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Js3 jet catastrophic failure.



 
 
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  #31  
Old September 1st 18, 11:44 AM posted to rec.aviation.soaring
Martin Gregorie[_6_]
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Posts: 699
Default Js3 jet catastrophic failure.

On Fri, 31 Aug 2018 18:15:06 -0700, Dave Nadler wrote:

On Friday, August 31, 2018 at 7:11:23 PM UTC-4, Martin Gregorie wrote:
...or join the winch queue....
Admittedly that needs a dedicated team (winch driver, cable truck
driver,
launch marshal and one or two guys on golf buggies...


And a site where this is practical, plus enough pilots to support the
operation... All not available in many locales.


Sure, but from what I see on r.a.s, winching seems to be making some
headway in America.

The minimum launch requirement is three people: winch driver, launch
marshal/wing runner and the glider pilot who, if needed, can tow out the
cable he launches from. IOW, not much different from aero towing except
that nobody in their right mind or half out of it would ever start a
winch launch with a wingtip on the ground.


--
Martin | martin at
Gregorie | gregorie dot org
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  #32  
Old September 1st 18, 02:58 PM posted to rec.aviation.soaring
Jonathan St. Cloud
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Posts: 1,463
Default Js3 jet catastrophic failure.

On Saturday, September 1, 2018 at 3:44:39 AM UTC-7, Martin Gregorie wrote:
On Fri, 31 Aug 2018 18:15:06 -0700, Dave Nadler wrote:

On Friday, August 31, 2018 at 7:11:23 PM UTC-4, Martin Gregorie wrote:
...or join the winch queue....
Admittedly that needs a dedicated team (winch driver, cable truck
driver,
launch marshal and one or two guys on golf buggies...


And a site where this is practical, plus enough pilots to support the
operation... All not available in many locales.


Sure, but from what I see on r.a.s, winching seems to be making some
headway in America.

The minimum launch requirement is three people: winch driver, launch
marshal/wing runner and the glider pilot who, if needed, can tow out the
cable he launches from. IOW, not much different from aero towing except
that nobody in their right mind or half out of it would ever start a
winch launch with a wingtip on the ground.


--
Martin | martin at
Gregorie | gregorie dot org


The cross wind on this thread has blown us on too an entirely different subject, while worthwhile. Course correction: Anyone know the cause of the turbine failure first mentioned in this thread? How much damage was done to the airframe when the engine failed? Have the problems of not starting at altitude been understood and resolved? Has anyone had these failure and care to comment?
  #33  
Old September 1st 18, 03:26 PM posted to rec.aviation.soaring
[email protected]
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Posts: 374
Default Js3 jet catastrophic failure.

On Saturday, September 1, 2018 at 2:58:31 PM UTC+1, Jonathan St. Cloud wrote:
On Saturday, September 1, 2018 at 3:44:39 AM UTC-7, Martin Gregorie wrote:
On Fri, 31 Aug 2018 18:15:06 -0700, Dave Nadler wrote:

On Friday, August 31, 2018 at 7:11:23 PM UTC-4, Martin Gregorie wrote:
...or join the winch queue....
Admittedly that needs a dedicated team (winch driver, cable truck
driver,
launch marshal and one or two guys on golf buggies...

And a site where this is practical, plus enough pilots to support the
operation... All not available in many locales.


Sure, but from what I see on r.a.s, winching seems to be making some
headway in America.

The minimum launch requirement is three people: winch driver, launch
marshal/wing runner and the glider pilot who, if needed, can tow out the
cable he launches from. IOW, not much different from aero towing except
that nobody in their right mind or half out of it would ever start a
winch launch with a wingtip on the ground.


--
Martin | martin at
Gregorie | gregorie dot org


The cross wind on this thread has blown us on too an entirely different subject, while worthwhile. Course correction: Anyone know the cause of the turbine failure first mentioned in this thread? How much damage was done to the airframe when the engine failed? Have the problems of not starting at altitude been understood and resolved? Has anyone had these failure and care to comment?


High altitude starts - see my earlier replies. The M&D jet is not intended to be started above 10,000 feet asl according to the manual and it starts fine up to at least 9,500 feet asl in my experience as long as a fuel that suits the climate is used. Mine was very unreliable hot on high in SA with Jet A1 and unreliable in cold UK weather on standard diesel but worked 100% until sold in both situations on premium synthetic (gas-to-oil)/mineral diesel (which, for clarity, is not bio-diesel). It was someone from the JS factory that told me a couple of years ago to use Shell V-Power Nitro diesel when I asked for help while in SA as that was what they used.
  #34  
Old September 1st 18, 06:31 PM posted to rec.aviation.soaring
Bruce Hoult
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Posts: 961
Default Js3 jet catastrophic failure.

