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7A - Improving CG - James "Long" Cowl IO360 Hartzell BA

N

ncarmon

Active Member
I'm at the point I need to make an engine decision. In doing the research, the majority of 7As are in the 79 and 80" CG range. CG can be a little tight at heavier weights after a long flight.

One option is to use the James "Long" cowl, IO360 and the Hartzell BA M2YR-1BF/F7497. The 40-50 lbs, moved forward the 3-4" required for long cowl would seem to help by moving the BEW CG forward.

Does anyone have this combination installed? Can you share your CG station along with your BEW? Any other thoughts or am I just hoping for a low cost CG solution when in fact it doesn't exist?

Thanks
 
Van's Limits

If I read the manual correctly, the forward limit is 79". Mine has the long SJ cowl and a 14 pound FP prop with 4" Saber extension. My empty CG is 79.24.
 
Prop Station?

Anyone know the prop station on a -7A without the extension? I'm going to use 4" and the weight of the prop along with data from Dan's W&B DB to calculate the effect, I'll post results here. Thanks.
 
Yes I got this

ncarmon said:
I'm at the point I need to make an engine decision. In doing the research, the majority of 7As are in the 79 and 80" CG range. CG can be a little tight at heavier weights after a long flight.

One option is to use the James "Long" cowl, IO360 and the Hartzell BA M2YR-1BF/F7497. The 40-50 lbs, moved forward the 3-4" required for long cowl would seem to help by moving the BEW CG forward.

Does anyone have this combination installed? Can you share your CG station along with your BEW? Any other thoughts or am I just hoping for a low cost CG solution when in fact it doesn't exist?

Thanks
Click to expand...

Firstly the the BA prop is effectively moved forward by 2 and 5/8ths of an inch...If you use the M series hub.

Or you can use the "C" series hub (the prop bought thru Van's) on a sabre 2 5/8ths extension.

Mine happens to be on a 2.25" Sabre extension.

I can't remember where th CG comes out, simply because its not a problem under any loading conditions.

So for me at least hanging the prop 2 1/4" forward enables me to forget about CG issues.

About the only downside is the airplane doesn't spin very fast!...:)

You can also join my James aircraft yahoogroup for lots of installation information.

Frank
 
Ohyes

And the airplane is a 7a with a parallel valve IO360 with an AFP FI system.

Frank
 
Recalculated...

Ok, I took all the 180 horse, IO360 RV7As with a Hartzel Props from Dan's W&B DB. The AVERAGES were:
CG 79.63
BEW 1122.16
Moment 89374.09

By subtracting the prop at some arbitrary station, I subtracted:
CG 1
BEW change 60lbs
I added
CG -1.625
BEW change 60 lbs

New CG 79.49
new BEW 1122.16
new Moment 89216.59

Effectively it moved the CG forward an average of 0.14

Anyone see an error in the logic? (Yes, I do understand that some of these airplanes may already have a long cowl and M hub.) Other than that?

Seems then like, as long as I'm not doing extreme aerobatics, this might be a good choice to improve CG.....No?
 
Uh oh

Well,

The statement of fact is that putting a C/S prop on an extension is an untested combo...can't argue with that.

Respected opinions seem imply that it is a small risk however.

The M hub prop is rated to 4G's I believe which is enough for most of what you will do in this airplane as its simply not an Extra or Pitts Special.

Frank
 
Well even though I didn't get much response from my post, you fellows have given me most of the information I needed. I personally am not comfortable with putting an extension on my cs prop and this is the only way I can have room for the alt and starter using the James cowl. Guess I will be ordering a Van's cowl. Anyone need a James Holy Cowl?

Leon
RV7A
0320E2A
N853LC
 
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