Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[JimG]

OK this ones for Martin, some info and details of my jet.

My main hobby is RC flying and I use a wide range of power types, electric, glow, petrol and the top of the range a turbine. This is a Wren Turbines Jubilee 75 with around 8Kg (17.6lbs) thrust and is mounted in a Boomerang Sprint model. At the moment I don't have photos of the assembled plane as it's too big to photograph indoors and I haven't taken a camera down to the flying field with it. The first two photos are of a previous Boomerang which is approximately the same size but had a smaller turbine with around 6.4Kg (14lbs) thrust.

The present model is 76 inch wingspan and 73 inch length, I don't have it's completed weight yet as I have only recently got a scale that will take it, I would guess that it is at least 8Kg dry.
The remaining photos are of the fuselage pod and wing centre section, the rest of the model is normally stored in my garage. The wings and booms mount onto a carbon tube spar which takes the loads.

There are 3 lipos mounted in the nose, One to power the turbine electrics and retracts and two two power the radio through a Jeti voltage regulator which can provide enough current for 6 high torque digital servos. The regulator converts the 2S voltage to 6V , will take power from the better of the batteries or both and failsafes to ON so switch failure is not a problem. The radio used is the Hitec Aurora 9 and uses all 9 channels.

The tank contains 3.75 litres of fuel (paraffin with 5% turbine oil) although I only fill it to the 3 litre mark and normally use 2 litres per flight leaving plenty for overshoots and extra circuits. The runtime for the flight is normally around 10 to 15 minutes with 6 minutes of airtime.
The Wren turbine is autostart with the FADEC fully controlling it during the start cycle. When running the idle is around 50,000 revs, full throttle is 140,000 revs and exhaust temperature around 500C.

I have the Hitec GPS telemetry fitted which gives the groundspeed of the model and height during the flight. The highest speed recorded so far is 130mph with it reaching around 800feet altitude in a loop. Flaps/airbrakes are fitted which brings the speed down to 30mph for landing and normal flying is around 80 to 90 mph. Electrical retracts are fitted with sprung undercarriage legs to soften the landings and electromagnetic brakes are fitted to the mainwheels to reduce the landing run.

Here's a video of the previous boomerang https://www.youtube.com/watch?v=2S-f8Vc9tTA
 with one taken on board at another club https://www.youtube.com/watch?v=9j8fHdGyKNs .

Jim

[Martin (Admin)]

Thanks Jim!   

1. What happened to the 'previous Boomerang'?

2. Interesting to see the fuel system right in with the avionics, is that usual?

3. What's the expected 'working life' of a model turbine engine?

[JimG]

Thanks Jim!   

1. What happened to the 'previous Boomerang'?

2. Interesting to see the fuel system right in with the avionics, is that usual?

3. What's the expected 'working life' of a model turbine engine?

1. Destroyed when it went through a fence after losing elevator control. The turbine is still OK however.

2. It is quite usual to have all of the systems together at the front of the fuselage as that is where weight is needed to get the balance right. In this case the receiver is hidden away underneath the rest. Everything on the right is fuel system:-  two solenoid valves , the pump and the bubble trap. The left has the voltage regulator at the front then the Hitec telemetry interface and at the rear the FADEC that controls the turbine.

3. Normal time between services is around 50 hours running although as long as the bearings are OK and there are no running problems this can be put off. I have heard of some with up to 100 hours running on a turbine.  Service normally involves replacing the bearings (ceramic bearings used) then re-balancing. Occasionally some work might need done to the combustion chamber although this should be rare.

Jim

[Martin (Admin)]

Is it true you can use almost any combustible fuel in a jet turbine?

[JimG]

Is it true you can use almost any combustible fuel in a jet turbine?

Martin,  I've heard that said about full size turbines which seem to have more leeway on their fuel. Model turbines are normally set up for paraffin / kerosene with a few now capable of running on diesel although the earliest ones ran on propane. Most model turbines don't have the capability of changing the settings in the engine controller to allow for a large range of fuel types.

Jim

[Mad Scientist]

Is it true you can use almost any combustible fuel in a jet turbine?

I think that it depends on the setup for the turbines...the main turbines on Canadian frigates are (apparently) optimized for distillate (NATO F44) and there are very specific rules on using JP-5 (NATO F76) in them. The ships were still 'under warranty' back when I was aboard.
IIRC, the turbines were GE LM2500. - Tom