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Aerobatic build considerations?

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inktomi

Active Member
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Hi!

I know that the down lines are the hard part of RV-8 aerobatics, because of the speed you can reach quickly when pointing the nose directly down.

I want to do sportsman level competition, and so am adding flop tubes, inverted oil, and an aerobatic prop with my injected engine. That said, it seems like the speed increase is directly related to aerodynamics right?

With that in mind, mods like the fastback or aftermarket cowlings would only make the situation worse, right? Those are claimed to be more aerodynamic than the default options - so the down lines would speed up even faster.

Is this logic sound? It seems pretty straightforward to me, but I’ve also been known to overthink things. Would it really matter?

I do think a canopy ejection would be easier with the fastback vs the slide back option, for the case of actually needing that IAC required parachute. But maybe not?
 
I have been flying sportsman aerobatics in my RV-8 in the past (don't have the time recently) and you seem to have a good plan. You don't NEED flop tubes and inverted oil for sportsman aerobatics as you won't be inverted long enough but it doesn't hurt. As for prop I got a light weight fixed pitched prop which works fine for sportsman but an aerobatic constant speed prop is of course nicer.

As for picking up speed I don't think the after market things will make a huge difference maybe a couple knots. The biggest problem is really point rolls on a down lines. The one common one in Sportsman is a 1/2 roll from inverted with a point at knives edge. For that you have to be fast enough that the nose doesn't drop at knives edge so you can't roll early AND you have to be able to make the line before the roll equal length to the line after the roll. That makes you pretty fast by the time you recover. If you plan your energy well you will still be well within limits of course but that's in terms of speed the most difficult one I remember. Otherwise I really never had a major issue with speed picking up.

Hope that helps!

Thx

Oliver
 
Thank you! I really like the look of the fastback, so if it doesn't matter much I might do it. The cowling.. if it's not needed for the engine (planning an IO-375) then maybe I'll just save the money and keep the weight of the prop a couple inches closer.
 
The aerodynamics of the fastback or other mods are not enough different to matter. Weight does matter. A lot! And I would think flatter pitch - so higher RPM with lower MAP - would be draggier. Which raises an interesting question from just a total amateur, occasional gentleman's aerobatics guy. How do you manage power when you do aerobatics? I just set the throttle to get me to the entry speed I want in level flight, with 2400 RPM, and fly the maneuver. I don't move the throttle during the maneuver. Should I?

(obviously my hand is on the throttle and I can pull back quickly if something ever doesn't go the way I want)
 
I would also love to know.. I know there are entry speeds, but I haven’t heard about throttle changes during maneuvers. I would think there isn’t really enough time during most to matter, and certainly in the Extra 300 training I did we left the engine and prop controls more or less set during maneuvers.
 
My view is your logic is not really accurate. If your aircraft accelerates quickly then shorten the line. Slow down before pulling to the vertical and throttle back. Theres no rule dictating how long a down line (or an up line) must be. Airframe mods will make little difference to the basic properties of the aircraft. As post #2 said a wobbly prop isn't necessary, but will probably make the figures easier.

Competition figures are completely different from recreational aeros. In a competition you would probably be running 25 to 2700rpm and leave it there, although some aircraft (not RVs) stall turn better if the pitch is pulled back momentarily. As you start pulling you could go to full power to pull harder, make a sharper corner and score better. Then throttle back to limit the height gain. In a slick aircraft speed management, and therefore power management, is important to present the figures in front of the judges to score well. I'm working hard to keep it all tidy. Going into a spin requires the most practice. At Intermediate getting to the right speed to snap also requires ŵork and planning.

Recreational aeros are just set a moderate power setting and drive around the sky, I don't go negative and don't spin.
 
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Another interest is to do some formation flights, and I’ve been told that a constant speed prop will be helpful there. Great point about down line length, so long as the judges see you hit the line it counts no matter how short.
 
scsmith said:
The aerodynamics of the fastback or other mods are not enough different to matter. Weight does matter. A lot! And I would think flatter pitch - so higher RPM with lower MAP - would be draggier. Which raises an interesting question from just a total amateur, occasional gentleman's aerobatics guy. How do you manage power when you do aerobatics? I just set the throttle to get me to the entry speed I want in level flight, with 2400 RPM, and fly the maneuver. I don't move the throttle during the maneuver. Should I?

(obviously my hand is on the throttle and I can pull back quickly if something ever doesn't go the way I want)
Click to expand...

