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RV-4 VNE .v. F1 Rocket

Steve Sampson

Well Known Member
The RV4 VNE is 210 mph. The Rockets, forget the Evo for this conversation since it has a different wing, have considerably higher limits stated. The F1 claims a top speed of 250 mph and presumably the VNE is higher. The Harmon ii is I think 275.

My question is this. Since they are all sharing the RV4 parts, what aspect of the -4 structure is limiting it to 210?

Just curiosity. 200mph is fast enough for me!
 
Tailfeathers

Hi Steve,
The -6 also has a 210 VNE. The tailfeathers on the -7's and F-1's have thicker/stiffer skins than we do for flutter considerations. There's an awful lot to counterbalancing control surfaces properly to avoid disastrous flutter. Alot of computation and engineering. Also keep in mind that it is NOT indicated airspeed for redline, it is TAS! So when you see 190 MPH on a hot day, you may well be at or over 210 true.

Regards,
Pierre
 
Just an interesting note, I see that Van lists top speeds above the 210vne for the -4 with 180hp, if VNE is 210 and it is then why list speeds for level flight above VNE? I know my -4 will go 230 and has in level flight, it has the thicker skins, I think Dave Anders -4 is over 250. I wonder if it?s all that different, RV verses Rocket or if Harman who started the rocket thing already knew that Vans numbers where conservative enough to accommodate higher speeds and maybe even higher with heavier skins, I also wonder if there running closer to 0 flutter margin then the RVs. I like the Rockets a lot and dream about one from time to time and this very question has crossed my mind before.
 
Need 4 Speed+...

Steve,
I have an RV4 and an HR2 in my hangar and fly both alot. The Rocket at 270 mph is solid as a Rock(et), smooth and controls forces heavier, but not excessive. It is more responsive in aileron, less in pitch than the RV4 and much more of a smooth ride in bumpy air (higher wing loading). It climbs much faster, cruises 20% faster (200 knots true at 13 gph) and lands slightly faster (67 knots vs 58)but equals or exceeds RV fuel efficiency over a given distance. It is not quite as light and nimble as the RV4, but more than makes up for it in vertical penetration, flat out speed and vertical takeoffs. They are alot of bang for alot more bucks.
Why a higher VNE? The airplane is significantly different structurally in a couple of areas. First, the fuselage forward of the baggage area is .040, tail feathers are stock RV4 with .020 elevator and rudder and fuselage beefier in the front. The wings are shortened but retain the same number of ribs moved closer together. All this combined with the longer fuselage, higher wing loading and heavier weight center section allowed John Harmons calculations (and testing) to increase the VNE above Van's recommended limit. After the RV8 structural failure several years ago, Van's has been passionately neutral about VNE questions. Their calculations remain unchanged and I believe will for a long time to come.

Rob Ray
Livin the Dream...
 
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The laws of physics are the same

Steve Sampson said:
The RV4 VNE is 210 mph. The Rockets, forget the Evo for this conversation since it has a different wing, have considerably higher limits stated. The F1 claims a top speed of 250 mph and presumably the VNE is higher. The Harmon ii is I think 275.

My question is this. Since they are all sharing the RV4 parts, what aspect of the -4 structure is limiting it to 210?

Just curiosity. 200mph is fast enough for me!
One is conservativily engineered by analysis and flight test with built in safety margins. The other is eyeballed engineered and flight test shows it is also OK, but it uses up the conservatism built into the airframe, operating with less structural and aerodynamic margins?


The good news is there are lots of Rocket's being "test flown" every day and none have broke in-flight yet. (There was Rocket II accident where in-flight break-up is suspected (not all parts in the same place(?); circumstance unknown but very turbulent flight conditions existed at the time.) So to answer you question the Rocket II has been proven in operation.


The original Harmon Rocket II (based on a RV-4 kit) clips the wing which helps wing bending to compensate for higher gross weight and speed. The tail I think was a stock RV-4 tail. However the Team Rocket F-1 does use a tail that resembles the later RV-7/8 tails now. The gage of metal may be increased, but I don't know. Thickness of skin (structural flexibility) has only a little to do with flutter. Google Aeroelasticity or airplane flutter. (Aeroelasticity) There is two or three ways to test for flutter: Flight test in the plane, Wind tunnel with scale models and analytically with computer models. Here is some sobering Flutter info: http://www.geocities.com/mgd3/flying/flutter

The question is does the flutter go divergent or is it non-divergent. There have been many RV's (one case documented in the RVator) where the pilot felt the "buzz" of flutter. Always keep in mind, go on TAS not indicated, so the higher you go the lower indicated Vne is. Any RV can exceed 250 mph TAS in a high altitude descent regardless of engine HP.

The laws of physics, aerodynamics and structural strength equally apply to RV's and Rockets. Whether the tail feathers are attached to a 200 mph RV-4 or 250 mph Rocket II, it is still subject to elevator, rudder and aileron flutter just the same. The result of flutter is also the same, from a buzz to total airframe failure.

The good news is Van has done a great job and there is some margin there. How much? Don't know, but apparently 250 mph is still OK. Dave Anders with his super fast RV-4 has been over 250 mph.

Would I fly a Rocket? Heck YEA! I would just watch the speed and flight conditions, slowing in turbulance and keeping Vne very much in mind.
 
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The F1 Rocket does not share ANY parts with a RV. It looks like it, but it doesn't. The fuselage and tail feathers are engineered with different thickness skins, ribs, and other strengthening that's not apparent to the eye. The hershey bar wing is pretty similiar except I think the spars have been lengthened, but otherwise they are the same.

BTW, I'm not referring to Harmon Rockets, and I'm not saying that one is better than the other. Just trying to keep the facts straight.
 
