Vne
 

Hi guys,

Long time lurker and multiple homebuilding offender, I'm gearing up to the next project and could use some info and opinions.

Background: I've got significant experience with several Subaru engine conversions and am successfully racking up the hours on one on my own aircraft now (not the RV, unfortunately). Perfect cooling, turbine-like smooth, runs on anything that remotely smells like gas, dirt cheap to operate and completely trouble-free.

That engine is normally aspirated. I would like to take the concept up a notch now. The gear drive that I am using was designed to take over 500 hp, and every knowledgeable Subaru tuner and engine builder that I talk to tells me that it is quite doable to build an utterly reliable 4-cylinder turbo engine that will pump out 450 hp. Even if I were to limit that to 350 hp, I'd still have an impressive engine to play with.

And the good part: all included, that engine and cooling setup will weigh about the same as an IO360. And so might actually fit a modified RV-4 airframe quite nicely.

Except the RV-4 has that vne of just 212 mph. We all know that Vans is very conservative here, but still. On our own RV4, we have to throttle back even our measly O-320 with fixed pitch Catto prop or we'll bust that Vne even in a shallow climb. So imagine having nearly three times the power available...

Enter John Harmon.

From what I understand, on the HR2, the mods are:
* clipped wing. For reducing bending moments on the spar at heavier MTOW mostly. Since I'll be looking at regular RV weights, I don't really need this.
* Wider front part of the fuselage. Mostly to accommodate the bigger engine. Plus it's a style thing, I guess. I kind of like the RV-4 look, and the Subaru is no bigger than a Lycoming 4, so that would not be needed.
* The front part of the fuselage is using thicker skins. Again, with the engine not heavier than a Lycoming 4, this would not be necessary. Stress analysis shows that the pulling force from more engine hp is negligible when compared to the G-forces on the frame when pulling that stick back hard. Same engine weight - same strength needed.
* The fuselage is lengthened by 4 inches. Again, great to counterbalance a heavier engine, but therefore not needed in my case.

According to some stuff that I've read (from an old Sport Aviation article I think it was), the tail section and tail surfaces on a HR2 are stock RV-4.

But if the tail sections are the same, and the only modification to the wing is some clipping to accommodate a higher MTOW, then where does the significantly higher Vne come from?

According to that same article, John Harmon had tested his planes in 5 mph steps for flutter to 300 mph, which is nearly 90 mph beyond the RV4 Vne. Is he just that ballsy, or am I missing the point (or some more modifications) here?

For this project, I am mostly interested in the motorization. So if I could simply start with a ready-made RV4, rather than having to build a complete new airframe, that would give me quite a jump start.

I'd have to be certain about that Vne thing though. Any thoughts very welcome!

Thanks,
Hans

Hans,
Are you sure you meant climb and not desent?
I am not a Rocket expert, but I am pretty sure the Rocket tails are built using a RV tail kit and adding more structural parts to it while building.
Best of luck with your experimental project!!

What I think I know
 

- The HRII uses a standard RV4 emp. I just talked to them.
- The F1 Rocket uses a modified (beefed up) RV4 emp.
- The newest F1/F4 kits have a new, custom design emp with a targeted design speed of 300 knots. Best hope is for @vfrazier to chime in.

Question?
 

Have you studied the 8 as well? The VNE is 230 S. mph. to start with and I think that tail has been used on some of the newer rockets. We tested ours to 10Kts. over VNE in phase one just to bee sure it met the limit and that it would be safe to use the recommended VNE from Vans' in our POHB. The 8 has more room under the hood and in the cabin as well.
Just asking, Yours, R.E.A. III # 80888

"The F1 Rocket uses a modified (beefed up) RV4 emp"
Absolutely Not true.

The Team Rocket F1 were engineered and manufactured as quick build kits by HP Aircraft in the Czech Republic. Their engineers put a clean sheet of paper design V-Stabilizer, rudder and elevators with external rivets on the trailing edges. The RV 4 never had a mass balanced or aero balanced rudder. The TR F1 did.

The original HP Aircraft TR F1 quick build has heavier (intentionally by design) stick force in pitch, compared to the Harmon Rocket, that is feather light as it has mostly an RV4 tail.

You want to send PM's to Tom Martin , F1 Boss,
RV8JD(Carl N.) and make some very detailed notes.

Not arguing, but...
 

Not trying to argue but i?ll Explain my short reply. The original F1 empennages were indeed modified RV emps. Mr. Frederick was nice enough to provide pages from those plans to me. There were later interations. As they are no longer available, I didn?t include. Thumb typing into a phone is not fun for me. As mentioned, @Vfrazier is now providing the newest F1/F4 hardware and kits. He and the F1Boss, Mr Frederick work closely. There is a lot of history and related with these aircraft. Way more than can go here, easily.

Thanks. And yes, I meant climb. In level flight, we're busting that 212 mph Vne with power to spare, even on 160 hp only. That Catto prop is working magic!

Good stuff. Thanks!

I've spread my assets a bit thin by investing heavily in developing a sports car that I have designed and hope to market shortly. 2200 lbs of 1950's looking design powered by a 580 hp Ferrari V12. That stuff (and owning three aircraft) gobbles up loads of time and cubic dollars, so the Subaru engine project needs to be that first and foremost - about the engine. At this time, I think I'd rather go with an existing RV4 and see where I need to modify that one, rather than starting from scratch or an F1/F4 kit.

It also rules out the RV8 a bit, since these tend to cost twice what an RV 4 costs.

Interesting conversation nonetheless on the various Rocket versions. Thanks guys!

I, for one, would love to know what you did to your -4 to get 212 statute mph in a slight climb with a stock 160 hp Lyc. I've owned two of them, and I thought the 1st one was quite fast for 160 HP, at about (true) 195 mph cruise, burning just shy of 9.5 gph. Wide open in a pass down the runway (after descent from pattern altitude) would brush just past vne (at a lot more fuel burn). Exceeding vne in any climb on 160 HP is impressive.

Charlie

We estimate the output on Bill Beaton?s HRII ?Race 57? is about 500 hp in race trim, on a relatively stock HRII airframe, it is heavy with a lot of ?stuff? in it, & it was getting over 280 mph average lap speeds on Reno?s race course. Airframe wise, we feel we max?d it out, to push it harder would mean major tail cone restructuring similar to what Mark is incorporating into his latest plane.

The turbo STI Subie RV7 I built some years ago would easily bust VNE. We de-tuned it so we wouldn?t hurt ourselves.

I agree that the EJ257 can be made to deliver crazy horsepower but just would not be usable (& safe) in a stock RV4 airframe without some serious airframe strengthening.