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

Lufthans said:

Hi guys,

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


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.

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.


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?

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

Thanks,
Hans

Click to expand...

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

Freemasm said:

- 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.

Click to expand...

"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...

F1R said:

"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.

Click to expand...

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.

Bob Martin said:

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!!

Click to expand...

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!

Freemasm said:

- 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.

Click to expand...

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.

rv7charlie said:

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

Click to expand...

I've got no idea. It's just very fast! Nothing out of the ordinary on this plane, just dual Pmags and a Catto prop. We've imported this one from North Dakota this winter and only have a dozen hours on it ourselves so far. The ASI was calibrated by the A&P checking the plane for registration here. I guess we'll have to do some three-way GPS runs to verify.

Ralph Inkster said:

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.

Click to expand...

Thanks Ralph. I've read the reports on the '7 STI. Nice work! And Race 57 isn't bad either ;-)

My current Soobie platform is a 1959 Jodel. These were designed for a Continental C90. I estimate my current EJ25 at 170-180 hp. Coupled to that awesome MTV-12, I'm having to hold back because of Vne all the time. In the mean time, I've grown to like the thrill of insane climb angles and the cloud dancing abilities when the fluffy Cumulus stuff starts to pop up. So I guess 40-45" MAP during climb, reduced to 25-ish for cruise would suit me just fine.

Comments duly noted though, thank you!

Hans

P.S. I would LOVE to hear what turbo you had on that STI engine....

Study up on flutter before attempting to exceed redline. It's potentially dangerous. It can destroy your airplane in a fraction of a second with no warning.

There are ways to test for flutter. They typically involve considerable instrumentation.

There are ways to improve flutter margin. They typically involve thoughtful structural beef-up. I say "thoughtful" since poorly-thought-out beef-up can actually be harmful.

Be very, very careful.

And don't take exceeding Vne casually. I have heard of some incidents of flutter with Rockets.

Even better, build the Team Rocket F1, which already has the engineering built in.

This whole discussion is scary. And I'm speaking as a retired aerospace stress analyst, with lots of experience with structural dynamics.

Dave

Freemasm said:

- 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.

Click to expand...

Vince here....

Interesting thread with many true, but confusing, comments. I'm not going to even try to sort all of them out, but it is true that the HRIIs used RV tails and a few of the early S/N F1s used beefed up 8 tails. However, by far, most of the F1s have F1 tails.

Since there is always room for improvement, several of us sat down last year at Oshkosh and made a few modifications to the F1 tail, which is now the Mk3 version. It has more ribs, a few doubler changes, and a trim tab that is modified and strengthened.

These changes are NOT to say that the Mk2 tails weren't doing the job, but there are always those who take their planes past the safe limits. The Mk3 tail mods are intended to provide an extra margin of safety.

I don't know where "targeted design speed of 300 knots" statement came from. There is no intent to raise the VNe speed above 275mph. There is much more to consider than just the tail before that number changes!!

Individual builders/pilots can design, build, and test their machines as they see fit, using their own discretion, engineering, and test plan. That risk is on them. As far as Team Rocket is concerned, the VNe is and shall stay 275mph.

Hi Vince,

Thanks for chiming in!

Good stuff! I'm wondering - Are the RV4 and the new Mk3 tail interchangeable? In theory, would one be able to build a new Mk3 tail and bolt it to an existing RV4?

And the other thing - on your web site in de F4 section, you mention that RV4 and RV8 wings are also possible (with Brad Hoods great looking F4 as an example of the latter), but then continue by saying that you advise to stick to the Vans numbers for MTOW and Vne for those wings

Focussing on Vne now - I'm wondering what makes that the sports wing (which I understand is a slightly clipped RV4 wing?) can take the higher speeds, where the RV4 wing doesn't? MTOW I understand, but what about the Vne? It is the repitching of the ribs?

Trying to understand...

Thank you!

Hans

vfrazier said:

Vince here....

Interesting thread with many true, but confusing, comments. I'm not going to even try to sort all of them out, but it is true that the HRIIs used RV tails and a few of the early S/N F1s used beefed up 8 tails. However, by far, most of the F1s have F1 tails.

Since there is always room for improvement, several of us sat down last year at Oshkosh and made a few modifications to the F1 tail, which is now the Mk3 version. It has more ribs, a few doubler changes, and a trim tab that is modified and strengthened.

These changes are NOT to say that the Mk2 tails weren't doing the job, but there are always those who take their planes past the safe limits. The Mk3 tail mods are intended to provide an extra margin of safety.

I don't know where "targeted design speed of 300 knots" statement came from. There is no intent to raise the VNe speed above 275mph. There is much more to consider than just the tail before that number changes!!

Individual builders/pilots can design, build, and test their machines as they see fit, using their own discretion, engineering, and test plan. That risk is on them. As far as Team Rocket is concerned, the VNe is and shall stay 275mph.

Click to expand...

Lufthans said:

Hi Vince,

Thanks for chiming in!

Good stuff! I'm wondering - Are the RV4 and the new Mk3 tail interchangeable? In theory, would one be able to build a new Mk3 tail and bolt it to an existing RV4?

