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RV Super 8: What could possibly go wrong?

A

aeropunk

Active Member
Having recently read and enjoyed Mike Stewart's RV Super 8 website, I thought it might be interesting to solicit some engineering opinions on this mod.

My intent is not to start a flame war; I think the idea of a Super 8 is awesome, especially when coupled with a Showplanes fastback. But as Mike mentions in his FAQ, clearly Van is totally opposed to the idea of strapping an IO-540 on his RV-8 design, as it can easily take you outside of the airframe's tested V-n envelope.

So my questions are as follows:

1. How common are these Super 8's?

2. What changes to aircraft stability and control or handling qualities have Super 8 pilots noticed as a result of the big engine?

3. If you were in Van's shoes, and wanted to redesign the RV-8 to safely accommodate an IO-540, what specific structural changes would you make, especially with regard to high-speed maneuvering, vibration, or flutter?​

Thanks in advance for any input, and my apologies if this material has already been covered elsewhere!
 
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aeropunk said:
3. If you were in Van's shoes, and wanted to redesign the RV-8 to safely accommodate an IO-540, what specific structural changes would you make, especially with regard to high-speed maneuvering, vibration, or flutter?
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I would say that a very small part of the population of this forum would be qualified to answer #3 regardless if they have first hand experience with a Super 8 or not.
 
Hi Brian...

...There are also about 6 Super -6's with IO-540's flying. I rode in this one last December: http://www.rocketsix.com/.

They obviously have to add 8" to the cowling to accomodate the extra 2 cylinders and most guys lengthen the fuse by 8-10 inches aft of the baggage area for CG purposes and also put the battery there. Thicker stabilizer and elevator skins as well.

Yep, cruise at or above redline (210 MPH for the -6). The -8 cruise right at redline as well.

You'll probably be hearing from Mike Stewart shortly.

Regards,
 
Clean sheet

aeropunk said:
3. If you were in Van's shoes, and wanted to redesign the RV-8 to safely accommodate an IO-540, what specific structural changes would you make, especially with regard to high-speed maneuvering, vibration, or flutter?
Click to expand...

I can't speak for Van, but I have to think that if he wanted to do something like this it would involve a clean sheet of paper. To make it work safely and meet Van's philosophy of "Total Performance" it would require a complete rethink.

John Clark
RV8 N18U "Sunshine"
KSBA
 
aeropunk said:
Having recently read and enjoyed Mike Stewart's RV Super 8 website, I thought it might be interesting to solicit some engineering opinions on this mod.

My intent is not to start a flame war; I think the idea of a Super 8 is awesome, especially when coupled with a Showplanes fastback. But as Mike mentions in his FAQ, clearly Van is totally opposed to the idea of strapping an IO-540 on his RV-8 design, as it can easily take you outside of the airframe's tested V-n envelope.

So my questions are as follows:

1. How common are these Super 8's?

2. What changes to aircraft stability and control or handling qualities have Super 8 pilots noticed as a result of the big engine?

3. If you were in Van's shoes, and wanted to redesign the RV-8 to safely accommodate an IO-540, what specific structural changes would you make, especially with regard to high-speed maneuvering, vibration, or flutter?​

Thanks in advance for any input, and my apologies if this material has already been covered elsewhere!
Click to expand...

My 2 very biased cents.
1. "as it can easily take you outside of the airframe's tested V-n envelope" This is a little iffy. The Super 8 has been tested well above Vans numbers. Given the zero info Vans delivers on these numbers, all hashed out before, going above them put me in the test pilot mode initially. Im way past that now and dont consider my blasting through Vne to any longer be a test pilot nor does it give me any concern. Mine is only one build and one data point. You results may vary.
2. They are very uncommon. There are ~10 of these flying now.
3. As for handling. I would not consider myself an expert. I have only flown ~20 different 8's of various shapes and sizes in my time so I have a limited pool to draw from. My limited experience has shown that pitch is heavier in the S8. Your displacing more weight in the vertical. It is obvious to the seasoned RV pilot. Most would not notice much difference if at all. But again im not a trained test pilot so I deferr this type of comment to those who have experience reporting real data in handling qualities.
4. Im not in Vans shoes and Im not touching that. IF I had it to do over again, I would change nothing except build larger tanks, which Im doing now. Going from 60 to ~85 gallons. Given the various models of ~RV's I have flown in the hot rod category to include HR's, F-1's, and S8's, Ill take mine for reasons I have stated on my site. I have only ~900 hrs on mine so the verdict on my frames ability to withstand my punishment is still out. I would not call the S8 a proven design by any stretch. I am but one man and one set of data points who has not managed to kill himself. Although I do try on occasion.:eek:

Im happy to answer any S8 questions you may have. Seems the other S8 owners are either too busy flying their machines, or cant find the submitt button on their computer. I seem to be it on the web front.
 
