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
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
