EZ Fuselage Extension for better CG

[Marc Zeitlin]

... It would seem that the elongation of the nose might push the C/L aft somewhat...

How would adding surface (lifting) area in the front of the plane move the center of lift (Aerodynamic Center) aft?

 

In fact, adding surface (lifting) area forward moves the aerodynamic center FORWARD, and because it's not a well defined "wing", does so non-linearly - there's more of an effect at high AOA's than at low AOA's (which is a bad thing). This was one of the main reasons that Nat decided to cut the canard shorter to avoid deep stall susceptibility in the wider COZY MKIV - the wider fuselage forward of the A/C was causing the aircraft to be able to reach an AOA at which the main wing could stall.

[Spodman]

To my knowledge, the shortening of the canard was never associated with the Long-EZ design. This was something that came out of a mod of that design (the Cozy)

Erm, no, first arose in the Vari.

[argoldman]

How would adding surface (lifting) area in the front of the plane move the center of lift (Aerodynamic Center) aft?

 

In fact, adding surface (lifting) area forward moves the aerodynamic center FORWARD, and because it's not a well defined "wing", does so non-linearly - there's more of an effect at high AOA's than at low AOA's (which is a bad thing). This was one of the main reasons that Nat decided to cut the canard shorter to avoid deep stall susceptibility in the wider COZY MKIV - the wider fuselage forward of the A/C was causing the aircraft to be able to reach an AOA at which the main wing could stall.

Brain indigestion--- sorry.. of course it moves forward.

[Limo EZ]

If what you are interested in is a stretched Long EZ with a larger heaverier motor you need to look at the Jan 96 CSA newsletter that describes Sam Kriedel's Limo EZ. It is stretched 4.5" but the canard went further forward an additional 2". The CG goes forward but the M.A.C has to go forward so he accomplished this by lengthening the canard. The main gear CL was moved forward so the rotational characteristics could be retained as well as it not flipping backwards when MT. Sam used a 0 360.

 

Joe Berki

Limo EZ

13B

[argoldman]

How would adding surface (lifting) area in the front of the plane move the center of lift (Aerodynamic Center) aft?

 

In fact, adding surface (lifting) area forward moves the aerodynamic center FORWARD, and because it's not a well defined "wing", does so non-linearly - there's more of an effect at high AOA's than at low AOA's (which is a bad thing). This was one of the main reasons that Nat decided to cut the canard shorter to avoid deep stall susceptibility in the wider COZY MKIV - the wider fuselage forward of the A/C was causing the aircraft to be able to reach an AOA at which the main wing could stall.

 

Now that I have taken my brain Tums and neural Immodium I can more clearly see what I was trying to get at.

 

Adding surface forward indeed moves the aerodynamic center forward. What I was attempting to convey, before my tongue got in the way of my eyetooth and I couldn't see what I was saying, was that doing that has the same effect on the flying characteristics as would moving the CG rearward on an unmodified plane, necessitating more nose down trim.

 

I gotta stop writing these things late at night.

 

Thanks Marc for the correction. The great thing about these fora and lists is that when a mistake is made there are the experts waiting to trounce on the perp--- And rightly so.

[AVI]

But that's not what you SHOULD be trying to get. See below.

 

Yes, and either putting more weight in the nose, or extending the nose so that a lesser weight at a longer moment arm can counteract the weight in the rear is something that is commonly done, as neither has a major affect on aerodynamics. The aircraft (Berkut, Esselstyn O-540 COZY MKIV with Velocity Retracts) that have been stretched 12" BETWEEN the wing and canard have different CG ranges than aircraft that are not stretched. between the aerodynamic surfaces.

 

Which is destabilizing. Hence the need for the understanding of the relationship of the aircraft Aerodynamic Center to the CG range.

 

If you move the canard forward, you change the aerodynamic center of the AIRCRAFT - the main wing is not the only lifting surface. Keeping the CG in the same position relative to the MAIN WING is meaningless - it needs to be in the correct position with respect to the aerodynamic center of the AIRCRAFT.

 

So, unless you understand the relationship of aerodynamic center (of the AIRCRAFT, NOT just the main wing) to the CG, and unless you know what moving the canard forward by an arbitrary amount will DO to the Aerodynamic center of the aircraft, you have no idea where the CG SHOULD be, and therefore have no idea whether moving some "stuff" forward to attempt to counteract the extra weight in the back is a good idea or not.

 

That's what I'm driving at, and what you're not picking up on. This is non-trivial, and even moreso with canard aircraft than with conventional ones.

 

So can anybody post what the published CG range of the Berkut is?

If it's not the same as that of the LongEZ, out of curiosity, what is it?