world Models Sky Raider mach-1 with TTPro .36.
I put everything together and checked the CG with tank empty, looks like I need to add about 3.5 oz (I placed 40 pennys above the firewall. whats a penny weigh? 2.5 grams?)

Anyway, I'll try to move the battery forward but I think I will still need weight added.
Where and how should I add this weight?

I'm thinking on the front of the firewall next to the front wheel shaft or inside the firewall under the fuel tank?


Thanks

Stev

The further out on the fuse you add the weight, the less weight needs to be added. 3.5 oz is not a lot, I would probably add it up front under the fuel tank.

My brother wrapped his receiver battery pack in foam, then wrapped that in clear packing tape; and attached it to the engine mount (in front of the firewall) to avoid adding any weight to a Sky Raider Mach II. He drilled a hole in the firewall to run the battery wire to the switch.

If you do not want to do that:
You can drill and tap the bottom of the engine mount for a 4-40 screw (do it as far forward as possible). Drill a hole through your weights and screw them to the mount. As mscic wrote, the further forward you can move the weight the less weight you will need.

As was said before, try to use what you have in the plane already first. Move around things like the battery and receiver to try and shift the CG of the plane. But when you do have to add weight there is no right or wrong way of doing it. I have used many different things to add weight to planes. Du-bro lead weights, coins, nuts and bolts, modelling clay with buckshot pressed in to it, or just about anything else that will fit into the area you need to add weight to. An important things to remember when you add weight to a plane is to make sure that what you add is secure and can't fall off or shift while the plane is in flight. One way that really works well is using Du-bro stick-on weights and secure them in place with epoxy, or by drilling through them and bolting them in place.

Hope this helps

Ken

Dubro sells spinner weights and heavier spinner/nuts...

Since these represent a longer lever moment, you can typically get away with adding LESS weight this way, to affect the C.G. location by the same amount as more weight behind the firewall.

I hate adding weight to a flying model airplane. You can cut a ring out of 3/8" plywood and use it as a spacer under your engine mount. Moving the engine further forward will increase move the CG forward. Just coat the wood in CA or epoxy to fuel proof it. That is, of course, if your engine mount won't allow for you to slide the engine forward without drilling too many holes in the material.

You can buy brass spinner nuts that help with a tail heavy plane. A friend of mine just finished building a Sig Something Extra and it was tail heavy when he was done. He tried a brass nut, but it still was not enough. He ended up turning a new spinner nut out of brass that was a little bigger than the one he bought and it worked great. Balanced the plane perfectly, and since out in front of the prop is the longest lever arm you are going to get out in the front of the plane, it was less weight than if he was to put it somewhere else.

Probably by placing some washers ( over the bolts ) between the firewall and engine mount will just about make it right. You get a little weight and it pushes the engine forward a bit. ENJOY !!! RED

Actually I've done this and was not happy with the results. The washers can get unevenly sucked into the firewall and change the thrust angles. A half-degree makes a difference, and I was not happy with the way the plane flew.

They supply a foam block that holds the battery and receiver behind the fuel tank.
The back of the tank is supported by the 1st bulkhead behind the firewall. This bulkhead prevents me from sliding the battery under the tank. this would put the battery forward up to the firewall. about 3" - 3.5" forward. Not enough but it helps.

What I'm thinking of doing is cutting a hatch into the bottom of the plane just behind the firewall. the battery, wrapped in foam, below the should fit just right.
OR I could cut away the bottom part of the 1st bulkhead (which is supporting the gas tank) inside the plane and that would allow me to slide the battery forward under the tank. I would have to add a shelf to support the tank if I did it this way.

So what would be less stressful to the airframe? or does it even matter?
1. Cut a hatch under the fusalage?
2. cut out the bottom of the 1st bulkhead.

I'm glad 3.5oz isnt alot of weight to add... I've never had to add before..
would the weight difference of a .36 to the recomended .40 account for it?

I like the idea of mounting the weight to the engine mount..The engine is all the way forward so theres room..

I bought allen screws today to replace the stock philips...

The bolt holes at the trailing edge of the wing do not line up with the blind nuts in the plane. I enlarged one wing hole and got the screw to catch. The holes are VERY close to the edge of the wing. metal screws VS the nylon screws I was expecting.. I cant tell if these holes are reinforce in any way. It doesnt look very strong???

Thanks

Steve


thanks

steve

Steve,
Can you remove the fuel tank and then place the battery under where the tank will go, and the replace the tank?? I have done this in several planes were I needed to have the battery up front under the tank. Pull the tank out and slide the battery in place, and then replace the tank.

Personally I prefer to not use heavy hubs for adjusting the CG, because if the engine ever throws the hub and the prop you are left with trying to deadstick a tail heavy plane.

Ken

Don't cut anything ... Yank the fuel tank out, put the stuff as far forward as possible, and then put the tank back in.

OK, I was thinking I needed access to the battery? (easy access)
Instructions do call for a block of bulsa to lock the tank in.
Easy enough to remove if I need to get at the battery.

steve

You don't need access to the battery.