On Saturday, September 1, 2018 at 3:44:39 AM UTC-7, Martin Gregorie wrote:
On Fri, 31 Aug 2018 18:15:06 -0700, Dave Nadler wrote:

On Friday, August 31, 2018 at 7:11:23 PM UTC-4, Martin Gregorie wrote:
...or join the winch queue....
Admittedly that needs a dedicated team (winch driver, cable truck
driver,
launch marshal and one or two guys on golf buggies...


And a site where this is practical, plus enough pilots to support the
operation... All not available in many locales.


Sure, but from what I see on r.a.s, winching seems to be making some
headway in America.

The minimum launch requirement is three people: winch driver, launch
marshal/wing runner and the glider pilot who, if needed, can tow out the
cable he launches from. IOW, not much different from aero towing except
that nobody in their right mind or half out of it would ever start a
winch launch with a wingtip on the ground.


I expressed that opinion at one club recently and was told, no we do it regularly.

It might not be too dangerous if the winch technique was adjusted to give an initial acceleration to 20 or 30 knots for a couple of seconds before giving it full noise, possibly in response to an "all out" radio call.

But I got the impression they didn't bother with anything like that.
  #36  
Old September 1st 18, 08:33 PM posted to rec.aviation.soaring
WB
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Posts: 236
Default Js3 jet catastrophic failure.

nobody in their right mind or half out of it would ever start a
winch launch with a wingtip on the ground.


I expressed that opinion at one club recently and was told, no we do it regularly.

It might not be too dangerous if the winch technique was adjusted to give an initial acceleration to 20 or 30 knots for a couple of seconds before giving it full noise, possibly in response to an "all out" radio call.

But I got the impression they didn't bother with anything like that.


Sorry to contribute to thread drift, but I just have to respond.

Launching with a wing tip down is probably the number 1 "NEVER DO" in winch launching. It only takes a brief snag of the down wingtip and the up wingtip will accelerate and fly over the top. The glider becomes a giant hammer with the cockpit as the hammerhead driven into the ground at high speed. When this happens, it is all over in a couple of seconds and is nearly always fatal. Same thing for dropping a wing on a winch launch. Release immediately if a wingtip drops on a winch launch (Should never happen with a properly driven launch as the very rapid acceleration makes the ailerons effective almost immediately).
  #37  
Old September 1st 18, 10:08 PM posted to rec.aviation.soaring
Martin Gregorie[_6_]
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Posts: 699
Default Js3 jet catastrophic failure.

On Sat, 01 Sep 2018 12:33:32 -0700, WB wrote:

Launching with a wing tip down is probably the number 1 "NEVER DO" in
winch launching. It only takes a brief snag of the down wingtip and the
up wingtip will accelerate and fly over the top. The glider becomes a
giant hammer with the cockpit as the hammerhead driven into the ground
at high speed. When this happens, it is all over in a couple of seconds
and is nearly always fatal. Same thing for dropping a wing on a winch
launch. Release immediately if a wingtip drops on a winch launch (Should
never happen with a properly driven launch as the very rapid
acceleration makes the ailerons effective almost immediately).


Yes, agreed. I've never seen a cartwheel and hope I never do.

At my club you're likely to be having a talk with an instructor if your
tip gets within 30cm (12") of the ground. We use 8 litre Skylaunch
winches with Spectra rope and like 'brisk' acceleration, so things do
happen quite fast.


--
Martin | martin at
Gregorie | gregorie dot org
  #38  
Old September 1st 18, 10:55 PM posted to rec.aviation.soaring
AS
external usenet poster
 
Posts: 653
Default Js3 jet catastrophic failure.

On Saturday, September 1, 2018 at 6:44:39 AM UTC-4, Martin Gregorie wrote:
On Fri, 31 Aug 2018 18:15:06 -0700, Dave Nadler wrote:

On Friday, August 31, 2018 at 7:11:23 PM UTC-4, Martin Gregorie wrote:
...or join the winch queue....
Admittedly that needs a dedicated team (winch driver, cable truck
driver,
launch marshal and one or two guys on golf buggies...


And a site where this is practical, plus enough pilots to support the
operation... All not available in many locales.


Sure, but from what I see on r.a.s, winching seems to be making some
headway in America.

The minimum launch requirement is three people: winch driver, launch
marshal/wing runner and the glider pilot who, if needed, can tow out the
cable he launches from. IOW, not much different from aero towing except
that nobody in their right mind or half out of it would ever start a
winch launch with a wingtip on the ground.


--
Martin | martin at
Gregorie | gregorie dot org


Total subject drift now but I have to respond to that one: I am actively involved in (re)-introducing winching in the US and am trying to teach safe procedures mostly based on the German set of rules. That is an absolute 'No-No' and many fatal accidents have resulted from this!
On the other hand, I should say 'go ahead - do it!' - It may be Darwin at work but it will give winching a bad wrap (again).

Uli
'AS'
  #39  
Old September 2nd 18, 06:39 PM posted to rec.aviation.soaring
2G
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Posts: 1,439
Default Js3 jet catastrophic failure.

