Alternate engine expierences and builds

Jason O

Junior Member
Joined
Jun 13, 2007
Messages
540
Location
Portland
Hello All,

I would like to start a thread on alternate engines. Please use this thread to share what your are building and why. Resist the urge to post unfounded pipe dreams and reasons you think your decision is better than someone elses. Tell us the type of engine you are using, the type and ratio of redrive, changes you have made to the intake and exhaust. Share with us your successes and failures. Do not use this forum to tell us why yours is better than theirs, how yours is less expensive than theirs, how yours is more reliable than theirs, share your expierence not your emotion.

I Have a Kolb MKIII that I spent 12 years building and when it came time for the engine, the ideal engine (Rotax 912S) was way out of my price range. Someone else on the list had put a BMW R100 (2cyl, air cooled, 1000cc) on their airplane. After much research, I discovered the BMW has a sterling reputation for durability on the motorcycle. I had the parts machined to mount a Rotax C gearbox on the BMW. I made the drawings and had the machineing done at a local community college, one part for each siemester. I purchased an engine (which has about 65 horse power in the motorcycle) and set to making it "the best" engine I could. My dream was to get 80hp out of the engine. The changes I made to the engine were all BMW parts or had a reputation of being good changes in the motorcycle. I put a BMW 336 cam in the engine, higher compressions BMW pistons, had the heads stage 1 ported. I installed another hall sensor in the pick up can so that one pick up triggered the upper plugs and one the lower plugs (truely redundent ignition except the battery electrical supply). I ran a Rotax 3:1 C gearbox and a 72" IVO ultralight propeller. I ran it and and it ran strong. The climb of the aircraft was good but the cruise speed was low. I had trouble cooling the engine and spent much time messing with the jetting on the carbs to try and get it to run right. I had one of the valves start to mushroom (I think because of heat) I had one of the cylinder hold down bolts pull its threads (yes I used a torque wrench), I had one of the spark plugs vibrate out of the cylinders (yes, it vibrated the aluminum threads in the head to dust). The tach had to be redlined between 1000rpm and 2800rpm because of vibration in that range. The IVO prop blades would not keep in position and would break the blade movement tape (I believe because of the rough idle). I flew it for about 25 hours and decided I had lost faith. Many people have run this engine for many hours and been happy with it, it just did not work for me. I believe what I learned is that I should not have tried to increase the horsepower and I would have been more successful If I had run the engine more stock.

Engine 2
Racer on this forum had been reporting about his Yamaha 120 snowmobile engine. I contacted him and he agreed to sell me his prototype set up to mount a Rotax C gearbox to that engine. He also manufactured the mounts to match my airframe. The block on the Yamaha engine has to have some brackets and knobs removed to make it fit my mounts, This may make it unusable in a snowmobile again. I am using the engine totally stock except the exhaust and different jets in the carbs. The gearbox is running 3.47:1 ratio and I have a 68" IVO medium propeller on it. I am using the stock voltage regulator and ignition controll unit. I am not using any of the stock instruments or engine pickups (temp, press). The Yamaha does not monitor oil pressure on the stock engine so I found a place to screw a plug in so I can monitor pressure and I run an aftermarket water temp sendor in the stock location. I have had my oil tank crack twice. The engine is set up with a centrifugal clutch between the engine and the gearbox. This makes the engine idle nice and smooth but does add another mechanical failure point in the drive train. At about 40 hours I had some parts of this drive train start to fail because of some alignment issues and after more money and a machined part, time will tell if this issue has been fixed. The engine is smooth and runs strong, and I am happy with it. If I can get 300 hours out of the drive train, I will be extremely happy. If I can get 600 hours out of the engine I will be able to call it a success.

I am to the point in my flying career that I really want to fly and do the minimum amount of work on the aircraft. If I had a financial choice today, I would pull my current engine off and put a Rotax 912S engine on my airplane and fly it for the next 20 years with a minimum of maint. This has been proven with a huge number of hours on these engines running in aircraft. Since I do not have the financial choice, I will continue to run this engine and keep a close eye on it.

What I think I have learned:
The only way to tell if an engine will be successful in an airplane is put it in an airplane. There have been many engineers and very smart people who have have tried and failed to make many different engines spin a propeller properly. There are many engine canidates out there for conversion and people seem to be very pasionate about why they think some of these engines will be well suited to use in an aircraft. The bottom line is that no matter how much research and analysis they say they have done, If you do not want to have a long road of testing and potential failure ahead do not go down that path. Engine reliability means nothing, it is engine, drive train, propeller combination reliability that we need and it is very tough to come by. That being said, If you enjoy the challenge and like tinkering with your aircraft as much as you like flying it, you could be the person who proves an engine, drive, propeller combination can be successful, at the very least you will learn what dosent work.

