G'day Mike & Dion
STATIC thrust is thrust at zero airspeed! Jet engines produce a low
thrust at zero airspeed that increases with increasing airspeed up to
a fairly high speed - so the acceleration of the jet ASW20 increases
significantly as airspeed increases up to about 80 kt from my memory
and observation at Waikerie - I saw the same flights as Dion did.
Best rate of climb came at 80 - 90 kt as I recall Allan telling us.
Further, a LAME cannot be self taught or amateur: to get a licence
he/she must undergo a 4-year apprenticeship with a significant
schedule of experience during training - even if the exams are done
by self-study!
The jet sailplanes look interesting, but they still seem to be a good
way to convert fuel into noise. (Even if the other losses are less
than propeller-driven self-launchers) Still a lot more efficient than
hauling 544 or 1200 kg of Eurofox or Pawnee into the air as well -
but I guess one tug is a lot less expensive than 20 or so self-launch units.
Wombat
At 19:39 29/05/2010, Dion Weston wrote:
Alan appears to be astoundingly gifted for a self taught amateur LAME.
The quality of workmanship on that Waikerie sailplane was superb.
Interesting you say the static thrust reduces slowly with airspeed.
The acceleration of the aircraft certainly appeared to increase
following rotation. And once he'd double backed to the threshold and
came across the top of us he indicated afterwards that he was
approaching 120kts and throttling back at that point. By rate he was
pulling away from the chase plane what we could see from the ground
certainly appeared to support this.
Presumably therefore the thrust required in near level flight is a lot
less that the 70Kg.
Would there not be a point of maximum efficiency? For instance the
prop on my ASH reaches max thrust at around 35kts - a compromise
between static thrust at rest being sufficient to overcome stiction
and 51kts - the best speed for climb. Later prop versions are
available with increased max efficiency speeds closer to the 51kts.
Longer ground roll but better climb rate. I had presumed the same
applied for the turbines.
On 29/05/2010, at 18:45 , Mike Borgelt wrote:
Thanks Dion,
I'm downloading it now.
Allan Hudson showed me in and out of cockpit video earlier this
month when we flew in to Waikerie and stayed with him and Marie
overnight.
I had a good look at the installation then. Apparently the ignition
difficulties were caused by a really bad batch of LPG(approximately
50/50 propane butane mix when it is good. Not certain what was in
what he got). He's located a source of pure propane since and things
are much better.
I got to start an AMT Olympus in late 2006 in a test cell and it lit
off right away just with the glowplug. In Perth last August we
tested the spark ignition on butane and had absolutely no problems.
That was with my prototype spark unit which fired about 4 times a
second and an unmodified spark plug. I've since modified the spark
unit to fire 60 times a second and the spark jumps from the centre
electrode to the plug body so we have a nice 3 mm arc. Testing as
soon as I have the engine mounts fabricated.
At full throttle Allan has about 70Kg thrust available. This is just
a little less than a TOP (76Kg) static thrust but the difference is
that the jet thrust only decreases slowly with increasing airspeed
where the TOP is down to 44KG at 50 knots. Hence the slower initial
ground roll.
Mike
Borgelt Instruments - manufacturers of quality soaring instruments
since 1978
phone Int'l + 61 746 355784
fax Int'l + 61 746 358796
cellphone Int'l + 61 428 355784
email: mborg...@borgeltinstruments.com
website: www.borgeltinstruments.com
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