subarubrat

My Feedback: (1)

I have picked up two Jetster 20 kits from ebay in the last month and want to adapt one over to fly on turbine power with a Kolibri. It flew well on the original gear which was a full sized (weight) 4 channel system and the RK720 ducted fan which made 3.5 ~ 4lbs of thrust. The Kolibri is right in that range of thrust, and overall weight can be shed with a modern RC system so it should be a good match to perform as better than it did as a DF. Being that it is a pod mounted engine like a HE162 and no thrust tube is present what can one expect thermally and what is usually done to mitigate the issue in a configuration like this?

Henke Torphammar

Hello,

Me and a friend have done alot of testing when developing the convertionkits for the foamies. Two things that we discoverd is that when converting EDF thrust to turbine thrust you need only half the thrust to match the EDF. So if you choose the smallest kolibri T15 it will make 4.2lb of thrust which would fly the plane as if it was equipped with a 8lb EDF setup. (8lb EDF would be a standard 6S setup or so)

Second thing is the heat. Of course the exhausts are hot, but they are directed backwards and cool pretty fast. 650mm behind a Kolibri making 7lb of thrust I recorded only 90Celcius. I did this test with my Baiojet laying 650mm in on a camping table and after the test no spot on the table was too hot to touch, tops 50Celcius. I can also hold my hand under the stab of the foamie Venoms with the engine at full power.

I think you are fine without any shielding.

Like this but further in



650mm from the cone to fin and no problems! On the larger Opus the engine are even lower.

subarubrat

My Feedback: (1)

Fortunately the Jetster 20 is a balsa built up kit originally flown with a .25 2 stroke ducted fan, so not quite as sensitive as the foamies. Ultimately I may have to build a mockup to make sure it doesn't have a problem, but your pic of the glider is encouraging. If you click on the picture in the first post you can see that there is not a center Vstab to worry about, and the kolibri should fit right in to the middle of the nacel intended for the RK720 ducted fan. Is your thrust angle parallel to the fuselage or is the tailcone tilted up at all?

Dr Honda

My Feedback: (4)

I would simply put some foil tape on top of the fuse, and call it a day. Think about all the shock, and reaction type jets. We have the engine mounted mid fuse, and just use foil tape to protect. (Like Henke's tail)

Henke Torphammar

No thrust angle, stright backwards. Better safe then sorry, but remember aluminium tape can be heavy, so don't over do it in the tail.

Dr Honda

My Feedback: (4)

what's the wing span, and aria on the jester 20?

subarubrat

My Feedback: (1)

Dr Honda, I am not familiar with the jets you mentioned, can you post a few links?

Wing span on the Jetster is 48 inches and area is 430sq inches, it was made in 1979 so it is pretty typical of a sport plane of that era, and was one of the first mass produced successful ducted fan airplanes.


-Edit; I found set of retracts that are prefect for this airplane, electric with trialing arm suspension that are about the right size and have the right sized wheels, intended for planes up to 10lbs so they should work great for this project.

Henke Torphammar

If they are from Delayking they are probably not worth it and over speced. The only ones around that have a suspention to talk about are the very simple trailing links from Tamjet or Jet 1A. Those with a simple Eflite 25 mechanism will work. Tamjet make struts with 2 pices that works, the chinese make struts with like 15 pieces which don't work at all. Even with softer springs the geometry are wrong and the aluminum/aluminum telescope sease.

Dr Honda

My Feedback: (4)

SHockJet and a Reaction 54.


Basically... the engine is just mounted in the belly... and we use foil tape to protect the fuse from heat. BUT... if you get a spewing, wet hot-start.... the only thing that will protect that, is using a start tube.