After I managed to break some fins on the monolithic block machined cooling fan, I got a replacement flywheel assembly from Compact Radial Engines.  A special pulled was loaned as well. The Fan and flywheel and alternator magnets come as one assembled per-balanced unit. Leon there made very clear he did not want me to remove and replace until he talked to me while I had the parts in hand.  However, when I got the parts and called, he was out of the country.  After calling a number of times, the staff told me to stop calling and they would make sure he called when he got back.  It has been months and I never heard anything so I assumed he had died before getting back.  Finally a week ago, I got a call from his office wanting to know why they had not gotten the return parts back.  Not much comment after I explained how they had not followed through from their end. 

Mid day yesterday I got a call from Leon.  Once I got to the warehouse where the gyro is, I found the necessary tools and called him back.  It only took a few minutes for me to change it while he was on the phone.  The only thing I would not have done is put rope in the cylinder chamber via a spark-plug hole so the piston had something soft to block against while torquing the main nut back to about 53 foot pounds.

Bolt Torque

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I am learning the ideas different people have about how to tension and retain bolts on the craft.  Historically, every bolt/nut on an aircraft used AN hardware and had a hole for safety wire.  That is not the case on this.  Most thinks do have nylon lock nuts.  I am making a practice of using blue locktite and I will be putting nail polish lines on everything as an indicator for something coming loose.

Larry says use the blue and tighten the engine mount bolts to 25 foot pounds.

Leon says to tighten the exhaust manifold bolts to 14 foot pounds.

Leon says to tighten the carb mount screws to where the rubber just starts to squish all the way around.

I don't yet have a torque value for the starter bolts.

I currently have the eccentric clamp bolt tightened to 14 foot pounds.



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Prerotation on this unit is accomplished with a small RC electric motor driving a sprocket and chain reduction which drives a Bendix type starter ring gear engagement of the 108 tooth gear attached to the rotor head shaft.  The motor is powered from an independent LIPO battery pack Velcroed to the mast through an electronic speed controller.  You slowly turn the speed controller up as the rotor speed comes up to avoid over-stressing the motor and drive-train--instead of just dumping full power into a dead stopped rotor system. Roger says he starts his takeoff roll at 120 rpm and turns off the pre-rotator motor at 170 rpm. If left on, the bendix does not seem to disengage and there is drag on the rotor from the motor and reduction drive.

The 10 cell battery pack puts out 30 some volts and takes a really sophisticated ground based charger to add energy to it. Larry says it takes about 5% out of the battery pack for each pre-rotation.  He said it ran my 24 foot blade up to 170 rpm at his 1300 feet elevation and should take them to 180 at my 6500 foot elevation in about 20 seconds (how did you measure rpm without out a rotor tach Larry?) With no blades attached, I see about 190 rpm meaning that is the maximum no-load speed for this motor and controller with this battery pack voltage and present gear reduction.  I did get a rotor tach that I have initially/temporarily installed.

The conclusion of all this is that it should be possible to add a second motor (and higher capacity controller?) or more powerful motor with half the speed reduction to prerotate to close to flight rotor rpm to minimize takeoff roll.

Butterfly Ultralight MZ202 related links

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Roger Hooker--Albuquerque, NM 40 plus hours flying  time.
Charles VanLeeuwen---Charles VanLeeuwen, Mountainair, NM Test flown and demo'd about an hour by Larry Neal--Engine currently back at factory.

Butterfly Aircraft LLC  Larry Neal

Compact Radial Engines  Leon Massa

Engine Jets Leading Edge Airfoils


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details to be added.


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to be added

Jetting the MZ202 engine with dual Bing 54 carbs

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The Bing 54 carburetors on the MZ202 engine need to be jetted properly for the altitude and temperature the engine is to be used at.  Leon sends them out with 190's so they run a bit rich at sea level at standard temperature to be sure they don't get cooked running too lean.  Roger says he has gone to 155's running at 5800 feet and is still a little rich.  Leon says the engine in his seaplane is running 180's at sea level and he is just moving the needle setting back and forth between winter and summer (in his rather mild climate).  He detects a "tic" in his engine at cruise power if he is too rich.  Otherwise, one looks at the spark plugs to see how clean they are.  I anticipate I will need 150's at my altitude and will probably have to change jets with the season due to the more extreme temperature variations here.

I have ordered sets from 145 to 160 which I think will cover the range I need unless I move to lower altitude.

I put in the 160's and did only a short run when the belt drive came loose.  Need to check carb synchronization when I get the other issues resolved.

The Belt Drive Problem

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This is the Larry Neal Butterly Ultralight gyro with the MZ 202 engine and belt drive reduction that Larry flew for a few minutes at Air Venture this summer.

The first thing I did when I got the machine to Mountainair (about 6500 feet and 85 F) was a thrust test. (The hour meter showed 1.35 when I got the gyro to MTA and 1.44 after this test.) I put a 400 pound capacity UPS type package scale with remote readout between the nose wheel and a forklift, zeroed the scale in the horizontal position, loosely tied down the the main wheels and fired up the engine.  It was kinda rough running as expected for a 2-stroke running rich at about 2K idle.  As I upped the throttle to about 3K, there was a lot of vibration.  I let it warm up so the CHT was showing over 200.  As I brought the rpm up between 3500 and 4000 the  vibration was so strong I thought the prop was coming off and I shut it down.  Inspection showed no problem--every thing still tight so I tried again.  It sort of smoothed out above 4500 but was not what I would consider comfortable.  Still got more severe in the 2500 to 4500 range when I eased it back down. 

