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Brodak P-51B Balancing

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Old 08-25-2019, 10:29 AM
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redtail
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Default Brodak P-51B Balancing

Hey guys trying to get back into CL so I a Brodak P-51B. I cut away what would have been the solid canopy area. I replaced that area with a Brodak P-40 plastic canopy that I cut up to somewhat match the P-51B canopy. Looks like I may need to put at least 6oz of nose weight to balance the airframe. Trying to stay "Old School", I will be running a McCoy 35 Redhead. Having cut away some of the fuselage wood canopy area, does 6oz of nose weight sound about right or does it sound like alot of weight????? Next the plans illustrate a 2" CG behind leading edge does that sound reasonable? Many thanks for any help. Chic

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Old 08-26-2019, 01:39 AM
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Gday Chic,

It seems to me that an additional 6oz is way too much. That seems to be about one sixth, or so of the total all up weight

What.stage are you at with the build? Sometimes the apparent balance point of unfinished models can be deceptive. Check and double check once it's completed.

One thing to remember is that you'll probably need to use a muffler (unless you fly in a non-noise sensitive area). Is this a factor?
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Old 08-26-2019, 03:59 AM
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I thought the same thing. But having cut away the solid wood canopy area and replacing it with the much lighter plastic canopy - I was beginning to think maybe that 6oz was necessary. Check the photos and let me know what you think. Many thanks and GDay to you also.


Chic
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Old 08-26-2019, 04:15 AM
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Hi Chic,

Your model looks great, Have you tested to see where it balances?

If you're coming back to Control line flying, it's probably worth having the CG forward of the 2" called for on the plan.

6oz sounds high to me, the amount of balsa removed to be replaced by plastic wound hardly even be 1oz, and you've replaced it with good detail which would probably be nearly as heavy. I would guess that a muffler would probably be around 1-1,5oz.

I'd suggest you have a trial balance to see where the CG actually is and try some weights to bring the cg to 1" from the LE for your initial flights.

Good luck with it.
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Old 08-26-2019, 04:24 AM
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Hey There Greggles47. Many thanks for the suggestion. Will do as you say and see if all that weight is needed. Smiling - which model are you talking about, the TBF Avenger in the background or the P-51B. Again, thanks. Chic
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Old 08-26-2019, 05:06 AM
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Chic,
I have built the Sea Hurricane (two times) and FW-190 from that series of kits. They came out nose heavy with an OS .40 FP and I actually shortened the nose on the second Hurricane and FW. I am currently flying the LAGG 3 which uses the same wing with a bit of stretching on the span. It is balanced at the spar, or maybe 1/8" behind the spar (hard to tell with fat finger tips). Flies pretty well at these conditions.
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Old 08-26-2019, 06:36 AM
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Based on what I'm ready, the McCoy 35 Redhead is a very light motor. Maybe that is my main problem. Chic
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Old 08-27-2019, 09:58 AM
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put it on pencils close to fuselage at at recommended CG LOCATION....Add modeling clay or pieces of solder to balance.. weight the ballast.....you have your answer...You can strap a muffler to the McCoy but they don't like the backpressure. Spinners or heavy HUBs might get you there. You have room to move the tank and engine forward 1/4 to 3/8 inch makes a BIG difference

You could drill a fairly large hole from nose to rear under the engine and fill with lead shot or solder pieces to balance and epoxy the hole shut....
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Old 08-27-2019, 11:26 AM
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Excellent idea. Many thanks. Chic
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Old 09-06-2019, 09:00 AM
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I hang my models from a point in the ceiling, One big loop of no tangle boat line I bought from Walmart looped around the wing and up to the nose around the prop and then up to a nail . From the same point I hang a small plumb bob, current one is a 1/4x20 nut, from a piece of kite string. Both items, the plane and the nut are now plumb bobs. The nut will be directly over the center of mass (current CG) of the plane. Add weight to the plane as necessary to get the cg to the desired location.
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Old 09-06-2019, 10:50 AM
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Thank you. Will certainly give that a try. Chic
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Old 09-12-2019, 07:11 AM
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Good morning Redtail. I believe that the D to B mod did not change the CG almost at all and virtually unmeasurable. What definitely will help is to move the tank as far forward as possible where it belongs, Another possible issue may be the way you are attempting to balance the airplane. If you try to acheve balance with the nose slightly nose down "for mother and country"will result in the perceived need for more weight than is actually required.

Beyond these two points my suggestion is not to be shy with needed nose weight. Yes muffler would be a big help but I agree with one of the prior responders that That McCoy would never be happy. Of course my opinion is I never agine wish to be old school with all my airplanes are full house RC for throttle with on board battery, Rx, servo and of course relatively modern throttled RC engine and muffler.

John
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