Van's Air Force
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How are gross weights derived?
- Thread starter JackT
- Start date
gmcjetpilot
Well Known Member
Physics, engineers and wives
What are the generalities? My take on this is wives and engineers are alike because they are ridged and follow a set or rules or principles (assumptions). Some of those rules or principles are the mystery (but no doubt they are always right ). Let me try and explain since many years ago I worked as a structural engineer for a Big airplane maker.
The big differnce between the wife and engineer is that if you don't follow the her rules, you make your wife mad. With the engineer, not following the rules, physics can come up and bite you, resulting in a bent/broken airplane. May be the rules are too conservative or restrictive but are intended to keep you in good stead (not divorced or balling your airplane up).
Engineers HAVE to follow criteria, at least in certified airplanes. These criteria ARE arbitrary but have stood the test of time, meaning airframes that takeoff in one piece safely land with all the same pieces attached, provided the pilot flys within the limits.
Strength of materials and aerodynamic loads are precise. There is no generalized issues. It's hard science. However there are assumptions made which may the generalization's you alluded to. Like your wife, engineers will not waiver or give on these rules. It's not a matter of accepting generalization's, its a matter of compromising on their assumptions and rules. If you ask why, it's because that's the way we do it.
These assumptions involve what the critical load cases are, like how strong vertical gust are (turbulence). The other assumption or arbitrary rule is a catch all called margin of safety; All are arbitrary but based on sound common sense (or FAR's). Example: margin of safety in an airliner is arbitrarily 1.50, in a fighter it's 1.25 and non-manned rockets even less. Why the arbitrary difference? Well one is carrying many people, the another has an ejection seat, and in the last example, a rocket, it has no people.
What is "Margin of Safety"? Its and arbitrary allowance for variation in construction, materials, extream conditions, pilot screw-up and possible loss of structure strength over time (corrosion). People consider that the 1.5 factor as the ultimate load factor. SO UNDER ULTIMATE load you will not break or fail structure HOWEVER YOU MAY BEND IT. That is where the LIMIT load comes in. ANYTHING OVER LIMIT LOAD CAN INVOLVE permanent deformation. So limit load has no factor of safety if you will. For example our ultimate aerobatic G factor is 9, but limit 9/1.5= 6 g's. Up to 6 g's you are good and this is the LIMIT LOAD. Over 6 to 9 g's you can and very well perminatly bend the plane. Over 9 g's all bets off, parts can bend and can come off.
I don't want to get into fatigue, since our little planes fly so little. However higher stress reduces fatigue life. We all recall caeses in the news of old T-34's or pipe patrol planes flown several 10's of thousands of hours experiencing catastrophic fatigue failure.
We of course do not need to follow anyone assumptions with experimental aircraft, but as was pointed out before, Van's Aircraft sees the wisdom in having a safety margin. I do also. Just remember exceeding any limit does have impact. It's not a matter of IF it impacts you, it's a matter of how much. Any change in weight will affect everything to a degree.
As far as speeds, the pilot controls the max G's limit at slower speeds like at Va, where the maneuver is intentional, under your control. So if you are flying at HIGHER gross you can just take it easy. Vne may need to be reduced slightly. The theoretical (FAR) vertical gust I recall is 50 feet/sec; I never meet or felt a "certified gust", but we know there are gusts or wake turbulence; some gust may be worse than 50ft/sec?
Bottom line, if you raise the gross know what you are getting into, there are limits. The higher the weight the closer you're to the maximum (ultimate failure). With the robust structure and excess performance RV's have we can expand the gross with a fair degree of safety (with in reasonable limits), but you need to reduce the "envelope" both in intentional maneuvering and unintentional (lower Vne). Also high (over) gross landings, especially soft field was mentioned a few times as an issue. Landing a extra heavy RV or taxing over soft dirt might strain the gear. My concern is the small 5x5 tires in soft grass with high weights.
