Hi folks,

Just a simple (hopefully) enquiry about the OS .55AX. I've got one of these and am hoping to use it in a 9 pound scale model that was originally planned around an FX 61. Obviously there's at least some power loss to be expected, but how much? Has anybody flown a model with both these engines installed so I can have some comparison to work with. The recommended prop sizes are almost the same so I'm guessing there will be only a difference in RPM (although OS quotes a difference of .15 horsepower). For a saving of 5 ounces, I'm thinking the power loss is acceptable. What do you all think?

Cheers,
Greg

9 pounds on a .55? What engine range is recommended by the kit manufacturer? What kit is it? Wing area? Wing loading? Just off the top of my head, you sound a little underpowereed there.

Dr.1

Great Planes Lancair. The more I look at the numbers, the more I think it will work. I'm happy to buy another 61FX if I need to, but I'm thinking I'll give it a go with the .55 unless anybody thinks the numbers quoted by OS are incorrect. I agree it seems to be too little power, but from all accounts the 61 has more than enough power for the Lancair so I'm wondering if the 55 might not be acceptable..... I'm not intending to aerobat it. Just tooling around like a Lancair should.

hey oldtimer,

if you are talking about the ARF Lancair, then you really will want to go to the larger engine.
the .55ax, albiet a strong engine, is probably going to need a half pound of lead to balance, and will at best, just get the plane in the air. now there was a thread in the pattern plane forum where a builder used a .55 in a Dirty Birdy which is essentially the same size, but lighter in weight (by about 2.5 lbs.), and it flew fine, but it also has a lot less drag.

the plane calls for a .61-.75..............the .55ax will swing a large prop, and that is what the AX series is aimed at (bigger prop, lower noise), but still will be on the weak side of a .61.
i fly 2 of GP airplanes right now after just getting back into the hobby after a 15 year layoff (benn flying since the late 60's), and i use the upper end of the recommended engine range in those birds.......niether (Big Stik, Super Skybolt) are overpowered at all............both could use more.
if you decide to buy another engine for it, i'd go with the .75.ax..........very impressive engine and will swing bigger props than a .61FX.

also, "tooling around" as you say is much more enjoyable when you can do it at less than full throttle.................odds are very good that you'll be hanging on the prop most of the time with the .55.

Thanks guys for your comments. On balance, I'm going along with your suggestions and I've purchased a .75AX that will be installed tonight. Once I've got it flying and set up, I might swap out the 75 and try the 55 just to satisfy my curiosity, but in the meantime I'll accept the half pound weight penalty and go with the larger engine.

Looking forward to getting this beastie flying.....

Cheers,
Greg