And the other thing - on your web site in de F4 section, you mention that RV4 and RV8 wings are also possible (with Brad Hoods great looking F4 as an example of the latter), but then continue by saying that you advise to stick to the Vans numbers for MTOW and Vne for those wings

Focussing on Vne now - I'm wondering what makes that the sports wing (which I understand is a slightly clipped RV4 wing?) can take the higher speeds, where the RV4 wing doesn't? MTOW I understand, but what about the Vne? It is the repitching of the ribs?

Trying to understand...

Thank you!

Hans

Click to expand...

Hans,

No, there is no reason to put a Mk3 tail on an RV-4. We won't offer the Mk3 for such use.

If you must swap tails, please consider an RV-8 tail.... which is heavier than the RV-4 tail... etc... you're the engineer and test pilot now!

Loyd Remus builds a spar carrythru (#4) bulkhead that will allow use of an RV-8 wing on an F4. This is for use with a 4 cylinder engine only and only if flown to RV-8 speeds and weights. Physics rules.

If you want a Rocket with a 6 cylinder, then the path is to convert a pile of RV-4 wing parts into a proven Sport wing configuration. There are plenty of HRII and F1 data on this wing.

Proving what any of these wings are ultimately capable of would require expensive testing and lots of engineering time. Since we're offering a sport plane, we're offering historically proven options. As mentioned earlier, if you want to bust VNe, or vary the proven wing loadings... you're on your own. We cannot recommend such changes, nor support something that we think is questionable.

You've got to consider the risks involved. We're all in this for fun. Going faster is nice, but the risks MUST be weighed with the err on the side of safety.

A Faster Horse

Lufthans said:

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.

Click to expand...

If you have a souped up subie with 450 ponies why not start out with an airframe designed for over 400 mph? Like this one.. Fast forward to the 1 minute mark.

Got it. Thanks!

Not planning anything at this time yet. Just trying to figure out what's what, what will work and what won't.

I completely understand your position and will not push the subject further with you.

And I'm with Dave completely on the "don't thread on this path lightly" kind of approach. That's why I am asking these questions and poking around. Getting beyond IO-540 kind of performance out of O-360 engine weight is kind of interesting. What part of the Rocket design was modified from the RV4 because of the weight, and what part because of the bigger speed potential? Trying to get my finger behind that one.

Thanks for all the good info!

Lufthans said:

Hi guys,

...snip

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?

snip...

Thanks,
Hans

Click to expand...

I think you may be too quick to discount how the Rocket structural modifications you've listed may affect flutter.

First of all, the Harmon Rocket wings aren't just clipped. They have the same number of ribs as the stock RV wing but re-spaced to accommodate the shorter wing span. This improves torsional rigidity of the wing which improves wing flutter margin.

Secondly, resistance to tail flutter involves more than just the strength of the empennage itself. The overall stiffness of the fuselage and tail cone as well as the control system have an impact on flutter speeds. This is where the larger cross section and thicker skins of the Rocket fuselage may come into play.

I caution you heavily against using speculation as a means to rationalize taking a stock RV-4 air frame up to speeds in excess of the published Van's limits.

Skylor
RV-8

What Skylor said....

"I caution you heavily against using speculation as a means to rationalize taking a stock RV-4 air frame up to speeds in excess of the published Van's limits."

Points taken!

Used an RV4 tail on #3 F1 rocket with .020 elevator & rudder skins. Worked fine & always respected VNE. Too slow, twin turbo Glasair III RG close to flying. Flutter tested to 360 knots. Better.

Were the guys claiming 350(450) reliable hp out of a Sube car guys or airplane guys?

Tim

RV8JD said:

Just out of curiosity, is that Vne 275 MPH IAS or 275 MPH TAS?

Thx,

Click to expand...

VNe is true airspeed.

And someone long ago, maybe John Harmon, used 275 mph instead of 239 knots, for the Rocket. Easier to remember? Maybe. I'd prefer it in knots... so 239 knots for me.

For those reading this thread, also remember that TAS varies with altitude. It is very possible to seriously bust VNe during a descent if you're not doing the math to convert IAS to TAS. This applies to other aircraft too... not just the Rockets.

You mean aerodynamic stuff works in other airplanes? I think you?re fibbing Vince. That TAS stuff is just CRAZY. Can?t wait to see the skunkworks side of the rocket house!

tjo said:

Were the guys claiming 350(450) reliable hp out of a Sube car guys or airplane guys?

Tim

Click to expand...

Admittedly - car guys. Endurance racing car guys that is, making fun of me for putting the bar at "only" this petty amount of power. Their words. But then, what they spend on these engines might make an IO-540 seem affordable...

I don't need the speed. All my buddies are flying Sequoia Falco's. We have 5 of them on our field. Beautiful aircraft, but can't keep up with our 160 hp RV4. So in formation flying, I have to hold back already. In a Rocket this would obviously be even worse. So I'm more interested in the vertical penetration capabilities of high hp engines, making the Vne thing more of a by-product of that than a target.

Typically, I fly my (normally aspirated) Subaru Jodel at 18" and 3950 rpm. 16" when I am not in a hurry, 22-23 when I am trying to stay in formation with the Falco's. This is also how I think I'd use a turbocharged version of it. At moderate power settings, with the occasional insane climb angle blasts in between.

Anyway, thanks guys for all the good info. At least now I know what I can work with and can decide to either stick a way too powerful engine on an RV4 that can only be opened up with the nose sticking way up in the air, or go all-out and build a Rocket - be it HR or F1 - to reap the benefits in level flight as well. Either way it will be fun