Cheers George
Humm engineers are like wives..... I think the analogy is funny.RVbySDI said:
What are the generalities? My take on this is wives and engineers are alike because they are ridged and follow a set or rules or principles (assumptions). Some of those rules or principles are the mystery (but no doubt they are always right ). Let me try and explain since many years ago I worked as a structural engineer for a Big airplane maker.The big differnce between the wife and engineer is that if you don't follow the her rules, you make your wife mad. With the engineer, not following the rules, physics can come up and bite you, resulting in a bent/broken airplane. May be the rules are too conservative or restrictive but are intended to keep you in good stead (not divorced or balling your airplane up).
Engineers HAVE to follow criteria, at least in certified airplanes. These criteria ARE arbitrary but have stood the test of time, meaning airframes that takeoff in one piece safely land with all the same pieces attached, provided the pilot flys within the limits.
Strength of materials and aerodynamic loads are precise. There is no generalized issues. It's hard science. However there are assumptions made which may the generalization's you alluded to. Like your wife, engineers will not waiver or give on these rules. It's not a matter of accepting generalization's, its a matter of compromising on their assumptions and rules. If you ask why, it's because that's the way we do it.
These assumptions involve what the critical load cases are, like how strong vertical gust are (turbulence). The other assumption or arbitrary rule is a catch all called margin of safety; All are arbitrary but based on sound common sense (or FAR's). Example: margin of safety in an airliner is arbitrarily 1.50, in a fighter it's 1.25 and non-manned rockets even less. Why the arbitrary difference? Well one is carrying many people, the another has an ejection seat, and in the last example, a rocket, it has no people.
What is "Margin of Safety"? Its and arbitrary allowance for variation in construction, materials, extream conditions, pilot screw-up and possible loss of structure strength over time (corrosion). People consider that the 1.5 factor as the ultimate load factor. SO UNDER ULTIMATE load you will not break or fail structure HOWEVER YOU MAY BEND IT. That is where the LIMIT load comes in. ANYTHING OVER LIMIT LOAD CAN INVOLVE permanent deformation. So limit load has no factor of safety if you will. For example our ultimate aerobatic G factor is 9, but limit 9/1.5= 6 g's. Up to 6 g's you are good and this is the LIMIT LOAD. Over 6 to 9 g's you can and very well perminatly bend the plane. Over 9 g's all bets off, parts can bend and can come off.
I don't want to get into fatigue, since our little planes fly so little. However higher stress reduces fatigue life. We all recall caeses in the news of old T-34's or pipe patrol planes flown several 10's of thousands of hours experiencing catastrophic fatigue failure.
We of course do not need to follow anyone assumptions with experimental aircraft, but as was pointed out before, Van's Aircraft sees the wisdom in having a safety margin. I do also. Just remember exceeding any limit does have impact. It's not a matter of IF it impacts you, it's a matter of how much. Any change in weight will affect everything to a degree.
As far as speeds, the pilot controls the max G's limit at slower speeds like at Va, where the maneuver is intentional, under your control. So if you are flying at HIGHER gross you can just take it easy. Vne may need to be reduced slightly. The theoretical (FAR) vertical gust I recall is 50 feet/sec; I never meet or felt a "certified gust", but we know there are gusts or wake turbulence; some gust may be worse than 50ft/sec?
Bottom line, if you raise the gross know what you are getting into, there are limits. The higher the weight the closer you're to the maximum (ultimate failure). With the robust structure and excess performance RV's have we can expand the gross with a fair degree of safety (with in reasonable limits), but you need to reduce the "envelope" both in intentional maneuvering and unintentional (lower Vne). Also high (over) gross landings, especially soft field was mentioned a few times as an issue. Landing a extra heavy RV or taxing over soft dirt might strain the gear. My concern is the small 5x5 tires in soft grass with high weights.
