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Aerobatic Weights and Relationships

G

glibejaja

I'm New Here
BLUF: Has anyone seen this +5g limit (Kevin Hortons POH), should it be followed? Can the MAW and MTOW be a linear relationship?

Morning All,
Im new to the Vans Air Force buying into an 1998 RV-8. Never thought the RV Grin was real until I flew her solo for the first time.
Im looking to get back into some aerobatic flying. Ive already started by revising the basics (loops, rolls, tail slides), but have found that unless I take no fuel I cant share these expirineces with family and friends in the back.

Looking into this, Ive found that Kevin Hortons POH (awesome document, well laid out) mentions a +5g limit? I cant find this anywhere else and would like some more context behind it if there is some?
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.ninelima.org/poh/Vans/RV-8A/RV8-poh-2011-kevin-horton.pdf

Else, can I extrapolate a linear plot between the weight and g-load limits on the aircraft?
Ex: +6g at 725kg and +3.3g at 816kg? Can a pick a point inbetween and say that I can pull +4g at 780kg?
Or should I treat the weights and g's like a cliff, where 726kg-816kg are a +3.3g limit.

Looking forward to hearing your comments on the above,
Safe flying!
 
Vans says +6 and -3 so that's what I'd use at any weight as they do not qualify that like some other aerobatic aircraft do (edit: I was wrong, they do limit the weight with -1 wings to 1600lbs). They do say not to do tail slides or other maneuvers that reverse airflow over the tail - be careful.
 
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inktomi said:
Vans says +6 and -3 so that's what I'd use at any weight as they do not qualify that like some other aerobatic aircraft do. They do say not to do tail slides or other maneuvers that reverse airflow over the tail - be careful.
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Woah there! They most definitely DO have an aerobatic gross weight limit. For the RV7 and RV8 it 1600 lbs.

This is a cut and paste from the marketing material on Vans homepage.

"...At the aerobatic gross weight of 1600 lbs., the RV-7/7A complies with the +6/-3G standards of the FAA’s Aerobatic Category..."

and this is from section 14 of the build manual

4. Maximum Aerobatic Gross Weight: The maximum weight that the structure of the airplane can support at the 6 G limit of the Aerobatic Category. For the RV-7/7A, this weight is 1600lbs.
 
glibejaja said:
Else, can I extrapolate a linear plot between the weight and g-load limits on the aircraft?
Ex: +6g at 725kg and +3.3g at 816kg? Can a pick a point inbetween and say that I can pull +4g at 780kg?
Or should I treat the weights and g's like a cliff, where 726kg-816kg are a +3.3g limit.
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No idea why Kevin's POH varies from Van's recommendations. I would use Van's weight and G limits as the bible.

And NO, you cannot extrapolate G limits that way. There is a ton of available information on this subject both using the search feature here or the Matronics archives.
 
Desert Rat said:
Woah there! They most definitely DO have an aerobatic gross weight limit. For the RV7 and RV8 it 1600 lbs.

This is a cut and paste from the marketing material on Vans homepage.

"...At the aerobatic gross weight of 1600 lbs., the RV-7/7A complies with the +6/-3G standards of the FAA’s Aerobatic Category..."

and this is from section 14 of the build manual

4. Maximum Aerobatic Gross Weight: The maximum weight that the structure of the airplane can support at the 6 G limit of the Aerobatic Category. For the RV-7/7A, this weight is 1600lbs.
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Whoa there again. He said it’s a 1998 RV-8. So it’s not a -1 wing spar unless there’s something in the logs that says it was removed and replaced which is unlikely. The limit on a non -1 is 1550.

Horton’s POH is for HIS bird, he was the manufacturer of THAT RV-8. You need to reference the material for your bird.

You need to call Vans and get some good advice.
 
Below is a sample W&B for a representative RV-8 with a non-Dash 1 wing (i.e., Max Aerobatic GW =1550 pounds). It assumes a 200 pound pilot, 126 pound passenger, 20 gallons of fuel, which gets you to the Max Aerobatic GW. Leave off a little more fuel and take a heavier passenger.

