Comet Mercury Question

[freeflight]

Hi Everyone,
I have a beautifully constructed Comet Mercury that was a gift to me several years ago. I haven’t yet flown it for various reasons.
Although I fly mostly Coupe and other rubber models I really love old time gas models and I’m ready to get it going.
It has an Ohlsson .19 that seems to run fine.

I have yet to glide test the model and my question is –
Currently, the CG is at about 63%. Is this a good location? Or what would be a good starting point?

Happy New Year,
Alan

[SIMON BLAKE]

That should be pretty close, so I would just fire it up and launch it with the ignition somewhat retarded to slow the motor for about a five-second run and see what it does. Sixty percent or so back from the leading edge is typical for an ignition pylon model with a lifting stab. Chances are, if it was trimmed out before, it will fly well.
I have been flying ignition models for years and one thing that I have learned is that test gliding is largely a waste of time unless you’ve got a pretty high cliff to pitch it off. On many occasions — I’m a slow learner — I’ve moved the batteries back further and further until I get a nice glide from a hand launch, only to find that when I send it up for the first power flight it stalls all the way down. So I don’t do that anymore. A good starting balance point is 60 percent from the leading edge if the model has a lifting stab and 40 percent back from the leading edge if it has a symmetrical or flat-plate stab.

[freeflight]

Thanks Simon!
Given the process of messing with the batteries, etc. and the tight fit in this model I foresaw just the conundrum you described.
Do you know who is currently making and selling electronic ignition kits? The Auston timer seems like a real hassle.
Alan

[SIMON BLAKE]

Hi Alan,
You’re right, the Austin pneumatic timers are a big hassle, in my mind anyway. I use the Texas Timers OT timer, which is excellent. Electronic ignition units are available from Larry Davidson (samchamp@jetbroadband.com). However, if the airplane doesn’t have one and if the ignition components haven’t been designed to be easily removable from the airplane, it’s going to be a lot of work to install the transistor and rewire the airplane. I use homemade transistor ignitions in my airplanes. The main thing they do is reduce the electrical load going through the points which makes the airplane easier to start if the points get oil on them. However, I know a lot of SAM fliers don’t use them and I’m beginning to wonder if they are worth the trouble.
Regards, Simon

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