On Thursday, August 30, 2018 at 10:44:06 PM UTC-7, wrote:
Watch this.....and consider your life.

https://youtu.be/oYpG0HDcFsA


That video claims that "the model jet engine is a scaled down version of the real thing. It is essentially the same technology that lifts enormous aircraft into the sky." This couldn't be anymore further from the truth. Watch this video and tell me that they are "essentially the same technology:"
https://www.youtube.com/watch?v=VfomloUg2Gw

What struck me on the models is that the most vital components, the fan and compressor blades, are manufactured out of aluminum. Aluminum is not a high temperature metal. One pilot who had multiple start failures of these jets told me that ONE problem was the clearance between the fan blades and the housing, which must be tight to begin with for the jet to work. The shear number of failures I have personally heard of convinced me that I would not a jet sustainer.

Tom
  #40  
Old September 2nd 18, 10:32 PM posted to rec.aviation.soaring
Mike Borgelt[_2_]
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Posts: 29
Default Js3 jet catastrophic failure.

On Monday, 3 September 2018 03:39:58 UTC+10, 2G wrote:
On Thursday, August 30, 2018 at 10:44:06 PM UTC-7, wrote:
Watch this.....and consider your life.

https://youtu.be/oYpG0HDcFsA


That video claims that "the model jet engine is a scaled down version of the real thing. It is essentially the same technology that lifts enormous aircraft into the sky." This couldn't be anymore further from the truth. Watch this video and tell me that they are "essentially the same technology:"
https://www.youtube.com/watch?v=VfomloUg2Gw

What struck me on the models is that the most vital components, the fan and compressor blades, are manufactured out of aluminum. Aluminum is not a high temperature metal. One pilot who had multiple start failures of these jets told me that ONE problem was the clearance between the fan blades and the housing, which must be tight to begin with for the jet to work. The shear number of failures I have personally heard of convinced me that I would not a jet sustainer.

Tom


The reason the compressor and diffuser are aluminum is because they do not get very hot. The compressor is usually a truck turbo compressor made by Honeywell or Garrett. IIRC Honeywell bought Garrett.
Yes the principles on which the small jets operate are the same as large ones although the small ones are turbojets with no fan, just a centrifugal compressor which is much less fussy about inlet flow distortion and much more robust than a small axial compressor would be to debris impact. At least one small axial compressor engine of about 27 Kg thrust has been made though.. It was intended to drive an alternator in a hybrid car to be made by Jaguar and fuel consumption was an issue hence the axial compressor to get higher pressure ratios. You could get higher pressure ratios by using a two stage centrifugal compressor (second stgae compressor needs to be steel)but nobody ever made a turbojet like this although the Rolls Royce Dart turboprop had this configuration.
The small engines are pretty much small scale models of the De Havilland Goblin engine from 1943 (it was a good engine)which shared their layout of single stage centrifugal compressor and single stage axial flow turbine, the difference is the small engines have a cannular combustion chamber instead of individual burner cans.
Modern turbofans use axial compressors for higher pressure ratios for better fuel economy. They operate at far higher temperatures in the hot end with actively cooled turbine blades by blowing cool air through them which comes out in many small holes. The turbine stage can operate at temperatures above the melting point of the blades. They also do things like blow ducted air around the outside of the turbine shroud to minimise clearances.
In the small engines the weakness is the rear bearing which is in the turbine wheel. It is the one that gets hot. Possible solution is to not run at 100%, where the turbine temperatures are much higher than at 75% to 85%.
There are now several engines in the thrust range required (around 40Kgf) made by AMT, TJ, Jetcat and BF Turbine. The BF 500 in particular is actually a 50 Kgf engine derated to 40 Kgf.
It is early in the development cycle for glider use. There are only the SharkJet with an AMT Titan, The PSR system and the M&D jet on the JS gliders.
One weakness is the kero start system on all these which is why fuel and vapor pressure and flash point of same is important and they are fussy on fuel. The M&D jet used to splatter fuel around. JS solution was to drill a nice hole in the bottom of the engine compartment. Latterly they have put the igniter in the bottom of the engine rather than the top and made a small improvement. I can see why. Kero or diesel can make a pretty good fire extinguisher in the right circumstances and can be difficult to get burning. There are possible solutions.
Chris Esselsteyn doesn't seem to be having much trouble with the 2 x Jetcat P300 engines in his HP18 jet but jetcat have an internal igniter which seems to work well. he told me he gets essentially no excess fuel on start. He was at Oshkosh with it again this year.
I suspect a large proportion of failures with the jets is poor operating procedures(dirt in fuel) and or poor/non existent inspections.
The other jet that needs mention is the TJ100 engine that Bob Carlton uses and sells. That engine has a real recirculating oil system and seems excellent. Being used in the SubSonex jet kitplane too. It started life as the APU for the MiG 29.

Mike
 




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