Nathan Moon
I'm New Here
Just wondering if anyone has done this. With O2 and cruise in the teens I would think that you could get speeds approaching 190 knonts true.
Nathan Moon said:Just wondering if anyone has done this. With O2 and cruise in the teens I would think that you could get speeds approaching 190 knonts true.
MCA said:Who makes a turbonormalized IO-390?
You seem to be arguing from the point of view of a 2 place RV.O.K., I can understand the concern about putting too much stress on a light RV airframe by pushing it past the Vne. And you do mention a 1000 foot per minute dive. Then you go to the manifold pressure and IAS and TAS.
My questions are these: Resolved: a 1000/min. dive will put an RV past it's Vne, but what does manifold pressure have to do with anything? Don't forget, the 7 & 8 are already rated for 200 H.P. so I don't see why a dive at one manifold pressure should be different than another as far as surface flutter is concerned. As for IAS, TAS: I plan an RV with a full glass cockpit, why would I worry about inaccuracies or conversion calculations for steam gages?
The turbo-normalized engine is to get me in and out of mountain valleys briskly and also allow me to cruise at altitude with 55-60% power. It has nothing to do with dives or loops which I can just as easily perform without a turbo. I think that VANS is worried that pilots will take their aircraft past Vne in straight and level flight and that an RV is just not designed for that kind of stress. I believe a prudent pilot can manage that risk.
As I have been unable to find a suitable alternative for the kind of mountain flying I like to do, so the TNIO 390X it will have to be. I very much hope I'm right.
Richard Vidaurri
My post would have made much more sense had I clarified that I was interested in an RV-7A or 8A. I've never even seen an RV-10. Personally, I'm not certain I'll be able to have an accurate TAS but Insight Avionics says I will - so I'll be your guest.
But all is well. After much discussion and research I have concluded that the RV is just not the plane for what I want to do. I love it and I wish I could afford two aircraft but I can't.
So there.
Best,
Richard Vidaurri
On the Vans site there is small piece about 60 RV-6s that they sold to the Nigerian Air Force. These are now that branch's primary trainer for it's pilots.
But how did he do it? Doesn't it seem to you impractical to train jet pilots in an airplane that has such a narrow Vne margin? He talks about making some aerodynamic alterations but doesn't say what those were. Do you have any idea? Does anyone?
Best,
Richard
I think I would build the aircraft as designed by Van, and remain within his recommended Vne.This makes sense but maybe they did something else. Somewhere on these forums a pilot was saying that he thought counter-balancing the rudder on an RV would improve the Vne margin. Any thoughts on this?
I can see that there are good reasons to stay within the design parameters of the RV (-7A in my instance), but what then does Van do about aerobatics -especially loops?
Thanks,
Richard
The article the last poster references has to do with flutter at altitude. In a nutshell, Vne is based on true airspeed, not indicated airspeed. Your indicated airspeed is about 2% low for each 1000 feet of altitude. Go up 12K feet at full throttle and put the plane in a 1000ft/min descent and you will exceed Vne and risk control surface flutter. (In the article that's what happened to the author). Potential catastrophic failure. Now put a turbo on, at 12K instead of the MP of 18-19 inches with a normally aspirated engine, you are now getting up to 30 inches! You may be at Vne in cruise, put it in a dive and OMG!
And have you seen how tight the IO-540 is? There may be more room if you go with a 360 or 390 with a turbo. But you will have to give up take off power going with the smaller engine. It's true that at altitude you will have the power of the IO-540 with a TIO smaller engine. The only other debate is fuel economy. From what I have read a IO-540 producing X HP uses about the same amount of gas as a TIO-360 producing X HP, it's just a bit heavier.
Vne in any aircraft except Van's apparently is IAS.
IAS is what the airframe "sees"...
Vne IS defined in terms of TAS (or combination of IAS and TAS) for a couple of certificated airplanes and most modern sailplanes to ensure that adequate flutter margins exist throughout the normal operating envelope. Instead of using a constant TAS Vne, some manufacturers define a decreasing IAS Vne with increasing altitude, basically mimicking the constant TAS value.
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What certified (GA) aircraft have ANY Vspeeds in TAS? I have never seen one. I am not absolutely sure they do not exist, but I have never seen one. Obviously I have not seen every aircraft.
I understand that it is a conservative approach.
I was merely responding to the statement that Vne IS a TAS measurement. AFAIK, only in Van's
You are correct: type certificated aircraft are required by part 23 to specify limiting speeds in IAS, presumably because many such aircraft have no direct display of TAS. However, the manufacturer may placard the aircraft with different limits in IAS as a function of altitude - which may be essentially the same as a single TAS number! Staying out of flutter trouble can be complicated. I personally wish Vans had followed part 23 here (which they are not legally obligated to do) and published an IAS vs Altitude chart for Vne, just to avoid all these posts.
THe manufacturer can placard many things. I have never seen a placard indicating a reduction in Vne with altitude. The only Vne I have EVER seen in any GA aircraft is the little red spot on the ASI. Can you provide an example?
THe manufacturer can placard many things. I have never seen a placard indicating a reduction in Vne with altitude. The only Vne I have EVER seen in any GA aircraft is the little red spot on the ASI. Can you provide an example?
And of course various helicopters have Vne speeds that similarly vary with altitude, but that's due to aerodynamic phenomena not applicable to airplanes!
Vne in any aircraft except Van's apparently is IAS. IAS is what the airframe "sees", and there is no way that a certified manufacturer would specify calculated TAS as a Vspeed. I doubt the FAA would certify it as such.