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Prop Dia. Problem - Tweedy Bird - 3/27/2009 4:06 AM   
JK1000


 

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From: Wisconsin Rapids, WI, USA
Status: offline 		I am building a Tweedy Bird kit that was purchased from ebay and would like to convert it to electric. It is a 3.5 to 4.5 lb airplane and is styled after the Dirty Birdy, only smaller. It calls for a .19 to .30 glow engine. The problem is that electric conversions all seem to use prop diameters that are too large. The palns call for a 8 or 9" dia. and show that I don't have the ground clearence for a 11 or 12". I really don't want to extend the landing gear.
Is there any way that I can deal with this problem? Any suggestions are wellcome. I don't have a motor for this plane yet so options are open. Last resort would be glow engine but I would like to get into electric.
Thanks, JK1000

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RE: Prop Dia. Problem - Tweedy Bird - 3/27/2009 3:59 PM   
normgoyer


 

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Status: offline 		Start with the recommended size for the motor battery combo you have, then reduce the diameter of the prop to the size that you need for clearance. Then add the inches you removed from the diameter to the pitch. The prop will have approximately the same power but will lack in instant thrust but will have a higher speed. Norm

or cut a ditch down the center of your runway for prop clearnace, or put on larger wheels, or make it a taildragger.

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RE: Prop Dia. Problem - Tweedy Bird - 3/27/2009 11:39 PM   
JK1000


 

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Status: offline 		OK so now the problem is that I can not find an electric prop with a dia. of 9" and a pitch of 9". Can a person put a prop on that is used for glow engines?

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RE: Prop Dia. Problem - Tweedy Bird - 3/27/2009 11:57 PM   
normgoyer


 

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Status: offline 		Hi, if the original plane used a 9 inch prop then the engine size had to be pretty small, about a 25 to 35 which means that your electric motor might be just too big. You have a mismatch of mumbers in there someplane. Norm

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RE: Prop Dia. Problem - Tweedy Bird - 3/28/2009 12:35 AM   
JK1000


 

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Status: offline 		The original plan called for a .19 to .30 glow engine. the proto type flew with KB .19. The weight of the plane is 3-1/2 to 4-1/2 lbs. Seeing as I like extra power I was thinking a Eflite power 25 or 32. I don't know but i may be all washed up in my thinking. That is why I'm here fishing for advice. Which by the way I thank you very much for your input.
JK1000

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RE: Prop Dia. Problem - Tweedy Bird - 3/28/2009 1:41 AM   
normgoyer


 

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Status: offline 		If you like speed, get a motor with a high wind count that is the dash number like -7 or -14 or dash 6, the higher the number the more rpms. Then you can use a a 9 X 9 prop and wind that sucker up, I gurantee your need for speed will be satisfied, but, will the Tweety bird hold together? Norm

I visited you beautiful state for 22 years attending the Oshkosh Air show now called the AirVenture, Norm

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RE: Prop Dia. Problem - Tweedy Bird - 3/31/2009 2:28 AM   
JK1000


 

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Status: offline 		Thanks Norm, I think you have me headed in the right direction.

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RE: Prop Dia. Problem - Tweedy Bird - 4/22/2009 5:49 PM   
gyrocptr


 

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quote:

ORIGINAL: normgoyer

If you like speed, get a motor with a high wind count that is the dash number like -7 or -14 or dash 6, the higher the number the more rpms. Then you can use a a 9 X 9 prop and wind that sucker up, I gurantee your need for speed will be satisfied, but, will the Tweety bird hold together? Norm

I visited you beautiful state for 22 years attending the Oshkosh Air show now called the AirVenture, Norm

For higher speed (high rpm), don't you look for a lower wind-count and a higher kV (rpm per volt) rating??
Doesn't a higher wind-count lead to a lower kV, higher torque and lower rpm?

You might consider the following from a "local" vendor.
http://www.headsuprc.com/servlet/the-1430/3542-dsh-10-Outrunner-Brushless-Electric/Detail

4-cell Lipo: APC 9 x 4.5E: 60 oz thrust @ 33 amps (470 watts)


< Message edited by gyrocptr -- 4/22/2009 6:00 PM >

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RE: Prop Dia. Problem - Tweedy Bird - 5/15/2009 4:27 PM   
ChicaWolverina


 

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Status: offline 		Can somebody please send me the wing rib patterns from the Tweedy Bird, I have the plans from the internet but it doesn't show the individual rib outlines and Great Planes has been a pain!?!


><
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RE: Prop Dia. Problem - Tweedy Bird - 5/15/2009 4:34 PM   
normgoyer


 

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Status: offline 		Great Planes is an excellent well run company. They are doing what all companies do, they help their customers, that is, modelers who purchase their products. Norm

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RE: Prop Dia. Problem - Tweedy Bird - 5/17/2009 5:20 AM   
swlarcham



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Status: offline 		Tomasina
I have a Tweedy Bird I purchased new in 1981. Finally built it about 5 years ago and flew it with an Irvine25 on a pipe.
I think the Eflite 32 would be a good choice. Don't have any experience with prop size on it for E power but I don't see how you'll ever be happy with na E powered Tweedy Bird with out longer gear. convert it to taildragger and longer mains.

as for the ribs I still have my plans, although they are in 25years old shape. i will attempt to copy the rib pattern for you.
eddie

< Message edited by swlarcham -- 5/17/2009 5:22 AM >

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RE: Prop Dia. Problem - Tweedy Bird - 5/17/2009 11:52 AM   
Glacier Girl



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Well APC does make a 9x9 if you had to go that way. You can use a gasser prop, they are just a lot heavier/stronger constructed then an electric needs.

And thing with electrics is you can play with volts to change a motors performance.  One of my old Stryker tricks, using low kv motors on high volts.  Could spin a larger diameter/pitch blade at still lower amps, then a high kv unit at lower cell count could.

If you are running into a prop clearance problem, and the esc can handle the higher cell count, up the cells, and drop the blade diameter, you can dial in the prop diameter/pitch to correct  it and get it dialed in for how you want the plane to fly.

Watts are watts. How you get there is up to you. Watts Law:  Amps x Volts = Watts.   10 amps x 10 volts = 100 watts, same for 1 amp x 100 volts, or 100 amps x 1 volt, still 100 watts.



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