I use two power settings. All the way forward and all the way backwards (e.g. spin). There is no reason to reduce power in a loop (I actually posted traces proofing that if the loop is round the exist speed will be equal or less to the entry speed even with full power all the way around) and as the prior poster pointed out even on downlines full power helps... .

Oliver
 
spatsch said:
I use two power settings. All the way forward and all the way backwards (e.g. spin). There is no reason to reduce power in a loop (I actually posted traces proofing that if the loop is round the exist speed will be equal or less to the entry speed even with full power all the way around) and as the prior poster pointed out even on downlines full power helps... .

Oliver
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Thanks. Yes, I agree based on physics that if you exit at the same altitude, your exit peed will be less than or equal to the entry speed.
But full power in level flight will give me a much higher speed than the desired entry speed. So do you have part-throttle in level flight and then full forward as you start the maneuver?
 
Anyone build just one tank with the flop tubes?? IOW make just one tank the 'aerobatic' tank?? Kinda what I'm thinking.
 
I think a lot of folks do that with a tube only in one tank. They’re easy enough to add though, so I was planning on having one in both and not needing to think about which tank I‘m on.
 
I disagree that only 2 power settings are needed. With a straightforward sequence and a powerful, low drag, airplane (RV-8) it is quite possible to gain speed and height throughout, and get further away from the judges and get a poor score. Particularly on the way into the spin speed control is important, throttle to idle only as the nose is forced down.
 
I'll chime in with another perspective. With respect to IAC Sportsman figures, keep it fun, light, and simple. I've been competing for a couple years (not in the RV). My -8 doesn't have any of the "aerobatic extras" (inverted fuel, oil, etc) and I'm very confident will be just fine in Sportsman. It won't see the light of day in Intermediate though, as Jerry E. pretty much proved that is best done in different airframe.
 
Pay attention to post #9. From a Citabria to a Glasair to a Sukhoi a full power loop should have the same speed at entry and exit if done perfectly. Full throttle all the way. This is based on g loads in the 3 G range.
Don't think that any of the high performance aerobatic airplanes (Extra etc) are as clean as an RV. Those airfoils are relatively high drag compared to an RV. Pulling a lot of G in those airplanes further increases drag.
 
I've been flying IAC competition aerobatics since 2016, recreational aerobatics forever. I flew 12 contests in Sportsman and dabbled in Intermediate in my RV before moving on to the Extra. I still have my RV; always will.

I agree that the minor aerodynamic improvements won't amount to anything. Speed is controlled with g and the throttle. In recreational aerobatics, I left the power at high cruise setting of 24" and 2400 rpm and performed aerobatics between 3 - 4.5 g all day long without touching anything. In competition, the power was set mostly like Oliver said, everything forward or idle. On hammerheads I would gradually bring the power back (about 1/3 throttle) during the pivot to avoid being overcome by the torque. If I had point rolls on the way down, I would leave the power back until initiating the pull out. Speed on down lines (45 or vertical) is also managed by line length.

My airplane is configured with a flop tube in the left tank, an IO-360A1A (200 hp), Christen inverted oil system, and a Hartzell constant speed prop. I never felt that I had too much energy or gained enough energy throughout a sequence to get so high that it impacted my presentation.

Oliver and others have proven that you don't "need" flop tubes, fuel injection, inverted oil, and a constant speed prop for RV Sportsman competition aerobatics. But having those accessories will make your aerobatics easier and more enjoyable. It will also allow you to things that you wouldn't be able to do otherwise. I had several Free programs with "interesting" figures that I couldn't have done without those accessories. And the best thing about the constant speed prop is the braking action. Don't underestimated the value of the acceleration and braking action especially if you're interested in formation. I have one flop tube in the left tank only. If I had to do it over, I would put two, one in each tank. The only negatives were that unusable fuel that went from 4 oz to 13 oz and the periodic required replacement of the rubber hose. Something about being in the middle of a Cuban 8 upside down pointed at the ground when you've been made aware that you forgot to select the correct tank will make you wish for dual flop tubes! The other accessory I wished I had was a ratcheting harness. If you're still building, figure out the structural changes to incorporate a ratcheting belt that has a secondary attachment point. Make it so that when you tighten the ratchets you are pulled down into the seat rather than aft. You may also have to incorporate something firm as opposed to a soft seat cushion that you sink into. The other thing is, my parachute destroyed my stock seat back. I had to remove the cushion when wearing the parachute. I've made a new an "improved" seat back, but I'm not flying competition in the RV anymore anyway. So it really doesn't matter.

