Tuned pipes and CG: Big diference?

The Chizler was meant to be powered by a Fox .35.

I am puttin' an OS.25VF on the one I'm building, and I was wondering where the CG would go.

On one side the VF has ball bearings and should be a couple of ounces eavier than a Fox, but there's gonna be some pipe behind the CG.

Will the balance point go forward, backwards or just stay where it is?

I just don't wanna bust my bills lightening up the wrong side.

What's the use of building up the finn, rudder, etc. if it's gonna be nose heavy, or cuttin' out half inch of nose if it's gonna be tail heavy??

Thanks in advance,

Ion (heads or tails?) Muniz

Do you have a good scale? Why not just attach the pipe to the engine and then lay it over the plan. See where the CG would fall on the pipe and, balancing it at that location check the weight of the engine on the scale. Now compare it to the weight of the Fox 35 and you will know the difference that you are adding/subtracting (well, adding). Easy enough to do.

Len,

I'm Brazilian.

Lazy...

I was hoping NOT to get this kind of reply...

>Len,
>
>I'm Brazilian.
>
>Lazy...
>
>I was hoping NOT to get this kind of reply...

Well, the most straightforward way it to simply build the airplane, and then add tail weight to get it to balance. An ounce or so isn't going to make a difference in the results.

An aside to what Len said: We are in the trimming stages of a large piped stunt ship. The original plane, as drawn, was powered by an OS 46VF. We are using a PA 61 which is lighter. We had to add nose weight to get the CG where it was originally specified. The pipe doesn't weigh all that much (compared to the engine), but does have an effect on cg.
Bill <<>

Ion:

Don't make it so complicated.

Take a yardstick or something like it and tape either a Fox .35 or something about the same weight (about 7 oz if I remember right) to the front at the engine location. Mark lengths to match the Chizler and add weight to the tail to balance at the proper CG. Now tape your OS in place of the Fox or equivilant and add weight to balance correctly. This will be ROUGHLY what the model should need and where, depending on your wood and building. Light wood and more sanding will tend toward nose heavy while heavy wood or less sanding toward tail heavy. Just be sure the length from engine to desired c/g and to the tail match the real thing.

I used this setup substituting a 14 oz K&B 40 & muffler for an 8 oz McCoy 40 in my Tempest and came out withing 1/8" of right on the cg. I also double checked using the system pilots of real planes use (datum point) and a computor program and the stick and lead were just as good. It's tougher on classics since we cant change the outside dimensions.

Good luck

I strongly suspect it's gonna be nose heavy.

Instead of worrying I'm just gonna put a tailwheight box on it.