Bought a model called the tiger sport 40L (thunder tiger) about a week ago. After building it checked the CG and the model was WAY tail heavy. When I mean way I mean that the tail rests on the ground and the nose wheel up in the air when it is sitting on the floor. I built the model according to the instruction manual so i dont know what it could be. I have an OS 40la installed.
To reach the proper cg I reckon that i would have to put at least 8 or so lbs of nose weight to the front of the model. Is this normal?This is my seccond plane and I have not had this problem before.
Both the receiver and the battery are as close as they could be to the fuel tank.
Any suggestions woul be great
Thanks for your help

I do not have any specific knowledge of this plane, however something does not sound right. The plane needs to be perfect on balance or nose heavy a smidge in order to fly. The OS 40 La is a light engine so nose weight is in order, although I would think only a few ounces of lead would be needed. Is it possible that you are checking for the balance using the wrong measurments for the balance point on the wing. Typcally using the spar as a starting point is good. Good Luck, Dave

Balance the aircraft upside-down. The CG is 3 inches behind the wing LE.

Are you sure you didn't build it as a tail dragger? [X(]

You must be off in your estimation of the amount of weight required to balance the model. The Thunder Tiger Sport only weighs about 5 1/2 pounds complete. There is no way that his model could require 8 pounds to balance properly. Even one pound would be grossly extreme.

That said, be sure that you have all of the radio components moved as far forward as possible before attempting to add weight to the nose. If the Sport has the same clamping motor mount system that the Tiger Trainer has, you can move the motor forward to the stops. Be sure that you are locating the C/G properly.

This model should be very close to the balance point without the addition of any weight if assembled properly and if all components are located forward. Good luck with the model.

Thanks guys for your help. I must be measuring wrong. Here in Australia we dont use lbs so maybe i made a mistake. I will try to move the engine more foward and recheck the cg upside down

You guys are life savers keep up the good work.

Dude ... like they say, balance the plane inverted. Also I know about this plane, it is a little tail heavy only, that is with a 46 sized engine in it. But it is not WAAAAAAY tail heavy. Not at all. Maybe you are down under so it to NOSE heavy!!!

I had one of these a few years back......I had a Thunder Tiger Pro .46 on mine, and it still required about 2 oz. of nose weight......move your battery under the fuel tank, move your engine forward, and put your rx behind the tank.....the LA is a light engine, so you might still need a couple of oz. to balance. It's a very nice flying sport plane.

A good link with all types of measurement conversions: [link=http://www.sciencemadesimple.com/conversions.html]Conversions[/link]

So, the cg is 76.2mm behind the wing LE (measured at the fuse, not at the wing tips).

But still, I find it terribly odd that your plane, a trike, sits on it's tail. Something is really, really wrong there. Please post when you find the problem. I'd like to hear about it.

It is possible that a plane be perfectly balanced, but rest on its tail when right side up. Case in point, the Goldberg Tiger 2. It will drag its tail with the gear installed per the instructions. The solution is to bend the main gear back about 1/2 to 1 inch, then re-check it.

Nebbie is right; whether the model sits on it's tail or not isn't directly related to it's balance about the CG. I don't know this particular plane, but many times landing gear are bent such that they angle away from the wing in the fore-aft plane. If this is the case, it could be that your gear is installed backwards, and should be reversed so that the wheels sit farther to the rear. Otherwise, it could be as Nebbie says and the gear may need adjusting. In either case, for a trike gear plane the main wheels must be behind the CG.

How dumb am I?
After posting my original post I weighed the lead needed to put at the nose again and realised that i miss read the scale. I only have to add about 175 grams or .7 lb. NOT 6 or 7 lbs in my original post. [X(]
I feel stupid im only 17 and lack the fundermentals of conversion.

Placing the battery under the tank is a great idea. And I will try it.
The tail does not sit on the ground after adding the nose weight so I dont think there is something wrong with the gear, however, I will check.

I am also having problems with the cowl. It does not fit right on the fuse (too small) but that is not as important as the cg so that can wait.

I will take the model to an experienced modeler at my club if all else fails.
It is a great looking plane and I can not wait to fly it.
I know where to come if I need anymore help.

Thanks for all your replies I will take or your opinions onboard.

You guys are legends your help is greatly appriciated.

I hate to say this but 0.7 lbs is a lot for that plane ... are you sure its all correct? Guess it must be the 40LA, yeah ... its about 5 oz lighter than the OS46FX.

It looks to me like it's getting better and better each time...[sm=thumbup.gif]

.7 pounds would be about 11 oz. (don't know if those are apothecary, avoirdupois (don't know him but I may have dated his sister once) or troy ounces [sm=confused.gif] )

However, according to that conversion thingy that Mutch included in a previous post (nice job), it looks like 175 grams comes closer to 5 or 6 oz. (depending on if you're using apothecary, avoirdupois or troy ounces [sm=spinnyeyes.gif] )


Justy, you are wise in wanting to get the thing to balance correctly.

Took the model to my old instructor yesterday and he added 5 o.z to the nose. He said that it is the engine which is causing the lightness in the nose. I am taking the model for its first flight on the weekend.
Extremely excited
Wish me luck

This is a nice plane and you should enjoy it. It does have a lot of adverse pitch roll coupling with rudder. Full right rudder in level flight will make the plane roll left and pitch down.

Good luck.