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Kevin Horton type question: RV-8's, Dash One Wings and Aerobatic Gross Weight.

R

RhinoDrvr

Well Known Member
Apologies if this has been asked before. I searched but was unsuccessful.

Regarding G-limits and aircraft gross weight; is the relationship between gross weight and G-limits linear?

I am a larger dude (6'3" / 220lbs) and am looking for an RV-8 for cross country flight, and leisurely Sunday aerobatic flights. I've come across a nice RV that fits my needs, but lacks the "dash one" wing, and therefore has an aerobatic gross weight of 1550lbs, and a utility gross weight of 1800lbs.

My actual aerobatic gross weight in a theoretical RV-8 would probably be;

Empty: 1050lbs
Fuel (20gal): 120lbs
Me + Chute: 235lbs (I'm guessing a parachute weighs 15lbs)
Pax+Chute: 220lbs (Another 15lb chute)

Total Weight: 1625lbs

Here's my question. If the airframe is rated to +6 G at 1550lbs (I'm not even going to worry about the negative g limit given the types of maneuvers I'm planning on) can I plot a line between 4.4G @ 1800lbs and 6G @ 1550lbs and interpolate what my maximum load limit would be at my actual gross weight?

Here's where the math starts and my 988/1000 college class rank starts to show....

I plot the line between (1800, 4.4) and (1550, 6) to be;

Y= -0.0064X + 15.92

Therefore; at my planned weight of 1625lbs, the G-limit would be 5.5G's, which is plenty for most maneuvers which can be safely completed at 3.5G's.

Does this logic hold up to how aeronautical structures are actually designed?

I'm attempting to justify looking at RV's that lack the -1 wing, but I don't want to compromise my requirements for dual aerobatics. The extra 50lbs on the dash one wing, plus getting rid of 5 gallons of fuel would put me at the legal weight limit per Vans.

Thanks! Hope everyone is having fun at OSH!
 
That logic isn't correct. The excess weight is concentrated in the fuselage, so the wing bending moments will be higher than the simple calculation would indicate.
 
What Kyle said. You can only assume a linear correction if you take the extra weight and spread it uniformly over all parts of the aircraft. If you concentrate all the weight in one place, you concentrate the overloading in one place.

This has been discussed ad infinitum here on VAF.
 
I'm about your size and my 8 was on the heavier side. To get it under aerobatic gross meant 10 gallons per side. I'd burn off about 8 gallons on the left, then the 10 remaining in the right was go home gas.

It's a good all around airplane, but it's more of an either/or per flight. FWIW that was usually an hour or more of playing around.

Get your vitamin G in someone else's airplane, particularly at corner speed on a 1v1. The 8 will be underwhelming, but doesn't come with a 2 hour tape debrief.

Got shore tour orders yet?
 
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Sig600,

Good to know; that's kind of the conclusion I'm arriving at regarding mission set, either/or and plan fuel accordingly. I still think I need the 1600lb gross weight wing to make 15 gals of fuel work though.

Not quite on shore duty yet...extended 8 months in the fleet, so I'll make our next cruise (a short WESTPAC) then check out early next year. Looking to try and make my way up to Fallon if at all possible.
 
No, although both those look like they'd be a blast to fly! The username comes from the F/A-18F that the aircrew call "Rhino" vice "Super Hornet"
 
Kyle Boatright said:
That logic isn't correct. The excess weight is concentrated in the fuselage, so the wing bending moments will be higher than the simple calculation would indicate.
Click to expand...

It depends on what assumptions Van made when it was designed. Wings don't tend to come out that much heavier from build to build. You can't load 'em up with stuff as easily as you can a fuselage, with bigger engines, more panel goodies or fancy interiors (unless you add tankage). So perhaps he assumed that the weight is not evenly distributed but rather concentrated in the fuse. I don't know. Only he or his engineering staff would know and if they thought that publicizing that might encourage people to take risks they might not tell you, which is understandable. He went through **** on the rv3 wing failure fiasco so I am sure he wants people to just respect the weights.

Fly aerobatics solo and you will be fine. The Mrs doesn't want to sit in the back for lots of G and a rotating horizon anyway.
 
G whiz...

RhinoDrvr said:
Apologies if this has been asked before. I searched but was unsuccessful.

Regarding G-limits and aircraft gross weight; is the relationship between gross weight and G-limits linear?

I am a larger dude (6'3" / 220lbs) and am looking for an RV-8 for cross country flight, and leisurely Sunday aerobatic flights. I've come across a nice RV that fits my needs, but lacks the "dash one" wing, and therefore has an aerobatic gross weight of 1550lbs, and a utility gross weight of 1800lbs.

My actual aerobatic gross weight in a theoretical RV-8 would probably be;

Empty: 1050lbs
Fuel (20gal): 120lbs
Me + Chute: 235lbs (I'm guessing a parachute weighs 15lbs)
Pax+Chute: 220lbs (Another 15lb chute)

Total Weight: 1625lbs

Here's my question. If the airframe is rated to +6 G at 1550lbs (I'm not even going to worry about the negative g limit given the types of maneuvers I'm planning on) can I plot a line between 4.4G @ 1800lbs and 6G @ 1550lbs and interpolate what my maximum load limit would be at my actual gross weight?

Here's where the math starts and my 988/1000 college class rank starts to show....