Ron Schreck had a power point presentation called RV Aerobatics. It got into the hardware and other stuff. I'll see if I can find it and post it here.

I highly recommend IAC competition aerobatics. It's extremely challenging and fun. It WILL make you a better pilot. You'll make a lot of new friends. Everyone is very helpful, even your direct competitors. I always have purpose when I fly. It's changed my life. I'll be doing this until I can't do it anymore.
 
Here's Ron's article. I'm still trying to figure out how to attach his PowerPoint presentation.
 

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RV8Squaz said:
... The other thing is, my parachute destroyed my stock seat back. I had to remove the cushion when wearing the parachute. I've made a new an "improved" seat back, but I'm not flying competition in the RV anymore anyway. So it really doesn't matter.
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I also made a different seat back for when I use my parachute.

RV-8 cockpit layout puts you closer to the instrument panel than many airplanes, and lots of people flying the -8 for the first time comment on that. If you add a parachute to that, you are very close to the panel. So I made a second seat back that has the side rails cut, then bent the seat back so the lower portion angles back more. Once I got the bend right, I riveted on reinforcement straps to tie the side rails together where I had cut them. This makes a world of difference! My parachute is about the same thickness as the seat back upholstery, so my seating position is about the same either way.

Here is a link to the old thread with a picture of my modified seat back.

Improved comfort for aerobatics

When I built my RV-8, I bought the Classic Aero Designs Aviator upholstery, so the original Vans front seat back was left over. I figured it would be useful for flying with a parachute, just swap out the upholstered seat back for the bare Vans seat back. My parachute is a Long-Softy, and it is...
vansairforce.net vansairforce.net

I also now get my parachute packed with the "diaper down" so that the thickness is less around the shoulders, and thicker in the lumbar area. This helps a lot as well.
 
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Here are some notes from Bill McLean I believe.
 

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Still trying to figure out how to attach Ron's Power Point presentation. Does anyone have any ideas?
 
scsmith said:
I also made a different seat back for when I use my parachute.

RV-8 cockpit layout puts you closer to the instrument panel than many airplanes, and lots of people flying the -8 for the first time comment on that. If you add a parachute to that, you are very close to the panel. So I made a second seat back that has the side rails cut, then bent the seat back so the lower portion angles back more. Once I got the bend right, I riveted on reinforcement straps to tie the side rails together where I had cut them. This makes a world of difference! My parachute is about the same thickness as the seat back upholstery, so my seating position is about the same either way.

Here is a link to the old thread with a picture of my modified seat back.

Improved comfort for aerobatics

When I built my RV-8, I bought the Classic Aero Designs Aviator upholstery, so the original Vans front seat back was left over. I figured it would be useful for flying with a parachute, just swap out the upholstered seat back for the bare Vans seat back. My parachute is a Long-Softy, and it is...
vansairforce.net vansairforce.net

I also now get my parachute packed with the "diaper down" so that the thickness is less around the shoulders, and thicker in the lumbar area. This helps a lot as well.
Click to expand...
Ha! My old seat back developed a bend that is similar to your intentionally modified seat back. That looks good Steve.
 
scsmith said:
Thanks. Yes, I agree based on physics that if you exit at the same altitude, your exit peed will be less than or equal to the entry speed.
But full power in level flight will give me a much higher speed than the desired entry speed. So do you have part-throttle in level flight and then full forward as you start the maneuver?
Click to expand...
If I stayed in level flight for a long time that might have been an issue but staying in the box you don't do that and even when you pull only 3G your drag goes way up and that's where your energy goes. Also most figures have a really wide entry speed. E.g. you can roll from about 90mph to VNE. Loop you do need to be fast enough to make it look good but the upper limit is VNE again. You just need to stay in the G limits and as more Gs you pull the more energy you bleed off.

Also a good sequence is designed so the speeds line up. E.g. you wouldn't put a spin after a 45degree down line. By the time you reduced the speed even at idle you would likely be out of the box. You put it after an Immelmann where you will be slow anyway.

I don't recall ever flying a sequence and ending up higher. Most of the time it was lower so the extra energy was appreciated. I am not saying that there aren't any acro airplanes out there which have an engine big enough so it becomes an issue. A 180hp RV-8 is not one of them.

Oliver
p.s. looking at your signature I want to get my LS3 back ... .
 