Screenshot 2024-05-15 at 9.42.37 PM.jpg


NOTE: Vne is in TAS: Vne = 230 MPH TAS/200 KTAS.
 
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Also, have the aircraft weighed on certified scales. In 26 years it undoubtedly “grew”. Aircraft gain weight over the years for lots of reasons. Also no telling how the original builder weighed it in the first place.

Monday morning quarterbacking, if doing aero with two people (perhaps larger) was a priority then the aircraft you were looking for should have been a -1 wing which adds 50 more pounds to the limit 1550 to 1600 gross aero, and an aircraft with a low empty weight. If your empty weight is already high (c/s prop, angle valve engine, etc etc) and it’s a non -1 then you might be severely limited depending on your loading situation.

Please don’t adopt someone else’s POH out of convenience.

There’s always research, engineering, and going back to phase 1 to prove changes.
 
I only saw it mentioned once here so I'll bring it up again. RV's don't tolerate tail slides well. Their empennage isn't as sturdy as more aerobatic focused planes.

I can already hear the replies I'll get for this next bit so flame away safety police. Many aerobatic maneuvers can be completed without stressing the airframe beyond normal category limits. Bob Hover demonstrated this many times. Tex Johnston rolled a 707, My last skydive pilot rolled a Beech 18 beautifully before Matt Younkin started flying airshows. In other aerobatic discussions on this forum most people don't exceed 4g's doing aerobatics in their RV's. That's within utility category limits.
 
I have rebuilt an RV-3 after tail-slides. The control surfaces exhibited no damage but the fuselage sides were wrinkled between the last 2 bulkhead.
 
Mel said:
I have rebuilt an RV-3 after tail-slides. The control surfaces exhibited no damage but the fuselage sides were wrinkled between the last 2 bulkhead.
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Thanks Mel, I incorrectly assumed the control surfaces would be the likely problem.
 
Jjackh10 said:
I only saw it mentioned once here so I'll bring it up again. RV's don't tolerate tail slides well. Their empennage isn't as sturdy as more aerobatic focused planes.

I can already hear the replies I'll get for this next bit so flame away safety police. Many aerobatic maneuvers can be completed without stressing the airframe beyond normal category limits. Bob Hover demonstrated this many times. Tex Johnston rolled a 707, My last skydive pilot rolled a Beech 18 beautifully before Matt Younkin started flying airshows. In other aerobatic discussions on this forum most people don't exceed 4g's doing aerobatics in their RV's. That's within utility category limits.
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No argument with anything you said…yet I’ll add that it isn’t about protecting folks from properly executed maneuvers - the real problem comes when they botch one. Then the G’s (especially rolling G’s) can get excessive. Hoover, Younkin, et al had skill levels beyond the average RV driver…..
 
Ironflight said:
No argument with anything you said…yet I’ll add that it isn’t about protecting folks from properly executed maneuvers - the real problem comes when they botch one. Then the G’s (especially rolling G’s) can get excessive. Hoover, Younkin, et al had skill levels beyond the average RV driver…..
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Agree completely. With the slippery airframe of an RV I'd think you wouldn't have to totally botch a maneuver. A bit off of proper could be trouble.
 
Jjackh10 said:
Thanks Mel, I incorrectly assumed the control surfaces would be the likely problem.
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I don't think that's necessarily an incorrect assumption. I would think that in most cases the control surfaces would be damaged. But in this particular situation they weren't. My best guess is that this pilot held the control surfaces firmly enough that they weren't slammed against the stops.
 
Mel said:
I don't think that's necessarily an incorrect assumption. I would think that in most cases the control surfaces would be damaged. But in this particular situation they weren't. My best guess is that this pilot held the control surfaces firmly enough that they weren't slammed against the stops.
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We know from SB history that the HS spar and elevator hinge attach points have enough trouble withstanding normal straight and level flight. Expecting them to withstand tail-slides seems like a dice roll I don't need to bet on.

- mark
 
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