Hi Guys,

Ive just finished my World Models P-40 and i have a SC 80FS upfront, with the batt pack etc as far back in the fuse as it can go, but its still very nose heavy......... ive weighed it and it needs 90 Grams of Lead on the back tail wheel to balance it at the recommended CG Point....................

Is this alot ????? just looks like...........

[]

Ok ive took some pictures to help anyone understand ........... the batt it at the rear with the black tape round and the second pic shows how much lead is needed in that postition to balance the model ...................

I gather i could just bolt it on and paint it............... but does anyone one else have other suggestions ???????????????

your are right . That is a lots of weight to put in the tail. Something does not add up. What method do you use to check the balance. The best way I know to check the balance is to put the plane in level position, that is tail up straight, level flying position, then lift it with tip of your fingers or some other method straight up on CG as close to fuse as possible, when you do this the nose should drop a bit. Great planes CG machine and jigs like that are notorious for balancing planes.

Thx for the reply i am using the Great Planes CG Balancing machine []

Do you have Retracts fitted to your plane? if so are they retracted or lowered when you are balancing your plane?

I guess we found the problem.

Wierd thou ive allways relied on that, guess ive just been lucky not loosing any planes as of yet.........................

I will try with my fingers tommorow on the CG Point.........

Yes i have retracts fitted and they are retracted into the wing when im balancing it ???

I assume thats correct ??

What's notorious about them? I've used one for going on 10 years now. Never a problem. Just curious.

Don

I had a World Models Midget Mustang with an OS .91 4 stroker on it. I seem to remember having to put about 4 oz in the back to balance. 90 grams is a little under that. I just cut the balsa off the back and glued the weight inside and then closed up the bottom and re-covered. I use past tense as I lost the plane when a clevis broke...flew very well. so well in fact I have another one.

The plane was designed for a .60 2 stroke and the .91 was a bit heavier. What size engine does the P-40 call for? 3 oz in the back isn't all that much. Better than 12 ounces in the nose. There's no way to move that battery back further into the tail tunnel with a servo wire extension?

Don

Hi,

The P-40 calls for a 70FS but ive gone for a bit larger with an 80FS soo thats why i may be having these problems.........

I will try to balance with my fingers tommorow like someone suggested......... but if its still alot out i will try to move the batt pack one step back and then cut some balsa away in the tail then glue wieght in............

Will it stay secure if i add weight that way ? will i need to reinforce the block im gluing the weight 2 ? i guess expoxy should hold it in place ok....

Thx for ur help just never had a tail heavy problem like this, as its allways been nose heavy....

I'm sure you guys know this, but in case, heres what i do with my low wing warbirds, balance inverted landing gear retracted.

Heavier CGed models will land, in turn, light non GCed models will be troulble.

Steve

Yeah i was balancing it inverted and with wheels up in the wing...... but still getting very nose heavy reading

There is nothing wrong with Great Planes CG machine. In fact, it is very accurate. I used it to balance my TF P-40, and that plane flies like a dream.

Yes, always balance a P-40 upside down with the wheels retracted.

Yeah, epoxy works great. Just epoxy the weight to the stabilizer...you have all the big flat area in there doing nothing.

Don

Everybody has their favorite way to balance a planes, I have tried all kind of contraptions including ropes and pulleys, etc. but the method I described here makes sense to me and works because it simulates the actual flying position of the airplane. The CG machine makes you to balance the plane upside down which normally do not fly that way. I modified my Great planes CG machine by putting two add-on pencil eraser , the type with flat edge, at the end of the rods, then position the erasers at the CG points and lift the CG machine with a home made cam. This set up is more accurate and helps the guys who object using fingers.

The CG machine makes you balance the plane in its most unstable configuration, ie, worst case scenario. So if the plane flies right side up, it is guaranteed to be more stable. Plus, if one decides to fly inverted, then one would rest assured that the plane will have no problem doing so. All low wing planes should be balanced inverted. Nuff said.

Richard a plane when is upside down has a totally different flight envelope and characteristics . the weight distribution and momentum are totally on the different plane of reference. You arguments is to optimizing the CG for the worst case scenario and once the plane is right side up CG move to most stable position. I would agree with you if there was such a direct relationship. I know this is not the case with large heavy aircraft such as a commercial jet liners, if they go over , not even totally upside down ,they could never recover. I know you are speaking from years of experience, but why not set and optimize the CG for the normal flying condition. after all we aways trim our plane for straight and level flight and the same should be true for setting the CG. Best regards

Well, I suppose you could balance a low wing plane on the CG machine right side up also. However, the CG of the fuse is above the pivot point, so one little delta would pull the nose or the tail down. This is similar to an inverted pendulum or trying to balance a stick vertically on your finger.

Ok Thx guys for all ur help and advice................

Ive pushed everything back as far as i can to save less weight and then used the GP CG Gauge and now all i require is 40 Grams which is no problem to put on the tail wheel............
Thx for everyones help.............

Well shes allready to go soo hopefully weather permitting she will be in the air on Sunday......

Ditto.... Every plane that I have balanced on the GP CG gizmo has been on the money or close to it. While I have had problems and have crashed planes, none were the result of the CG machine by GP screwing up. When I have a plane that is doing something that I don't immediately understand, I re-create the problem in the sim. to better understand what the problem might be.

One problem that I encountered with balancing my P51, I measured CG point from the wider part of the wing surface rather than close to the fuse. This made the CG more than 2" off and the plane tail heavy by more than 7 ounces. CG gizmo did its' job. I did not do mine in my hurry to get the plane in the air and it wasn't in the air long balanced like that. Plane crashed, I figured out what the problem was, fixed it, plane flew/flies fine since. Lesson learned.

Richard L. should know, just watch some of his videos of his planes flying and landing. Nobody does it any better than he.

Thanks Flieger Abwehr.