OS 91 FX in Shoestring Racer
 

Hi All,

I am considering a Great Planes 1/4 scale Shoestring ARF racer for a "speedy" plane. I was wondering if anyone has or has tried an O.S. 91 FX 2-stroke in this plane. If someone has what kind of servos were used and were any modifications needed? The instructions say any .60 2-stroke or up to a .90 four stroke for power.

I'm just not sure if this plane could handle the 91 FX. Thanks much.



Jeff

OS 91 FX in Shoestring Racer
 

Hi Jeff,


I have the Shoe with a 91 FX in the nose. It balance perfect with the battery in the rear fuse. The plane is ballistic. However you need to do some reinforcement. I fiberglassed the center wing
and added some epoxy at the back of the firewall. You also need to install flying wire on the rear stab if you want to push it.
I used 1/8 aluminum tube and it works great!

The plane is a total blast to fly but need attention.

Oh also, Don't forget to reinforce the landing gear plate.

Serge

OS 91 FX in Shoestring Racer
 

Hey thanks Serge!


I have had my eye on this plane for a couple of years now. Last weekend when I took my Aeromaster up for it's maiden flight, another member was flying a Shoestring. He had an O.S. 70 fourstroke in his and he let me fly it. It moved out pretty good, but, I would want mine faster. It was a pleasure to fly too. I had no trouble doing knife edge, snap rolls, hammerheads and inverted flight. It did have to land a little fast, but nothing that really concerned me. Taking off was very straight forward also.

I am also curious as to what kind of servos you use for aileron, rudder and elevator and what kind of torque they require. I fly with a combination of Hitec and JR with all of my other planes. And if I do go ahead with this plane, I will definitely take your advice on the reinforcement tips. Thanks again Serge.


Jeff

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.... (post # 1)

Jeff,


I use Hobbico CS-70 Super-Torque Metal-Geared Ball Bearing Servo . They deliver a huge 106 Oz of torque and cost only $39.95. I almost bought a saito 100 at first to power the plane but a 2 stroke is better suited for that plane. Its a racer
after all and a 2 stroke give you more speed.

I have 7 planes in my Hangar:

http://www.wspromotion.com/SansNom.html

The shoestring is one of my favorite so far. Everyone
at the field love this plane. Its fast, handle like a dream
and easy to land if you know what you're doing.

I bought another one just in case i lost it..

You're gonna love this plane but Warning: You will fall in love!

Serge

OS 91 FX in Shoestring Racer
 

that paddy wagstaff scheme extras on that page. is it artf? looks very shiny!

OS 91 FX in Shoestring Racer
 

Yes thats the P.W extra 300 ARF. Gorgeous plane for sure.

Serge

OS 91 FX in Shoestring Racer
 

Beautiful planes!

OS 91 FX in Shoestring Racer
 

Hey Serge,

Thanks again for replying back. I gotta tell you though. I felt a little nostalgia when I saw your Kyosho Giles G-202. I had one for about 2 and a half years and just recently lost it in a midair. I had an O.S. 91 four stroke in it and it was just a great flyer. Sure was a major bummer when I lost it. I don't know why Kyosho has discontinued it.

You have a beautiful collection of planes. I am envious. I am waiting for the aforementioned O.S. 91 to get back from repair so I can use it in a Great Planes U Can Do 3D that I have almost ready to go. When it went in with the Giles, it sustained a little damage.

Take care Serge and thanks again for the info on the Shoestring.


Jeff

OS 91 FX in Shoestring Racer
 

serge 1

I don't know what I like better, your clean garage or your neat toys in your clean garage.

Who am I kidding, I like them both.;)

OS 91 FX in Shoestring Racer
 

Thanks

Serge

OS 91 FX in Shoestring Racer
 

LOl...Ya..I must say I cant live with my garage !

Plenty of space to hang my toys.

