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  #1  
Old 06-02-2007, 02:38 AM
Steve Sampson Steve Sampson is offline
 
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Location: N. Yorkshire, England
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Default RV-4 VNE .v. F1 Rocket

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!
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Circuits at my 1000' strip.
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  #2  
Old 06-02-2007, 05:40 AM
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pierre smith pierre smith is offline
 
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Location: Louisville, Ga
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Default 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
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  #3  
Old 06-02-2007, 08:38 AM
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Russ McCutcheon Russ McCutcheon is offline
 
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Default

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 itís 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.
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  #4  
Old 06-02-2007, 09:36 AM
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smokyray smokyray is offline
 
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Default 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...

Last edited by smokyray : 06-02-2007 at 09:51 AM.
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  #5  
Old 06-02-2007, 09:39 AM
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gmcjetpilot gmcjetpilot is offline
 
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Default The laws of physics are the same

Quote:
Originally Posted by Steve Sampson
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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Last edited by gmcjetpilot : 06-02-2007 at 10:09 AM.
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  #6  
Old 06-02-2007, 11:12 AM
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f1rocket f1rocket is offline
 
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Default

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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Last edited by f1rocket : 06-02-2007 at 11:14 AM.
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  #7  
Old 06-03-2007, 07:29 PM
UH60Hwkdrvr UH60Hwkdrvr is offline
 
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Location: Ft. Bragg, North Carolina
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Smile

Quote:
Originally Posted by gmcjetpilot
......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
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  #8  
Old 06-04-2007, 01:22 AM
Steve Sampson Steve Sampson is offline
 
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Location: N. Yorkshire, England
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Default

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!
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G-IKON Build log here , or Index to blog here.
RV4 #4478 - Flying since 16th June '08. First flight video here.
Circuits at my 1000' strip.
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  #9  
Old 06-10-2007, 08:29 PM
Dave Dollarhide Dave Dollarhide is offline
 
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Default

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.
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  #10  
Old 03-26-2018, 12:38 PM
DTARM1 DTARM1 is offline
 
Join Date: Feb 2016
Location: VA
Posts: 7
Default

Quote:
Originally Posted by smokyray View Post
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.
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