End of the Sprite project
 

The end of the Sprite project


My winter project this year was to build up all the sets of parts I had for the Sprite into engines to reduce the number of boxes of parts lying about the house. Amazing how much more room the engines take when in bits!


Originally I had ideas of making the engine for sale but rapidly found that having a running engine and having a reliable engine that was simple to assemble is a totally different thing. In the years since making the first engines I have had to shorten the shaft and thicken it to remove shaft vibration. I had new shaft tunnels made from stainless steel to help protect the rear bearing which runs very close to the exhaust outlet. The compressors all needed modifying and new compressor nuts.


The most difficult thing to get right was the preload. With this particular engine design and the compressor the shaft moves differently under load and with no load. This took lots of time and experiments before finally devising a solution.


I now have 31 engines complete so should have a some good runners among them! I still have some mods to do to the older engines to get them to the same spec. Please don't mail me asking for engines, as I will not be selling them to the general public. Now all I need is a project that needs 31 engines with 100Kg thrust! Seriously I am now making up a Falcon 120 powered by 2 Sprites that I am converting to a flying wing. I shall post some info on how it is done and what the results are. My Arado will need its 6 engines that are now hopefully reliable so it can complete the LMA schedule.


The spec of the engines is unchanged. Thrust is 3.25 - 3.5 Kg at 250,000 rpm.


As you know this has morphed into Gaspars new Merlin 35. Gaspar has achieved what I struggled to achieve, a reliable engine that is simple to manufacture. The long wait will definitely be worth while. Every aspect of the engine has been looked at and often changed. The only thing that has remained constant is the spec, where Gaspar has the engine running with a slightly less high max rpm. This is very much a next generation engine especially the electronics.


John

http://www.rcuniverse.com/forum/atta...mentid=1981894http://www.rcuniverse.com/forum/atta...mentid=1981898

Sprite on test

http://www.youtube.com/watch?v=ioBf4GAe8wU

You could just sit and stare at those most evenings !!

John,

Very impressive work to develop an engine like this from scratch. Specially on hobby basis. There can not be more then a hand full of people in the world capable of this. Now team up with Chris Golds and have some B-52's flying :)

That's a heck of an achievement John.
What is pre-load?

Excelent work with this engine, John.

Félix

Does this mean we might see the Habu fly again:confused:

m

John

Obviously a massive achievement but I can't wait until you take it one step further and get a turboprop/heli version ready.

Jason

Thanks everyone. Frankly I am glad just to have kept going and getting them finished. No Jason not a chance for a turboprop.

Mick, Only if you don't mind air start. I still have not tamed the brushless motor and get a vibration free start. Amazing what you can do with brushless motors of high Kv.

Harry Preload is the way the bearings are loaded to ensure they remain in contact with the side of the raceway at all times and not be left free to float.

Henke

I did some research and the only model that uses a lot of jet engines would be an Ekranoplan at 10 engines, then not sure if this would be a jet plane or a boat.
It is nice now to get back to some plane making ready for the flying season.

John

No don't mind at all, be nice to see it in the air again. I just have to find a better method of getting air into it.

m