wheels - Where to mount???  
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All Forums >> RC Airplanes >> Aerodynamics >> wheels - Where to mount???
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wheels - Where to mount??? - 2/9/2008 2:43:36 PM   
neuroza


 

Posts: 118
Joined: 11/17/2007
From: Porec, CROATIA (HRVATSKA)
Status: offline 		Hi, I build my first hand made airplane, so I need to know is there some rules that I need to know for mount the wheels or I can mount it independently anywhere...

I mean where the wheels must be regarding the center of gravity....

Thanks!
       Post #: 1

RE: wheels - Where to mount??? - 2/9/2008 2:48:59 PM   
highhorse


 

Posts: 624
Joined: 11/16/2006
From: Memphis, TN, USA
Status: offline 		what is the general configuration? nosegear? tailwheel? hi-wing or low wing? trainer use or sport use?

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RE: wheels - Where to mount??? - 2/9/2008 4:01:23 PM   
Mike Connor



Posts: 1384
Joined: 1/10/2002
From: Tulsa, OK, USA
Status: offline
quote:

ORIGINAL: neuroza

I mean where the wheels must be regarding the center of gravity....

Thanks!

if it is a taildragger...

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RE: wheels - Where to mount??? - 2/9/2008 4:29:21 PM   
HighPlains


 

Posts: 2669
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: offline 		Well yes and no.

Yes, 15 degrees down forward from the CG is a good starting point on a tail-dragger.

But no, you are showing the balance point on your drawing, not the CG. Unless the wheels are made of lead, the actual CG will be much higher up in the fuselage. This is typical of many model designs, as they show the CG mark anywhere on the plans that is convenient, but it only represents the balance point.

To find the actual CG of a model you would have to hang it from multiple points on the model. The CG is the 3 diamentional point where the vertial lines from the hanging point would converge.

As far as the good starting point for the location of the gear. It also depends upon the surface you will be operating the model from. Grass field models typically need the gear slight farther forward to avoid tipping up on the prop. Whereas, models flown from hard surfaces tend to ground loop easier when the gear is too far forward.

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RE: wheels - Where to mount??? - 2/9/2008 4:36:53 PM   
neuroza


 

Posts: 118
Joined: 11/17/2007
From: Porec, CROATIA (HRVATSKA)
Status: offline 		This is my plane:

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< Message edited by neuroza -- 2/9/2008 4:47:27 PM >

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RE: wheels - Where to mount??? - 2/9/2008 4:57:26 PM   
HighPlains


 

Posts: 2669
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From: Over da rainbow, KS, USA
Status: offline 		Put your wheels so that the front of them is aligned with with leading edge of the wing, and you will be pretty close.

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RE: wheels - Where to mount??? - 2/9/2008 5:54:47 PM   
highhorse


 

Posts: 624
Joined: 11/16/2006
From: Memphis, TN, USA
Status: offline 		Yup, that type is not so critical...I'd shoot for gear that give the longest prop you will likely use about 2" of clearance in a level attitude (to keep it out of the grass) and place the AXLES even with the leading edge of the wing or perhaps just a touch forward of that.

Highplains, you make an excellent point ref the difference between balance point and CG. Unfortunately, the term CG is a universally misused one. Fortunately, that's alsmost never an issue.

< Message edited by highhorse -- 2/9/2008 5:56:57 PM >

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RE: wheels - Where to mount??? - 2/9/2008 7:14:07 PM   
da Rock



Posts: 6705
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		There is a good picture taken from an excellent book by Andy Lennon, "R/C MODEL AIRCRAFT DESIGN".

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RE: wheels - Where to mount??? - 2/9/2008 8:23:33 PM   
Mike Connor



Posts: 1384
Joined: 1/10/2002
From: Tulsa, OK, USA
Status: offline 		You should consider the most forward CG is probably forward of my line and you may want more prop clearance. Considering that it seems the leading edge of the wing should be somewhere between the front of the wheel and the axle.

Note - CG location is an estimate. Balance point is as supplied.

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RE: wheels - Where to mount??? - 2/9/2008 8:37:28 PM   
neuroza


 

Posts: 118
Joined: 11/17/2007
From: Porec, CROATIA (HRVATSKA)
Status: offline 		Thanks, everybody...
This help me a lot!

When I manage to fly my plane I will upload some video to show...

Thanks again!

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RE: wheels - Where to mount??? - 2/9/2008 10:01:20 PM   
Villa



Posts: 873
Joined: 8/12/2003
From: Wilson, NC,
Status: offline 		Hi neuroza
Is your plane made from sign material such as COROPLAST like those shown further down this page under S.P.A.D. Aircraft - Coroplast design? That is what I build and fly. Are you familiar with the SPAD website http://spadworld.net/forum/ ? That is where many of the SPAD designers/builders discuus this topic. I usually have the center of the tires even with the leading edge of the wing, with tail raised to flying level position. About 1/2 inch back is probably good also.

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RE: wheels - Where to mount??? - 2/10/2008 5:48:36 AM   
BMatthews



Posts: 8951
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Mike's recomendation works great on a very smooth golf green like strip or on a paved strip. For lumpy grass fields I like to double the distance. On narrow winged designs this generally means the axle is at the leading edge. On wider wings like this one the axle would be more like at around the 10% chord point. Putting the axle much closer results in a higher percentage of nose over landing rolls.


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