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1/4 scale Bob Holman Boeing F4B-2 CG

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1/4 scale Bob Holman Boeing F4B-2 CG

Old 03-08-2018, 08:53 PM
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langerl
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Smile 1/4 scale Bob Holman Boeing F4B-2 CG

Hi all!
I've finally finished restoring a quarter scale Bob Holman Boeing F4B-2 / P-12 biplane fighter. I met a gentleman at a SMMAC event and he indicated the proper CG location for this model was 6" aft of the leading edge of the top wing. Can anyone familiar with this model confirm this data? I haven't bought the Holman plans and will soon to see what they say, but I'd love to know a good figure for this so I can get my initial balance weights using this 6" CG. I'd also be interested in anyone who has actually FLOWN a Holman quarter scale F4B2 and what they've used for their "actual" vice plan CG point.

Thanks in advance.
Lynn
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Old 03-09-2018, 08:45 AM
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foodstick
 
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I can't help with the CG, but that sure is a nice plane. Its a rare enough build I don't know how many people have the plans to browse...I will keep my eye open for the info though..
Old 03-10-2018, 07:07 PM
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BobH
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You can establish the CG at 30% MAC. Measure from the front of the top wing to the back of the bottom wing. This is the total dimension you are interested in.
Take 30% or 25% of that from the LE of the top wing and see where that point lies.
That will bet you pretty close to a decent CG.
Old 03-13-2018, 06:06 PM
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langerl
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Question F4b-2 cg

On the model, the 30% mean cord point of the combined top and bottom wings is exactly 6" aft of the top wing leading edge. This precisely confirms my initial information for this model's CG. Oddly enough though, the Holman plans I just received show just an arrow pointing down at what I suspect is the intended plans CG. This however measures only 3"(!) back from the leading edge of the top wing or about 15% of the mean cord!? I can't imagine this is correct.

I appreciate the feedback so far. If someone has further CG data on this model, please continue to chime in!!

Thanks!
LRL
Old 03-13-2018, 06:46 PM
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BobH
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Better safe than sorry. Thirty Percent is typical. Twenty five percent is too. You can start at 25% as a safe starting point then move it back if you are comfortable with it.
Fifteen percent? No way! lol
Old 04-16-2019, 11:03 AM
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KCCraig
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This is a cool bipe, Id like to find a giant scale of this Boeing F4B as my first war bird. I love bipes. I guess it is not a war bird strickly speaking, as it did not see combat.
Did you ever fly it, how was the CG?
Old 04-16-2019, 07:11 PM
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langerl
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Nope. Not flown yet. Last year was a wash out for several flying events I try to attend and I only had time (or room) to campaign one model; a 1/4 scale Duncan Hutson Tiger Moth that I also restored. 1st flight by a VERY RESPECTED warbird pilot was, to say the least, very traumatic for my Test Pilot. Reason was ….yep, you guessed it, another erroneously PLANS INDICATED CG. I can't believe two plans I've use to determine the model's CG were BOTH WAY OFF!! Dang. I'm starting to think none of the plan CGs are believable. From now on I use CGs indicated by builders that have FLOWN their models repeatedly and determined the proper position by first hand experience. Hope I can get my S**t together this year to fly my fleet. Gonna' be a challenge though, as both our local flying fields were flooded (and may be occasionally so again this season). Wonder if Someone is trying to tell me something....???
Old 04-18-2019, 06:52 AM
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KCCraig
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Providence is trying to tell you, Triple check CG

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