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Calculation of Aerobatic gross weight

E

eddieseve

Well Known Member
Hi Guys,

Sorry if I am opening an old topic, but I am really hoping that someone might be able to explain the following;

This is taken from an old post by Randy Lervold about a discussion he had with Van. I have removed the references specific to the RV-3 and left the other statements alone.

"Aerobatic gross weight for the RV-? (all models, all wings) does NOT include fuel in WING tanks. Note that any fuel in a fuselage tank WOULD be included in the Aerobatic gross."

Can someone with a better brain than myself please explain this, the reasoning was never clearly expanded in the original thread and I would love to understand why this is so?

Cheers
 
eddieseve said:
Hi Guys,

Sorry if I am opening an old topic, but I am really hoping that someone might be able to explain the following;

This is taken from an old post by Randy Lervold about a discussion he had with Van. I have removed the references specific to the RV-3 and left the other statements alone.

"Aerobatic gross weight for the RV-? (all models, all wings) does NOT include fuel in WING tanks. Note that any fuel in a fuselage tank WOULD be included in the Aerobatic gross."

Can someone with a better brain than myself please explain this, the reasoning was never clearly expanded in the original thread and I would love to understand why this is so?

Cheers
Click to expand...

The weight of the fuel reduces the bending moment at the wing root.
 
As posted in an RV-3 thread:
The debate about wing fuel will roll on. Given the RV-3 was designed with a fuselage wing tank, and was good for 1050lbs, then moving to wing fuel would seem to indicate that fuel can be excluded, provided the "weak point" is the wing/fuselage junction (unfortunate early RV-3 evidence would indicate this).

The RV-3B uses an internally redesigned wing, based on an RV-8 design. The early RV-8 accident had the wings fail mid-span, and that would not support deducting wing fuel before determining weight for aeros. But the RV-8 wing was then re-designed (-1 wing).

Randy has the word from Van, but currently Vans will not support that (but to be fair, they will not "support" much of the RV-3 given the time, records and personnel changes). I doubt you will get a definitive answer supported by engineering data, but then it is experimental :eek:
Click to expand...
 
As has been oft-repeated, fuel weight wouldn't count towards aerobatic gross if the fuel load was evenly spread across the span of the wing. It isn't, of course, and as a result the weight of the fuel should be taken into account against aerobatic gross weight.

While fuel in the tanks may reduce bending moment at the wing root, it increases the load on the spar at the point just outside the fuel tank. A failure there is just about the safest place a failure can occur since it will only just barely kill you :)

Factually, Randy's site makes those claims but Van's doesn't support that position.
Your choice as to which path to take, of course.
 
Last edited:
eddieseve said:
"Aerobatic gross weight for the RV-? (all models, all wings) does NOT include fuel in WING tanks. Note that any fuel in a fuselage tank WOULD be included in the Aerobatic gross."
Click to expand...
I wish I had a dollar for every time i've heard someone talk about gross weights in RV's. Or for every time someone said "Van himself said to me (or my friend) once at a fly-in..." I could buy another RV with all those dollars... :)

As pointed out by others, fuel in the leading edge tank reduces the load at the wing root under positive G, but creates a stress concentration at the outer end of the tank... So more fuel doesn't increase your G margin when doing aerobatics.
 
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