I am "re-building" a 50cc ESM Corsair and initially removed about six pounds of lead from the cowl. Now it looks as I get closer to completing the rebuild that I will need to put some of that back but I hate to put any weight on a cowl. The orginal owner placed the elevator servos in the tail but their weight is nominal and I don't believe repositioning them forward would make that much difference, I did however reposition everything else forward as much as possible.
As to the weight in the cowl, I am planning on using lead sheeting that can be molded into the curvature of the cowl and strengthening the cowl mount with glass impregnated Hysol-20HP epoxy. I am also going to move the RX battery out onto the engine supports along with the IGN battery. I'm guessing that the cowl weight will be in the 3-4 pound range. Hate to do this but these planes cannot function when tail heavy. What are y'all's thoughts?

Happy Flying!

Bullseye52

If the cowl mounting is strong enough to carry the weight it should not be a problem. Another way to get weight forward is to build a strong structure out over the top of the engine. The structure can be plywood, or better yet steel. Get it as far forward as possible and bolt any additional weight to it.

There are pictures of this in some of the threads in the Warbird forum.

I'm likely on the anal side when it comes to adding weight. Maybe you've done it already, but I would spend some time figuring a way around the tail mounted servos. Possibly going with a single (center mounted?) pull-pull setup?

Just a few ounces back that far can cost you several times that amount in weight required to balance them up front.

Hi!
Yeah!
Remove those rear mounted servos and use thin steel wires for elevator and side rudder.
Adding weight is a No No!

Bullseye52
Two steel gear elevator servos = 4 oz. Nose weight to balance = 12 oz.

Do all the easy stuff first.

Bigger motor, bigger batteries in the cowl area, heavier prop & spinner and cheat the engine as far forward as possible.

I wonder if you could add a spacer between the engine and the firewall..?

If the distance from the CG to the tail is 2 or 3 times the distance you have from the CG to the prop, you can see how much help shifting weight forward is.

I don't think using those "Heavy Prop Hubs" is good for the engine long term, but in some cases they might make sense.

I thought about moving the tail mounted servos back forward but then you'd have the added weight of the pushrods, may not be that bad though. Oh well more work for me!

Happy Flying!
Bullseye52

That's why I was thinking about a single servo setup. The weight of whatever you do for control linkage back to the elevator off set by the loss of the weight of one of the servos. Unless you're planning on acrobatics that are going to stress the elevator, one sturdy servo should be plenty.

I'd go one piece elevator for sure. Then, even if you don't move the servos forward, you could eliminate one of them pretty easily.

I wouldnt add that much weight to a cowl. Too hard to make something that will hold together long term. I would use a cf pushrod for the elevator. There is at least 1/2 lb of nose weight gone. Then I would build a shelf on the firewall above the engine to get the weight as far forward as possible. Use your lead sheet here and stack/ form it to fit within the cowl but not be attached to it. I like to build boxes to contain my lead shot or powder, when i have the right amount i will put it in a paper cup, dump in some gorilla glue, add a splash of water and mix till all the lead shot is coated. Then i dump it back in the box and let it set up. You dont need a lot of glue and it will foam up and lock it all together. You can also dig it out vice using epoxy.

what ever you do make sure your firewall is secured and strong enough to take the added weight up front.

I secon or maybe that is third the recommendation on moving the tear empennage control servos forward, ahead of the CGpoint if you can. As for getting control back to those rear surfaces, don't use rods, use cables. Once you have done that, since you have moved all the other weighty items forward, you can then evaluate just how much weight you will need to add up front. The ideas others have mentioned that put the weight up in the nose without resorting to putting it on the cowl itself are good ideas. It will take some thinking and work to build those platforms to take the weight, but you will be better off in the long term; no cowl deterioration.

Lars

In my last two models, I've drilled and tapped into the sides of the carbon fiber engine mount, then attach fishing weights to the mount with 4-40 bolts. Also consider a Higley Heavy Hub http://www.harryhigley.com/EngineAccessories1.htm

I mounted a steel plate between engine stand-offs and eng. mount ears and bolted lead bars to them.By moving the mount point forward it reduced weight reguired by 6oz.. This was on a TF F4U ARF. If you mount weight in the cowl lip the vibration will break down the cowl at the mount holes or mount ring glue joint.I have tried this and that was the result.It takes a while but it will sooner or later.

Well for me I do not like to add weight at all. If it were my plane every servo in the fuselage would be right behind the firewall. Just because the servo tray is near the back of the wing doesnt mean it has to stay there. Move ignition box as far forward as you can, you can even mount the throttle servo right next to the engine and have the pushrod going backwards to the carb to help. Pull pull with kevlar cord is a good choice. Now if still need more weight look at a bigger engine or twin or some sort. This way you can spin a bigger prop at lower rpm for a more scale look.

You have to add weight as far forward as possible is key.. Friends of mine that flew in the Striking Back shows with Zeros ALWAYS had to add weight to make them balance. 4 pounds was the norm if you had the motor Byron suggested ! With that 4 pounds of lead in them they flew like a dream...

One of the ways my friends would move the weight out as far as possible is to put BIG all thread bolts thru the firewall, the Byron planes didn't have a traditional firewall usually but they did a variation on the same technique. They would run a couple 3/8 or bigger bolts thru the firewall, with a locktite nut in front and behind the firewall. They would make this bolt go up as far as they could.. Then they would balance the plane to see how much lead up on the end of the bolts it would take. Most would make lead bars and slide them on the bolts and use nuts to hold the weights in place. Often you can have the lead right behind the front of the cowl, or even partially in the front cowl lip.

I once built a Guillows rubber band ME 109 type model that was 18 inches in the kit, I enlarged the plans and built it to 80 inches. When it came time to balance it the entire plane weighed 9 pounds.. However I had to add THREE pounds of lead to balance it! 1/4 of the planes weight was lead ! Flies like a trainer.....

You have a lot of good ideas above. My first thought would be to move the engine forward as someone already suggested. DLE60CC twin would be sweet in that thing :-)

David