Electric3D

Getting back into CL after a very very long time. Just finished a great kit , Blackhawk Model, American Flyer and ran the engine through 3 tanks. I need to adjust CG. It is 18 inch span, 3 in chord, rectangular. The Curent CG , the way it built out is at 1 inch behind the LE . This is excatly where the Bell crank Screw is. I want a pretty forward CG to use it as a RE Trainer. The Drawing schematically shows the trainer CG like at the High Point on the wing at 0.3 to 0.4 inches fro LE .

I have attached some photos below. But it looks like it will take 2 ozs or more at the nose to move it half inch or so. Not much real estate at engine firewall to do that. Currently all up weight , reday to maiden before CG adjust weight is at 5.5 ozs.

Thanks in advance for all assistance and suggestions.

miltwood

May want to try a metal spinner. It would be so far forward that you may not need as much weight.

mikeainia

My Feedback: (1)

If you are using a Baby Bee, switch to a Golden Bee or Black Widow The extra tank volume moves the whole engine forward.

While typing this, your pictures came up - I see that you have one of the external tank type engines.

Well, it will still help if you can switch to an engine with an integral tank. Also, heavier wheels. I don't particularly like 'heavy hubs' or anything added to the crank shaft, but sometimes it is the best solution.

You can also bend the landing gear so those heavier wheels are farther forward - the way they are now, this will most likely cartwheel on landing anyway. Over grass, it will probably cartwheel regardless of where the wheels are.

BtnFlyGuy

If it was me, I'd try flying it first. Ya just might get lucky! Otherwise, weighted spinner/thrustwasher would be a good idea as suggested.

build light

I really woudn't try flying this till you get the CG forward. Models like this fly best with the CG truly at the leading edge and I have seen at least a couple show the CG in front of the LE.

Having a model plane with the CG even slightly too far rearward will result in gross control problems wheras even if it is far too forward, just mushes the control a great deal but you still have positive control you can trust.

Electric3D, your model looks well assembled and painted. A joy to look at.
However I can see two mitakes that in the future you might try to avoid. Both of which have played a part of your CG so far back from where it needs to be. I think you went too heavy with the paint as well.

You can help by sanding all portions behind the CG. A lot. Much sanding. Agressive sanding. Then repainting with just a light coat of paint.

The left front wheel needs some care as this will not track in your favor.
Another potential problem is the elevator hinge. It must move freely. By this I mean that the weight of the elevator alone would be enough to cause the elevator to droop all the way down when at rest. If not you will have little or no control in flight. Without the linkage hooked to it you should be able to blow gently on the elevator and have it move all the way up or down.

I am so glad you have chisen to share this wonderful project here and am glad also you have run the engine before taking it to the flying field!

Robert

downunder

It seems from the photos that the model is covered with an iron on film so any sanding/lightening holes in the rear would be a fairly major undertaking. What I would do is to extend the nose to shift the engine forwards by gluing a block of balsa maybe 1" thick to the firewall then a layer of around 1/8" ply on the front of that to bolt the engine to. The U/C definitely needs to be bent forwards as far as possible (which will help the balance anyway) because it's sitting far too high at the moment which would make even taking off quite tricky.

BtnFlyGuy

I can't help but admire the irony of this thread since my first successful U/C plane was the cox flying brick PT-19 and my first kit was the Baby Ringmaster painted with Krylon. Two finer examples of bumblebee aerodynamics (shouldn't fly but does) would be hard to come by, but we perservered, right?

Jim Thomerson

What build light says about forward CG on 1/2A's is the facts of the matter. If you fly the airplane with CG where it is, when you rebuild it, you can extend the nose forward. There is a Higley heavy hub for your engine will help solve the problem. I would extend the nose as Downunder suggests.

Electric3D

Thank you all very much. I have incorporated all your ideas. Now the plane hangs on a string level ( a bit heavy on right wing due to tip weight). The airplane is mono Kote not painted. Now I hope that the TD 051 with a 5x3 prop starts. I had bought it in mid 90's flew ita while and boxed it up.

The plane now weighs 6.4 ozs or gain weight of almost 1 oz. I think it should be OK . Did bend UC forward.

Now to start the engine and maiden it.

miltwood

One more point, take it from an old not very skillful CL stunt guy. Use modeling clay stuck to the front to add weight amd determine exactly what you need. Start with weight forward and take off weight to please. THis technique can save re-building pain.

Jim Thomerson

Way to start a TD is to get a good battery which will make the plug light up. Suck fuel to the venturi. Then put a prime in the exhaust with the piston up. Turn the prop backwards until it is vertical. Hook up the battery and hit the prop forward with your GLOVED finger. With a little practice, this works every time. Flipping a TD is an exercise in frustration.

