ckreef

Maxford USA 40" wingspan electric Gee Bee "Y" to glow conversion.

I started this project a few nights ago. I bought a new electric ARF from the swap meet in Perry GA at the begining of the month. First I have to put the basic ARF together. Here is what I have as of tonight. The only thing I am disapointed about so far is the way the tail wheel assembly attaches. I figure I will have to replace that within the first few flights but we'll see. Reinforceing the fire wall will be a little tricky. Other then that should be a fairly straight forward conversion. Ihave 3 different motors I am considering but I want to get it all together (complete minus motor) and then weigh things and check CG before I decide. Hopefully will have this complete within the next few weeks.

Twin_Flyer

My Feedback: (4)

Looks nice!

What engines are you looking at?

Bill S.

ckreef

The plane is originally spec'ed for an electric motor turning a 10" prop putting out about .37 hp. With suck a large cowl I want to swing atleast a 9" prop and would like .50 hp or a little more.

OS .15cv-A can swing a 9x4 and produces about .49 hp - lightest motor of the 3

TT GP .28 can swing a 10x5 and produces about .7 hp. It has both vertical and horizontal motor mount holes so could be bolted directly to the firewall saving a little weight with no motor mount.

OS .25 LA can swing up to a 10x4 and produces about .6 hp

Those are the 3 main contenders. Originally I thought about using a pitts style muffler but now I am considering a tuned pipe with a deep header which helps spread that weight up under the CG.

Going to the LHS today (well 1 1/2 hour drive local) to pick up all the extras I need to complete this. Rx, battery, and a bunch of little items (everything except motor). Once I get everything installed will hang some weight off the firewall to see if CG can be easily obtained using which motor. At that point I can also get a rough idea of total weight and wing loading.

If anybody has some alternative motor suggestions please let me know.

phatboy

Awesome project. Take lots of pics!

ckreef

Did some measurements with a scale tonight.

The original electric plane was spec'ed for AUW 32 oz with a wing loading of 15.1 oz. sq. ft.

I weighed all my parts except the motor and muffler at 32 oz. So I can have a motor and muffler weight not to exceed 12 oz. which would give me a AUW of 44 oz. and a wing loading 20.7 oz. sq. ft. A little heavy but not tragic. All three motors I am considering fit this criteria. A member of the Emerald City Flyers Club (my local club) has a OS .25 motor he will sell for cheap. It has never been flown only broken in. He's not sure of the "flavor" but will bring it to the field tomorrow. I will bring my scale and a prop and prop hub/nut and weigh it. If it comes in at 12 oz. or under I will go for it.

Will bring my cowl to make sure it fits that also.

Twin_Flyer

My Feedback: (4)

I am going to guess but the .25 LA, as a bushing engine, will probably be the lightest in that size range. IMO, the .15 wouldn't really satisfy (power wise) in the air.

Use a small tank and maybe a lipo pack to help keep weight to a minimum and it should be a blast to fly!

I want to know if anyone has converted any of the currently available e-flight or similer biplanes to glow...

Bill S>

ckreef

Bought a very slightly used OS .25 LA engine. it should just barely squeeze into the Cowl. I still haven't decided on what style of muffler would be best.

I had 12 oz set aside (so to speak) for the engine/muffler/prop/prop nut combination. This setup comes in at 9oz total for a 3oz saving.

To move on with the build. I changed out the aileron servo linkage for something a bit smaller and lighter. The plane just doesn't need the super heavy duty setup that was supplied with the ARF.

In the pic below my nylon setup is installed and the all metal seup is shown above that.

mike early

I love this plane as a glow conversion. Great idea.

Are you going to have to add lead to the nose?

ckreef

I haven't gotten that far in the conversion yet. I have all the parts needed to complete it and will hopefully have an answer for you within the next couple of weeks. It has a really long nose so I suspect I would have to add weight to the tail if anything. I plan on installing the Rx battery (6v 1100 mah long battery) just behind the wing in the fuselage so I hope I can get the CG fairly close without having to add any weight. I have also considered removing about 1/2" - 1" of the nose length just behind the cowl if I need to for correct CG.

ckreef

There is also a fiberglass cowl ring that is glued onto the front of the nose to hold the cowl in place. I am going to try and remove that so I can install a reinforced firewall underneath that. You almost have to see it to understand what needs to be done. If I can't get that piece off I will go to plan "B".

pencon

If a 25 fits so will a thunder tiger 36 . Make it into a rocket . You can always throttle back is my theory

ckreef

I basically agree with the "Make it a rocket" approach but ........

