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Js3 jet catastrophic failure.



 
 
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  #51  
Old September 6th 18, 05:58 PM posted to rec.aviation.soaring
John Seaborn (A8)[_2_]
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Posts: 6
Default Js3 jet catastrophic failure.

Good information on the pump. Can you expand on this a bit? What voltages are needed on the pump for a normal start on the M&D Jet? What makes sense for tuning based on fuel, jet vs. diesel? What is the best way to monitor the voltage to the pump under power?
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  #52  
Old September 7th 18, 09:11 AM posted to rec.aviation.soaring
David Salmon[_3_]
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Posts: 54
Default Js3 jet catastrophic failure.

At 16:58 06 September 2018, John Seaborn A8 wrote:
Good information on the pump. Can you expand on this a bit? What voltages
a=
re needed on the pump for a normal start on the M&D Jet? What makes sense
f=
or tuning based on fuel, jet vs. diesel? What is the best way to monitor
th=
e voltage to the pump under power?


I've been reading this long long thread, as I'm on a gliding holiday and
the weather could be better.
Something not mentioned, pertinent, but not to the reliability problem, is
noise. May not matter too much in the wide open spaces, but can be a bit
anti-social in the UK. We had a Shark jet fly from our club, and it could
be heard at 2 to 3 times the distance of a Solo engine. I have flown a bT
for 11 years, it has never failed to start, except for human error. Of
course one day it might fail, so advice given in this thread is good.
As to winch launching, which I have survived for over 50 years and into 5
figures, taking off with a wing on the ground is only for those with
suicidal tendencies. I have witnessed the result.
Look at the simulated videos on the BGA web site, under Safe Winch
Launching. No need to re-invent the wheel.
Dave

  #53  
Old September 7th 18, 02:42 PM posted to rec.aviation.soaring
kinsell
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Posts: 546
Default Js3 jet catastrophic failure.

On 09/07/2018 02:11 AM, David Salmon wrote:
At 16:58 06 September 2018, John Seaborn A8 wrote:
Good information on the pump. Can you expand on this a bit? What voltages
a=
re needed on the pump for a normal start on the M&D Jet? What makes sense
f=
or tuning based on fuel, jet vs. diesel? What is the best way to monitor
th=
e voltage to the pump under power?


I've been reading this long long thread, as I'm on a gliding holiday and
the weather could be better.
Something not mentioned, pertinent, but not to the reliability problem, is
noise. May not matter too much in the wide open spaces, but can be a bit
anti-social in the UK. We had a Shark jet fly from our club, and it could
be heard at 2 to 3 times the distance of a Solo engine. I have flown a bT
for 11 years, it has never failed to start, except for human error. Of
course one day it might fail, so advice given in this thread is good.
As to winch launching, which I have survived for over 50 years and into 5
figures, taking off with a wing on the ground is only for those with
suicidal tendencies. I have witnessed the result.
Look at the simulated videos on the BGA web site, under Safe Winch
Launching. No need to re-invent the wheel.
Dave


I mentioned both the noise and the fuel consumption. Seen two jets run
out of fuel on self-retrieves, even though neither had done a sef-launch.

And yes winching starting with a wing down is a terrible idea. Our club
had a two-place Grob drop a wing during launch, pilot didn't release in
time, and bent the fuselage in half.
  #54  
Old September 9th 18, 05:16 AM posted to rec.aviation.soaring
Mike Borgelt[_2_]
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Posts: 29
Default Js3 jet catastrophic failure.

On Friday, 7 September 2018 23:43:00 UTC+10, kinsell wrote:
On 09/07/2018 02:11 AM, David Salmon wrote:
At 16:58 06 September 2018, John Seaborn A8 wrote:
Good information on the pump. Can you expand on this a bit? What voltages
a=
re needed on the pump for a normal start on the M&D Jet? What makes sense
f=
or tuning based on fuel, jet vs. diesel? What is the best way to monitor
th=
e voltage to the pump under power?


I've been reading this long long thread, as I'm on a gliding holiday and
the weather could be better.
Something not mentioned, pertinent, but not to the reliability problem, is
noise. May not matter too much in the wide open spaces, but can be a bit
anti-social in the UK. We had a Shark jet fly from our club, and it could
be heard at 2 to 3 times the distance of a Solo engine. I have flown a bT
for 11 years, it has never failed to start, except for human error. Of
course one day it might fail, so advice given in this thread is good.
As to winch launching, which I have survived for over 50 years and into 5
figures, taking off with a wing on the ground is only for those with
suicidal tendencies. I have witnessed the result.
Look at the simulated videos on the BGA web site, under Safe Winch
Launching. No need to re-invent the wheel.
Dave


I mentioned both the noise and the fuel consumption. Seen two jets run
out of fuel on self-retrieves, even though neither had done a sef-launch.

And yes winching starting with a wing down is a terrible idea. Our club
had a two-place Grob drop a wing during launch, pilot didn't release in
time, and bent the fuselage in half.



A few of comments:
Nobody with the current jet sustainers has made the slightest attempt at noise reduction.
Landing out is rapidly becoming anti-social too. I've seen one piston self launcher run out of fuel and land out too. Lots more have had the engine fail to start and when the piston engine is extended the L/D becomes not much better than a Cessna with an engine failure.

It is 2018. Why are we even talking about winch launching?

