twostroker

My Feedback: (37)

Hello,
I just got a 93" Citabria and want to go gas for the first time do you guys have any ideas for me. I'm looking for something simple and reliable with enough power for scale flight.
The airframe is 11# 15oz. with no servos in it. Do you have any powerplant suggestions for me.
Tim

Postal FLyer

My Feedback: (9)

If you want a no hassle, no extra battery and isolated servo I would suggest a zenoah G-38 or G-45 depending on the manufacturers recommendation for cubic inches in a gasser. Tower Hobbies also had the Fuji line but I have never used one yet. Just don't under estimate the power. I bought a Giant Scale Planes Decathalon (96") and was told a G-38 would be a good choice. It was too heavy and too powerful. Now they recommend a G-26 or 120 4 Strike.

twostroker

My Feedback: (37)

Thanks for the input. I have seen this model fly with a Moki 135 and it seemed to have good power for scale flight and airbatics. So I guess I'd be looking for something with about the same power. Maybe a new G26 or RCS140. The RCS140 requires an additional battery for the ignition, no big deal, I could deal with that. So what do you think?
Tim

Postal FLyer

My Feedback: (9)

Tim both engines are fine but you may want to get some input about radio interference problems and solutions involved with an engine with electronic ignition. Some guys say you must keep the battery for the engine up front with the firewall and also the servo linkage to the throttle can cause enough noise. I'm not well versed in this but you may find answers in the radio equipment discussion.

G.F. Reid

My Feedback: (1)

Basic rules of thumb with any ignition engine- Keep everything that's connected to the engine and ignition at least 12 inches from anything connected to the radio system. This includes everything....switches, servos, batteries, etc. The one exception is the throttle servo. By it's very nature, it has to be connected to the radio system electrically and physically and it has to be connected to the engine physically. For this reason, you must keep the servo 12 inches from the engine/ignition and use a nylon control rod from the servo arm to the throttle arm. . . Some folks have broken all these rules with no problems, but for me it's just easy insurance during the installation phase.

twostroker

My Feedback: (37)

Thanks for the input. I did buy the RCS140, (hope it's a good engine). I understand the radio equipment must be 12" away from the engine and ignition system, but you say the throttle cable also should be non-metalic also? This engine also has it's own battery for ignition, does that and the switch/ charge jack stay isolated with the engine? Should I try to mount everything to the firewall beside the engine?
Tim

Postal FLyer

My Feedback: (9)

I will tell you one more thing to look out for when you use this gas engine. A friend of mine has one he put in a Edge 540. I have a couple Gas powered planes and I have always had to be extra careful that things are tight and check over the plane after each run to make sure that nothing has come loose. He said that the engine was producing a lot of vibration compared to other gas engines that he has.

G.F. Reid

My Feedback: (1)

Re: throttle cable, Yes the throttle cable should be non metallic. I guess it's easier to remember and understand if you understand the reason behind all this. A spark ignition engine can radiate a voltage spike for every firing cycle. The operative word is radiate. Any metallic object that is connected to the reciever can pick up this radiated signal and conduct it into the receiver. This includes the servo motors, switches, batteries, wiring and metal pushrods. It's not a very strong signal but it can be strong enough to confuse the receiver, what, with these spikes being received right along with your transmitter signal. That's the reason for the physical seperation, ie. Your transmitter signal will likely always overpower any noise from the ignition module in that configuration. If you use a metal throttle cable or rod, it's sitting right there next to the ignition source. It can pick up the signal like an antenna and route it right back into the radio compartment. The module doesn't have to be on the firewall side, just a foot or so from the radio compartment will be fine and always take special care to do ground checks when flying spark ignition engines. Do them with the engine running at full power. The difference in range shouldn't be more than 10% as a rule. That is, if you get a good ground check out to 100 feet with engine off, you should get real near 90 feet with the engine running.
Again, the easiest rule of thumb to remember is that anything connected to the engine equipment should be 10~12 inches from anything connected to the radio equipment. Since the throttle servo has to be connected to the engine, use a nyrod but keep it long so that the servo can maintain the 10~12 inches of seperation.

twostroker

My Feedback: (37)

Thanks Greg,
This information explains a lot to me. You see a few months ago Model Airplane News test flew a 1/3 scale Pitts, with a Fuji 50 on it. A few days later my Pal bought the same set-up, plane and engine combo and set it up the way they did at MAN....throttle sevro on the firewall. He's had nothing but trouble with it, the throttle servo jumps all over the place past 1/2 throttle and once it starts doing that it takes a while to get it back. I be sure to tell what you said, thank a bunch.
Tim

G.F. Reid

My Feedback: (1)

Well, there's quite a few things that can cause a problem like that but I'd definitely start with moving the servo way back and use nyrod. If that doesn't get it, he'll have to start from there. Could be a bad plug wire shield, wrong plug (needs to be a resistor plug) bad servo, could be metal to metal vibration somewhere, flying wires rubbing against each other, etc.
BTW, those last two things can cause glitches on any kind of plane, whether spark ignition or glow. One of the most common is using a metal clevis to move a metal throttle arm on carbs that are equipped with that setup.