Cheers George
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Gordon Henry
I'm New Here
Performance envelope
About 100 years ago when I flew A4 Skyhawks for the Navy, we used a VN Diagram or performance envelope to determine how many G's we could safely pull at a certain speed and weight. As the gross weight and speed increased the allowable G load as decreased. A reduction in G was required for rolling maneuvers due to the asymmetric wing loading. This was obviously to stay within the design strength of the airframe. The pilot could do any maneuver he wished as long as he stayed within the "envelope". MY question is - what is the 1350 lb. acrobatic limit all about? If you can pull six symmetrical (no rolling) G's at 1800 lb. then why limit acrobatic manuvers to 1350 pounds? Is it a CG issue? Is it an attempt to stay within the strength limits while pulling rolling G's? How can one teach his fat brother to do acrobatics? Any of you aero engineers have any ideas on this?
About 100 years ago when I flew A4 Skyhawks for the Navy, we used a VN Diagram or performance envelope to determine how many G's we could safely pull at a certain speed and weight. As the gross weight and speed increased the allowable G load as decreased. A reduction in G was required for rolling maneuvers due to the asymmetric wing loading. This was obviously to stay within the design strength of the airframe. The pilot could do any maneuver he wished as long as he stayed within the "envelope". MY question is - what is the 1350 lb. acrobatic limit all about? If you can pull six symmetrical (no rolling) G's at 1800 lb. then why limit acrobatic manuvers to 1350 pounds? Is it a CG issue? Is it an attempt to stay within the strength limits while pulling rolling G's? How can one teach his fat brother to do acrobatics? Any of you aero engineers have any ideas on this?
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Kevin Horton
Well Known Member
I'm not sure what model RV you have, but on my RV-8 you can only pull 6g at the aerobatic weight limit. If you are heavier than that, Van says the limit is 4.4g, if I recall correctly.Gordon Henry said:
az_gila
Well Known Member
FAA gusts
A 50 ft/sec FAA gust is 3000 ft/minute.
I've been soaring in the Sierras and White mountains in 2000 ft/minute thermals (exact strength unknown since my variometers maxed out... ...)
While certainly not typical, I'm sure gusts of these strengths, and with "sharp" edges, can occur in mountainous terrain and in the vicinity of large cumulus build-ups... as well as the rotor area of mountain waves.
gil in Tucson - an engineer, but I don't think I'll tell my wife of your analogy...
George,gmcjetpilot said:
As far as speeds, the pilot controls the max G's limit at slower speeds like at Va, where the maneuver is intentional, under your control. So if you are flying at HIGHER gross you can just take it easy. Vne may need to be reduced slightly. The theoretical (FAR) vertical gust I recall is 50 feet/sec; I never meet or felt a "certified gust", but we know there are gusts or wake turbulence; some gust may be worse than 50ft/sec?
.......
Cheers George
A 50 ft/sec FAA gust is 3000 ft/minute.
I've been soaring in the Sierras and White mountains in 2000 ft/minute thermals (exact strength unknown since my variometers maxed out...
...)While certainly not typical, I'm sure gusts of these strengths, and with "sharp" edges, can occur in mountainous terrain and in the vicinity of large cumulus build-ups... as well as the rotor area of mountain waves.
gil in Tucson - an engineer, but I don't think I'll tell my wife of your analogy...
osxuser
Well Known Member
Vne... havent' we kinda settled on Vne on RV's being set because of flutter, not structural issues? If thats the case, I don't think that Vne would need to be reduced at higher weights. The FAR gust is pretty extreme, being in a 2000FPM up/down draft is one thing, being in an INSTANTAINIOUS 50ft/second or 3000FPM gust seems.... extreme. Sorry, I can't find a better word. I was up in the desert this weekend, and we saw 1500FPM up a couple times, but it was more of just a rising force, not a sheer gust.gmcjetpilot said:
I'm not saying they don't exsist, but here is the problem. Usually when you hit gusts like that, you are not expecting it, so you will probably be above Va, by the time you get to Va.... the instantainious gust will be gone, and hopefully your wings will still be on....
Steve Brown
Well Known Member
Really dumb (but important) question about gross weight
In response to a builder's request for information showing 1800# gross weight for the -9, I went looking for my paperwork which shows that.
