The planetary gear drive for Moki S250!

The most important first: Our SP-250-X gear drive is available since 2017!

We had a great debut during the 9th warbirdmeeting in Oberhausen / south germany in 2017. Top pilot Stefan Jahnke gave the visitors goose bumps when he presented the power plant in the air!
The jury was impressed as well so they granted us the award “Best of Show”! This was a big pleasure to us and made us very happy. It seemed as if we reached the goal after a hard time of developing.

A very big thanks Horst Zeller from RC Scale Airplanes: He produced an unbelievible good video clip for Youtube during the night! Thanks and thumbs up, Horst! Click here to watch it!

The developing project “Moki geardrive” made it to final success. A lot of test runs and flights have been solved positive.

Download the flyer of SP-250-X here, please!

Seafury (Airworld) equipped with SP-250-X 5-blade-prop 35×54″

The gear drieve is assembled on a Moki S250 which is tuned with parts from Heilemann-Sternmotoren. It has a ratio of 3:1 and allows swinging full scale diameter propellers on warbirds scale 1:4 and bigger.

In alternative we install the gear to your own well serviced Moki S250!

Assembly of SP-250-X with our „Engine-Mount-System“

The gear drive can swing 4-blade props up from 35″ diameter. Perfect scale optic and sound is combined with absolute suitability for daily use. Enthusiasts will be excited! The low idle rpm as well as the full speed is exact the same as the original planes have.
Share the first flights with us and be inspired!

Engine data SP-250-X:

Engine type: 5-cylinder fourstroke radial engine
Displacement: 250 cm³
Idle Moki 250: 900 / 6000 rpm (low idle ground / deep dive in the air)
Shaft power: 15 hp (Data Airworld)
Gear ratio: 3:1
Airscrew speed: 300 / 2000 rpm
Capability of propeller diameter:
3-blade-props up from 38″, e.g. FW-190, Wildcat, Corsair
4-blade-props up from 35″, e.g. Corsair, Thunderbolt, Bearcat
5-blade-props up from 34″, e.g. Seafury


SP-250-X with Moki S250 and screws for propeller mounting: 6595 gr
4-blade-propeller “Corsair” 38×58″: 1100 gr
Spinner cup type “Corsair” (size Moki 400) : 85 gr
SP-250-X ready to fly: 7780 gr

Weights of direct drive for comparison:

Moki S250 with screws for propeller mounting: 5820 gr
4-blade-propeller “Corsair” 28×16″: 450 gr
Super-Scale-Spinner “Corsair Moki 250”: 175 gr
Moki S250 ready to fly: 6475 gr

additional weight by SP-250-X: 1305 gr

Comparison of 4-blade Corsair propeller: left side 28×16″ for Moki S250 direct, right sight 38×54″ for SP-250-X

Notice: To have a real scale diameter Airscrew on a F4U-Corsair you exactly need 38 inch. Smaller looks like Micky Mouse 😉

Additional information:
The gear design:
Our demanding customers expect a reliable, durable and perfect tuned power plant for thier radial driven warbirds. Like most components in aircraft design the gear is optimised to weight and therefore high loaded. It’s free of maintenance for the pilots. As a “new car” we ask for the gear-drive back for a complete inspection at our service-center after one flying season. This first check is free of costs (exceptionally shipping and neccessary spare parts) for you. Additional service checks with widerange maintenance require a fee for working time. In case of exchange of spareparts like bearings, sealings or grease you’ll be informed. In our experience customers honor to fly a reliable power drive.

Our SP-250-X is integrated quite compact in the front of the Moki S250. A new or even you well maintenanced engine will pass our income tests. After this the motor will be tuned up with sencefull parts from Heilemann-Sternmotoren to rise the durability of the Moki to maximum:

– Carbon push rods save wearing in valve drive and allow higher rpms.

– A specially developed set of valve springs is inserted which have no more lifetime limitation.

– The original Moki ignition including spark plugs and coils is exchanged by a specialised RAINBOWTRONIC ignition system.

– A optimized intake funnel is attached for more constant midrange idle and more tidiness behind the carburator.

We build up the geardrive and let it run with the propeller you ordered on our test bench. After positive measured values like temperatur, rpms and additional data the complete unit is ready to be shipped.

The assembly of the unit is difficulty. We use special made tools and chucks and insert optimized grease. Every uncorrect assambly may result in a spontanous breakdown of your power plant without any warnings. You can imagine the consequences for your motor and plane. Therefore every warranty is valid if any changes on the geardrive have taken place.

We are happy if we made you curious! For all questions or comments call us any time! We’re looking forward to get in touch with you!

Please let me cite an Youtube-Fan from france:
„Congratulations Mario! This device is the best thing since years in the R/C Giant Scale A/C world! Curious to see the result with more load on the engine. Regards from France“
That’s what we think, too! Commends like this are the trust for our developings! Big thanks to france!

Best pilots wishes, yours

Mario Seidel