Ron Van Putte AC Help

[CloudyIFR]

Attached is an MS Excel spreadsheet for detereming the CG of a Canard.

It's built off of this one page article from Ron Van Putte, I wish I knew who built the spreadsheet so I may give credit where it's due but I can't recall where I found it.

http://www.palosrc.com/instructors/putte.pdf

Right now I'm only interested in understanding how he comes up with the AC on the top portion of the spreadsheet.

If you have a Hershey bar wing, 10" root chord and 10" tip chord how can the AC be at 8" aft of the root leading edge? That's 80% of the MAC where the MAC is 10".

It should be 25% of the MAC or 2.5" aft of the leading edge.

What am I missing here?

Thanks for looking and helping.
Curtis
Montana

[kcaldwel]

...

[Derfy]

Right now I'm only interested in understanding how he comes up with the AC on the top portion of the spreadsheet.

If you have a Hershey bar wing, 10" root chord and 10" tip chord how can the AC be at 8" aft of the root leading edge? That's 80% of the MAC where the MAC is 10".

It should be 25% of the MAC or 2.5" aft of the leading edge.

What am I missing here?

It looks to me if this is just a typo.

Cell C9 has the following contents:

=+(1/ 6*(Root^2+Root*T+ T^2) /(Root+T)) +D/3+((Root+T^2)/(Root+T))

where in fact, from the pdf file, it should be:

=+(1/ 6*(Root^2+Root*T+ T^2) /(Root+T)) +(D/3)*((Root+T^2)/(Root+T))

This should give the correct answer (I hope :D ).

:cool:

[CloudyIFR]

Derfy,

Now I compared those formulas but for the life of me I didn't catch it. Yes, that does give the correct answer, hope folks aren't using the file as they'll have serious balance issues!

Thanks for the thorough review!

Curtis

[Mel Duval]

I'll give Ron an email and see what he says.....

[vanputte]

You guys are going WAY back. I wrote those equations about 40 years ago for an aircraft stability and control class I was teaching at the Air Force Institute of Technology at Wright Patterson AFB, OH. I published them in an issue of American Aircraft Modeler magazine and it was reprinted in the June 1980 issue of Model Aviation, with permission. The Palos R/C club picked it up and put it on their web site. I have since modified the equations to make it easier for the average modeler to determine aerodynamic centers and proper starting CG locations, but the heart of the equations are exactly as they were presented in the late 1960s.

Ron

[CloudyIFR]

Ron,

Very nice to meet/see you here.

If you have a few minutes check out the spreadsheets I've put togther. You many download them at my website.

One day I'd like to get a Canard one put together but that's for a project in the future.

I'm finishing up a flying wing sheet that uses Dr. Panknin's wing twist formulas.

Curtis
Montana
USAF Retired

http://h1.ripway.com/cloudyifr/files.htm