I have it in my POH, but I cannot find any "official" documents which specify any gross weight whatsoever.
Where should I be looking?
In response to a builder's request for information showing 1800# gross weight for the -9, I went looking for my paperwork which shows that.
I have it in my POH, but I cannot find any "official" documents which specify any gross weight whatsoever.
Where should I be looking?
pierre smith
Well Known Member
Would Van's be good enough...
....for 'Official" info?
http://www.vansaircraft.com/public/rv-9spe.htm
Best,
....for 'Official" info?
http://www.vansaircraft.com/public/rv-9spe.htm
Best,
Steve Brown
Well Known Member
How about during the build & sign off process?
Pierre,
I didn't build my airplane. There's a lot of chatter on this site about setting and/or changing gross weight.
How is that done? I have the POH from the builder that lists it as 1800#.
Is that all I need?
Pierre,
I didn't build my airplane. There's a lot of chatter on this site about setting and/or changing gross weight.
How is that done? I have the POH from the builder that lists it as 1800#.
Is that all I need?
Steve Vans AC says the gross weight is 1600-1750. I don't know why there is a range, maybe someone else can comment on that. the builder decided to up the gross weight to 1800, you might find some info on that if you have a build journal or maybe not. He might not have done any engineering to justify it and just upped it arbitrarily. It isn't a very large increase, in comparison i think the 6 regularly gets bumped up 200 pounds (from 1600 to 1800)
C5Engineer
Member
It's an experimental airplane..there's no such thing as an "Official" gross weight. You won't find it on any FAA paperwork related to your airplane. The gross weight comes from the builder. The kit manufacturer tells us what we can safely carry based on their testing but ultimately it's up to you. If you can take off and safely manuever your plane at 2000lbs there's nothing stopping you from doing so except maybe that common sense thing
ArVeeNiner
Well Known Member
At what point do you set gross weight?
At what point do you set gross weight? I would imagine that you'd want to fly at that weight at least once to prove that it's doable. Obviously that won't happen if you need to provide that number during the submittal of the registration paperwork prior to Phase I testing.
At what point do you set gross weight? I would imagine that you'd want to fly at that weight at least once to prove that it's doable. Obviously that won't happen if you need to provide that number during the submittal of the registration paperwork prior to Phase I testing.
scsmith
Well Known Member
Look at your data plate?
My data plate has the gross wt. Somewhere in the airplane there should be some form of placard listing gross wt if its not on the data plate.
Mel should chime in here, but doesn't the builder specify the gross weight somewhere on the airworthiness paperwork that that DAR gets? So the FAA would have a record of it?
A good POH should also give the limit load factors (flight envelop). If a builder arbitrarily sets a higher gross wt, he should also adjust the limit load factors down. For example, a RV-9 at 1650 may have a +4.4 g maneuver limit load (equivalent to utility cat) but the same airplane at 1800 would have a +4 g maneuver limit load.
My data plate has the gross wt. Somewhere in the airplane there should be some form of placard listing gross wt if its not on the data plate.
Mel should chime in here, but doesn't the builder specify the gross weight somewhere on the airworthiness paperwork that that DAR gets? So the FAA would have a record of it?
A good POH should also give the limit load factors (flight envelop). If a builder arbitrarily sets a higher gross wt, he should also adjust the limit load factors down. For example, a RV-9 at 1650 may have a +4.4 g maneuver limit load (equivalent to utility cat) but the same airplane at 1800 would have a +4 g maneuver limit load.
John Clark
Well Known Member
Balance
Remember that besides the gross weight figure, which can be adjusted by the "manufacturer," the builder (if the DAR or FAA inspector will buy off on it), you need to have the numbers to figure a proper weight and balance. Remember "ARROW?" These are all things that must be in the airplane to be legal.
Airworthiness Certificate
Registration
Radio Station License (a non-issue unless you are crossing international borders)
Operating Limitations A copy of the aircraft's specific "Ops Lims" from the FAA, plus placards, instrument markings, or a combination with a POH. A POH is not required if the information is covered by other means.