Jason
 
Good post Jason, I will post some of what I have done and experienced when I get more time to type.
 
Good thread idea. When I have some extra time I might try to chime in with my experiences
 
Well done Jason, this could become a very educational thread, keep it running.
 
It takes a special poster to post what he has learned rather than what he is supporting or trying to get other people to try. The generac 4 stroke engine is a sample of that. I hope the rest of the feed back is as straight foward as yours. I am very interested in alternative engines.
Scott ,
I hope you can use this thread to update the Artic Cat engine as well as the thread you have started.
 
Engines:
Since I have started flying gyros I have had some varoius experience with different engine MFG's.
My first gyro was bought as a project that needed rebuilding. It was a KB3 with an Arrow GT500.
The Arrow for those of you not familiar with it, is an Italian engine designed for aircraft, it is a very nice clean
design, air cooled opposed twin. The engine that I had was complete but had not been run for years.
Then I find out that the company, Arrow is out of business, and there are little to no parts available.
My magneto was bad and so was the starter, I found a place here in Atlanta to rewind the starter.
As far as the ignition I had to build my own. I used a Pertronix kit from a chevrolet with the hall effect
sensor, and machined a rotor that held one magnet. And an adjustable plate to move the pickup to set the timing.
I used a pair of Dyna 1.3 ohm Harley coils with dual plug leads to fire the 2 spark plugs in each cyl.
The engine ran very well for about 50 hours until it blew a head gasket on takeoff,
Consequently I put the gyro down in a tree farm and it was a total loss, but no injury.

My second gyro had a Hirth engine, the hirth had its ups and downs, it constantly vibrated the coil bracket
cracking it and breaking screws etc. Fan belts stretching, leaking oil, Then it blew out a spark plug and I set down in a hay field.

I then acquired a gyro with a Rotax 582, the 582 was the answer to my prayers, it ran great, started easy,
never a hickup!, I even started to get cocky and fly low around fields, cruise at 300ft enjoying the view, etc.
Then all of a sudden the rotax locked up and put me down in a hay field, just after doing a very low high speed pass
over the runway.

So I got to thinking that even all these "aircraft" engines were unreliable, i might be able to have at least the same if not better luck with another engine.

Arctic Cat: The SHORT version.
I had acquired the Arctic Cat 530 some time ago, but it had been on the back burner since the rotax was running so well.
I had fabricated an adapter plate for the rotax gearbox, it was not hard to do, I was able to do it without any complicated machining.
Once the rotax quit, I decided the arctic Cat would go on the Dominator, I had to make new motor mounts, new wiring, all new brackets for dang near everything. The engine was stock except for the R&D pipe. I flew at Bensen Days '09 long enough to end up in a cow pasture. YouTube - Gyroplane (Gyrocopter) Engine Out! Emergency Landing During Bensen Days 2009
I ended up seizing and burning a hole in a piston, and tearing up the cylinders..

I found an Identical engine on Ebay new in the box, never used, for a very good price.
I got the new engine and changed over all the external parts, pressure checked the engine to test the seals etc.

This time I was able to get the factory snowmobile pipe, I figured that this would fix the problem.
I used the rotax Bing carbs, after about 15 min flight time burnt up a piston and cylinder,

Rebuilt again, talked to numerous knowledgeable people about jetting, carbs, exhaust, everything, even talked to a guy in New Zealand that was using the same engine since 1994, got all his engine info.
I had the pistons and heads ceramic coated and the skirts teflon coated.

I flew for 10 minutes and melted holes in both pistons. the week before Bensen days '10.

I have just rebuilt the engine again and have retarded the timing 7 degrees.
So far I have about an hour on the engine and the pistons have not melted yet.

Some of the threads: kind of a chronological listing of the things I have encountered.

http://www.rotaryforum.com/forum/showthread.php?t=19383&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=20187&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=20920&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=21190&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=20726&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=22341&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=21578&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=22078&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=22586&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=25129&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=25442&highlight=arctic
http://www.rotaryforum.com/forum/showthread.php?t=25561&highlight=arctic



I have not bothered to add up my time or expense as I really do not want to know, At least the Arctic Cat parts are only 1/4 the cost of Rotax parts, I flew less that 5 hours last year because of the R&D, the year before I flew around 70 hours.