RV8Squaz said:
Here are some notes from Bill McLean I believe.
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In those notes the author states:

"1. Fuel. It doesn’t count in the wing tanks for aerobatic weight according to Van, ..."​

Note that Van's Aircraft does not agree with that statement. See Service Letter 15-11-20 for a full explanation, but the short answer is that the aerobatic RV's have the fuel tanks too close to the wing root and therefore are not effective in relieving the wing bending moment. They go on to say, "In fact, the root stress will increase with the added fuel weight. Trust us, we've done the math."
​
Also from the SL:

"Bottom Line:​
The weight of the fuel, whether it is in a wing tank or a fuselage tank, must be included in the aerobatic gross weight of all RVs."​
 
It's great to see a lively discussion of aerobatics on VAF again. After 10+ years of RV aerobatic competition up to the Intermediate level I thought I had pretty much learned everything about the plane and the competition. I never did modify my RV-8 seat back to accommodate the parachute. I just adapted to the further forward position. Wish I had done something about that. I will stress that a ratcheting seat belt that holds you DOWN in the seat is probably the best mod I ever made to my RV. I posted an article here on adding a second seat belt attach point for that mod. Maybe someone can find it. I sold my RV three years ago and now get my kicks flying the B-25. (FYI, I think the Mitchell bomber would do a nice Sportsman series if I had a bigger aerobatic box!) I just re-read Van's article and my article on equipping your RV for aerobatics and although they were written seven years ago, except for the seat back mod I don't think I would change or add a thing. Dick wrote his article at my request and he offered me about five edits before publication. I barely got him to admit that the RV-8 did pretty nice snap rolls and did nothing to compromise the structure if entry speed was carefully watched. Dick is understandably conservative as liability could ultimately be costly should he recommend activity which might lead to structural failures. Bottom line: stay within the recommended aerobatic weight and balance and speed limits and the RV is a very capable aerobatic mount. It's harder to make figures look good but beating out the Extras and Pitts in competition really feels good! And you can do that!
 
I would like to join too but being a low time pilot with no personal airplane until just a few months ago. I think many would like to do try out the primary but there are quite a few lessons along the way before actual flying in an event.
 
One person reached out (thank you!) to tel me about an RV-8 they know which got bent up over time flying aerobatics. Is this something to expect? I know aerobatics are hard on the planes - but within the design g limits I don’t expect any deformation.

Can anyone talk to any accelerated wear and tear you e seen in your planes?
 
inktomi said:
One person reached out (thank you!) to tel me about an RV-8 they know which got bent up over time flying aerobatics. Is this something to expect? I know aerobatics are hard on the planes - but within the design g limits I don’t expect any deformation.

Can anyone talk to any accelerated wear and tear you e seen in your planes?
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Matt, that's a good question and I think my experience with the RV-8 is not typical. I flew with Team RV, Team Aerodynamix and Redline Airshows for eight years and flew in IAC competition up through Intermediate level for 10 years. My RV-8 had over 2200 hours on it when I sold it. Over that time I suffered one cracked canopy and had to do the SB involving cracks in the root of the stabilizer spar. I regularly flew up to 5.5 positive and 2.5 negative G's and performed hundreds of snap rolls. I would have ventured beyond the Intermediate level of competition but that would involve tail slides and that is a no-no with the RV. I don't think my RV had any more maintenance or damage issues than those that never flew aerobatics but I never exceeded the published aerobatic gross weight, balance or G limits. I did exceed Vne by 20 knots on one occasion when the formation leader entered a loop with too much speed. Post flight inspection revealed no damage. I always did a very thorough preflight inspection and never flew if something was amiss without making it right. I did find that the four AN-3 bolts that hold the front of the horizontal stab to the fuselage stretched over time. I made a point of yanking the stab tip up and down and torqued those bolts if I felt any movement. I replaced all four bolts at every condition inspection. I found no other airframe issues that might be attributed to aerobatics. I second your opinion that you can expect no problems if you stay within design limits. Have fun!
 
ronschreck said:
I did find that the four AN-3 bolts that hold the front of the horizontal stab to the fuselage stretched over time. I made a point of yanking the stab tip up and down and torqued those bolts if I felt any movement. I replaced all four bolts at every condition inspection. I found no other airframe issues that might be attributed to aerobatics.
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Good info. Thx!
 