Weight and Balance Make sure the latest such record is aboard, not only to satisfy legal requirements but also to compute an accurate weight and balance for the flight.
John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
Remember that besides the gross weight figure, which can be adjusted by the "manufacturer," the builder (if the DAR or FAA inspector will buy off on it), you need to have the numbers to figure a proper weight and balance. Remember "ARROW?" These are all things that must be in the airplane to be legal.
Airworthiness Certificate
Registration
Radio Station License (a non-issue unless you are crossing international borders)
Operating Limitations A copy of the aircraft's specific "Ops Lims" from the FAA, plus placards, instrument markings, or a combination with a POH. A POH is not required if the information is covered by other means.
Weight and Balance Make sure the latest such record is aboard, not only to satisfy legal requirements but also to compute an accurate weight and balance for the flight.
John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
terrykohler
Well Known Member
Isn't the Gross Wt. listed on the Ops Limitations?
IIRC, my gross wt is listed there along with wt & balance data. That paperwork was prepared by my DAR (Ted Gauthier). Regarding an earlier question about a range of weight provided by Vans, I believe that addresses both Utility Category as well as Normal Category. Just working from memory, as all the paperwork is in the airplane. John Clark (post above) has pretty much covered everything else you need to know.
Terry, CFI
RV-9A N323TP
IIRC, my gross wt is listed there along with wt & balance data. That paperwork was prepared by my DAR (Ted Gauthier). Regarding an earlier question about a range of weight provided by Vans, I believe that addresses both Utility Category as well as Normal Category. Just working from memory, as all the paperwork is in the airplane. John Clark (post above) has pretty much covered everything else you need to know.
Terry, CFI
RV-9A N323TP
John Clark
Well Known Member
Made me look!
After Terry's response, I looked at my paperwork. (it has been 6 years) On mine the weights are not on the actual Opps Limitations letter. The weight and balance is a separate document, which makes sense, in that it can change due to modifications, paint and the like. Updating the W&B is not a big deal, changing the Opps Limitations can be.
John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
After Terry's response, I looked at my paperwork. (it has been 6 years) On mine the weights are not on the actual Opps Limitations letter. The weight and balance is a separate document, which makes sense, in that it can change due to modifications, paint and the like. Updating the W&B is not a big deal, changing the Opps Limitations can be.
John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
Bill Wightman
Well Known Member
RV9 limited by gust loading
In an article from the RVator:
"The RV -9A Vne was set based on flutter considerations. But in cruising flight, gust loads are the limiting factor.
(emphasis added)
Certified aircraft are designed to not exceed maximum +/- load factor when encountering 50 fps vertical gusts at V_c, max structural cruising speed. Seems Van did look at this condition, and it wound up being the limiting factor for the structure. This can be seen on the RV9 V_n diagram.
If the builder decides to fly at higher weights, maybe it would be a good idea to run an independent analysis of the plane's gust loading to see what kind of reduction might be required on V_c. Just a thought... (ref FAR23.341)
In an article from the RVator:
"The RV -9A Vne was set based on flutter considerations. But in cruising flight, gust loads are the limiting factor.
(emphasis added)
Certified aircraft are designed to not exceed maximum +/- load factor when encountering 50 fps vertical gusts at V_c, max structural cruising speed. Seems Van did look at this condition, and it wound up being the limiting factor for the structure. This can be seen on the RV9 V_n diagram.
If the builder decides to fly at higher weights, maybe it would be a good idea to run an independent analysis of the plane's gust loading to see what kind of reduction might be required on V_c. Just a thought... (ref FAR23.341)
Steve Brown
Well Known Member
Thanks all
Between comments on this thread and communication with the builder of my airplane, my conclusion is that at the moment the most "official" think I have is the data plate.
I'll take a good picture of that, keep it in my records, and go back to worrying about other things
Between comments on this thread and communication with the builder of my airplane, my conclusion is that at the moment the most "official" think I have is the data plate.
