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Gross weight, likely revisited

RVMike

Member
As I will likely be making my first venture into the Experimental world after 40> years of flying with an RV-4 purchase, I am as usual a bit confused.:confused: So, does the definition of gross weight and it's legal implications change since the aircraft is certified in the Experimental category? Some are 'certified' with 1500 gross, others with 1600 lbs. I am aware of the fact that aircraft can be safely operated above published gross weight (Alaska FAA regs allow a 10% increase in some situations..) and that yes, once must be careful as always. Results may vary, this is not advice from me, and this remains between you, me, and the NSA. I also know ramp checks can be very rare but one must always be prepared, and that was not the reason for my question. I am just continuing on the path of knowledge to some day reach the lofty goal of being an RV-4 aviator. Thank you very much.
 
You bust gross, you bust a reg. That said, I've never seen a ramp fed in Wyoming. I think they're all up in Montana rubbing elbows with the glitteratti.
 
Welcome to the wonderful world of RV's!

A coupla points that may shed some light. First, RV's aren't "certified" at any gross weight, since they are not certified aircraft. Minor grammar point, but may help you understand a key difference.

Regarding weights, you're right. The 'seemingly' same aircraft (i.e. RV-4) can be registered with different gross weights. Think of it this way. Who determines an aircraft's gross weight? The manufacturer. Who is the manufacturer of RV-4's? The builder (i.e. not Van's). Ergo, two different individuals manufacturing two different RV-4's can have two different gross weights.

Now all that said, whether it is smart to diverge from Van's recommendations is a totally different question.
 
Wow. I had never read that article before. As an Aero Engineer myself, it is information to take to heart for EVERY builder. Thanks for the post.
 
Some are 'certified' with 1500 gross, others with 1600 lbs.

I saw an RV4 with 1800 gross listed on its id plate, that is the highest I have seen. I can't remember the empty weight but it was pretty heavy.

agreed thats a good read.
 
Is the -4 really a 2- seat XC machine?

I read the article mentioned and I take it to heart.

With that in mind, I begin to wonder if the -4 can really be considered a 2 seat Cross Country machine'.

The Van's web page says that the Gross Weight is 1500 pounds. I'm sticking with that.

Ok so if you take me and my girl in back, we have 180+120 pounds.

32 gallons of gas is 192

say 26 for 2 chutes

50 pounds baggage

And that useful load adds up to 568 pounds.

You get a 1000 pound empty machine and your are 68 over.

And from what I can tell, I bet most -4's are a bit over 1000.

I don't want to bust gross.

I don't like taking off without a full fuel load

So do people really think of -4's as a serious 2 seat XC machine?

And then there's single seat acro with me, full tanks and a chute and I'm 5 pounds over the acro limit of 1375.


I suppose I could fly acro with less than full tanks. But that brings up a totally unrelated question:

Does everyone fill the tanks after a day's flying to avoid condensation? If so then every flight is a full-tanker. Burning off 5 pounds for start/taxi/run-up isn't too hard, I suppose.
 
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Gregg,

I did the same math; I'm 175 and my wife is 125. We plan to take the machine to Michigan 2x yearly and TX or CO once yearly.

Personally, I omitted the chutes and plan for ~25lb baggage. I don't know of a good justification for flying with chutes X/C and we've spent enough time traveling by motorcycle (2-up on a sportbike) that she knows how to pack light.

IMO, launching with less than full tanks is no big deal, in most cases I prefer to.

A -8 is a more humane traveling machine, and makes 2-up acro possible, but without partners is out of the budget range for me.

I read the article mentioned and I take it to heart.

With that in mind, I begin to wonder if the -4 can really be considered a 2 seat Cross Country machine'.

The Van's web page says that the Gross Weight is 1500 pounds. I'm sticking with that.

Ok so if you take me and my girl in back, we have 180+120 pounds.

32 gallons of gas is 192

say 26 for 2 chutes

50 pounds baggage

And that useful load adds up to 568 pounds.

You get a 1000 pound empty machine and your are 68 over.

And from what I can tell, I bet most -4's are a bit over 1000.

I don't want to bust gross.

I don't like taking off without a full fuel load

So do people really think of -4's as a serious 2 seat XC machine?

And then there's single seat acro with me, full tanks and a chute and I'm 5 pounds over the acro limit of 1375.


I suppose I could fly acro with less than full tanks. But that brings up a totally unrelated question:

Does everyone fill the tanks after a day's flying to avoid condensation? If so then every flight is a full-tanker. Burning off 5 pounds for start/taxi/run-up isn't too hard, I suppose.
 
