engines

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Postby JPXman » Mon Nov 08, 2004 1:55 am

Don't only look at maximum thrust and ask "why do you need that much thrust?"

Its nice having all that thrust on takeoff from small fields with lunch, a tent and a full tank of gas. But when airborne, you can still do 40mph on 40% thrust, and be burning WAY less gas than a struggling engine clawing its way through the air at 40mph...

Just because your 15HP engine with redrive CAN develop a lot of thrust, chances are you won't be using it when flying around the patch, but its nice to have to get you out of small fields/trouble :)
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Postby Chappy » Mon Nov 08, 2004 10:03 pm

You bet, the extra thrust is great for that. I was trying to point out that putting lots of power, or thrust, on a Lazair in the expectation of nice, high cruise speeds isn't realistic, comfortable or safe.

I'll also point out that direct drive on larger, heavier engines, when fitted to the Lazair, have other problem. Fairly small props are required on any direct drive setup if the engine (particularly 2 strokes) is to be allowed to rev high enough to get into the power band. The props make a fair amount of noise. Generally, on Lazairs, overly large props are installed on these large engines to reduce noise, but that means the engine becomes prop limited and can't turn up to achieve anywhere near rated power. If the props, either shorter at higher speed, or longer at lower speed, allow the tip speeds to reach the speed of sound, they will produce a LOT of noise, and may fail due to heating at the tips. I've burned my fingers when I touched the tips on a wooden test prop that had gone supersonic after just a couple minutes test run! The glue had melted and the tips were delaminating.

Ultraflight experienced lots of problems with some of the direct drive setups they tried. I remember modifying the carbs to permit adjustable mixture control on the float carbs used on the NGL Westlake twin because the engines were operated near wide open throttle, but the engine was not operating at the high rpm that it was designed to be running at. The large wooden props (very high quality laminated ones) would experience cracking near the hubs due to the high peak power pulses produced by the opposed twins. When large props were fitted to the NGL Westlake drone engines, the crankshafts flexed so bad that the ignition module would "kiss" the flywheel, over heat, and fail. (Note that the ignition modules were on the far end of the crankshaft from the prop!) Also, the capscrews that attached the cylinders would work loose in just a matter of minutes. None of the first ten engines tested had cranks that made it past 60 hours; some had cracks after just a few hours. The KFM, which was heavier, but a lot stronger internally, was more tolerant of the larger props.

Anyway, just some things to ponder...

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Postby Guest » Mon Nov 08, 2004 10:57 pm

Hi,
About the Solo engines, they have ball bearings supporting the crank(same with Rotax 185) and generally this bearing isn't known for taking thrust as well as radial load. I wonder how the Rotax 185 stand up with redrives as compared to direct drives? The bi-props are very light and this probably helps the Rotax 185's to last longer but I think the redrives on the 185's should last even longer. Anybody experience this?
I wish I knew exactly where I got this information about the Solo's not lasting as long in direct drive configuration, but it does make sense to me.
On the other hand, the JPX's actually have two needle thrust bearings and two radial needle bearings to support the crank. This makes a tough engine for supporting propellers in a direct drive configuration. I had them for years and never had a problem in this area. My original Rotax 185 ;) siezed a front bearing (next to the prop) one day on take off. That's when I learned that it had ball bearings. Just my two cents worth. ;)
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Postby rayjb60 » Wed Nov 10, 2004 3:26 pm

Ive got a question about the Rotax 185's.

I currently don't have any kind of filter or airhorn on my Rotax's
but think it would be a great idea to help the engines not consume any dirt.

What are people using for an airfilter on the Rotax?
<H5>Nothing is impossible...Even the word tells you Im-Possible!!!</ H5>
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Postby Chappy » Wed Nov 10, 2004 10:02 pm

Ray,

A long velocity stack, or just flared end tube stack, will keep your wings cleaner, help obtain a lower fuel burn, but most importantly, make for a better running, better throttled engine. The stacks help contain the fuel standoff that occurs, keeping most of it from just being blown away.

I don't know if anyone has had any great success fitting an air filter to these engines on a Lazair...maybe someone will enlighten us.

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Postby Guest » Wed Nov 10, 2004 11:57 pm

Guest @ Nov 8 2004, 10:57 PM wrote: Hi,
About the Solo engines, they have ball bearings supporting the crank(same with Rotax 185) and generally this bearing isn't known for taking thrust as well as radial load. I wonder how the Rotax 185 stand up with redrives as compared to direct drives? The bi-props are very light and this probably helps the Rotax 185's to last longer but I think the redrives on the 185's should last even longer. Anybody experience this?
I wish I knew exactly where I got this information about the Solo's not lasting as long in direct drive configuration, but it does make sense to me.
On the other hand, the JPX's actually have two needle thrust bearings and two radial needle bearings to support the crank. This makes a tough engine for supporting propellers in a direct drive configuration. I had them for years and never had a problem in this area. My original Rotax 185 ;) siezed a front bearing (next to the prop) one day on take off. That's when I learned that it had ball bearings. Just my two cents worth. ;)


You mean to tell me all these Rotax engines Lazairs have been flying with all this time shouldn't have been flying direct drive. I don't know , what you are saying just doesn't seem to reflect whats been going on now for a long time. I'm sure there have been some problems and failures with the Rotaxs but look at all these planes still using them ? One spun bearing could have been caused by a number of things including a defective bearing, bad seal, or wrong oil ratio. Anyway the Solos appear to have bigger shafts and bearings than the Rotaxs. Seems like they would do as well as the Rotaxs direct drive.

From what I've read the 9.5 hp engines do well with re-drives but vibrate like hell at certain power. I guess you either run them full power or at idle ? Thats not ideal at all in my book. You also have more parts to worry about and replace. The engines also will weigh a good bit more with the reduction drive units and bigger props.

Yes, too bad the JPX engines are not available. That a nice HP and weight for a Lazair.
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Postby Guest » Thu Nov 11, 2004 1:08 pm

Guest,
You made a good point, the Rotaxes do work really well in direct configuration as there are many still using them. My bad experience with one shouldn't reflect on how all the others perform. Although making an emergency landing just wasn't in my books when I was just learning to fly... The first time the engine quit was only after about 5 hours of flying time and somehow the carb worked loose and forced me to land in a ploughed field. Then the siezure the second time, that really put me off. I then went to JPX engines because they were designed for ultralights. I have had good success with these engines. Too bad they quit making them. Now I will try Solo's w/redrives and hope this is the last set of engines for this plane. Daffy
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Postby xgary » Thu Nov 11, 2004 1:35 pm

rotax 185 worj great without filters so why even trry to mess it up ?

just holds back gas from clinging to top of wings

plus 185 rotax seem to like to eat up the bugs lol and stit em out the rear

is that like bugfarting they out ?
Shorty .............
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