Your chance to recommend a technique for mounting the fuel tank, servo tray and Rx / battery.

The plane is a low wing pattern Chaos with a tank hatch on the bottom between the firewall (F1)and F2. The suggested servo location is towards the rear of the wing box just in front of F3 with throttle, elevator &rudder servos mounted side-by-side. This will require a single opening to serve all 3 servos. The suggested location of the battery is just behind F2. The Rx is a Spektrum AR something or other with a remote device. Battery will likely be a 6.0v NiMH.

Do you CA balsa rails and fab a lite ply tray attached with sheet metal (servo)screws?
Do you separate the throttle from the elev/rudd servos?
How about the fuel tank (12 oz Sullivan)?

TIAfor your opinions!

Use the locations called out on the plans.

DON"T USE BALSA FOR YOUR SERVO RAILS! Make them out of 1/4 or 3/8 spuce. Make up 4, 1" square pieces of light ply with a square hole in the middle that fits the servo rail snugly. Slide two light ply pieces over each servo rail before gluing everything to the fuse sides. This "captures" the servo rails and gives more gluing surface so the rails won't pop out from the fuselage sides as easy. I only use a servo tray for large models. You can mount the servos directly to the rails or put them in the tray that comes with the radio.

I don't know what you mean about separating the throttle servo from the others. Line all three of them alongside one another on 1 common set of servo rails.

I usually glue a 1/4" spruce rail in the fuselage to support the fuel tank at the rear. I use Sullivan RST tanks and always drill a large hole in the firewall to put the front of the tank in. Jam foam rubber on top of and along each side of the tank to prevent movement. Run a bead of silicon around the hole after the tank is installed to keep oil out.

Ok - here's some pics ...

pic 1 - tank bay - 2 1/2" wide. A Sullivan 12 oz tank barely fits in the width
pic 2/3 - the wing bag - no pass thru of F2
pic 4 - measurin' stick
pic 5 - standard servos 3 abreast - not much room for servo arms, control rods or adjustment
pic 6 - throttle servo positioned ahead of the elevator / rudder servos
pic 7 - balsa-n-ply open face sandwich

Carl - I think you say to install rails laterally. I was thinking of using 1/4" balsa stock w/ 1/8" ply glued to the top of the balsa making 3/8 x 1/4 rails. I like the 1"x1"lite ply end plate idea. I just don't think that there's sufficient room to mount 3 servos side-by-side. I've got pretty fat fingers ...

Just may have to rethink use of slant nose Sullivan tank. That's what's pictured in the plans.

Did a search on the Sullivan RST 12 oz. tank. 2 1/8" wide leaving 3/8" for foam, 2 1/2" high not an issue, 5" long plenty of room. Will have to be set back from the firewall because the back plate of the engine is only 15 mm from the firewall. Doesn't provide much routing room for fuel line.

Take a thick white tube sock, (Yea, the kind you wear on your feet) slide the fuel tank inside the sock. Zip tye the sock around the fuel tank stopper. Trim the excess sock off. The sock will pad the sides of the fuel tank.

Add Dubro foam to the upper and lower sections of the fuel tank compartment so you can adjust the height if need be.


Servos, Use the locations called out on the plans.

A Dubro S-16 drops right in.

BW - you filling the entire tank compartment with foam? Or is there something firm between the bottom of the tank and the tank hatch?

Also, just looked at the plans more closely at the servo location. The fuse's rear wing mount blocks (1/4" ply) are attached on the sides flush with the wing saddle. These blocks totally cover 1 mounting bolt of the outside servos and leave 1 1/2" access between them to get to the servo arms / clevis. Iknow that your are on your 3rd one of these - just don't see how to get my fat little fingers in there.

Carl - why not make 1 mounting plate for each side with 2 holes cut out that will space the rails "prefectly" every time?

See page 23 and 32 of this document for servo rails and servo installation
http://manuals.hobbico.com/gpm/gpma0220-manual.pdf

I used Carl's suggestion and built lite ply end mounting plates. The servo rails are made out of 1/4" balsa sheet laminated with 1/8" air ply on top. Aband saw was used to cut the individual rails.

pic 1 - 1/8" lite ply with 1/4 x 3/8 rail holes
pic 2 - 1/4" balsa / 1/8" ply laminate
pic 3 - componets
pic 4 - just gotta remember to put the ply on top
pic 5 - with standard servo