I also have a BMW K100 engine on the back burner, A tad heavy at 178lbs @90HP (178lbs, just engine and gearbox, starter, alternator, throttle bodies, exhaust header.)
Will post about if I ever get back around to it.
 
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finding that gremlin

finding that gremlin

Scott Wrote: "I have just rebuilt the engine again and have retarded the timing 7 degrees.
So far I have about an hour on the engine and the pistons have not melted yet."

Hello Scott:
I hope you have finally cracked the nut. I chased too high CHT's for a while in my BMW. It is very hard to tell if it is mixture, timing, or exhaust or a combination of all. It almost defies logic how an engine can run so well and be so reliable in something else and when we go to great lengths to make the engine think it is still in that original vehicle it will still melt down.

Like I said, I hope you have found the magic bullet and your persistance will finally pay off.

Fly safe
Jason
 
Most aircraft engines are detuned for reliability. Lower compression, etc. Large capacity for their horsepower. If you hot up an engine and flogg it, things will break. It's like going uphill, with the throttle wide open towing a caravan.
 
Good thread Jason. Scott that is some pretty extensive experience with various engines...and successful engine out emergencies.:yo:
 
Well the one thing that I learned, is that they ALL quit sooner or later.
That is why the whole new snowmobile small light 4 strokes look so attractive, might be at least get the failures to hold off until "later" rather than sooner :D

It does make you appreciate the amount of work and documentation that Rotax has put into their program.
 
...and the cost, unpalatable as it is.:)
 
I put another 15 minutes on the engine last night, did not burn any pistons. :)
 
Trying to find the sweet spot

Trying to find the sweet spot

I am running the Yamaha 120 carbed engine on a Kolb MKIII fixed wing. It is a very high drag airframe. I am now to the point of testing that I am trying to determine some base line parameters that I should use to continue to opperate the engine at. I put some EGT probes in this last winter. They are running between 1150F and 1350F depending on altitude and power setting. In the snowmobile manual they state the max RPM at 8500, I currently have the plane propped to turn about 8000 on take off an climb out and it will turn about 8300 in level flight at full throttle. I am cruising at 7000 RPM which is max torque according to the manual. My airplane is crusing a little slow for my taste so I am thinking of starting to mess with the prop and RPM combinations. I am trying to guess how much effect running at higher RPM will have on longevity. I know this is an apples to oranges compairson, but I have been looking at the Rotax 912S specs
Max RPM 5800
Max Continuous RPM 5500
Max Torque comes at 88% of Max RPM
Max continuous RPM is 94.8% of max RPM
Max cont RPM (95HP) there is 220.36ft/lb torque and 2263.37rpm at the prop
Piston speed 38.51ft/sec at 5800rpm


My engine
Max RPM 8500
Max Continuous RPM 8058 ??? (Based on the Rotax number of 94.8% of max)
Max Torque comes at 82.3% of max RPM
7000 RPM (99.9HP) 260ft/lb torque and 2017rpm at the prop
Piston speed 61.28 ft/sec at 8500rpm

The BMW R100 does have a max RPM and a Max continuous RPM published
Max RPM 7400
Max Cont RPM 7200 (97.3% of max RPM)
Piston Speed 56.91ft/sec

As you can see from above, one thing that I need to determine is what should be my max continuous RPM should be set at. Is it valid to use the 94.8% of Max RPM that the Rotax 912 has? How much effect on longevity does 1000 RPM have if it is always kept withing the max 8500 rpm? I am messing with prop pitch and RPM over the next few weeks and then I will take a blade off of the IVO and try it with 2 blades and see what happens. I took a 4 hour flight last weekend and had to fly between 6,000 and 7,000ft, at that altitude and 7000 RPM I burned 3.5gal/hour. I would love to bump that up to 8000 RPM, for faster cruise speed, but I will have to see how that feels.

Jason
 
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Good idea for a thread Jason!

I am keeping my fingers crossed Scott, that the retarding 7* works out. Both the snowmobile and gyro engines applications are highly loaded....I think the main difference is that the snowmobile engine doesn't run at constant high rpm and the pistons have a chance to cool down during the low rpm moments. A guy I know has over 7,000 miles of hard riding on his AC 582 sled and he said that he would crash and die if he ran at 6000 rpm for very long. From what I've read, retarding the spark may have somewhat the same effect (reducing heat and pressure) for longer piston life.
 
