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Jet turbine reliability



 
 
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  #51  
Old June 8th 15, 10:44 AM posted to rec.aviation.soaring
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Default Jet turbine reliability

On Sunday, June 7, 2015 at 4:15:05 PM UTC+10, Craig Lowrie wrote:
Climb and glide with the Jet is NOT optimal...



Actually my spreadsheet says that climb/glide is the optimal method even with the jet. I was somewhat surprised by this as with piston retractable engined motorgliders it obviously is as the L/D with engine extended is so bad.. Airplane range is a function of a number of things and L/D is a big one (see Breguet range equation). The L/D with the extended jets would seem to be much better but you don't operate it at best L/D for the climb as the jet best rate of climb speed is very much higher than with a piston engine (thrust drop off with speed is much less and power to aircraft = forward speed x thrust). The single engine jet turbos have much lower thrust to weight than a self launcher so use most of the thrust to stay in level flight particularly if you throttle back to be easier on the jet, so climb/glide probably doesn't work so well there.
There is another consideration and that is the specific fuel consumption of the engine. Jets don't do deep throttling well and 70% is about as low as you want to go before the SFC starts to go bad. This is a good reason for two engines on the self launcher. Just shut down and retract one if you need to fly level because of airspace or meteorological considerations.

One benefit of the high climb airspeed is that you aren't waffling around in a high drag configuration near the stall.

Unless you have a very high thrust/weight, 200 knots is way above the best rate of climb speed for a glider.

To make CS22 takeoff performance you a a T/W of about 0.13 to 0.14. So to let you run the engine(s) at say 70% for takeoff and climb the nominal installed T/W needs to be about 0.18 to 0.20 . This gives reasonable takeoff distance with margin over CS22 and an excellent climb rate at around 100 knots for a modern glider.

As my Ventus has the motorglider CM wings I chose to put the fuel in the fuselage rather than in the wings. Operationally easier when operating out of trailer and no mods to the wings. Weights and speeds are all within the Ventus CM envelope.

Whilst a piston self launcher will use less fuel the jet is comparable to aerotow for launch. Not surprising as the efficiency of the jet is 10 to 11% of fuel energy and SO IS A PAWNEE doing an aerotow.

The jet compares very favorably with a car retrieve also and flying back home in your jet is way more fun than a car retrieve.

I'm not the least little bit interested in retrieve only jets. As a friend of mine once said about the turbo concept: 10% of the utility and 90% of the trouble of a self launcher.





  #52  
Old June 8th 15, 01:08 PM posted to rec.aviation.soaring
Bruce Hoult
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Default Jet turbine reliability

On Monday, June 8, 2015 at 12:44:48 PM UTC+3, wrote:
On Sunday, June 7, 2015 at 4:15:05 PM UTC+10, Craig Lowrie wrote:
Climb and glide with the Jet is NOT optimal...



Actually my spreadsheet says that climb/glide is the optimal method even with the jet. I was somewhat surprised by this as with piston retractable engined motorgliders it obviously is as the L/D with engine extended is so bad.


I'm glad someone else worked this out. You're pretty clean with a jet, but it's most efficient at as close to Vne as you dare to go, so your L/D is probably only 15 - 20, whereas once you shut the jet off you'll want to fly at a speed where your L/D is 40+ (well, 30+ anyway).

Running a jet to sustain level flight at 60 - 80 knots is silly, unless that's all the thrust it has, but even then a slightly more powerful jet that lets you go faster will use less fuel.

  #53  
Old June 8th 15, 01:25 PM posted to rec.aviation.soaring
Bruce Hoult
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Default Jet turbine reliability

On Saturday, June 6, 2015 at 8:04:07 AM UTC+3, wrote:
I've been working on the jet glider concept for over 10 years.


I find it interesting to compare against this post I made on rocket engine launch, just over 15 years ago!

https://groups.google.com/forum/#!or...I/r3mTaAhMSDcJ


Yes if one engine makes a turbo, two make a self launch and two are better than one even if the installation is a little more difficult. As a slight bonus two Titans of 400N each are in fact cheaper than one Nike of 800N thrust from the same manufacturer.


There, I worked out that 50 kgf (490 N) was not enough for adequate launch performance, but 100 kgf (980 N) looked pretty nice. 160 kg (1570 N) would be nice if you could get it, but much over that starts to make everything just happen waaay too fast.

So your 400 N and 800 N are in the same ballpark I worked out waaay back when.
  #54  
Old June 8th 15, 01:42 PM posted to rec.aviation.soaring
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Default Jet turbine reliability

On Monday, June 8, 2015 at 11:44:48 AM UTC+2, wrote:
I'm not the least little bit interested in retrieve only jets. As a friend of mine once said about the turbo concept: 10% of the utility and 90% of the trouble of a self launcher.


It's rather 10% of the trouble, at least with the many selflaunchers and turbos I know of. A Solo 2350 can run many years with minimal maintenance and no major issues, something that doesn't seem to happen with selflaunchers very often...
  #55  
Old June 8th 15, 01:52 PM posted to rec.aviation.soaring
Tango Whisky
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Default Jet turbine reliability

Am Montag, 8. Juni 2015 14:25:59 UTC+2 schrieb Bruce Hoult:
On Saturday, June 6, 2015 at 8:04:07 AM UTC+3, wrote:
I've been working on the jet glider concept for over 10 years.


I find it interesting to compare against this post I made on rocket engine launch, just over 15 years ago!

https://groups.google.com/forum/#!or...I/r3mTaAhMSDcJ


Yes if one engine makes a turbo, two make a self launch and two are better than one even if the installation is a little more difficult. As a slight bonus two Titans of 400N each are in fact cheaper than one Nike of 800N thrust from the same manufacturer.


There, I worked out that 50 kgf (490 N) was not enough for adequate launch performance, but 100 kgf (980 N) looked pretty nice. 160 kg (1570 N) would be nice if you could get it, but much over that starts to make everything just happen waaay too fast.

So your 400 N and 800 N are in the same ballpark I worked out waaay back when.


For a piston engine, static thrust in daN is about 2x installed horsepower.
My Ventus cM has 30 hp, and 60 daN is on the low side for takeoff (I know what I'm talking about...). The V2CM and DG800 have 50 hp installed, and from watching them taking off I'd think that 100 daN is on the generous side.

A also was thinking along the lines of Mike Borgelt that in case my Solo engine died on me, two Titan engines would be a nice fit. Space would not be a problem; tank capacity would probably be limited by max mass of no-lifting parts.

Bert TW
  #56  
Old June 8th 15, 04:44 PM posted to rec.aviation.soaring
bumper[_4_]
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Default Jet turbine reliability

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.
  #57  
Old June 8th 15, 05:47 PM posted to rec.aviation.soaring
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Default 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
  #58  
Old June 10th 15, 09:46 PM posted to rec.aviation.soaring
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Default Jet turbine reliability

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.
  #59  
Old July 6th 15, 07:37 PM posted to rec.aviation.soaring
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Default Jet turbine reliability

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

  #60  
Old July 6th 15, 09:47 PM posted to rec.aviation.soaring
Ramy[_2_]
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Default Jet turbine reliability

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
 




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