I found a peak thrust of right at 250 pounds at about 5750 rpm.  I got a peak rpm of about 5900 rpm but the thrust was off about 25 pounds at that peak rpm.  Leon Massa  (the engine and reduction provider) indicated this combination with the right prop can provide around 330 pounds of thrust at sea level.  Larry Neal said about 280 pounds at 1300 feet with this prop and had predicted 250 at 6500 feet.

I called up Roger Hooker, the one other BFUL (Butterfly Ultralight Gyro) owner I know of to discuss my experience.  He said he had never done a thrust test but had experienced a high level of vibration.  He had belt issues in the 3.5 hours he ran his belt reduction unit, including a broken belt and not being able to keep the belt tight.  One key thing he mentioned was that the belt would go from tight to loose as he rotated the prop.  I then checked mine and sure enough, the belt would go from very tight to more loose with each rotation of the engine.

I got out a dial indicator and figured out how to probe the drive pulley mounted on the engine crankshaft.  I found a total swing of nearly 30 thousands of an inch.  That resulted in a call to Larry Neal who then consulted with Leon via phone.  Larry called me back before I got the pulley off and said to leave it on, strip the engine of anything that could get broken, and send the engine and drive back to Canada (Leon) where he would figure out what the problem was.

After a strenuous effort protectively packing the engine, using lots of rigid foam and tap, I made the 4 hour round trip to Albuquerque to get the 76 pound package to the UPS station.  I paid the healthy fee to get it to Canada in a couple days (rather than 2 weeks) which totaled about $500 in materials and shipping fees.

When Leon got it, he found that the drive pulley did indeed have a wobble.  He had it pulled off and found 25 to 28 thousands of wobble in the end of the crankshaft.  When he had the engine pulled apart, all the components checked out in  spec. but the output end support had been moved out of place by the flexing of the output end of the crank shaft.  The crankshaft on this engine is multiple pieces that are pressed together with about 20 tons of force.  Once everything was pressed back and reassembled the the output wobble was back to just under a thousandth of an inch.  Leon also noted that the drive pulley showed a lot of wear, more than he would have expected after 50 or 100 hours of use.

The current thinking is that over-tightening of the belt is what caused the crankshaft output end to get pulled out of place and wobble.  The eccentric tension mechanism can exert a great deal of force on the crankshaft if someone uses a cheater bar.  Both Roger and Larry have indicated that keeping the belt tight has been an issue and that the belt was either stretching or the eccentric was backing off. The original belt is made of kevlar and the newer one carbon fiber which is supposed to be some 25% stronger.  Are either one really supposed to stretch?  There is a spec for how much deflection there should be for a given amount of force in the middle of a given amount of unsupported belt length but I don't have these numbers at the moment. 

When I get the engine back, I expect to indicate it, run it to see the vibration level, add the belt to spec tension and run and indicate it again.  Then add the prop and repeat the above.  Then, assuming no wobble or excess vibration has been found, do some extensive ground running to see what if anything happens.  I will mark the eccentric to be able to determine if it is backing off or if the belt is stretching. 

I just got word the engine is being shipped back from Canada via ground.  Expect it will take about 2 weeks to get here.

The engine is back.  Leon says the crankshaft has just under a thou of wobble.  I measured 7.5 to 8 inside the drive pulley.  Leon says they don't hold that to any particular spec. I measured 4.5 to the top of the teeth.  Again, they don't hold any particular spec on this but it is machined at the same time as the bottom of the teeth.

I put the belt on and rigged up a way to measure deflection while applying force to the side of the belt.  The spec that Leon had for the belt he stocks (mine is actually a different belt but I don't have a spec for it) calls for 3/32 deflection with 21 pounds force in this case.  The tangent line is 5.5 inches long as near as I can measure.  It is really tricky to get the tension set.  You have to get enough force on the clamp so the eccentric will stay put as you tension but not so much you can't tension.  I could find no perceptible movement in the eccentric between 12 and 22 pounds of force for the 3/32 deflection using a standard 1/2 inch ratchet to turn the eccentric. This means it would be extremely easy to over tension the belt such that the  crankshaft might get pulled off center.  The spec really needs to be translated to an eccentric torque spec to make setting easy and accurate.

After several attempts, I ended up with 3/32 deflection at pressures ranging from about 21 to 28 pounds.  This means there is still considerable wobble between the drive pulley and the driven pulley.





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The intent of the "BLOG" is to provide a place to record and exchange information regarding the Butterfly Ultralight Gyrocopter. At present, I only know of two of us that have these little machines--Myself and Roger Hooker.  These machines being defined as the ones with the MZ202 engine and belt drive reduction.  There are supposed to have been 2 or three more kits shipped but I have no idea if any of these are running.  There are supposed to be several more on order.  We hope to make contact with the other owners so we can all benefit from each others experience and share tips and safety information.

Now know of 2 others with ultralight butterfly gyro's.  Kevin Eaton and Greg Hammer.

First day with the Butterfly

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ultra5.jpgGot back with the Butterfly, discovered more play than makes me comfortable in the drive pulley.