Serge

OS 91 FX in Shoestring Racer
 

Dam.. Very sorry about your loss....That Giles is a fantastic performer. The model is now discontinued and Its such a drama
for us!!. The plane is now a collectors item and I am not sure
that mine will fly again. I cant bare the fact that I can lost it
without the chance to buy another one.

The colors on that plane are simply gorgeous.

Shame on kyosho!!

Its very hard to put your hand on a kyosho giles
by these days. I check on e-bay each week to find
one....

Serge

OS 91 FX in Shoestring Racer
 

Serge...you are a genuine RC-addict...:)

OS 91 FX in Shoestring Racer
 

Serge,

I just took my Shoestring with a .91 FX and a Bisson 70 degree Pitt's muffler on it out for the second time. I'm flying it a bit harder but I still have the engine running pretty rich as it's a new engine. I was wondering if you found the air inlet openings in the front of the cowl sufficient enough to cool the engine. They seem pretty small. I had two dead sticks today at 4 minutes and 9 minutes which seem to be the result of overheating. I was pushing it a bit more on the shorter flight. Just curious how yours was working out and whether you added more intake area.

Jeff

OS 91 FX in Shoestring Racer
 

Jeff,


No overheating problem so far with my set up. The engine run like a clock. Make sure the clunk in your tank is ok. Perhaps you're right about overheating ... About the deadstick, does it happen at Full throtle?

Serge

OS 91 FX in Shoestring Racer
 

Instead of putting flying wires on the stab... try sheeting the bottom of the stab with 1/64" plywood. This method works great on our warbird racers.

Jacob

OS 91 FX in Shoestring Racer
 

Serge,

Yes, it happened quicker when I was at full throttle for longer periods of time but I was only at half throttle when it actually died. When I test ran a few tanks through it at home I found that it would not four cycle no matter how much I turned the needle out. That told me that there wasn't enough back pressure in the muffler for the tank so I plugged one of the pipes on the muffler. It's a Bisson Pitt's 70 degree. Now I'm wondering if I have plugged it too much. After I wrote my last message I went out and searched on FX91 and found a bunch of solutions many have tried. Solutions from enlarging the fuel line supply to shimming the head. Problem is I have little experience with this and am not too sure where to start. What muffler are you running? I think I'm gonna start with only partially plugging the one exhaust port to see what happens. Then I'll try removing the cowl. Those seem like the easiest to try first. As far as the clunk goes, do you mean to make sure its free or something else. I've made 4 successful flights but those were running very rich and at half throttle. If you have any other ideas, please let me know.

Jeff

OS 91 FX in Shoestring Racer
 

Jeff,


First thing to do is to remove your fuel tank for inspection. Make sure the clunk move freely. Check also the silicone tubing in the tank for holes. Make sure the back pressure tube in the tank is well curved ( to the upper).

I run a pitts muffler with a 13X8 APC prop. I use Wildcat 20% fuel.
Ckeck the glow plug after the engine die. It will tell you a lot.

Let me know.

Serge

OS 91 FX in Shoestring Racer
 

Serge,

I spent the whole day working on the problem and I think I have it licked. Everything in the tank checked out fine. I never did have the air in the line problem that many report. One thing I noticed was that the needle valve adjustment just didn't seem to affect the engine like the smaller ones I am used to. I messed around a bit with blocking the muffler exits but it only seemed to make it better on the needle but worse on the overheating. I finally bit the bullet and bought a Perry pump. It was a little disappointing at first as it actually seemed to create bubbles in the line after the pump. I adjusted it a bit for more pressure and they disappeared. After a bit of messing around with the adjustments I am now able to run a complete tank of fuel through it (while on the ground) without the engine quitting. The head still seems to be a bit hot to me but I'm inexperienced and it may just be due to the engine still being new......hopefully!!!! Do you know if the spit method works for airplane model engines like cars? Dribble some spit on the head after it shuts off and if it immediately dances and boils away it's too hot. If it slowly bubbles, it's okay.