One engineer's perspective:

Hey Brian,

I've explored the idea of a Super 8 in detail. Yes, some are out there flying and I haven't taken a close look at any of them from an engineering standpoint so I will refrain from any comments specific to those aircraft.

To answer your questions, there are a great many major areas to explore in doing such a project. First off, I assume you'd use the stock wing spar box and wing spars. Given the higher firewall forward weight, and probably a more forward empty CG, that WILL require a reduction in max-g allowable if you want to retain the original structural safety margins. This is due to the unavoidable increase in spar bending/shear loads and increased tail trim loads. For me, I'd insist on staying within the stock structural safety margins.

Here's a laundry list of what I found in my prelim study of this idea:

1. Wing bending/shear loads: heavier fuselage weight places higher loads on primary structure during all symmetric maneuvers.
2. Fuselage bending: Forward fuselage bending increases substantially. Will require heavier longerons, possibly thicker fwd fuselage skins, and heavier firewall attach brackets.
3. Engine mount loads: Will require heavier mount due to heavier/longer engine and propeller. Gyroscopic propeller loads increased also. Maybe use a mount from the Rocket, or have a mount designed for the heavier loads. Its been done already.
4. Landing gear: Stiffer sub-floor structure, saddle brackets and attach hardware upgrades. Gear tower weldments, I think, will be OK as will the gear legs themselves.
5. Tail section: Enlarge horiz and vert stab to offset bigger prop and longer nose. No need to increase skin gages, but on the HS I'd probably ditch the outboard rod end hinge hardware and replace those with machined billet brackets. Too much deflection using rod ends as hinge points. (nice source of flutter there)
6. Needs more fuel than the stock 42 gal. Add more wing tank volume, or aux tanks.
7. V_ne: retain the original design airspeed limits. Just stay under them.
8. V_n envelope: Reduced max-g to keep original wing structure margins.

In summary, I found that I could live with doing the structural mods, but not with the forward CG, thirst for fuel, and overall weight increase. The whole plane would get heavier (if I did it) and I never could figure out how to get it to balance to my taste, unless I moved the pilot into the rear seat and made the front seat the passenger seat. That balances nicely, pretty close to stock (rear cockpit stretched 8 inches)

I did mock this aft-cockpit idea up in full scale, but ditched the project as a whole in favor of reducing drag & weight on the stock airplane -vs- adding horsepower.

*************************************

NOW - for you Super 8 flyers out there: I'm being careful to not step on toes here. I know you're out there flying. As an engineer, I'm only pointing out the obvious, straight-forward physical realities, structural changes and aerodynamic implications of doing this as I see them. I think it *could* be done, with existing structure, but have no idea where the margins would wind up. Maybe you do, but I've reserved my comments and refrained from any direct critique of your specific airplane. So, put the flamethrowers away please. ;)
 
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Yep, Yep, Yep........

FYI, a Show Planes cowl will fit a 6 cyl on a shortened mount.

I have also spent a huge amount of my allotted daydream quota on a "Show Planes"ized super 8.

All it takes is $$$$;)
 
rv72004 said:
And then it crashed! I think it was at sun and fun on landing, never did hear if the plane was rebuilt.
Click to expand...

Yep on landing at sun and fun if we are talking about the 'jawbreaker' glasair:
http://www.aero-news.net/Community/DiscussTopic.cfm?TopicID=1031

NTSB version:http://www.ntsb.gov/ntsb/brief.asp?ev_id=20040421X00493&key=1

And of course it ends up in court:
http://www.avweb.com/eletter/archives/avflash/1097-full.html

If memory serves me correctly there was an article in kitplanes around 2003, and the already by design 'hot' glasair III was in the jawbreaker case up to somewhere around 110mph over the fence thanks to the extra weight. But thats is just from memory.
 
