J

Juan Pablo

Member
Hi from Argentina. Is there any restriction to do aerobatics with 2 people onboard in a RV-8? in addition to max TO weight acro, of course. I heard some rumors that with two people onboard, and the CG placed near AFT limit, you have to avoid spins, because it can degenerate into a flat spin, it is true?Thank you
 
Aerobatics

Juan,

I think the correct answer is that in the right hands, you can do anything. But I will share with you my experience in an RV4 with 180HP and CS prop: With just me, the airplane can do some incredible things. Add the second person and it has a complete new personality to be very careful with. I lost that RV4 and two great people in what may have been an unintended action that resulted in a flat spin. The irony is that my stepson (the pilot in the front seat) had done aeobatics in a Mustang several times. A Mustang with two people is not the same as an RV4 or RV8. Needless to say, in the wrong hands, bad things can and do happen. An aft CG is not your best friend in a bad situation.

Ned Bowers
 
I guess I don't fully understand why you ask. How many people are in the plane during acro is irrelevant. All that matters is the aerobatic gross weight and associated CG limits as stated by Vans for your model. You need to put together a W & B calculator so you know your total loaded weight and where the CG falls with different passenger weights, fuel levels, etc. If you're within limits, there's no reason to second guess anything.
 
Juan Pablo said:
Eric, thanks for your answer.
My questions is, if the CG is within limits, there will be no problem with spins?
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I would assume the RV-8, like other RV's, has different aft CG limits and gross weights for acro vs. normal (non-acro) operation. If you are within the aerobatic aft limit and gross weight then there should be no problem doing spins. Of course, you should do full aerobatic flight testing before carrying passengers.
 
Go test this yourself. Be conservative and work from fwd to aft CG in small increments. The CG in which you become uncomfortable in the recovery or the published AFT limit (the more fwd of the two) now becomes your aft Spin limit.
 
If what you're looking for is some actual experience with aft CG's and Acro, then I'll contribute - the Tandems (both -4 and -8) handle VERY different with aft CG - stick forces get extremely light, so it is easy to over-G the airplane if you are not aware of this fact. Yes, light stick forces can be delightful - many would argue that the handling is better at aft CG, and that all depends on what you like. The point I want to make is that you need to be careful with your maneuvering until you have adapted to the feel at aft CG's.

I personally did not like the spin recovery at very far aft CG's, and won't choose to spin the plane in that condition. I generally would restrict Acro to simple loops and rolls if I had a passenger. The reality is that I simply don't do Acro with passengers because I don't have an extra parachute, so I can't meet the (US) regs with someone in the back seat. (All my aft CG testing was done with ballast)

Paul
 
Over 100 spin tests at different weight, CG, control position and no. of turn variations were made when the RV-8 gained its UK aerobatic approval and no unsatisfactory recoveries were experienced. These were all conducted within Van's published aerobatic weight and CG limits.
This letter summarises their recommendations.
I'd concur with the advice given re the characteristics at aft CG conditions.
The RV-8 especially with the -1 wing does allow a lot more versatility than the -4.
 
The only caveat I'd throw in is that no two airplanes are alike when built without configuration control as in factory built. Small changes in fairings, antenna placement, differenct canopy shapes (Todd's vs Stock) can have a profound effect on spin recovery characterisitics. It is a great baseline knowing the extensive testing conducted in the UK was completed with satisfactory results but each builder MUST repeat the test themselves in the configuration they intend to fly.

Nothing particularly tricky about this testing. In fact the word "testing" is misleading. The only difference in a "test spin" and a "fun spin" is the intent to be critically observant during the spin rather than simply enjoying the experience.

When I conducted my Phase 1 spin testing I first ensured I was at the most fwd CG I expected to fly my plane and went up and conducted a bizzillion 2 turn spins (yes a bizzilion). I maintained a constant DA and GW the best I could and kept CG fixed. My observations were a mix of qualitative and quantitative. I rated the nose attitude, the stall break, the turn rate as: Steep, benign, moderate. I conducted spins the same way each time for consistency.

Quantitatively at I would say out loud, "stall buffet, break, theres 1 turn, 2 turns, recover - one-one-thousand, two-one-thousand, three-one-thousand " until the turn rate was stopped and under control. I used same recovery technique for each.

Then I would rate the nose attitude qualitatively as "steep, mild, shallow"

I had a knee board card for each spin and filled it out after the spin based upon what I heard myself say during the spin. No need to have a hard to read matrix of tiny little spaces to fill in. Don't save trees use one card for each test and write big (use a mechanical pencil - ask me why!)