Electric3D

Thanks for the tips. Jim a special thanks for TD engine tip. I remember the frustration. I had this in RC Dynaflite Piece of Cake Glider. Do you rember or know if I am to open the venturi 4 turns or 3 to begin with. I will run a full tank out in my garage before maiden next weekend. Cheers !

PS : If I use a shorter line , say 24 feet versus normal 30 feet or so, is it harder ? I know, shorter the line, faster I turn and hence possible vertigo.

build light

The Tee Dee is a high performance engine! It may not seem so on a plane as large as a Piece O' Cake Glider But you will certainly find out on a plane with 18" span C/L plane like this one!

Best to use a 6X2 prop if you do. Don't bother to try shorter lines till you start with the 30' lines first, then you decide whether you need to go shorter.

Have you made sure your elevator hinge is free yet? Neither line length, balance nor engine choice will matter if you cannot control the plane.

Robert

gcb

If you have any problems with fuel draw, you can turn the needle valve assembly and spring over so that the fuel inlet is on the same side as the fuel tank pickup line.

George

Electric3D

Robert, The elevator is very free to move. When I move my whole arm up ( not wrist) it very easily goes up. Same thing on elevator down when I move my whole arm down. When I move the elevator with my wrist, it is just too quick and instantaneous. This similar to what my Cox Plastic PT19 used to do. Same level of flexibilty.

I plan too fly in re training after so many years by just moving my arm up and down not wrist to avoid over control and I will have the lines at the handle closer together. that is how i did the experiment before maiden. George , thanks for the tip . Let me give it a shot as is and then make the change if needed.

I only have a choice betwen a 5x3 or 6x3 prop in my inventory at home. So i will go witha 6x3 prop. Again , thanks all of you.

BtnFlyGuy

You can turn the (6-3) prop around backwards to take some of the "bite" out of it...

gcb

You can also move the line spacing at the handle closer together so it is less sensitive.

George

skylark-flier

Total agreement - a metal spinner is definitely the way to go. If you have to add more after that, try drilling under the nose and adding a FEW ball-type fishing weights right behind the engine on the bottom side.

That's a good looking plane there - I like the color scheme. It'll show up for the student quite well.

Dave

gcb

In all honesty, I think you are severely beating a dead horse. That is, solving a problem that is not a problem.

I looked at the prototype on the Blackhawk Models site and noticed that the model was done similar to what you showed in your first pictures. The model has not been tapered and lightened, the wing has not been airfoiled, it is blunt. I think the finish is approximately the weight of yours.

Why don't you give them a call or email Larry and ask him where it balanced and how it flew?

They are offering this setup to complete beginners so I'm guessing they would appreciate the input.

George

build light

Actually the model of the Air Scout shown on the Black Hawk web site is a non flying 'model' created just for these pictures. It has no fuel tank, no bell crank, no push rod, no lead outs and since this one was not meant to fly, it was not important where the CG fell on this one.

Robert

Electric3D

Guys, I did correspond with Larry. Wonderful person to deal with. Great kit. He has HELPED ME A LOT. After I corresponded with him, he actually build a brand new proto type. His plane balnced as it should straight out of the box. He asked me to check my dimensions. It turns out that his spacer was 3/8 inch at nose block. That put his engine further out then mine. He almost bet that my spacer was 1/4 inch that put my engine back closer to nose. This morning when I saw his email I ran down and measured my spacer block. Sure enough it was 1/4 inch and not 3/8 inch . That was was the whole story. It was mistake that instead of putting a 3/8 spacer they by put in a 1/4 inch spacer.

talk about your customer realtionship. What a great manufacturer with such good service. I am very happy with Larry and his product. He tells me that the TD engine will be fine. Now to just get it started ( 10 years old) and run out 3 tanks. Hopefully no wind this weekend, so might maiden and am looking forawrd to it.

Again thanks to you all for all your suggestions and help.

Cheers !

Electric3D

Update : Great News . Plane flies like a charm. With a 3/8 ozs wedge tank tucked in in the right underside near the fuse, the plane flew great for what seem to be forever.The CG came out at 0.45 inches from LE just ahaed of the bellcrank screw. It pulls like crazy and I had to do nothing . It flies level from wing tip to wing tip and nose to rudder. Massive out pull. So the Right wing tip (mounted ahead of the the CG almost near the LE worked great. I flew it with 25 foot dacron line and the wind was clam, slight breeze every now and then to 7 mph. I had a 6 by 4 windsor black carbon prop. It goes fast. To train my flying buddy, we may just reverse the prop ? Maybe not, lets see.

Good trainer and I enjoyed my first flight.

Thank you all for your inputs and support.