Revolver 46 with Saito FG 14

[Charles Aldous 1]

I have assembled a Great Planes Revolver 46 and fitted a Saito FG 14 gas engine and today went through the static run-in procedure as per the manual. I have no previous experience of running gas engines, only glow and electric.

 

I was pretty disappointed at first as the level of vibration through the airframe was massive. Everything shaking quite alarming really. This was whilst the engine was being run very rich as per the instructions. I hadn't connected the wings but the rudder and elevator servos (Hitec HS 645MG) started deflecting randomly with no tx input, but the throttle servo (Futaba 23003) was unaffected. There was also a steady stream of air bubbles in the fuel line. I by-passed the Dubro two way fuel filler and that reduced the bubbles a lot and then I removed the in-line filter and that almost eliminated them, buy not entirely. I disconnected the servos to continue the run-in. The remote satellite, mounted just near the tank started flashing rapidly during the vibrations and only performed again once I released it from its fixing on the tank bulkhead and disconnected and re-connected the tx, at one point the spark plug cap came loose also.

 

I noticed that the twin push-rods (which connect together and then to a single servo arm to the elevator) vibrated far more than the the rudder push-rod, almost oscillating like a pair of guitar strings as the engine revved through a certain range. Once I had completed the run-in I reconnected the servos but they were no better. The vibration was slightly less than at the start and is still a bit lumpy during transition from idle to full power, but I expect that will settle a bit more on fine tuning of the slow running needle next time I run it.

 

I guess I'm wondering if the servos are up to the job, or if the ignition unit might cause the servo issues or could it be the vibration? Why wouldn't the throttle servo be affected also? The ignition unit is installed forward of the firewall well away from the rx, which is mounted on the bulkhead just forward of the servo tray. There is an Optical kill switch mounted near the rx.

 

Any views /observations gratefully received.

[Martin Harris - Moderator]

I'm assuming you've checked prop (and spinner) balance and run-out issues?

The first thing I'd do beyond this (and as a general practice) is to fit those wings. It's very common for an airframe to vibrate - sometimes to the point of being damaged - if run without the wings, which have both damping and stiffening effects.

Your servos and receiver may well have been affected by the loose plug cap - it's imperative that the plug cap is firmly connected and running with it loose (or attempting to start the engine with it disconnected) can cause failure of the CDI unit. The arcing resulting from a loose cap can cause massive interference/glitching issues.

Edited By Martin Harris on 16/05/2019 23:59:17

[Engine Doctor]

You say "You never connected the wings " Do you mean you never fitted the wings or were they fitted and not plugged in ? Running an engine on any model without the wings fitted will allow it to vibrate badly . The wings dampen and absorb most of the vibration from the engine . Try it again with the wings fitted , it should be a lot smoother..Its also worth checking the prop and spinner balance.

Re the servo deflection . Is the Ht plug connector pushed down firmly on the plug ? Some times they have to be tapped down to connect properly.

Are you using a separate Ignition battery ?

I had similar issues with my first petrol engine and had to replace the ignition unit . Anything above idle the throttle went berserk and the rudder and elevator would kick randomly from side to side . The aileron servos worked fine..

ps . Sorry Martin didn't mean to double up on your post, you beat me to it and  posted while I was typing 

Edited By Engine Doctor on 17/05/2019 00:08:53

[Ron Gray]

As a matter of interest, what radio gear are you using?

[Jon H]

I have used 645mg servos on my 80 inch warbirds, they are more than enough for the revolver

I agree with the comments from the other guys that strapping on the wings will make a massive difference. I have had a number of customers complain about vibration over the years only to find they didnt put the wings on.

Saito use a glorified rcxel cdi unit and you can get a little spring that lives inside the plug cap. I found that without the spring the connection is not always 100% so that could give a little arcing as the guys above mention.

I would slap the wings on and tune up the engine so you know exactly where you stand.

[Charles Aldous 1]

Gents, many thanks for your comments and advice. In summary, so far, then:

Prop is balanced but I will check the spinner which is brand-new. What are run-out issues please?

The wings were not atttached to the fusilage so I'll do the transition tuning with them on.

The plug cap is a tight fit, but I have routed the HT lead through the engine mounting box so it is in close contact with the airframe. I'll re-routed that to allow for more flex.

I am using a separate pack for the ignition.

The radio gear is spektrum from another model and which worked faultlessly. The rx was fine and held a solid signal, just the sattelite started flashing and didn't like to re-bind after the flashing issues. I re-connected it and released it from the bulkhead fixing point and it was ok. If it does it once the vibration is dealt with, I will swap it out.

Many thanks and I'll post my progress.

[John Stainforth]

Are you using a plastic engine mount? I found that those are not really adequate for the Saito 82 and resulted in a lot of vibration. The Saito metal mounts are good, but the add yet more weight, and you already have a rather heavy engine for a Revolver 46 - which was more or less designed for the OS55AX.

[Martin Harris - Moderator]

Posted by Charles Aldous 1 on 17/05/2019 08:43:50:

Prop is balanced but I will check the spinner which is brand-new. What are run-out issues please?

Things running out of true - back plate distortion, holes drilled off centre, grit under the prop boss, badly moulded prop etc. etc.

[Woody49]

I have two of these engines, one in a Sig 4 Star 64 and one in a Seagull Gypsy Moth. Both now run very well with no unduly significant vibration, in fact vibration levels are very similar to a glow 4 stroke. I did have very similar problems to you when running the first engine in, very frustrating it was too!

This eventually proved to be a self induced problem with the mixture high speed/low speed needle balance. To resolve it I reset both carb needles to the default settings (given in the instruction leaflet if I recall correctly). The instructions stress the need to make very fine adjustments - one click at a time rather than the quarter turn approach used on glow engines and they are absolutely right about this. Adjustment from the default took a fair amount of time (about 1/2 an hour) - adjust, try, stop, adjust, start repeat as needed etc. Once adjusted the engine has been fine with normal vibration levels.

On both models I use a felt filter "clunk weight" in the tank rather than an in-line filter - no problems with bubbles. The 4 Star has 55 "transmitter" hours on it now and all with the FG 14.

Re the plug cap coming loose; I had this problem on the 4 Star. No amount of fiddling with the Saito cap retaining spring worked. Resolved by using a light spring one end attached to the exhaust pipe and the other to the carb intake pipe with the spring passing over the top of the chrome plug cap. In the Gypsy Moth the approach angle of the ignition lead is different and the problem hasn't occurred so your solution should work.

I also bought an "on board mini tachometer" just over £15 from Just Engines. It plugs into the tacho lead on the CDI unit. I don't leave it installed, but use it for setting up the idle and top end RPM - much more accurate than my ears! Once set, the engines don't seem to need any more adjustments. 14x7 APC props used on both engines.

I also have an FG 17 fitted in a Hangar 9 Katana artf. This is a very lightly built model fitted with digital servos. On the ground and at low idle rpm the airframe definitely vibrate much more than the the 4 Star and Moth. This vibration clears as soon as the throttle is opened and is not apparent in the air at all. Servo's are not affected by this and operate normally at all times.

[Charles Aldous 1]

Update:

Yesterday I ran the engine with the wings attached and all the problems went away. What a transformation! when I looked at a plug cap on another Saito gas engine I have I found the clip Jon mentioned, so used that to make a solid fit.

Tuned the engine and have an impressive transition now. Seems to miss the occasional beat at full throttle though, so I will keep my eye on that as the engine beds in. There is still the odd mini air bubble that might be the cause, so I will try a felt clunk next.

Thanks for all the contributions

Happy landings!