I am building a stinger 1.20 size plane. I am going to be putting a U.S. 41 cc engine in it. I have read to move the firewall back because of the weight. I would like to know how far to move it back. I am thinking of putting the servos in the rear of the fuse, to help out the balance problem, and to shorten the control rods. I saw a plane last week that had titanium rods. I think I will go that route. I have also read about sheeting the tail surfaces. I plan on doing this, and also adding the flying wires there. The kit says to use 1/4" brass tubing, cut out with a knife, to cut the 3/8 square balsa, for the dowel rods. I have tried my home-made cutter, and it still crushes the wood on a test piece. I'm not sure to go with the 80" wingspan, or the 72" yet. I am going to cut out the foam in the wings, between the cap strips either way. I am going to carbon fiber the top, and bottom of the wing, along the spars. I am also going to add 1/4" ply to the bottom of the landing gear to beef it up. I also have a problem with the engine mount. The muffler is about 1/2" farther back than the engine. Will the GP isolation mount correct this? I don't have a engine mount included when I bought the engine. I do see one listed at Tower, but i'm not sure if I need it or not. I have a 16 oz fuel tank for it. I'm looking to get at least 10 min flying time. Is that size tank big enough?. I will be not be using a pcm receiver on this plane. I have read that there could be electrical interference with the ignition system. I will use non-conducting push-rods for the throttle, and will get the Bosch plug cover. Is that all I have to be worried about? I have also heard about glassing the plastic parts. I have never done this before. Just wondering if it's worth it or not. Sorry about the long post. This will be my first "Big" plane, and I want to get it right the first time. You can email me directly, or post here. Any answers are greatly appreciated.

I've never built one. But I have flown a few big Stingers.

Here's what I'd do:

Build your wing 80" and cut out the foam as you plan. Use the carbon fiber as you had planned.

Try to build the plane with balance in mind. I built my Midwest 80" Extra 300S with a huge engine. I built the entire plane with the engine- radio- servos-linkages and landing gear. But I left it uncovered. That way I could check the balance before covering it. Build it and make all your linkages. Install all your radio gear and drill out for your hinges. Tape the control surfaces on with masking tape. Cut and tape your plastic parts on. Assemble the entire plane with no covering.

Then check your balance.

You can then decide how much to cut the firewall. You may not need to cut it back if your servos are in the tail.

As for your dowel rods: Just tape the wing on and drill out the wing with a drill bit. Epoxy your dowels in and then realign everything. Get it all straight and then tape it in again. Drill out for your rear bolts and your done. If you screw up with the rear bolts-- just fill with microballoons and 15min. epoxy and try again. No big deal.

I don't know about your engine mount.

I'd use about a 20oz tank for the gas engine. It might be a bit much- but it beats deadsticking on an empty tank.

As for the plastic parts. I don't think I'd want to add the weight of the glass. You have a front and rear former for the turtledeck and you also have a front and rear former for the hatch cover. Glue the formers in and sheet with 1/32" plywood or 1/16" balsa. Throw the plastic turtledeck and hatch cover in the trashcan. Your cockpit will still be plastic- but that area seems to hold up well on most Stingers I've seen. The hatch cover and turtledeck start getting a bit ragged and ugly rather quickly on the Stinger. If you decide to use the plastic-- avoid the temptation to attatch the turtledeck with screws. Just glue the sucker on with CA and forget about it. One of my friends used 4-40 screws with small blindnuts to attatch his turtledeck. The screws vibrated out and made a mess of the turtledeck. The vibrating screws just eat the plastic up like a grinding wheel.

With that big motor up front- there probably won't be a lot left of your cowl by the time you get it hacked up to fit around the engine. Leave it off and tell everyone your flying a Stinger/Stick. The cowl will be so flimsy and weak when your done that it will just come apart and serve to frustrate you.

Just my $.02

Ram:
With the US 41, at 4½ pounds, you are giving two pounds away to the four stroke 150 engines, with about the same power. It is 6 inches long, and the Great Planes Large Engine Isolation Mount will add 0.460 to the length.

On the top view of the fuselage measure 6.46” from the back of the propeller as shown. Noting any offset in the thrust line, and mark the plan. Use a pencil in case you need to change it. On the side view do the same, again, noting any downthrust.

Before you do any cutting, get the GP mount and check compatibility, not only with the engine, but the fuselage mounting as well. You may have to do some fancy dance steps to get everything to mate. You might even decide not to use the isolation mount. I have one I got for an UltraStick 120, the plane is flying, the mount is in my unused stock.

Also consider the fuel tank mounting. If you want it close to the engine you’ll need to leave room. The stinger series has a rather squat fuselage, but you might be able to mount the tank on the CG, either above or below the main spar. The fuel draw wont be a problem with the Walbro carb’s built-in pump.

Anyway, if you can, if you have room for everything, go one inch more than you marked on the plan, and make your firewall mounting at that position. Should it turn out to be too far back in the final stages, it’s much easier to space the engine out than it would be to move the firewall further back.
As I said, up to 0.460” distance, the engine can be mounted with the muffler overhanging. And the US 41 does not need a separate engine mount, whether you use the isolation mount or not.

That’s enough to get you started, bring your other questions back as you go.

Bill.

I have built several for myself and others used quadra 42 ,homelite 25cc, g62(72"), currently flying one zdz40 wtih a 76"wing to fit my shortbox chev truck.

all were hard mounted with no problems

move firewall back 2" but leave sides full length. You then can use a spacer to move the engine forward if needed to adjust cg and get muffler clearance

add a doubler from rear of firewall to rear of wing saddle. This means narrowing f2 to fit.The fuse failures I have seen have all been at f2 where the fuse is notched out .

16 oz tank will get you 10 min safe but I would go with a 20oz

glassing the abs. I did the cowl and wing cover with .6oz cloth and thin CA the rest I just glued on.

go with the 80"wing with the gasser you can set your hinges and cap strips so you can trim it later if you like

any questions email me

Randy