Once I had completed the bizzillion spins in the fwd CG configuration I jumped right to a mid CG spin and conducted the same test many times. The idea was to test CG sensitivity while still in a fwd CG configuration. The change in characteristics with a large CG change (but still in the safe range) can give big clues to how incremental changes in CG will go when moving more aft. Make sense? What I learned was the -8 isn't very sensitive but it is noticable (slightly shallower entry, slightly faster spin rate, slightly longer recovery, slightly shallower recovery attitude). This gave me confidence to continue sliding aft but at smaller increments. I went to full AFT CG and found the results to be noticable but still very acceptable and safe.

Now here is my additional CAVEAT - this test was conducted with left spins at a narrow DA range. A full test would include holding CG constant and testing at various DA and again to the right. Until I do this in more detail I'm not going to spin aft of the middle of the CG range.

Conditions:
Power Idle
Flaps Up
Stick full aft
Ailerons neutral
Full left rudder at the stall

recovery:
at 2 turns
Stick relaxed just fwd of full aft with simultaneous
Full opposite rudder until rotation stops then neutral with gentle pull to recovery in level flight with power as needed.

my .02
 
Largely covered above, but in summary, each aircraft should be test flown and written up by someone with appropriate experience in the spinning arena. That testing will start at Fwd CG, and work Aft.

RV-8s do take a little longer to recover 2 up than 1 i.e. aft CG - a 3 turn spin taking typically 1500' from intitiating recovery to climbing again. The spin is far from "flat". It does speed up noticeably after 1-2 turns, is somewhat oscillatory, but is not as "exciting" as the SBS types :eek:

Aeros - as above, a delight at aft CG, but easy to overstress and not suitable for aeros training.

Andy
 
RV8R999 said:
recovery:
at 2 turns
Stick relaxed just fwd of full aft with simultaneous
Full opposite rudder until rotation stops then neutral with gentle pull to recovery in level flight with power as needed.
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In general, It's not good technique to make simultaneous inputs with the stick and rudder to recover. Rudder first is best and generally accepted as proper technique to ensure you don't accelerate the spin (and further blank the rudder) with fwd stick before the rudder has a chance to have some effect.
 
The word "generally" doesn't apply to a specific airplane under specific configurations. I fully tested MY RV-8 spin recovery using an iterative approach to 6 different recovery combinations and found the simultaneous (ok lets call it near simultaneous) recovery to be the best. Your results may and likely will vary.
 
spins

The Pitts S1S and S2B, the Sukhoi SU26 and 29, as well as MOST high performance aerobatic monoplanes, will recover from an upright flat spin with simultaneous application of controls. Using the Pitts as an example, left rudder spin, full power, full aft stick, full right stick, leave the throttle full open, simultaneous full right rudder and stick in forward left corner, recovery in less than 1/4 turn. The rotation rate is moderate, recovery on a point is relatively easy if you have some good reference points. I taught myself flat spins in the S1S, starting at 13,000 agl and working my way down about 1000feet a year. Best to get some instruction.
 
RV8R999 said:
The word "generally" doesn't apply to a specific airplane under specific configurations. I fully tested MY RV-8 spin recovery using an iterative approach to 6 different recovery combinations and found the simultaneous (ok lets call it near simultaneous) recovery to be the best. Your results may and likely will vary.
Click to expand...

I guess we're talking two different things here. I was referring to emergency spin recovery. If you found yourself in an accidental spin, you would not need to be trying to remember which specific configuration you are currently flying, and which method you need to use to stop the spin the absolute fastest. If you found the technically quickest recovery method, which differed for multiple load, CG, etc. conditions, then that's great. I'm speaking more to an across-the-board "general" recovery method that will always serve you for emergencey spin recovery regardless of the airplane you're flying, as well as the specific configuration it's in. For this model, it really is best to use rudder first.


jrs14855 said:
The Pitts S1S and S2B, the Sukhoi SU26 and 29, as well as MOST high performance aerobatic monoplanes, will recover from an upright flat spin with simultaneous application of controls. Using the Pitts as an example, left rudder spin, full power, full aft stick, full right stick, leave the throttle full open, simultaneous full right rudder and stick in forward left corner, recovery in less than 1/4 turn.
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I have done flat spins in a Pitts, but never paid attention to what turn fraction it took to stop. Recovery from an inverted flat spin is quite a bit more positive than an upright flat spin due to the increased exposed rudder area during the inverted spin. If you are stopping the upright spin in less than 1/4 turn, how about the inverted? Should be a bit faster.
 
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