reduced during the design process? I wouldn't approach GW increases without KNOWING those answers first. Having done increased gross weight testing in a fully instrumented Naval aircraft with hundreds of engineers on the team I still found myself on the wrong side of a handling qualities cliff with the houses getting big really fast so I'll warn you to be very cautious and not so cavalier about this. I will increase my useful load, which is really what we are talking about here, by carefully managing the stuff I put into it, staying in top physical condition, and making sure if bubba wants to fly with me, he has to meet my aircraft limits, not the other way around. Just my opinion..to each his own.
Ken, one very important thing to keep in mind here is the G-loadings we're talking about. When you factor in the G-loadings on the airframe, at design gross of 1600 and 4.4G, your airplane is lifting 7040 lb! That means your airplane is capable of carrying 7040lb before you bend something. Therefore, you *should* be able, with reasonable safety, to load the plane in any configuration that mimics that load condition. It's not a question of "rationalizing" anything. It's an exercise in reverse engineering, and determining how the structure will be affected (if at all) when you change your loading configuration.
All things being equal, if you increased your gross to 1800lb, and reduced your limit to 3.8G, you're reducing the max load on the plane to 6840lb, which should be *less* stressful than flying it at Utility limits at design gross. As I said before though, the question becomes "where does the 200 lb go?"
You can't add it to the baggage compartment because the floor is limited to 100 lb. Of course, that's at Utility, so you can probably put about 115lb in there in Normal category, if it doesn't throw your CG out. That leaves 185lb, that can only go in the passenger compartment. You could make larger fuel tanks, but that changes the wing loading configuration and may have an effect on structural limits. You could add a larger engine, but that changes the loading around the engine mount. Two 250lb passengers? Well, each seat can individually carry 250lb, so maybe that's a possibility if you're a "larger" person.
Of course, once you've done all this, the performacne will suffer. Climb will be slower, and cruise slower as well (or it'll take a higher power setting for the same cruise). So you do reduce your margins by doing it. But you always have the *option* of flying lighter and quicker, or carrying more load slower and more carefully.
Does anyone know why there isn't a Normal category limit given for any of the RV's? I haven't seen that answered anywhere. It might give some insight.
All things being equal, if you increased your gross to 1800lb, and reduced your limit to 3.8G, you're reducing the max load on the plane to 6840lb, which should be *less* stressful than flying it at Utility limits at design gross. As I said before though, the question becomes "where does the 200 lb go?"
You can't add it to the baggage compartment because the floor is limited to 100 lb. Of course, that's at Utility, so you can probably put about 115lb in there in Normal category, if it doesn't throw your CG out. That leaves 185lb, that can only go in the passenger compartment. You could make larger fuel tanks, but that changes the wing loading configuration and may have an effect on structural limits. You could add a larger engine, but that changes the loading around the engine mount. Two 250lb passengers? Well, each seat can individually carry 250lb, so maybe that's a possibility if you're a "larger" person.
Of course, once you've done all this, the performacne will suffer. Climb will be slower, and cruise slower as well (or it'll take a higher power setting for the same cruise). So you do reduce your margins by doing it. But you always have the *option* of flying lighter and quicker, or carrying more load slower and more carefully.
Does anyone know why there isn't a Normal category limit given for any of the RV's? I haven't seen that answered anywhere. It might give some insight.
Sorry, forgot about that question. it's common for airliners to have fuel dump valves to allow for this situation. It's possible for a homebuilt to have the same setup. But in an emergency situation, if you had to get back on the ground that urgently you would probably just risk the landing gear collapse and land anyway. If it's not that urgent, stay up, burn 50 lb of fuel off first, and then come back (assuming we're talking about the 1600 vs 1650 lb case).
Landing capability is a very significant consideration for most light a/c, amateur-builts included. We all know how nosegear RV's are prone to collapse when overloaded, and I can't be the only person who has seen a collapsed gearleg on a homebuilt a/c or small Cessna due to a hard landing. I'd have to look up the exact number but I seem to recall that the FAR part 23 design suggestion is something like a 4G impact on the gear... I forget if they consider them both carrying the weight or just one (as in a crosswind).
I do plan to do the calculation on the RV-6 gearlegs and see what they can withstand, I just haven't done it yet. That's one of the steps I want to complete before I pursue an increase. What I *expect* is that they're going to be good for more than 1600 lb, but I don't have a good feel for how much more.
Would appear that RV-6 ''test pilots'' have verified 1850...
If someone was suggesting a max weight of 3000lbs I would understand all the back and forth on this. But, it seems to this builder that 1850 is a safe max weight, provided of course the CG is within limits. Am I missing something other than debating the accuracy of engineering limits. I say that with tongue in cheek because in my 40 years prior to retiring, I had several discussions with design engineers about why they added 40% to the restricted weight limits on certain steel structures. The answers were to add a safety margin. I shortened those conversations to the above statement to point out that in my opinion, engineering limits are not absolutes, especially with regard to the RV-6 or -6A. But, I'm just a builder who accepts the results of others who went before me with raised max gross weights.
If someone was suggesting a max weight of 3000lbs I would understand all the back and forth on this. But, it seems to this builder that 1850 is a safe max weight, provided of course the CG is within limits. Am I missing something other than debating the accuracy of engineering limits. I say that with tongue in cheek because in my 40 years prior to retiring, I had several discussions with design engineers about why they added 40% to the restricted weight limits on certain steel structures. The answers were to add a safety margin. I shortened those conversations to the above statement to point out that in my opinion, engineering limits are not absolutes, especially with regard to the RV-6 or -6A. But, I'm just a builder who accepts the results of others who went before me with raised max gross weights.