Do you guys have any tips on rigging the slider canopy to be easy to jettison in flight if we need to bail?
 
bmellis11 said:
Do you guys have any tips on rigging the slider canopy to be easy to jettison in flight if we need to bail?
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On my first RV-8, I replaced the bolts that attach the canopy to the rollers with pip pins (as many have done). I'm pretty sure꙳ I could open the canopy enough to just clear the windscreen fairing, pull the pip pins, and then push up and let the airstream rip the canopy off. The catch is that the canopy may strike the pilot's or passenger's head (even if pilot leans forward), rendering the pilot and/or passenger unconscious/dazed/injured if they are not wearing helmets.

Years ago Sean Tucker was practicing for Sun 'n Fun 2006 when he had an elevator disconnect. He was able to fly with elevator trim and climb to an altitude that allowed a bailout. He said that even though he had time to think through what he was going to do, when he released the canopy, it hit his helmet even though he leaned as far forward as he could. He said that the hit was hard enough that he thinks that it may have rendered him unconscious had he not had the helmet. He mentions this in this video at about 3:55 (although the whole story is quite good). His airplane had a full canopy though, unlike the RV-8 that has a fixed windscreen that may help the pilot avoid a hard canopy hit, but possibly not the passenger. Also, starting at about 5:15 he mentions that when he left the airplane the stab and bracing wires were there and he gently pushed away from them with one hand.


Pip pin installed. Attach a short lanyard to facilitate pulling them out in an emergency.

i-WfMqxGH-XL.jpg

Here is the one from McMaster-Carr:

​
꙳ You may not be able to open the RV-8 canopy very far (and it will be difficult) since air pressure is pushing down on it. However, in 1999 there was an RV-8 that caught fire in flight. The pilot did get out, but unfortunately he was not wearing a chute. The NTSB said that the fire may have been so intense in the cockpit to be intolerable (the WWI scenario before chutes were widely used). Here is the NTSB Final Report.

 
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RV8JD said:
Years ago Sean Tucker was practicing for Sun 'n Fun 2006 when he had an elevator disconnect. He was able to fly with elevator trim and climb to an altitude that allowed a bailout.
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Thanks for posting that video. Elevator disconnect. Yikes. That video made me queasy thinking about his experience, but definitely a great story.
 
I used the pip pins as well. I do know that you can easily pull the canopy back well past the overlapping windscreen in flight. Jon Thocker fashioned a clip to hold his RV-8 canopy open about six inches. I don't recommend this as the rear of the canopy would only be secured by the delrin slider. (I can tell you that the canopy will open fully at zero airspeed at the top of a hammerhead turn if it is not latched properly. It is also possible to close it with one hand while holding onto one's hat with the other hand before completing the 180 degree turn and plummeting toward the ground!) I sometimes learn things the hard way. :rolleyes:
 
The Tucker elevator control failure was caused by a failed rod end bearing. All the rod end bearings had been replace and there was one cheap bearing mixed in with good ones. There have been Pitts and Eagle aircraft landed successfully after various elevator problems ranging from a screw jammed in the tail to failed weld on center bearing bracket on the Eagle. I worked with the guy who had the jammed controls. No aft of neutral stick movement was available and the landing was a VERY fast wheel landing. With the Pitts and Eagle systems a 1/16 cable can be run from the bottom of the stick to the elevator horn. This will give up elevator only but the trim can be used for some down elevator.
The chances of a successful bailout in competition are very poor. Anything occurring on a vertical downline-not enough time. John Morrisey wrote an excellent article in Sport Aerobatics years ago on this subject.
 
bmellis11 said:
Do you guys have any tips on rigging the slider canopy to be easy to jettison in flight if we need to bail?
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Here is a series of photos from my Rocket on my canopy ejector. I cut relief slots in the top of the rails just aft of the forward ends. I fabricated a sliding cover for normal flight. For aerobatic flight, I install the machined ramps with the pins installed. Sliding the canopy back in flight will cause the leading edge to rise up into the airflow and tear off in flight. I also made a relief cut in the spine track to match with the forward cutout.

It also makes the canopy easily removable for ground service.

I also have seasoned pilots ask me if I'm worried about the canopy damaging the tail when ejected. Kind of funny.
 

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bmellis11 said:
Do you guys have any tips on rigging the slider canopy to be easy to jettison in flight if we need to bail?
Click to expand...

Instead of the pullable pins I cut a gap in the top of the canopy rails. If I open it and push up while pulling back after about three inches I can lift the canopy out. I presume the wind blast will take it from there.
 
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