The .25 LA is already a 1/4 hp more then what the plane is spec'ed for (for a 2 lb plane) and the TT Pro .36 is an extra 2 oz. Doesn't seem like a lot of extra weight but every ounce counts especially when trying to obtain a correct CG without adding dead weight. 2 oz more on the very front end will add more weight to the back end so the .36 becomes more like 4 or 5 oz heavier to make CG.

On top of that I got a brand new .25 LA with prop and nice prop hub for $40

ckreef

To properly install a new plywood firewall I had to cut off the fiberglass cowl ring hopefully keeping it intact as it's a needed part.

Here is the cowl ring installed in the ARF kit.

ckreef

I very carefully cut and pried the cowl ring off the fuselage nose,

ckreef

This will allow me to install a plywood firewall the full size of the fuselage. The ARF kit came with a repair bag that contained some extra black and yellow covering which will allow me to cover over the new fatter firewall joint. Both the original fuselage nose and the cowl ring will need a little cleaning up and I will also need to make a new cowl ring support piece out of balsa.

ckreef

This is the original battery compart on the underside of the plane (minus the hatch.)

ckreef

I cut out most of the battery tray. I installed 2 plywood strips to help support the fuel tank. I also installed 2 hardwood stringers seen on each side of the fuel tank. Tank is a Sulivan 4oz flex tank.

ckreef

Installed a fuel dot which was not an easy task. Here is what I did:

Cut a small piece of plywood which fit from the firewall to the 1st bulkhead and snug between 2 stringers.
Drilled a hole in it to fit the fuel dot.
Beveled the bottom to help match the curve of the fuselage.
Glued it in place using thick CA.
Carefully cut a hole from the outside of the fuselage to match the hole in the plywood piece.
Installed fuel dot.

ckreef

The bottom side of the cowl ring after being cleaned up a bit. Note the 5 hardwood blocks glued in place so the cowl screws have something to hold onto.

ckreef

The new balsawood cowl ring support piece glued in place. This gives the cowl ring an attachment area when glueing it down to the firewall.

ckreef

The Gee Bee "Y" is a round fuselage made up of round bulkheads and stringers. Within that is a square inner structure made up of plywood. This presents 2 issues when doing the conversion.

1) The square inner structure is fairly small makeing it a tight fit for all the standard electronics that need to be installed.

2) If you want to mount anything flush to the outside of the fuselage (fuel filler/dot, charge jack/switch, ect....... ) you have to mount it between bulkheads within 2 stringers and you have to go in from the inside working around the square inner structure.

To illustrate what a pain point #2 is, here is the Charge Jack/switch install.

This picture is looking in from the bottom where the wing attaches at the small area of the fuselage skin where the charge jack/switch will be installed.

ckreef

This is the charge jack/switch back plate and the thin plywood reinforcement I cut. It fits snugly within the area pictured above and was glued in place using thin CA.

ckreef

I then carefully cutout (from the outside) the rectangular hole for the charge jack/switch and the 2 screw holes.

This is the charge jack/switch installed as seen from the inside.

ckreef

Here is the charge jack/switch installed as seen from the outside. The charge jack/switch is installed just above the left wing, just forward of the trailing edge.

Of course wing is not installed in the pic

ckreef

For flush mounting items on the fuselage I failed to properly show 2 important steps. So I thought I would illustrate these while installing the fuel tank pressure/overflow "valve". This is the 2 missing steps in the above charge jack/switch install as posted above.

Once you have the plywood reinforcement (w/ mounting holes cutout) glued in place, take a "T" pin and from the inside, poke a hole through the outter fuselage along the edge of the cutout. Repeat this process untill you have the mounting hole outlined with pin holes. Put a pinhole in the middle of the screw holes if needed. These pin holes should be about 1/8" apart.

Pictured below is the the fuel tank pressure/overflow "valve" mounting plate with a "T" pin making the 1st pin hole.