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I think the most important point to be taken from Van's article is if you think you know better than the designer and incorporate your own safety of flight mods to the design, it has become a single place airplane. You have no right to subject your pax as unknowing test subjects.
 
Well, you might consider that the RV-4 was never designed as a full-up 2-place, with lots of baggage, cross country aircraft. It was designed because people loved the flight characteristics of the RV-3, but wanted to take a passenger along.
At first, Van baulked at the idea but gave in under pressure.
The RV-4 is one of the greatest RVs flying, but it was never intended for these operations.
If you want this kind of machine, maybe you should be looking at the RV-8.
 
...Does everyone fill the tanks after a day's flying to avoid condensation? If so then every flight is a full-tanker...

Short answer - No.

When I do fill the tanks (there is no fuel at my private strip), I generally land and offload all but about 15 gallons once I get back to the hangar. I add whatever is needed for the mission of the day. The airplane flies so much better when it's light on fuel that I just can't stand tanking around the extra weight.

Keep in mind that I live in a climate that is almost completely devoid of humidity - condensation is just not an issue.
 
To be clear, RV's and other homebuilts are "Certified" airplanes. They are certified in the "Experimental - Amateur Built" category.

What they lack is a Type Certificate. Thus there is no pre-defined Gross Weight they must adhere to. Yes, the designer lists a suggested GW, but like those yellow speed limit signs before a turn, they are merely a suggestion.

As mentioned earlier, the builder sets the GW and the GW can be increased by a log book entry putting it back into Phase 1 (Assuming it has the newer Operating Limitations.), tested at the new GW for five hours, and then signed out of Phase 1.
 
As mentioned earlier, the builder sets the GW and the GW can be increased by a log book entry putting it back into Phase 1 (Assuming it has the newer Operating Limitations.), tested at the new GW for five hours, and then signed out of Phase 1.

Does the data plate need to be updated? Any paper work need to be filed with the FAA?
 
Overload

In the world of charter flying, overloading aircraft, sometimes by obscene amounts, is unfortunately all too common. This is especially true in cargo flying. The unfortunate truth is that usually all one has to work with is the shippers paperwork. it is very unusual for the cargo to actually be weighted where the pilot can witness the loading.
I just finished reading the book by Jerry Mock, who was the first woman to fly solo around the world. Cessna 180, at times way over gross. The book is a real interesting read. After reading this book one tends to look at a 50# over gross event in a small homebuilt in a totally new perspective.
 
Gross weight or C of G

I am new to the RV4 world, purchasing mine in May this year. Having a blast for the 65 hrs since then! Just a little info I have gained in my short time with the new bird.

There are three 4's at our field all below 950 lb empty (948, 944 & 931) and all registered at 1500 lb gross. All 3 are O320, fixed pitch painted machines.

We all are very sensitive to the rear CG issue when carrying a back seater.
Just to show the differences in our 3 planes....

#1 - Pilot - 180, Pass - 120, Baggage 25 = 1464 lb gross, CG OK full fuel to 2 gal remaining
#2 - Pilot - 180, Pass - 120, Baggage 55 = 1491 lb gross, CG OK full fuel to 2 gal remaining
#3 - Pilot - 180, Pass - 120, Baggage 41 = 1464 lb gross, CG OK full fuel to 2 gal remaining

Not one can carry gross weight and remain within the rear CG limit once enough fuel is burned. The plane becomes very pitch sensitive outside the Vans rear CG limit. One of the guys flies his like that often with a 200 lb passenger in the back and him at 220 (over gross with no baggage).

For what it is worth.

Al
 
Does everyone fill the tanks after a day's flying to avoid condensation? If so then every flight is a full-tanker.

Absolutely not. No reason to lug all that extra weight around if you're just going up for some local fun and acro. You have plenty of time available for fun with 20 or even 15 gallons on board. (If you're going x-c, obviously it's a different story.)

As to condensation, my 4 lives in a hangar in a fairly humid climate, is routinely put away with only partially filled tanks, and I can't recall finding condensation in the tanks in years. I had the same instincts as you in the beginning (fill the tanks to avoid condensation), but found it just wasn't an issue for me. Doesn't mean I don't carefully sample the fuel before every flight though.

Thanks for the link to the excellent article by Van. Had missed that one. After reading that, I don't consider his recommended gross weight as just a mere warning sign.
 
