On Sunday, June 7, 2015 at 6:39:22 PM UTC+1, OG wrote:
Some comments from actual experience:
I have flown both self launching and sustainer gliders (Schemmp & AS), and now own a JS with turbine. I have no experience with the FES, although I have seen it ground run. For this post I will mostly ignore the FES, although I think it is an excellent system, save for the minimal drag which is a large concern for contest pilots. Plus, our national electicity supplier are all out of electricity and options, so charging might be difficult at times 😄 ( just kidding)

Operation:
The jet is by far the easiest to deploy, start, run, shut down and retract. It is a simple 3 step process. Turn on the master switch, switch the turbine to run, wait for turbine to spool up, and add power by turning a knob, all on one 57mm LCD instrument. The software can actually spool up the turbine to max rpm automatically, elliminating step 3. Shutting down is equally effortless. Switch off, and the controller does the rest. It waits for the turbine to cool, and then retracts automatically. Once retracted, you can turn the engine master switch off.
Safety: I have deployed the jet sucessfully from 150' agl (thats feet agl). Normally, I switch the master on at about 1000' agl. I extract the engine at 600', but do not start it yet. At 250' agl I switch on the jet, and it is at idle rpm at 150-160' agl.
Compared to the AS wankel engine, which I would start that at 600'. The solo sustainer I would normally start at 1000' agl. Both the wankel and turbo engines have a significantly higher workload than the jet.
In all of these scenarios I obviously have a landing field available in case of a failed start. I have had failed starts, and subsequent outlandings, with all three systems. No system is 100% reliable.
Initially (I had one of the early installations ) the reliability was about 60%. M&D and JS have however ironed out the initial problems and reliability issues (expected with any new system). I dont keep exact track, but I have not had a failed start or problem for the last year, except a glowplug glitch on the ground before flight for the last 18 months, so reliabilty is now a small worry.
Use
I have used the jet 5 times now in the last 100 cross country flights, with the longest retrieve about 220km straight line through dead air, I climbed from about 1000' agl in light rain, flying at about 70kts ias. I continued climbing up to about 11000' amsl, or 6000' agl and switched off the jet.. I burned 30 liters of fuel. I estimate that a 380-400km range is possible in dead air. The rain stopped after the first 5km.
General:
Maintenance is all but non existant, apart from the ocasional wipe off to get rid of dust, and a visual pre flight inspection. I had the actuator that extends the engine replaced (under guarantee). Refueling is very easy. I prefer using Jet A1, as I think it is a more efficient fuel, and it smells better 😄. The fuel filter gets cleaned or replaced during the annual inspection.
Noise in the cockpit is not intrusive, even when wearing no earplugs or a headset. The radio can be heard clearly through the normal speakers, as can the vario. Noise on the ground during a flypast is less than the traditional internal combustion engine. It gets noisy when doing a stationary ground runs, but no more than a prop driven self launcher.
When the jet has not been in use for an extended period, a ground start before flight is advisable to purge the fuel supply of air, ensuring an immediate start in the air.
As the glow plug and fuel pump needs constant current during operation, it is advisable to have your battery charged up.
The jet goes from master on to full power in 45 seconds. Idle rpm is 30 000 rpm, and full power delivers just under 100k rpm. I normally limit the rpm to 95k. At 95k rpm the fuel burn is 40liters per hour, and fuel capacity is 42 liters. Fuel burn drops to about 35 liters per hour at 9000' amsl. Exhaust gas temprerature is about 650 deg celcius at full power. Temperature change on the vertical tail skin is minimal, even on the ground as the engine is slightly offset.
On the test aircraft, during the endurance test, which was flown for an hour above 20 000' amsl and at 110 000 rpm continously, a blade did separate from the rotor. The blade was contained in the housing with no other damage to the engine or glider. This specific engine had run all the certification tests before throwing the blade. I dont know how many hours it had, but it was significant.
I can honesly say this is the best system if you want to avoid landouts. The airfield I fly from mostly has a tug available, so I dont need a self launcher. Apart from the simplicity and efficiency of the jet, the biggest factor is the sheer joy of playing around with the jet running.

Hi Oscar,

A very helpful post but you mention "at 95k rpm the fuel burn is 40liters per hour".

Is it not about 60 litres per hour at that rpm and the potential range calculation correspondingly reduced?

John Galloway