Js3 jet catastrophic failure.

I've never managed to find an image of the current JetCat igniter, not for lack of trying. I suspect it is a flat heated strip with fuel sprayed on to it as droplets which would seem much better.

The older JetCat igniter is just a rod and always seemed to work work well on both kero and diesel. I am not sure if they changed the igniter for the newer RXi with internally mounted solenoids.

There is only one pump which requires a certain minimum voltage to start but then produces too much flow rate into the igniter resulting in excess fuel.

I'm glad you mention the pump. Turbine is one thing but the pump and its settings are the key to successful starts(of course together with a good battery). The pump voltages(sometimes referred to as pump power) supplied at different start stages are critical to getting a reliable start. Too much and you get a flaming hot start, too little and it wont stay lit and restarts thereafter result in residual fuel and another hot start. Getting it just right is a tuning process(through various params in the ecu and also depends on fuel type) but is also complicated with breakin of the pump over time in the case of new pumps. So as an owner, monitoring the pump power during operation so as to monitor "pump health" is fairly important. Think we all agree clean filtered fuel is must but they can and do wear out. I've had one with 200 hundred runs overshoot on rapid throttle advance and never expected to see 6 foot of flame out the back which actually extinguished the engine. After a new pump, all was good again after a retune.

On Thursday, 6 September 2018 01:29:45 UTC+10, wrote:
There is only one pump which requires a certain minimum voltage to start but then produces too much flow rate into the igniter resulting in excess fuel.

I'm glad you mention the pump.....

Thanks for that. Good information on break in of the pump.

As for close clearances just contemplate the clearances in the crankshaft and bearings of a two stroke or the clearances in the cylinders. BTW your piston engine ought to melt. The fuel burns hotter than the melting point of the metal but there is a boundary layer in the gases at the surface of the metal.

The origins of the M&D engine mentioned are in accordance with what I was told by someone who ought to know.
Last time I looked the certification on jets for sustainer use was that it wasn't allowed to blow up or catch fire. M&D seem to handle the blow up bit by limiting the number of cycles before overhaul. HpH in the Sharkjet went the ballistic shielding route.
The turbine blade of a Titan weighs about the same and moves at the same speed as a standard velocity 0.22 rifle bullet. It was fun doing ballistic shielding tests. 1 mm of 4130 dents but does not break. 8 layers of 170 gm Kevlar catches the bullet. Interesting.

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?

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

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.

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

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'

One potential problem with multiple jets is if one starts while the other doesn’t but pumps fuel through.
Good engineering may help but there is a known issue there. (PM)