If you want more than 100Km range you are better off to replace the extra fuel with a second engine and just climb fast, then shut down and retract the engines
and use the excellent glider L/D to fly further. Alternatively use a bigger engine so the thing has a decent climb rate. the downside of that is if you must fly level, jet engines have poor SFC when throttled below about 70%. Two engines have advantages as you only need one to avoid an outlanding. If the start failure probability is 2% failing to get one out of two running is 1 in 2500.
Two also means it self launches. You need a thrust to weight ratio of about 0.13 or better, optimally 0.14 to 0.15 and actually full thrust ratio of around 0.18 or so which allows de-rated operation. Some attempts have not had this and I've been amazed at the projects that have been done where no estimated performance calculations were done. It isn't quite as easy as you might think as the best rate of climb for an optimal jet self launcher is in the region 90 to 100 knots.
It is also important to minimise the drag of the extended engines as this can have large effect on achieved rate of climb at these higher airspeeds. Gliders are very slick and it doesn't take much to make them perform worse.
I have a nice spreadsheet that lets you enter the glider mass, polar, jet thrust, temperature, pressure, runway surface, slope, extended engine drag increment and gives rate of climb vs IAS and liftoff distance and to 50 feet at 1.3Vs. What sketchy reports I've got on the jet projects' actual performance seems to validate it.

Mike



  #55  
Old September 9th 18, 05:44 AM posted to rec.aviation.soaring
AS
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Posts: 653
Default Js3 jet catastrophic failure.


It is 2018. Why are we even talking about winch launching?


Mike


------------

Because not all of us are independently wealthy and can plop down a couple big ones to get a jet retrofitted into our ships or even purchase a new glider with that factory option!

Uli
'AS'
  #56  
Old September 9th 18, 07:41 AM posted to rec.aviation.soaring
Mike Borgelt[_2_]
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Posts: 29
Default Js3 jet catastrophic failure.

On Sunday, 9 September 2018 14:45:00 UTC+10, AS wrote:
It is 2018. Why are we even talking about winch launching?


Mike


------------

Because not all of us are independently wealthy and can plop down a couple big ones to get a jet retrofitted into our ships or even purchase a new glider with that factory option!

Uli
'AS'


Also very workload intensive and dangerous.

Mike

  #57  
Old September 9th 18, 08:44 AM posted to rec.aviation.soaring
Paul T[_4_]
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Posts: 259
Default Js3 jet catastrophic failure.

At 06:41 09 September 2018, Mike Borgelt wrote:
On Sunday, 9 September 2018 14:45:00 UTC+10, AS wrote:
It is 2018. Why are we even talking about winch launching?


Mike


------------

Because not all of us are independently wealthy and can plop down a

couple big ones to get a jet retrofitted into our ships or even purchase

a
new glider with that factory option!

Uli
'AS'


Also very workload intensive and dangerous.

Mike



Yeah that's why nearly every club in Europe has one.

  #58  
Old September 9th 18, 09:47 AM posted to rec.aviation.soaring
Bruce Hoult
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Posts: 961
Default Js3 jet catastrophic failure.

On Saturday, September 8, 2018 at 11:41:43 PM UTC-7, Mike Borgelt wrote:
On Sunday, 9 September 2018 14:45:00 UTC+10, AS wrote:
It is 2018. Why are we even talking about winch launching?


Mike


------------

Because not all of us are independently wealthy and can plop down a couple big ones to get a jet retrofitted into our ships or even purchase a new glider with that factory option!


Also very workload intensive and dangerous.


Hmm. I don't think the figures bear out winch launching be any more dangerous than aerotow. A different set of dangers, certainly -- you don't get much time to reject the launch while still at a safe height if the glider doesn't seem to be flying right, but on the other hand you'll never find yourself low and slow just past the fence and pointing away from the field.

Modern winches give modern gliders a very high chance of contacting lift if there is lift around. And if there isn't then why are you flying? (at least you find out cheaply)

  #59  
Old September 9th 18, 12:26 PM posted to rec.aviation.soaring
Dave Walsh
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Posts: 83
Default Js3 jet catastrophic failure.

Off topic but in Europe, including the UK, some gliding sites are
"winch only" for planning or noise reasons. However the
primary reason that many other clubs have winches is that
winching is cheap compared to EU aerotow costs.

If the aerotow costs are high enough you can don rose
coloured spectacles and use man-maths to show that even
self-launchers make economic sense.

I fly at Sisteron, French Alps, each aerotow would be 50-60€,
minimum, tow a bit further/higher and the cost can be 80€
plus. Take 40 launches a year = ~2400€.
Dave Walsh


  #60  
Old September 9th 18, 04:43 PM posted to rec.aviation.soaring
Jonathan St. Cloud
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Posts: 1,463
Default Js3 jet catastrophic failure.

On Sunday, September 9, 2018 at 4:30:11 AM UTC-7, Dave Walsh wrote:
Off topic but in Europe, including the UK, some gliding sites are
"winch only" for planning or noise reasons. However the
primary reason that many other clubs have winches is that
winching is cheap compared to EU aerotow costs.

If the aerotow costs are high enough you can don rose
coloured spectacles and use man-maths to show that even
self-launchers make economic sense.

I fly at Sisteron, French Alps, each aerotow would be 50-60€,
minimum, tow a bit further/higher and the cost can be 80€
plus. Take 40 launches a year = ~2400€.
Dave Walsh


Wow, those aero tows are cheap compared to a lift ticket in the French Alps!
 




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