I'll take a good picture of that, keep it in my records, and go back to worrying about other things
rv9av8tr
Well Known Member
gross weight
Van's recommended GW for the -7/7A is listed at 1800 lbs.
The only real diff between the 7 and 9 series is the engine & fuel capacity (both bigger).... which would easily account for 50 lb difference.
Based on that, so long as the builder tests the envelop to 1800 lbs, I don't see a problem with using 1800 lbs for the 9 series. (It's only 1 hr worth of fuel difference).
A person might consider limiting the -9's 4.4G limit to something less during that first hour when operating over 1750.
Van's recommended GW for the -7/7A is listed at 1800 lbs.
The only real diff between the 7 and 9 series is the engine & fuel capacity (both bigger).... which would easily account for 50 lb difference.
Based on that, so long as the builder tests the envelop to 1800 lbs, I don't see a problem with using 1800 lbs for the 9 series. (It's only 1 hr worth of fuel difference).
A person might consider limiting the -9's 4.4G limit to something less during that first hour when operating over 1750.
The most "official" thing you should have is the current weight & balance documents in your airplane.
The data plate doesn't mean anything.
jnorris
Well Known Member
Actually, the "official" gross weight of your homebuilt is whatever is listed in the most recent flight test entry in the logbook. At the end of any phase 1 flight test the following entry is made in aircraft records:
I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: speeds Vso ______, Vx ______, and Vy ______, and the weight ______ and CG location ______ at which they were obtained.
Whatever weight is called out in this statement becomes the legal gross weight of your aircraft. This is due to the fact that the aircraft cannot be flown in a given condition during normal operations until said condition is flight tested to show compliance with 14 CFR 91.319(b). This entry in the records states that the aircraft was tested to the listed weight and performed as shown. Any operation at a weight greater than what it shown in the most recent flight test entry is outside the tested parameters.
So the answer to your question about what is the gross weight of your particular airplane lies in the aircraft records (probably in the airframe log). Find the most recent (usually there's only one, but there may be more if major changes were incorporated) flight test record and see what weight is listed.
I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: speeds Vso ______, Vx ______, and Vy ______, and the weight ______ and CG location ______ at which they were obtained.
Whatever weight is called out in this statement becomes the legal gross weight of your aircraft. This is due to the fact that the aircraft cannot be flown in a given condition during normal operations until said condition is flight tested to show compliance with 14 CFR 91.319(b). This entry in the records states that the aircraft was tested to the listed weight and performed as shown. Any operation at a weight greater than what it shown in the most recent flight test entry is outside the tested parameters.
So the answer to your question about what is the gross weight of your particular airplane lies in the aircraft records (probably in the airframe log). Find the most recent (usually there's only one, but there may be more if major changes were incorporated) flight test record and see what weight is listed.
Radomir
Well Known Member
so if you go aft of that C.G. number you specified there... you're illegal?
What C.G. would that be?
the part that says "..at which they were obtained" is confusing me.. to say the least.. I'd read that as weight and C.G. at the moment of testing.. not max allowed number(s).
What C.G. would that be?
the part that says "..at which they were obtained" is confusing me.. to say the least.. I'd read that as weight and C.G. at the moment of testing.. not max allowed number(s).
N941WR
Legacy Member
Once upon a time I asked Van's about this. The lower GW has to do with how much weight a 115 hp O-235 can lift. With my O-290 I still set th GW at 1750 lbs which gave me a 760 pound useful load.
thanks for letting me know, i appreciate it Bill.
I thought the 9 had longer HS and wings, with a different airfoil. Those aren't significant differences???
YEP!
Those are significant differences!
The only things common between the two is, that they share common fuselage parts and they are both RVs.
Those are significant differences!
The only things common between the two is, that they share common fuselage parts and they are both RVs.
rv9av8tr
Well Known Member
Differences in weight
I agree, sorry for the confusion, but in the context of the thread, I was only referring to significant reasons for differences in listed gross weights.