Jan Johanson

Jan Johanson had one time approval from Vans for takeoff at 136% of normal gross weight for the RV4. I believe on later flights this was increased, but can't find anything specific.
10% over gross is standard FAA approval for certified aircraft for long distance ferry flights.
Max Conrad was nearly twice the certified gross weight of the Twin Commanche for the Capetown- St Petersburg flight.
For around the world Hawaii to San Francisco is normally the longest leg. Fuel availability in recent years in the Pacific may have changed that.
 
To be clear, RV's and other homebuilts are "Certified" airplanes. They are certified in the "Experimental - Amateur Built" category.

Actually, they are certificated, not certified. They have been given a special airworthiness certificate. They are not certified to meet any standard.
 
As I will likely be making my first venture into the Experimental world after 40> years of flying with an RV-4 purchase, I am as usual a bit confused.:confused: So, does the definition of gross weight and it's legal implications change since the aircraft is certified in the Experimental category? Some are 'certified' with 1500 gross, others with 1600 lbs. I am aware of the fact that aircraft can be safely operated above published gross weight (Alaska FAA regs allow a 10% increase in some situations..) and that yes, once must be careful as always. Results may vary, this is not advice from me, and this remains between you, me, and the NSA. I also know ramp checks can be very rare but one must always be prepared, and that was not the reason for my question. I am just continuing on the path of knowledge to some day reach the lofty goal of being an RV-4 aviator. Thank you very much.

Its worth reflecting on the fact that increasing GW beyond the designer's recommendation makes your aircraft even more "experimental" than it would otherwise be. To believe that adding an extra 100 pounds will have no impact performance or safety is purely wishful thinking. How risk-averse are you? How well informed is your passenger?
 
In the UK amateur built aircraft go through a type approval process that has been delegated to the Light Aircraft Association. They have a Type Approval Data Sheet similar to the TCDS for certificated aircraft. In most cases they accept Van's recommended limitations but will deviate if they have sufficient evidence to either raise or lower it.

For the RV-4 they have approved 1550 lb MTOW and all UK RV-4s will have that limitation. I'm not aware of where the 50lb concession came from, but such concessions are usually hard to gain and need some kind of engineering justification.

RV-4 TADS is here
 
To believe that adding an extra 100 pounds will have no impact performance or safety is purely wishful thinking.
To believe that all who chose to cert to a higher gross weight did so without assessing the performance or 'safety' impact is equally misguided. ;)
 
Consider

Keep in mind that an RV-4 at 1500 lbs, pulling 6 G's, which it is rated for, loads the wings to 9,000lbs. If the same airplane weighed 36% more, or 2,040 lbs, it would take almost 4.5 G's to load the wing to 9,000 lbs, well above the Utility category and as long as no aerobatics were performed, where's the problem, as long as the CG is within limits?

Best,
 
Keep in mind that an RV-4 at 1500 lbs, pulling 6 G's, which it is rated for...
It's only rated to 6 at or below aerobatic weight (1375? off the top of my head), 4.4g above.

Utility category and as long as no aerobatics were performed, where's the problem, as long as the CG is within limits?
Presumably you're going to take off and land at some point in your flight so understanding the loads under those conditions at increased weight is equally important :D
 
Keep in mind that an RV-4 at 1500 lbs, pulling 6 G's, which it is rated for, loads the wings to 9,000lbs. If the same airplane weighed 36% more, or 2,040 lbs, it would take almost 4.5 G's to load the wing to 9,000 lbs, well above the Utility category and as long as no aerobatics were performed, where's the problem, as long as the CG is within limits?

A valid point but only one consideration. The location of the additional weight adds structural and dynamic response considerations as well. Perhaps the are most 'unknown' as to the effect of additional weight is the changes to dynamic response of the aircraft. Obviously this this impacts control response (roll rate, etc) but also the aero-elasticty of the air frame and things like spin characteristics.

While you might not exceed the 'G' limits of the wing spar will you have enough control authority to recover from a spin or prevent entering one? The math is hard to impossible to completely model this in any simplified way therefore extensive testing is used to validate designs. Spin chute anyone?, etc.

Hence increasing gross weight is simply putting more experimental in the experimental. Not that it can't or shouldn't be done but careful testing should validate before blasting off thinking that because the wings didn't fall off that is the end of it.
 
To believe that all who chose to cert to a higher gross weight did so without assessing the performance or 'safety' impact is equally misguided. ;)

I think you're absolutely correct. I'm not implying that these aircraft haven't been tested thoroughly in their heavier configurations; presumably they have. However, the laws of physics dictate that the performance and safety margins will be reduced, and no amount of testing can change that. The question is how far can you acceptably go. The designer has "weighed in" with his opinion, which I certainly do not feel qualified to disagree with.
 
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