I plot the line between (1800, 4.4) and (1550, 6) to be;

Y= -0.0064X + 15.92

Therefore; at my planned weight of 1625lbs, the G-limit would be 5.5G's, which is plenty for most maneuvers which can be safely completed at 3.5G's.

Does this logic hold up to how aeronautical structures are actually designed?

I'm attempting to justify looking at RV's that lack the -1 wing, but I don't want to compromise my requirements for dual aerobatics. The extra 50lbs on the dash one wing, plus getting rid of 5 gallons of fuel would put me at the legal weight limit per Vans.

Thanks! Hope everyone is having fun at OSH!
Click to expand...


Evan,

G loading on an Experimental Design (RV)as previously mentioned, is at your own risk, calculated as it may be. After building and flying my RV4 for 10 years, owning a Rocket for five more and a half a lifetime flying the F16, I somehow became G aware.

"G forces" as you well know stress airplanes, period. Aluminum stress is cumulative until failure. Even the 80's vintage Block 30 F16's I flew now have big .060 scab patches riveted on the wing roots to beef-up crack prone areas. Even a 9G design gets stressed to failure. http://www.f-16.net/forum/viewtopic.php?t=16060
The RV4 and Six wing were sandbagged 9G's without failure. I'm not sure about the 8. It's a single-billet spar compared to the 4 and 6 laminated design which AE's tell me handles cumulative stress better. That also didn't include the tail.

That said, back in 98' The Van's RV8 demonstrator shed a wing near Blythe CA with 2 fatalities, apparently an Over-G or rapid onset at high speed. Lesson: Just like in the F16 or in your case Super Hornet with stores on the wings (G limits) At high speeds use a smooth onset not to exceed limits.
https://www.ntsb.gov/_layouts/ntsb....ev_id=20001211X10121&ntsbno=LAX98FA171&akey=1

I performed positive G sport aerobatics in my RV4 (and HR2') with the G meter only exceeding 3.5 once. * My rule was simple, solo, below 1/4 tanks and no "yanking on the pole". so to speak.
The RV is a Sport Aerobatic airplane, if you want to pull G's and do unlimited acro, buy something designed for it.

For your 8, discretion is the better part of valor.

V/R
Smokey

*To avoid a midair in a air traffic controlled airspace. See and avoid, bigtime.
 
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Thanks for the replies, gents!

Please don't get the idea I want to try and yank the wings off my RV, I'll limit the high G stuff to an airplane Uncle Sam is paying for; I just want a good safety factor for my ~3.5 G gentleman's aerobatics showing some of my non-pilot friends what a loop or barrel roll looks like.

I guess it's really a moot point which wing the airplane has as long as we treat 4.4 as the g-limit and don't exceed that, which makes sense anyway on an airplane I'm paying for the maintenance on.
 
RhinoDrvr said:
Thanks for the replies, gents!

Please don't get the idea I want to try and yank the wings off my RV, I'll limit the high G stuff to an airplane Uncle Sam is paying for; I just want a good safety factor for my ~3.5 G gentleman's aerobatics showing some of my non-pilot friends what a loop or barrel roll looks like.

I guess it's really a moot point which wing the airplane has as long as we treat 4.4 as the g-limit and don't exceed that, which makes sense anyway on an airplane I'm paying for the maintenance on.
Click to expand...

As long as you're smooth you'll have a hard time getting past 4.5. I went out one day with about 10 gal total and tried to get to 6 just to see how it performed. Couldn't do it, at least not without snatching the stick back in an uncontrolled manner. No guarantee I could stop it at 6 with how hard you'd have to jerk back. Once you get above 4 it bleeds energy like a stuck pig. You'll be fine if you're conservative.
 
It can be done....

Sig600 said:
As long as you're smooth you'll have a hard time getting past 4.5. I went out one day with about 10 gal total and tried to get to 6 just to see how it performed. Couldn't do it, at least not without snatching the stick back in an uncontrolled manner. No guarantee I could stop it at 6 with how hard you'd have to jerk back. Once you get above 4 it bleeds energy like a stuck pig. You'll be fine if you're conservative.
Click to expand...

Oh, I don't know...It's not that hard to exceed 4.5 g's in an -8. In this video, I'm regularly sustaining ~ 5.7 - 5.8 g's (the g meter is slightly left of center on the PFD and it goes to inverse font @ 5.5...

https://youtu.be/FmXAbintNY8

This is in a nose-heavy RV-8 with a high stick-force gradient...and it's much easier with pax,although the energy bleeds off a bit faster .

Skylor
 
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skylor said:
Oh, I don't know...It's not that hard to exceed 4.5 g's in an -8. In this video, I'm regularly sustaining ~ 5.7 - 5.8 g's (the g meter is slightly left of center on the PFD and it goes to inverse font @ 5.5...

https://youtu.be/FmXAbintNY8

This is in a nose-heavy RV-8 with a high stick-force gradient...and it's much easier with pax,although the energy bleeds off a bit faster .

Skylor
Click to expand...

Using the vertical, yes you can "get" there. However I suspect you and we (rhino and I) have vastly different definitions of "sustained g." i.e. Level altitude, maintaining airspeed. Show me a video of you doing that at 5.7. :D

Mine too was nose heavy solo, w/ 230hp.
 
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