For example the gross weight ranges for the -9/9A by Van's.... it's just different engine weights, has nothing to do with structure limits.
I agree, sorry for the confusion, but in the context of the thread, I was only referring to significant reasons for differences in listed gross weights.
For example the gross weight ranges for the -9/9A by Van's.... it's just different engine weights, has nothing to do with structure limits.
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jnorris
Well Known Member
Only if you do not record a flight test with a CG elsewhere. A complete flight test regime is supposed to include testing the aircraft to gross weight, and to the extremes of its CG range. The Vx and Vy are supposed to be determined at gross weight. So a combination of other flight test records and the entry completing the phase 1 flight testing should document all these conditions as being tested.
Now, in the real world I have not seen any homebuilt aircraft that actually includes all these records, but to be completely legal they should. The only time lack of these records is likely to become an issue is if there is an accident and the aircraft if found to be configured or loaded in some way that is not supported by flight test documentation. In such a case the FAA could pursue action against the pilot.
The gross weight limit would be the easiest of all for the FAA to take action on. All they have to do is open up the aircraft records, read the number called out in the phase 1 sign-off, and if the aircraft was found to be operating over that weight, you're busted. That's why it's important to test the aircraft to a realistic gross weight, record the proper gross weight in the phase 1 sign-off, and make sure the aircraft's weight and balance documentation reflects this same gross weight.
flyboy1963
Well Known Member
gross wt calculations
...I keep seeing these gross wt questions, and I certainly don't have the engineering to advise.
Here's one guy who made calculations to satisfy transport Canada; essentially showing what the wing would lift. See Todd's spreadsheets on the left menu bar.
http://www3.telus.net/haywire/RV-9/C-FSTB.htm
Now if you take any weight, and keep in withing CG ( which means yet more calculations and flight testing to prove elevator authority at x angle of attack etc.) that weight is going to determine safe g loading.
I personally choose not to mess with the margins built into the design at the design recommended gross, but as others have observed, that number is relative to many other operational factors.
...I keep seeing these gross wt questions, and I certainly don't have the engineering to advise.
Here's one guy who made calculations to satisfy transport Canada; essentially showing what the wing would lift. See Todd's spreadsheets on the left menu bar.
http://www3.telus.net/haywire/RV-9/C-FSTB.htm
Now if you take any weight, and keep in withing CG ( which means yet more calculations and flight testing to prove elevator authority at x angle of attack etc.) that weight is going to determine safe g loading.
I personally choose not to mess with the margins built into the design at the design recommended gross, but as others have observed, that number is relative to many other operational factors.
jjconstant
Well Known Member
unintended assuptions....
I think it might be best to backtrack a bit and simply acknowledge that the RV7 and 9, while having some obvious and numerous similarities might best be treated as COMPLETELY DIFFERENT airplanes, built for very different missions. I know that you were speaking in a specific context but folks can run with a quote in very strange and scary directions.
The RV7 and 7A are designed for aerobatics and the 9 isn't. Those are very different structural limits. There are MANY other differences including speeds, load limits, weights, including weights at which aerobatics may be performed in the various aerobatic models etc...That question alone has sparked entire threads due to some abiguity about fuel being included or not, and responses from Vans!
No flame intended, just worried about unintended consequences...
Jeremy
I think it might be best to backtrack a bit and simply acknowledge that the RV7 and 9, while having some obvious and numerous similarities might best be treated as COMPLETELY DIFFERENT airplanes, built for very different missions. I know that you were speaking in a specific context but folks can run with a quote in very strange and scary directions.
The RV7 and 7A are designed for aerobatics and the 9 isn't. Those are very different structural limits. There are MANY other differences including speeds, load limits, weights, including weights at which aerobatics may be performed in the various aerobatic models etc...That question alone has sparked entire threads due to some abiguity about fuel being included or not, and responses from Vans!
No flame intended, just worried about unintended consequences...
Jeremy
