its a single seater challenger already built that I have been removing heavy chub off ofOriginally Posted by Jim Heffelfinger
its a single seater challenger already built that I have been removing heavy chub off of
its a single seat challenger already built that I have be cutting the fat from
I have 67 lbs to work for total weight of the powerplant. (I weighed the airframe and prop)
Is that with a parachute? If not, you could probably get one of the hand thrown parachutes that Belight uses and come up with an extra 12 or 14 pounds of weight allowance.
With 67 pound allowance, you could possibly just squeak by with a 277 but by the time you built a mount and put oil in the gearbox, you'd be right at the limit. You'll almost certainly need a fan cooled 277 on a Challenger. A free-air in pusher configuration is very hard to keep cool. Mine was mounted above the wing on a very clean airframe and I could not keep it cool without running it overly rich or having a large air scoop on the cylinder head. The vibration was so bad that I was never able to make an air scope last much more than 10 or 20 hours. I tried three different designs out of aluminum. Fiberglass or carbon fiber would probably be more tolerant of vibration but I decided to go with the Kawasaki instead.
The other problem with the free air 277 was the excessive cooling on low power descents. I had a free air 277 on a very clean air frame and it was necessary to pull power back to idle for landings. During the descent, even from 500 feet, the engine would cool to where the CHT went below 250. I usually use 250 as the minimum temperature for the first takeoff of the day. The Rotax engines with steel cylinder lines are really prone to cold seizures if you put full throttle to a cold engine and the piston heats up faster than the cylinders. So touch and go landings were always nerve wracking for me. I would try to add power gently until the temp came up above 250 but that meant climbing slowly and spending more time at altitudes that provide fewer forced landing opportunities. Fan cooled is definitely the way to go with a Rotax, IMHO. A fan cooled engine cools down slowly at idle because there isn't much wind blowing across the cylinder at idle RPM. The temperature is much more even on a fan cooled engine than on a free air. Water cooling is even better, way better in fact.
If you're within a few pounds of legal weight, not carrying more than 5 gallons of fuel, and fly responsibly within the FARs, there's very little chance you'll ever get ramp checked. Even in the case of an accident, if the airplane looks like an ultralight and isn't sporting N numbers, the NTSB and FAA are happy to consider it an ultralight. I've read that it costs the NTSB a minimum of about $20,000 just to open an accident investigation case. If it's an ultralight, they can just walk away and turn it over to the county sheriff or highway patrol because it's a vehicle and not an aircraft and therefore not under their jurisdiction. I guess the one place where being overweight might be a problem is if you had UL insurance coverage and your aircraft didn't meet the specs for a UL. I can imagine (although I've never heard of this happening) that an insurance adjuster could weigh the wreckage and deny a claim if the aircraft was seriously overweight. I'm not encouraging anyone to flaunt the law here, just saying that if you follow the spirit of Part 103 and don't create a hazard to yourself or others by flying irresponsibly, there's nobody out there with a set of scales likely to come looking for you.
The Mount is already on airframe as it was on when I weighed the project. I plan on mounting the engine right side up to improve cooling and get around all the inverted engine issues. I was unaware of the cooling issues when running free airs.
thanks for the info!
As you may have inferred by wakataka you might be disappointed by the 277 as a power source.
NikaSil found in a number of engines has greatly increased the reliability (and weight reduction) of these small engines. https://en.wikipedia.org/wiki/Nikasil.
As I mentioned in my first post to you the road to Part 103 success is paved with scales all along the way. Belite has the most contemporary struggle with a legal commercial product. James has a whole list of weight saving products. You will notice that he has lightening holes everywhere. His planes are fairly priced considering the use of carbon and very limited production numbers. Part 103 is a constant battle with weight and performance (safety) .
When building to part 103 Every part of the plane is scrutinized for weight savings. I am sure you are realizing that starting with a built plane is a bit of a handicap. Even prop selection has several pounds of difference ( let alone the allowable mass for the reduction) The education curve is pretty vertical.
Having enough power to have a reasonable ROC is a safety factor. When wing loading gets as low as UL levels you are a feather in the wind.
Best of success for your project.
jim
Last edited by Jim Heffelfinger; 12-24-2015 at 12:41 AM.
I often wonder why someone would put the time, work and money into something like this trying to meet Par 103. When there are some very nice airplanes that do meet Par 103 and do not use single cylinder two stroke engines. As mentioned in one of the above post you have Belite, if money is burning a hole in your pocket. But if you can build, weld, for almost nothing you can build a Legal Eagle compared to the Belite. You will then have a nice twin or four cylinder, 4 stroke and many hundred of hours flying your fun airplane at a fraction of the cost of what that conversion trying to meet Par 103, in something that really will not make it and be a joy to fly. That Legal Eagle will be a Hoot or blast to fly, as would the Belite. Not so with this project you are working on. JMHO.
Tony
Yes, there are a few of the open air flying coleman tent type airplanes that probably would make part 103 with twin cylinder engine. I fly in northern Minnesota so I need an enclosed plane like the single seat challenger.
Last edited by aeroschmitz; 12-23-2015 at 03:59 PM.
Interesting power/weight relation
TBO > 500 h
almost vibration-free
http://www.aieuk.com/category/products/
price ???
cool link
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