Flying the Mosquito
Wind Drifter
Technical Info

Mosquito NRG Electric Start Conversion

The Swedish Aerosports Mosquito Electric Start conversion kit is not cheap - approximately $12-1300 USD depending on exchange rate, shipping, etc (as of Summer 2002).  That is because much of the harness power train is replaced with new components. Electric Start Conversion Kit from Swedish Aerosports
The full kit is shown in the photo above.  Starting at the top left and going clockwise: pressure(starter) switch and hose, wiring, velcro and assorted fabric pieces for harness modification, bag of shims and other hardware, instructions, replacement prop shaft, new Radne engine, battery charger, and battery pack.

So many components are changed with the electric start engine that it is easier to replace the entire engine than to modifiy an existing one.  The only parts that are reused are the carb, exhaust system, clutch and prop brake. Electric Start Engine
The pull start mechanism is done away with and a different crankcase is required.  The increase in weight of the electric start engine over the pull-start is only one pound (1/2 kg). Electric Start Radne Engine showing starter mechanism
The above photo shows the flywheel cover removed.  The starter is seen on the top right.  It engages with the toothed plate behind the flywheel.

A new prop shaft is required because the engine must be relocated slightly sideways. Prop Shaft Comparison
The manual-start prop shaft is at the top and the electric start shaft below it.  The difference is in the location of the bolt holes on the engine mounting flanges towards the right end of the shafts, where the e-start engine is shifted to the left relative to the harness (upwards in the photo).  One of the reasons I was able to justify spending the money for the conversion is that there was a crack in the prop shaft housing on the drive belt end.  The replacement cost of the shaft assembly alone was nearly one third the cost of the conversion kit, which meant there would never be a cheaper time for me to buy the estart kit.  The crack was temporarily held together with a hose clamp - which can be seen in the photo - while waiting for the kit to arrive.  This did allow me to get a few more flights, but even with the clamp as tight as I could get it the crack continued to grow - use this 'fix' at your own risk, with the understanding that it is purely temporary and could fail at any time.

The engine is bolted directly to the prop shaft assembly, which is in turn mounted to the harness frame with rubber mounts. Harness Frame with Engine and Prop Shaft Assembly removed
Because the carb is reused it was not necessary to detach the throttle or choke cables or the fuel line, greatly simplifying reassembly.  The carb was simply unbolted from the engine and left attached to the harness.  The exhaust system and prop brake were also removed, leaving only the 3 rubber mount attachment points. Pull start engine and shaft assembly removed from harness
Once those 3 mounts were undone the engine/prop shaft assembly was easily removed.

It now becomes very easy to do the actual engine switch at a comfortable work bench rather than bending down working on the harness frame. Switching engines on the workbench
This is convenient because some time must be spend properly aligning the engine with the drive pulley so that the belt tracks properly. View of belt alignment process
The shaft housing has slotted bolt holes to allow movement of the engine, and shims are used to set the belt tension.  See  Clutch Disassembly  for details of removing the clutch from the old engine and installing it on the new one. Aligning Engine and Prop Shaft
Once the alignment has been carefully carried out (be sure the belt is tracking properly and not rubbing against the side of the engine pulley), and the tension is properly set, reinstalling the assembly in the harness requires only re-attaching the 3 rubber mount points. Installing the new engine and prop shaft assembly
Attach the exhaust system, prop brake and carb.  Because the control cables were not disconnected everything should still be properly adjusted.  One part I found missing from the kit was a plug to close up a port in the carb spacer block.  The compression release has been modified so that this connection to the carb base is no longer required.  A quick trip to the harware store yielded the plug necessary to close this hole.

Now you are almost done.  If you had the foresight to charge the battery while doing the mechanical work,  you may be tempted, as I was, to temporarily connect the wiring and try out the starter!  A few easy cranks of the engine provided all the incentive I needed to finish the job.

The battery pack and starter switch are located over the pilot's back.  A rubber tube from the pressure (starter) switch is located at the pilot's left shoulder, next to the mouth throttle.  Blowing into the tube activates the starter, and is a clever system to prevent accidental activation of the starter.  The starter wires must be routed from the engine to the battery location, and some tabs attached to the harness to hold the battery and starter switch. Speedy Stitcher Sewing Awl
This sewing was accomplished with the humorously mis-name "Speedy Stitcher" Sewing Awl.  It may not be speedy, but it does get the job done. Completed Installation of the Battery and Starter Switch

This shows the completed installation.  The battery is held in place by two velcro loops and a plug is used to connect and dis-connect it from the harness wiring.  The plug and pressure switch are protected within a velcroed pocket (shown open in the photo above).  It is a simple matter to remove and replace the battery.  The instructions recommend keeping the battery separate from the harness at all times except when flying with it (to have it available for charging and so that an accidental short does not cause damage).

The battery pack weighs less than 2 lbs (1 kg), so the total weight penalty for the electric start conversion is slighty under 3 lbs (1.5 kg).

Attach grin and go flying!  The main drawback I see to this is that now you have to break in a new engine all over again!

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(updated December 23, 2023)