Jet turbine reliability

On Friday, June 5, 2015 at 3:15:06 AM UTC-7, Craig Lowrie wrote:
The HPH Shark takes 28 liters of Jet A1 + 4% Aeroshell 500. That will
give about 55 minutes cruising at 80-90 knots... The technique is not
climb and glide, rather dolphin flying... pulling up in any residual
energy and in notime you have gained quite a lot of height... It works.
Typically The Shark Jet will do 170km on a tank. The FES version will do
about 100km, whilst the Shark MS (Self Launcher) will do over 300km
on a tank...

Craig

At 08:30 05 June 2015, wrote:
"Gobble as well as gulp...with Jet A at +/- $5 a gallon and AeroShell
560
at $15 a quart that works out to north of $100 to fill up the JS-1"

Well......you could certainly calculate a worst case scenario like that.
But as 11USG of Diesel / 2-stroke (4%) oil mix is flight manual
approved,
this may be a more commonly employed option.

(US prices: 10.6USG @ $2.70 + 0.42USG & $20) is $37.

Glider pilots: Tighter than a fish's a....... :P


For reference, an ASH26E uses about 2 liters for a warm up and climb to 2500 ft agl, and will do 680 Km on its 16 liter tank (according to the book - never had a retrieve that long!). To do that you climb to altitude limits then fold the engine and glide, and repeat as needed. Is the climb performance on a jet significantly better so that the climb and glide technique improves retrieve range over a level cruise?

Climb and glide with the Jet is NOT optimal...

The best speed for the Jet engine is probably over 200 knots (!)....
and whilst this is not possible, the faster the better... so after
briefly climbing away from a field, it is better to accelerate to 80-90
knots and then dolphin-fly, varying speed in accordance with any
residual lift (these is always some)... This technique will produce
the best range...

Craig

At 19:02 06 June 2015, jfitch wrote:
On Friday, June 5, 2015 at 3:15:06 AM UTC-7, Craig Lowrie
wrote:
The HPH Shark takes 28 liters of Jet A1 + 4% Aeroshell 500.
That will=20
give about 55 minutes cruising at 80-90 knots... The technique
is not=20
climb and glide, rather dolphin flying... pulling up in any
residual=20
energy and in notime you have gained quite a lot of height... It
works. =
=20
Typically The Shark Jet will do 170km on a tank. The FES
version will do=
=20
about 100km, whilst the Shark MS (Self Launcher) will do over
300km=20
on a tank...
=20
Craig
=20
At 08:30 05 June 2015, wrote:
"Gobble as well as gulp...with Jet A at +/- $5 a gallon and
AeroShell=20
560
at $15 a quart that works out to north of $100 to fill up the
JS-1"

Well......you could certainly calculate a worst case scenario
like
that.=
=20
But as 11USG of Diesel / 2-stroke (4%) oil mix is flight
manual=20
approved,
this may be a more commonly employed option.=20

(US prices: 10.6USG @ $2.70 + 0.42USG & $20) is $37. =20

Glider pilots: Tighter than a fish's a....... :P


For reference, an ASH26E uses about 2 liters for a warm up and
climb to
250=
0 ft agl, and will do 680 Km on its 16 liter tank (according to the
book -
=
never had a retrieve that long!). To do that you climb to altitude
limits
t=
hen fold the engine and glide, and repeat as needed. Is the climb
performan=
ce on a jet significantly better so that the climb and glide
technique
impr=
oves retrieve range over a level cruise?

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.

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.

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...

Op zaterdag 6 juni 2015 21:02:52 UTC+2 schreef jfitch:
For reference, an ASH26E uses about 2 liters for a warm up and climb to 2500 ft agl, and will do 680 Km on its 16 liter tank (according to the book - never had a retrieve that long!). To do that you climb to altitude limits then fold the engine and glide, and repeat as needed. Is the climb performance on a jet significantly better so that the climb and glide technique improves retrieve range over a level cruise?

Yes. The higher the thrust/weight ratio is, the more it pays off. Best CLIMB speed for example for a 450 kg ship and a 800N jet is way above 100 kts.

For highter thrust/weight ratio's, fuel efficiency goes up too; a dolphining flight can get similar mileage to a decent car, even with the typical fuel burn of such a jet (70 kg/hr for the 800N AMT).

I have seen various slightly different graphs from JS for ways of using their jet but consistently they predict the greatest theoretical range being from a full power climb at around 80 knots and then glide.

Next best is the economical cruise at about 75,000 rpm and around 75-80 knots - similar to the HpH scenario but JS haven't included the dolphining effect. All flight traces I have found of the JS1 jet being used for real life retrieves seem to show it being used for slow climb and cruise around 75 knots.

I am not sure if including extra range from dolphining gives a valid comparison as there is no stated model of the amount of dolphin-worthy lift being flown through. Also I would have thought that if there was enough lift to gain significant range from dolphining I would turn off the jet and get proper netto and STF info to dolphin efficiently - bearing in mind that these computations rely on the polar in the computer being the same as the glider which it clearly isn't with any engine running (even without considering prop/jetwash effects on the fin probe).

What range does JS predict when using these techniques?


On Sunday, June 7, 2015 at 3:12:48 AM UTC-7, wrote:

I have seen various slightly different graphs from JS for ways of using their jet but consistently they predict the greatest theoretical range being from a full power climb at around 80 knots and then glide.

Next best is the economical cruise at about 75,000 rpm and around 75-80 knots - similar to the HpH scenario but JS haven't included the dolphining effect. All flight traces I have found of the JS1 jet being used for real life retrieves seem to show it being used for slow climb and cruise around 75 knots.