A friend of ours is about to install a Rotax 912 ULS in his Zenith CH750 STOL. The firewall forward kit is the standard package from Zenith. We measured the weight of the engine itself, plus all the related components. While I was surprised about how all the small stuff adds up, I believe that it is overall still the lightest engine on the market:

Components Weight, lb
Engine mount 12.2
Exhaust, muffler 6.2
Exhaust, pipes 3.8
Radiator 2.4
Heater hose, throttle cable, etc. 4.8
Mounting hardware, oil cooler and tank, water cooling components, air filter, miscellaneous parts 19
Total parts 48.4
Engine 0.8 gal 5.44
Oil tank 0.8 gal 5.44
Oil radiator, hoses 0.3 quarts (assumption) 0.51
Total oil 11.39
Cylinder heads, water pump, expansion tanks, coolant hose. 1.5 liters / 0.4 gallons as per Rotax installation manual. 3.3
Total coolant 3.3
Engine, dry 131.6
Total fwf, minus cowling 194.69

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Interesting info, Oliver - I appreciate the detail!  You state the FWF weight at 194.69 "minus cowling," but I also assume that is minus a prop?

I've always thought the Rotax was the lightest option for the 750, but real-world comparisons need to include all the systems, accessories, hardware, etc. required to actually operate the engine!  Oliver's weight break-down is by far the most comprehensive (and realistic!) that I've seen ... I was surprised to see the actual operating weight approaching 200 lbs!

My air-cooled Jabiru 3300 has a total (including accessories, exhaust system, etc.) weight of 178 lbs.  However, that does not include the engine mount (no idea what that weighs!).  So, if one takes Oliver's figures and subtracts the mount's 12 lbs, the Rotax would weigh 182.69 lbs vs the Jab's 178.  However, virtually all Jab 3300's in 750's will require an oil cooler, slightly increased oil quantity, and associated plumbing, which I would estimate weighs a few pounds at most, so looks to me that the Rotax vs the Jab are very, very close to the same weight!  I deleted the heavy Bing carb and mechanical fuel pump on my Jab for a Sonex/AeroInjector gravity-fed throttle body carb and lost an additional 7-8 lbs of weight, so that likely makes my much-modified Jab a few pounds lighter than the standard installation.

If one were comparing other engines that happen to be fuel-injected and require return fuel plumbing and/or a header tank, it would only be fair to include the weight of these components, too, because they are required for the engine to actually operate!



Hi John,

You are right, prop, spinner and related installation hardware is also not included.

For accuracy (and simplicity) reasons, we had thrown all the bags with the smaller parts into a bucket after we zeroed the scale. The line item with a total weight of 19 lbs actually consist of three individual measurements of 6.8+8+4.2 lbs. I thought however that it makes no sense to break it down that far since it was always a pretty random mixture of parts.

I used the same scales as when I weighed our AeroMomentum engine, for which I ran a number of sanity checks to confirm the accuracy of the not certified scales. I am therefore confident that the total weight should be accurate to about +/-1 or 2 lbs.

Our friend's Rotax installation will be around 50 lbs lighter than our AeroMomentum AM15, which is currently the lightest auto conversion in this power range. AeroMomentum is working on reducing the weight by 10 lbs, it will then however still be 40 lbs heavier than a Rotax 912.


Good reporting Oliver. If the Aeromomentum AM15 (117 hp) is 40 lbs heavier than the Rotax 912 (100 hp) then it is quite close in weight to the Rotax 914 (115 hp). 

Just noticed that you list 0.8 gallons of oil twice, once for the engine and once for the tank. This is not correct. There is just 0.8 gallons (3 liters) for the engine and the oil tank together. There would be some additional for oil hoses and oil radiator but the 3 liters is what flows from the tank, through the engine and then back to the tank.

Thank you for the correction. From reading the instructions, I (mis-)understood that it would be 0.8 gal. in the tank and 0.8 in the engine and gearbox.

This means the total installed weight, minus cowling, prop and spinner is 189.25 lbs.

Pretty impressive!

Thanks, Oliver, any unbiased info of actual weight really helps clear the fog that seems to surround actual engine weight. Because builders claiming that engine weights are at times not factual and really hard to pin down, I started the below thread awhile back to strictly list completed aircraft weight  from actual weight and balance declarations. Though engine weight is not listed, it's up to the viewer to draw their own conclusions about how a particular engine weight may have impacted the build through the average aircraft weight with that aircraft. 

This list is strictly a factual compilation, and yes, there are variables, and that's why there's a listed average

I'm hoping to have more builders list their weights, particularly with the newer models and engines that are flying, we are lacking somer current models.  I found is a reluctance of a few to list their true weight, so if you can send it to me in a PM it will be anonymous. And I really appreciate those that have taken the time to list theirs, I'm sure it really helps other builders. 




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