Jet turbine reliability

On Monday, June 8, 2015 at 4:44:10 PM UTC+1, bumper wrote:
On Sunday, June 7, 2015 at 12:29:34 PM UTC-7, wrote:
OG--thanks for your input.


Once you buy Jet A, how long would you keep the fuel before you would consider it "bad"?

Self launch and turbo gliders sometimes have low fuel throughput, and this gives HUMs (hydrocarbon utilizing microbes) a chance to thrive in the fuel/water interface - and there will always be some moisture. HUMs have been an issue for Stemme and Schleicher owners, as the HUMs excrete acid that can corrode metal parts and they attack fuel lines and clog filters.

The shelf life of Avgas (at least a year) and Jet-A (even longer) in the US is not the issue, it's keeping the microbes from contaminating fuel and fuel system. Many of us use BioborJF (the JF is for jet fuel for which Biobor is certified - though it works in gasoline too). It only takes 4 ml per 5 gallons for initial dose and then 2 ml per 5 gallons after that.

Note that Biobor also has a "MD" and "EB" version for diesel and ethanol laced fuels, though the "JF" version is the only version I'm aware of that includes antimicrobial ingredients.

That is very interesting Bumper but unfortunately I can't find BioborJF on sale in the UK. I find an 2008 UK magazine review of marine diesel products that has a reference to legislation that meant that "any product which claims a controlling effect on microorganisms should be registered with the Health and Safety Executive (HSE) and by 31 October 2008 they will need a technical dossier confirming the product is safe, environmentally acceptable and effective. Because registration involves significant expense, some biocides such as Biobor JF have been pulled from the market".

Also some US sellers on Ebay or Amazon say they cannot ship it to the UK.

John Galloway

I've never had a problem with microbes/algae. But after using kero/Jet-A and diesel, I just use Chevron diesel now and never had a problem since my engines are rated for all these fuels. Don't forget diesel give you a bit better performance over kero/Jet-A.

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

There was a recent landout of a brand new JS1 in the middle of nowhere near Hobbs during the contest due to jet failure. Multiple attempts were made to start it.
So much for jet reliability. Apparently can't trust them either.
I heard of at least 3 landouts of motorgliders recently.
Hopefully electric motors will be more reliable.

Ramy

On Monday, July 6, 2015 at 1:47:38 PM UTC-7, Ramy wrote:
There was a recent landout of a brand new JS1 in the middle of nowhere near Hobbs during the contest due to jet failure. Multiple attempts were made to start it.
So much for jet reliability. Apparently can't trust them either.
I heard of at least 3 landouts of motorgliders recently.
Hopefully electric motors will be more reliable.

Ramy

HpH 304 Shark jet sustainer owners have reported a very reliable jet start. HpH uses a TBS J40 Engine.

Sean Franke

At 20:47 06 July 2015, Ramy wrote:
There was a recent landout of a brand new JS1 in the middle of nowhere
near
Hobbs during the contest due to jet failure. Multiple attempts were made
to
start it.
So much for jet reliability. Apparently can't trust them either.
I heard of at least 3 landouts of motorgliders recently.
Hopefully electric motors will be more reliable.

Ramy

It would be interesting to know why that jet didn't start and also whether

it had been run in the air or on the ground before the task that day.
The
jet glider pilots I have spoken to don't seem to routinely do test runs but
I
can imagine simple problems that could be found - e.g. airlock in the fuel

line after trailering. The JS1 jet overhaul interval is going to be based
on
number of starts rather than hours so perhaps that is a disincentive. In
22 years I never intentionally took a 2 stroke turbo cross-country without

doing a test run before starting the task. I occasionally uncovered
starting
problems that were easily fixed back on the ground. Any time the turbo
didn't start there was always a straightforward reason for it. At least
the
jets can be started on the ground for a few seconds so a problem could be
found found before taking a launch rather than afterwards.

John Galloway

I don't have more details except that the jet engine was later removed and sent for repair.

Ramy

On Monday, July 6, 2015 at 1:47:38 PM UTC-7, Ramy wrote:
There was a recent landout of a brand new JS1 in the middle of nowhere near Hobbs during the contest due to jet failure. Multiple attempts were made to start it.
So much for jet reliability. Apparently can't trust them either.
I heard of at least 3 landouts of motorgliders recently.
Hopefully electric motors will be more reliable.

Ramy

May be a good thing it didn't light after multiple start attempts.. it's usually the condition under which you'll get a wet start. May not be a big deal in this configuration but depends how much residual fuel was there.

On Monday, July 6, 2015 at 1:47:38 PM UTC-7, Ramy wrote:
There was a recent landout of a brand new JS1 in the middle of nowhere near Hobbs during the contest due to jet failure. Multiple attempts were made to start it.
So much for jet reliability. Apparently can't trust them either.
I heard of at least 3 landouts of motorgliders recently.
Hopefully electric motors will be more reliable.

Ramy

I am interested in knowing which type of motorgliders and was a start attempted vs landing because there was insufficient altitude for a restart. My experience is that engine restart is very reliable because you have the benefit of windmilling to spin the prop faster (I know nothing about the jets). Most failures to start are the result of pilot error (myself included). But everything mechanical is subject to failure (that includes towplanes!).

Tom

On Tuesday, July 7, 2015 at 4:46:43 PM UTC-4, 2G wrote:
On Monday, July 6, 2015 at 1:47:38 PM UTC-7, Ramy wrote:
There was a recent landout of a brand new JS1 in the middle of nowhere near Hobbs during the contest due to jet failure. Multiple attempts were made to start it.
So much for jet reliability. Apparently can't trust them either.
I heard of at least 3 landouts of motorgliders recently.
Hopefully electric motors will be more reliable.

Ramy

I am interested in knowing which type of motorgliders and was a start attempted vs landing because there was insufficient altitude for a restart. My experience is that engine restart is very reliable because you have the benefit of windmilling to spin the prop faster (I know nothing about the jets). Most failures to start are the result of pilot error (myself included). But everything mechanical is subject to failure (that includes towplanes!).

Tom

It's a frikkin jet..... not much "windmilling" going on within VNE of the glider........

Guess you didn't read most of the thread...... ;-)