By the way, thanks for the glow plug tip, I never thought to look and see what condition it was in.

Jeff

OS 91 FX in Shoestring Racer
 

Hi Jeff,


Glad you got the dam problem fixed. I use the spit method on my nitro rustler but never tryed that on a plane...By the way make sure you're not overcharging the engine with to large prop. The best prop period for the 91 FX is the 13X8. Anything larger put to much load on the engine. If your engine's max RPM is under 10,500 then the engine is working too hard and not making peak performance. Remember, this is a 2-stroke engine. It cannot be expected to turn the same enormous load of prop as a far more expensive, pumped or super-charged 91 4-stroke engine.

I run My 91 FX with an APC 13X8 without any pump and the engine run like a cadillac. 4 Gallon of fuel and no deadstick yet.

Serge

OS 91 FX in Shoestring Racer
 

Serge,

Yep, I was using a Master Airscrew 13x8 and just switched to an APC as I like them best. When I bought the engine well over a year ago I bought a 15 inch prop for it but it was never used. The manual must recommend one that size. Fortunately, I just happened to check out the OS site and read about using slightly smaller props. Oh well, now I just have to hope for no rain this weekend....something we haven't been too lucky with lately here in "sunny" South Carolina. Thanks for the help....I'll let you know how it goes. :D

Jeff

OS 91 FX in Shoestring Racer
 

I run a G90 in mine with a 13/8 apc. It handles just fine.

OS 91 FX in Shoestring Racer
 

Well, I managed to sneak out yesterday to the field, before the heavy winds hit this weekend, dragging my two kids along....relaxing!! The new Perry pump has cured all my woes and I got two full flights out of my Shoestring without a hiccup. Now I just have to figure out why the plane insists on climbing all of the time. There's always something!!! :)

Jeff

OS 91 FX in Shoestring Racer
 

I dont mean to be a poop here but I have a vriety of size engines and never needed any of those pumps. I had two 91fxs a couple years back and returned them both due to overheating. We have beat this engine to death here on the RCU. I firmly believe there is a problem with this engine.
*I finally installed a OS 1.08 in that plane. I have several size OS engines and all are fine but the 91.
If you had to install the pump on a 91, I do not believe you cured the problem, just somehow bypassed it. I run a ST G90 in mine with a Pitts and 13/8 and it is so reliable its scary. I have had that engine for two years.
*I did have one problem once with what I thought was overheat but finally saw that the fuel line coming fron the tank to the engine was bent to much,(crimped) thus runups were fine b flights lasted about 2 minutes before it overheat and quit and that head was hot.
So I replaced it with a couple extra inches of fuel line and no problems since.
* Some people here thought the overheating was due to air leaks in the remote needle assemble. Any engine that requires that much attention to get it to run is not worth it. Als the opening for my muffler on the bottom of the Shoestring is very large to allow for better cooling. Its about the width of the cowl and around 2 1/2 inches deep.

OS 91 FX in Shoestring Racer
 

Cyclic Hardover,

I wouldn't want to hack on O.S. for this problem until I tried to run it with the stock muffler....which is an excellent point that someone in either this or another thread made. I never did run the engine with the stock muffler. I believe that this problem was due to the aftermarket Pitt's muffler not supplying enough pressure to the tank. When I ran it with the muffler the first time I could all but remove the needle valve and it would keep on running. The engine would never richen up and die as it should have. Then I plugged one of the muffler exits and it improved but the needle still was too far open for a typical OS engine telling me it was still starving for fuel. Realizing that increasingly restricting the exhaust exit will actually worsen the overheating problem my only possible solutions were to put the stock muffler on and hack up the plane to make it fit or to install a pump. The pump seems to be working great and has thus far eliminated the overheating problem. Unfortunately, I purchased this motor before I found this site as I'm sure I would have opted for something else considering all of the problems reported here. I've also had it too long before using it to even think of returning it so finding a solution was necessary.



Jeff