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gmcjetpilot said:
......The question is does the flutter go divergent or is it non-divergent. There have been many RV's (one case documented in the RVator) where the pilot felt the "buzz" of flutter. Always keep in mind, go on TAS not indicated, so the higher you go the lower indicated Vne is. Any RV can exceed 250 mph TAS in a high altitude descent regardless of engine HP......


If I am not mistaken, the RVator flutter article was written by SmokyRay, who by the way, posted just before gmcjetpilot. :)


Michael
 
Thanks for all the inputs.

Since I have never seen a Rocket, except an Evo in the factory, I had not noticed the F1 span is less than the -4, and did not realise the rib spacing was different. The back end sounds as though it is pretty much like the -4 with the heavier skin option, which I have.

As I said before 210 is enough for me!

Back to wrestling with the canopy!
 
Smokey,
Don't you have a story about flutter in your 4? As I recall, you went for a sucker hole around 12,000' or so and the tail fluttered at something like 250mph TAS. Your experience pointed to the fact that VNE is TAS, not IAS. I keep TAS displayed on my EFIS, mostly as a result of your story.
 
Steve,
I have an RV4 and an HR2 in my hangar and fly both alot. The Rocket at 270 mph is solid as a Rock(et), smooth and controls forces heavier, but not excessive. It is more responsive in aileron, less in pitch than the RV4 and much more of a smooth ride in bumpy air (higher wing loading). It climbs much faster, cruises 20% faster (200 knots true at 13 gph) and lands slightly faster (67 knots vs 58)but equals or exceeds RV fuel efficiency over a given distance. It is not quite as light and nimble as the RV4, but more than makes up for it in vertical penetration, flat out speed and vertical takeoffs. They are alot of bang for alot more bucks.
Why a higher VNE? The airplane is significantly different structurally in a couple of areas. First, the fuselage forward of the baggage area is .040, tail feathers are stock RV4 with .020 elevator and rudder and fuselage beefier in the front. The wings are shortened but retain the same number of ribs moved closer together. All this combined with the longer fuselage, higher wing loading and heavier weight center section allowed John Harmons calculations (and testing) to increase the VNE above Van's recommended limit. After the RV8 structural failure several years ago, Van's has been passionately neutral about VNE questions. Their calculations remain unchanged and I believe will for a long time to come.

Rob Ray
Livin the Dream...

Rob, thank you for what you've written here.
 
....Dave Anders with his super fast RV-4 has been over 250 mph....

Dave Ander's RV-4 does not have the stock tail. I don't remember if he changed thicknesses, but he glued it as well as riveted it, and if I remember correctly, he has extra ribs in it. So his speed does not change whatever Vne margin there might be on a stock RV-4.

Dave
 
It's riveting...

Dave Ander's RV-4 does not have the stock tail. I don't remember if he changed thicknesses, but he glued it as well as riveted it, and if I remember correctly, he has extra ribs in it. So his speed does not change whatever Vne margin there might be on a stock RV-4.

Dave

Dave,
I've inspected Dave A's RV4 up close and spoken with him many times over the years. As David mentioned, his 4's elevators trailing edges are riveted, not bent. He also has wing extensions and carbon fiber parts and a counterbalanced rudder. Anything that sticks out in the breeze is faired. It's a clean machine through and through. His IO-360A1B6 (angle valve/counterbalanced crank) was custom built by LyCon and dynoed well North of 220HP mated to a WW constant speed composite prop. Dave's quote is on speed mods: "It's not one big thing but alot of little ones. "
https://www.youtube.com/watch?v=gCONImxbs7g

It smokes...:)

V/R
Smokey


PS: My HR2 had the stock RV4 tail with .020 elevator and rudder skins, no mods whatsoever.

 
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TRUE to form...

Carl,
Four score and many moons (14yrs) ago, (right after my RV4 flutter incident), Van and I exchanged emails. He queried me on my numbers and shared his thoughts on what actually happened. They were as you could figure, logical, well thought out and calculated.
In the split second I had to take a mental snapshot glance at all of my flea market purchased steam gauges in "The Bandit" when the incident occurred, Van had crunched some fairly accurate numbers on TAS VNE that I (and many other early RVers) hadn't considered. Potential litigation notwithstanding, I'm sure that is what they now publish as gospel.

Of course like all the other RV's, mine says "Experimental" on the canopy rail...
Your mileage may vary...

V/R
Smokey

PS: During the ensuing post-incident airframe inspection on "The Bandit", the only glitch I found was my elevator trim tab with 1/4" up and down play. I remedied this and in the next 500hrs never had a repeat although I never approached those TAS numbers again. .
Leaves one to wonder...
 
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Flutter Bug...

Michael,
As we all know, Van is the Mr. Spock of the sport aircraft world. He speaks in analytical and logical terms and doesn't jump to conclusions or hypothesize unless backed up with facts.
In my case he didn't conclude as to the how but to the why.

In the end, Inconclusive.
V/R
Smokey

PS: I have my theories and have watched numerous flutter videos and spoken to several very smart Aeronautical Engineering qualified people including my good friend a former Van's engineer "KK".
We all believe that it was indeed flutter possibly accentuated by trim tab "buzz"....I may never know for sure.
 
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Understand.

At least for the RV-8, there appears to be a fair amount of structural and flutter margin with the Vne set to 230 MPH TAS. See my post:

http://www.vansairforce.com/community/showpost.php?p=1241673&postcount=86

Just because someone once got away with speeds well above VNE without flutter and destruction does not necessarily mean there is a "fair amount of structural and flutter margin." It just may mean that that particular aircraft on that particular day didn't experience the stimulus needed to initiate flutter, particularly if control tap tests were not conducted at those speeds...

Skylor
RV-8
 
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