Kahuna said:
My 2 very biased cents.
1. "as it can easily take you outside of the airframe's tested V-n envelope" This is a little iffy. The Super 8 has been tested well above Vans numbers. Given the zero info Vans delivers on these numbers, all hashed out before, going above them put me in the test pilot mode initially. Im way past that now and dont consider my blasting through Vne to any longer be a test pilot nor does it give me any concern. Mine is only one build and one data point. You results may vary.
2. They are very uncommon. There are ~10 of these flying now.
3. As for handling. I would not consider myself an expert. I have only flown ~20 different 8's of various shapes and sizes in my time so I have a limited pool to draw from. My limited experience has shown that pitch is heavier in the S8. Your displacing more weight in the vertical. It is obvious to the seasoned RV pilot. Most would not notice much difference if at all. But again im not a trained test pilot so I deferr this type of comment to those who have experience reporting real data in handling qualities.
4. Im not in Vans shoes and Im not touching that. IF I had it to do over again, I would change nothing except build larger tanks, which Im doing now. Going from 60 to ~85 gallons. Given the various models of ~RV's I have flown in the hot rod category to include HR's, F-1's, and S8's, Ill take mine for reasons I have stated on my site. I have only ~900 hrs on mine so the verdict on my frames ability to withstand my punishment is still out. I would not call the S8 a proven design by any stretch. I am but one man and one set of data points who has not managed to kill himself. Although I do try on occasion.:eek:

Im happy to answer any S8 questions you may have. Seems the other S8 owners are either too busy flying their machines, or cant find the submitt button on their computer. I seem to be it on the web front.
Click to expand...

Reviving an old thread almost 5 years later. How has your S8 held up?
 
BHunt said:
Reviving an old thread almost 5 years later. How has your S8 held up?
Click to expand...

I assume you mean by held up, have I had any structural issues? No. I did replace the wings a number of years back to full length leading edge tanks. One elevator hairline crack fixed over a year ago that is the subject of the SB. Engine replaced with a new one a couple of months ago from runout. She is doing great.
 
Personally I would beg to question, why would you want to do that to a perfectly brilliant airframe design. The parallel valve (I)O-360 with a hartzell two blade is the perfect engine/prop for this airplane. Slightly nose heavy when solo and perfectly balanced control harmony two-up. There seems to be this race to have the most gadgets and the most horsepower over the next guy. Sure it's a free country but come on now! Control harmony is what it's all about with RV's. Large, heavy engines, overloaded airframes and information overload seem to be what some folks dream of. Believe me, the lighter these airplanes are the better the fly, the better they feel and the more reliable they are. I used to think it would be really cool to install an angle valve 200+ horse engine in my '8 but not anymore. After building a few "large engine" RV's for customers I've decided there's no way I would do that to mine. Having very light ailerons and very heavy pitch is not my idea of control "harmony". If you just want to go fast and have bragging rights then you will certainly achieve that. If you want to have a fun and nimble sport plane then keep it light. Of course that's just this person's opinion. To each his own.
 
R. Daniels said:
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-------------------------------- To each his own.
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Exactly - to each his own.
 
R. Daniels said:
Personally I would beg to question, why would you want to do that to a perfectly brilliant airframe design. The parallel valve (I)O-360 with a hartzell two blade is the perfect engine/prop for this airplane. Slightly nose heavy when solo and perfectly balanced control harmony two-up. There seems to be this race to have the most gadgets and the most horsepower over the next guy. Sure it's a free country but come on now! Control harmony is what it's all about with RV's. Large, heavy engines, overloaded airframes and information overload seem to be what some folks dream of. Believe me, the lighter these airplanes are the better the fly, the better they feel and the more reliable they are. I used to think it would be really cool to install an angle valve 200+ horse engine in my '8 but not anymore. After building a few "large engine" RV's for customers I've decided there's no way I would do that to mine. Having very light ailerons and very heavy pitch is not my idea of control "harmony". If you just want to go fast and have bragging rights then you will certainly achieve that. If you want to have a fun and nimble sport plane then keep it light. Of course that's just this person's opinion. To each his own.
Click to expand...

While I respect your opinion, it's yours, not mine. For me, my airplane is a serious transportation tool but I can still very much appreciate the great handling of these little airplanes. Lighter may handle better, but mine was a day only VFR airplane when I bought it and I had difficulty going safely from A to B. It's now a serious IFR machine and I'm comfortable with that at this time. No ice and no thunderstorms, but I'll comfortably go have a look at other stuff.

I also have a Titan Stroker 370 205 HP engine and in my camp there's no such thing as too much horsepower.

So, Enjoy your plane and I'll enjoy mine and we'll have a beer at OSH and enjoy each others company.
 
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You can get more HP (205) than an angle valve engine in the parallel valve ECI IOX370 or Aerosport Power IO 375.
 
