V-N Diagram

[mplafleur]

Does anybody have a legible soft copy of the V-N diagram for the Cozy IV?

[Marc Zeitlin]

Does anybody have a legible soft copy of the V-N diagram for the Cozy IV?

What V-N diagram? I don't ever remember seeing one - am I having a senior moment?

 

All the performance charts of which I'm aware are (and have been, for 12 years) at:

 

http://www.cozybuilders.org/performance/

[raiki]

I think what he is asking for is a Vn list. eg Vs, Va, Vne etc. Not a diagram as such.

 

The V speeds are all in the Pilot Operator Handbook (manual) are they not ????

[mplafleur]

I'm looking for a V-n diagram. Here's an example. I'm surprised no one has done one for a Cozy.

 

[Marc Zeitlin]

I think what he is asking for is a Vn list. eg Vs, Va, Vne etc. Not a diagram as such.

No, Mike was asking for a specific, well known thing called a V-n diagram, of which he then posted an example. It graphically indicates many of the V-speeds, but shows the relationships.

 

I'm looking for a V-n diagram. Here's an example.

I'm quite aware what a V-n diagram is. You asked as though you knew that one existed, and just wanted a copy. Since I've never seen one, I was surprised that one might exist. Had you asked for a copy of "A" V-n diagram, rather than "THE" V-n diagram, I would have said "there isn't one" :-).

 

I'm surprised no one has done one for a Cozy.

One would have to get design limits for the COZY MKIV aircraft that the designer has not been willing to commit to. If you ASSUME a normal category aircraft, then knowing the stall speed and Vne, one could easily construct a V-n diagram, but it's based on the assumption above - who knows how accurate that is.

 

I base my maneuvering speed on such an assumption, however, and use 140 mph. This all assumes gross weight, obviously, and Va is lower at lower weights.

 

PS - Your example V-n diagram is defective, BTW. It shows Vs at a load factor greater than one. In fact, for the aircraft in question, Vs is 50 KEAS, not 60 KEAS, which is why the stall speed is 97 KEAS (50 * 3.8^.5).

[mplafleur]

I'm quite aware what a V-n diagram is. You asked as though you knew that one existed, and just wanted a copy. Since I've never seen one, I was surprised that one might exist. Had you asked for a copy of "A" V-n diagram, rather than "THE" V-n diagram, I would have said "there isn't one" :-).

I assumed, or rather hoped, that one existed for the plans built Cozy.

 

One would have to get design limits for the COZY MKIV aircraft that the designer has not been willing to commit to. If you ASSUME a normal category aircraft, then knowing the stall speed and Vne, one could easily construct a V-n diagram, but it's based on the assumption above - who knows how accurate that is.

The two that I've seen seem to be not based on the design, or demonstrated limits, but rather the category limits. Is this usually the case?

 

PS - Your example V-n diagram is defective, BTW. It shows Vs at a load factor greater than one. In fact, for the aircraft in question, Vs is 50 KEAS, not 60 KEAS, which is why the stall speed is 97 KEAS (50 * 3.8^.5).

The University of Kansas did that one. I'll be sure to let them know.

 

Here's a V-N for the RV9A

 

[Marc Zeitlin]

I assumed, or rather hoped, that one existed for the plans built Cozy.

You and me both. It would be relatively simple to construct one for a generic COZY MKIV - one could build one for Normal, Utility, and Aerobatic categories in about 5 minutes. But none would be official, and we wouldn't know which one was the "right" one. I treat my plane as if it's a Normal category aircraft, as that's the most conservative.

 

The two that I've seen seem to be not based on the design, or demonstrated limits, but rather the category limits. Is this usually the case?

Well, certificated aircraft, whatever they've been tested to by the MFG, have specific "G" limitations positive and negative. Those "G" limits, along with the stall speed and Vne (as set by the MFG) determine what the envelope looks like. So its partially based on MFG testing and partially by category limits.

 

For experimentals, there are no "category limits", since there's no category - the "G" limits are whatever the MFG claims, if anything.

 

The University of Kansas did that one. I'll be sure to let them know.

I'm sure they'll appreciate that :-).

 

Here's a V-N for the RV9A

This one's better, but I don't understand why Va (maneuvering speed) is where it is. I would have expected it to be at the intersection of the 3.8G limit line (bottom of the "structural damage" region) and the "accelerated stall" curve, at about 110 mph. That's where full deflection of the controls could start to cause more than 3.8 G's.

 

You can see that the stall speed (aircraft and weight dependent) will determine Va; aircraft limits will determine Vne, but the category "G" limits and the 50 fps gust will set the Vc.

[Edge 513]

It would be great visually to have one of these generated on a stock Mark IV airframe/power plant. Very neat indeed.