I am running the Yamaha 120 carbed engine on a Kolb MKIII fixed wing. It is a very high drag airframe. I am now to the point of testing that I am trying to determine some base line parameters that I should use to continue to opperate the engine at. I put some EGT probes in this last winter. They are running between 1150F and 1350F depending on altitude and power setting. In the snowmobile manual they state the max RPM at 8500, I currently have the plane propped to turn about 8000 on take off an climb out and it will turn about 8300 in level flight at full throttle. I am cruising at 7000 RPM which is max torque according to the manual. My airplane is crusing a little slow for my taste so I am thinking of starting to mess with the prop and RPM combinations. I am trying to guess how much effect running at higher RPM will have on longevity. I know this is an apples to oranges compairson, but I have been looking at the Rotax 912S specs
Max RPM 5800
Max Continuous RPM 5500
Max Torque comes at 88% of Max RPM
Max continuous RPM is 94.8% of max RPM
Max cont RPM (95HP) there is 220.36ft/lb torque and 2263.37rpm at the prop
Piston speed 38.51ft/sec at 5800rpm


My engine
Max RPM 8500
Max Continuous RPM 8058 ??? (Based on the Rotax number of 94.8% of max)
Max Torque comes at 82.3% of max RPM
7000 RPM (99.9HP) 260ft/lb torque and 2017rpm at the prop
Piston speed 61.28 ft/sec at 8500rpm

The BMW R100 does have a max RPM and a Max continuous RPM published
Max RPM 7400
Max Cont RPM 7200 (97.3% of max RPM)
Piston Speed 56.91ft/sec

As you can see from above, one thing that I need to determine is what should be my max continuous RPM should be set at. Is it valid to use the 94.8% of Max RPM that the Rotax 912 has? How much effect on longevity does 1000 RPM have if it is always kept withing the max 8500 rpm? I am messing with prop pitch and RPM over the next few weeks and then I will take a blade off of the IVO and try it with 2 blades and see what happens. I took a 4 hour flight last weekend and had to fly between 6,000 and 7,000ft, at that altitude and 7000 RPM I burned 3.5gal/hour. I would love to bump that up to 8000 RPM, for faster cruise speed, but I will have to see how that feels.

Jason


I have a dyno sheet for the 120 Yamaha Vector engine from Dynotech.
I wish I could upload it for you but when I try it says the file is to large for this forum. Dynotech must measure differently than what you have on the engines you decribe as they don't have TQ numbers as high.

Here is the HP and TQ highs.

It has max HP being at 8600rpm with 118.8 CHp and 72.5 Clb-ft of torque.

Max torque is at 6900rpms with 106.2 CHp and 80.8 Clb-ft of torque.

What's really interesting is that even down at 5000rpm it has 74.1 Clb-ft of torque which is still more than where it makes max HP. It shows these engines like to pull and pull hard. This makes me wonder if you need all that RPM or would you be better off lowering it down into the max torque range and giving it more work with the prop????

opsled
 
...and the cost, unpalatable as it is.:)

The only justification Leigh that rotax have for their high prices is that they are the only engine that you can buy, bolt on and expect fairly trouble free flying for thousands of hours.

There is no business case for them reducing their prices.
 
Phil, just be careful not to get caught in that "torque is what matters" misconception. Thrust comes from horsepower, and 74.1 lb/ft at 5,000 RPM is only 70.5 HP. Put a 2:1 reduction drive on it, and performance-wise you'd essentially have a much heavier 582 that burned less fuel.
 
I am running the Yamaha 120 carbed engine...Is it valid to use the 94.8% of Max RPM that the Rotax 912 has? How much effect on longevity does 1000 RPM have if it is always kept withing the max 8500 rpm?

Jason, these are not generic numbers which work across manufacturers and applications. Rotax has traditionally marketed snowmobile and aircraft versions of similar two-stroke engines which had widely varying max RPM specs. For example, the Rotax 583, similar to the 582 but using a rotary valve and different tuning, was rated at about 100 HP, with max RPMs approaching 8K RPM, if I recall. So the de-rating for that engine in aircraft use was to about 75% of max RPM, and about 65% horsepower.

De-rating the Yamaha similarly would mean 6,000 RPM, where it would make around 88 HP max, which is 75 percent of max rated power. Or, derating to the same 65 percent horsepower would mean limiting max RPM to around 5,500 RPM, etc.

But we don't really know how all the reciprocating parts were designed and balanced. One engine may have stronger connecting rods, another might outrun its ability to move oil at higher RPMs, etc.
 
I do agree Brian. You get what you pay for.

In this case thousands of hours of operation and experience that has produced a measure of peace of mind.

They can go t*ts up of course, but less likely to do so thank a lot of whatever else is out there for the time being.
 
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