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!

what is the general configuration? nosegear? tailwheel? hi-wing or low wing? trainer use or sport use?

if it is a taildragger...

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.

This is my plane:

Put your wheels so that the front of them is aligned with with leading edge of the wing, and you will be pretty close.

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.

There is a good picture taken from an excellent book by Andy Lennon, "R/C MODEL AIRCRAFT DESIGN".

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.

Thanks, everybody...
This help me a lot!

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

Thanks again!

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.

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.