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Author Topic: Biplane Tip Weight  (Read 1775 times)

Offline Rob Swider

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Biplane Tip Weight
« on: February 19, 2010, 10:43:41 AM »
My dad picked up an old Guillows STEARMAN PT-17 at a swap meet that was setup for rubber free-flight.  He's working on setting it up for CL with a Cox .09 that was laying about looking for an airframe.  Anyway, without the benefit of the original instructions, we were wondering if the tip weight(s) should be placed in the lower, upper, or both wings?  For that matter, does anyone have a suggestion for how much weight?

Thanks,
Rob
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Offline Allan Perret

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Re: Biplane Tip Weight
« Reply #1 on: February 19, 2010, 02:43:10 PM »
Hang it from the leadouts with 2~3 feet of lines and split up the tip weights so that the wings are plumb with the lines.  My guess would be around 3/8 ~ 1/2 oz total.
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Allan Perret
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Offline Rob Swider

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Re: Biplane Tip Weight
« Reply #2 on: February 19, 2010, 10:15:56 PM »
Sounds like a good plan, I'll tell Dad.  Anyone know where we can get a spanner-wrench for the Cox .09 glow-heads?

Thanks again,
Rob
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Offline Bill Gruby

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Re: Biplane Tip Weight
« Reply #3 on: February 20, 2010, 06:57:41 AM »
 Allen is correct here. When we built the Big Ringmaster Biplane (715 sq in) we put a tip weidght box in both wings, hung it by the lead outs from a dor jamb and added half to each wing. No problems encountered.

  "Billy G"  H^^
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Offline Paul Smith

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Re: Biplane Tip Weight
« Reply #4 on: February 20, 2010, 07:53:13 AM »
A biplane typically has less wingspan than a monoplane with the same area.  So the tip weight will have less moment from the centre, or less leverage.  So the ounces need to be a little higher.

The same principle applies to a 15-powered Perky speed plane with a 18" wingspan.  It needs a lot more weight than a typcial 36" 15-stunter.

PS: If you have too much tip weight, it hinges and you lose a few points in a stunt contest.  Unless you intend to test fly it in a contest, there's no penalty for too much.
« Last Edit: February 22, 2010, 07:15:44 AM by Paul Smith »
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Offline Allan Perret

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Re: Biplane Tip Weight
« Reply #5 on: February 20, 2010, 08:55:03 AM »
Quote from: Paul Smith on February 20, 2010, 07:53:13 AM
So the tip weight will have less moment from the centre, or less leverage.  So the ounces need to be a little higher.
And likewise the moment of the lines weight and drag acting on the inboard wing.  
So I would not expect to use more tip weight for a biplane of equal area vs monoplane.
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Offline Will Hinton

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Re: Biplane Tip Weight
« Reply #6 on: February 20, 2010, 11:55:14 AM »
Hey Bill G,
Did you ever post final pics of the big Ringmaster bipe?  I missed thgem if you did.  Plus, how does it fly?  And are the plans available?  And can anyone say "highjacked thread"? y1
Thanks,
Will
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Offline Rob Swider

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Re: Biplane Tip Weight
« Reply #7 on: February 20, 2010, 09:24:52 PM »
Good stuff.  No plans to fly in a contest, so the extra weight won't be a big deal. 

Thanks again
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Offline Bill Gruby

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Re: Biplane Tip Weight
« Reply #8 on: February 22, 2010, 05:41:15 AM »
Quote from: Will Hinton on February 20, 2010, 11:55:14 AM
Hey Bill G,
Did you ever post final pics of the big Ringmaster bipe?  I missed thgem if you did.  Plus, how does it fly?  And are the plans available?  And can anyone say "highjacked thread"? y1
Thanks,
Will

 Will;

  Thanks for asking. The Bipe was never done in any trim. We flew is 6 or 7 times in base coat white, no pictures were taken. My son has it now in Georgia where he is stationed. I will ask him to send me pics of it now that he has finished it up. It flew fairly well off the board, but after tweaking it it was a joy to fly. I plan to build another and make a few changes with Pat Johnstons help. We need to stabilize it some on landing. Sometimes it had a mind of its own.

  "Billy G"   H^^
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Offline Will Hinton

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Re: Biplane Tip Weight
« Reply #9 on: February 22, 2010, 09:32:31 AM »
Great Bill,
Sounds like maybe I can plan on one in my future sometime in the next couple of years!  LOVE THOSE BIPES!!
Will
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Offline Jim Thomerson

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Re: Biplane Tip Weight
« Reply #10 on: February 22, 2010, 08:27:33 PM »
If you are not really familiar with the TD 09, I'd suggest you run it on a test stand before you put it in that airplane.  The TD 09 is a very powerful engine. It is way over propped with an 8 x 4 but will turn it very similar to a Fox 15X. I can picture the wings coming off.
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Offline Rob Swider

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Re: Biplane Tip Weight
« Reply #11 on: February 23, 2010, 10:44:32 AM »
Quote from: Jim Thomerson on February 22, 2010, 08:27:33 PM
If you are not really familiar with the TD 09, I'd suggest you run it on a test stand before you put it in that airplane.  The TD 09 is a very powerful engine. It is way over propped with an 8 x 4 but will turn it very similar to a Fox 15X. I can picture the wings coming off.

I don't have any experience with the .09, so I'll take your word on the power.  Do you think an .049 would be a more appropriate engine for the Guillows Stearman?  We're just looking to putter around in circles...

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Offline Jim Thomerson

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Re: Biplane Tip Weight
« Reply #12 on: February 23, 2010, 02:33:15 PM »
Am I correct in thinking the Stearman has 28 in wingspan?  If so, it is a little large for an 049.  I googled around about conversions and found many electrics, but did not see any glow conversions, though surely there are some.  My concern was about structural strength.  The TD 09 might work OK if you go ahead and run a prop like an 8 x 4 with a low nitro fuel.  I do suggest running the 09 on a test mount to see what you are dealing with.  The Cox 7 x 3.5 prop is about the best for the TD 09, but may give you more power than you need. 
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Offline Rob Swider

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Re: Biplane Tip Weight
« Reply #13 on: February 23, 2010, 08:13:48 PM »
Jim,
Yep, it's a 28-inch wingspan.  I've been flying electric R/C for a couple of years, but I just started to play around with electric C/L after a miserable experience with a Brodak .049 last summer.  Would gladly trade it for a decent brushless out-runner...  The mailman brought a Stevens Aeromodel RingRat here yesterday.  I can't wait to get started on it...

  #^

Anyway, we'll heed your advice on the .09 and try it with the 7x4.  Since Dad's just planning basic level circles, we can set the needle on the rich side.  I'll suggest adding a little additional support to the wings since power won't be a big issue.   ;D

Rob
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