R. Daniels said:
..Control harmony is what it's all about with RV's...
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Depends on the owners mission. Yep, the RV-8 is a nice flying airplane and sits right in the fat part of the bell curve for the pilot population. However, there are people more towards the edges looking for something more specific. After all, there are plenty of airplanes that fly "better" than the -8. Something like a Pitts, Eagle or a Hiperbipe will rip the lungs out of any RV in a dogfight. Then there are those that need a good amount of power to drag a bunch of equipment off the ground and cover long distances in a hurry. In this case, a big engine and lots of flight equipment trumps "control harmony".

I'm fortunate to have both an 8 and a newly acquired Rocket in my hangar, and I can tell you that the -8 just gathers dust since the Rocket came on the scene. The 4 banger -8 is just like a child's toy in comparison.
 
Toobuilder, out of curiosity since you have both and 8 and a rocket, what are your thoughts on a super 8?

I ask because I'm early on in an 8 build. I started the 8 build with the idea of a super 8. It seems like everyone that I have talked to has tried to talk me out of it. I hear things like why ruin the great flight characteristics of the RV, or you are going to kill any resale value down the line, and of course everyone's favorite is don't do it because the airframe was not designed for an IO-540.

All of those sound like valid reasons and it's causing me to really reconsider.

I decided to build an 8 over a rocket because of the great support community for vans and I'm a first time builder.
 
Insurance

The cost for full insurance on a Rocket is a bunch more than an 8, even a Super 8, as it's still considered an 8.
 
jump4way said:
Toobuilder, out of curiosity since you have both and 8 and a rocket, what are your thoughts on a super 8...
Click to expand...

The -8 is a great airplane, but I prefer the Rocket due to cockpit ergonomics. The Rocket just fits me better. In fact, if I were willing to stick with a 4 banger, then I'd likely do a "Rocket lite" before I'd build an -8.

I've never flown one, but I'd imagine that a "super -8" is going to feel heavier in pitch than a 4 banger version, but that may not matter if your mission is lots of long cross country work primarily on autopilot (like mine). Based on my experience, if your mission is sporty, fun flying and the ocasional pancake breakfast flight, then a light 4 banger RV will give plenty of performance. Feeding a 540 really only starts to make sense when you are going high and far.

I'm not going to comment on the engineering behind a 540 on the nose of either airplane other than to say that it apparently works (so far). And if you are building with resale in mind, then the closer you stay toward the "norm", the bigger your market will be. Look at the sales prices for Rockets and comparable (4 banger) -8's... The -8s are pulling more money and selling faster.
 
Toobuilder said:
The -8 is a great airplane, but I prefer the Rocket due to cockpit ergonomics. The Rocket just fits me better. In fact, if I were willing to stick with a 4 banger, then I'd likely do a "Rocket lite" before I'd build an -8.
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Couple years back, Larry Vetterman changed out his Rocket to a 4 cyl, and he says it is a much better handling plane now.
 
RV8iator said:
The cost for full insurance on a Rocket is a bunch more than an 8, even a Super 8, as it's still considered an 8.
Click to expand...

Jerry is spot on here. The rocket is not cheap to insure. I pay 1200 a year for a RV6 with 200 HP. I got several quotes for a rocket and they were around 3400 a year. Insurers said that the rocket has a bad history with going over on its nose. I understand the issue is mostly with the Harmon version but sadly the F1 gets lumped in with the Harmon.

George
 
Thanks for the information. I currently own a great flying RV4 and use it mostly cruising with the more occasional sport type flying. I envision using my 8 in the same manner so maybe the 540 makes more sense for my mission all other things being equal.

Engine price will likely be a factor. I have yet to look in to the costs and various angles of an engine purchase. On the surface though it seems an io540 can be had for less than one of the high compression IO360 that can get fairly close in horse power. Any of you have any experience or thoughts in that area?
 
It is easy to tell when Winter is still in effect. Almost as humorous as an oil thread and it brings out the worst in a few. :rolleyes:
 
RV8iator said:
The cost for full insurance on a Rocket is a bunch more than an 8, even a Super 8, as it's still considered an 8.
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How about a semi super eight. My dream plane would be a eight with a IO 409. It would be a great aircraft without a weight penalty. A IO390 would be another option.

George
 
Toobuilder said:
What's this "winter" thing you speak of? We completely skipped it this year in California.
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They do seem to have skipped winter in CA however they also appear to have skipped the whole water thing! On a real note lets hope they get some precip in CA or things are going to get serious there fast with water. Flew over the Sierra' 2 weeks ago and have never seen less snowpack.

George
 
Yeah, sorry I didn't mean to "step on toes" regarding my opinion on big engines. Again, just my opinion. No need to get worked up! After all it's a chat here.
 
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