Jet Glider Sparrowhawk

Alan Baker wrote:

Project Dog Whistle. LOL

And Bill rightly points out that if the thrust
is behind the CG, any yaw at low speeds means
a ground loop on takeoff unless the tailwheel is
firmly tracking.

No it doesn't. The thrust is always directed through the centre of mass.

It's position of the main wheel with respect to the CM that matters for
a ground loop...

Alan Baker

Correct. I'm mixing apples and oranges. In our Sparrowhawk design,
the engine(s) thrust is through the center of mass, so this
doesn't matter.

I wonder about the Genesis mock-up, where this may not be the case.

Vaughn wrote:

One more reason why the twin Cri-cri version had it
right, with the two engines well ahead of the
CG, and with exhaust away from anything that might burn.

But introduces the possibility (certainty?) of asymmetric thrust! I
saw a Cri-cri (piston) lose power on TO one year at Oshkosh, it crashed
almost at the crowd line.

Vaughn

Probably because the Cri-cri is such a terrible glider...
A lot in common with the BD-5: rotation speed = Vne = Va =
Vmc = Vs... (or nearly so). ;( The Gruman Yankee also had
critical speeds close together, and the Speed Canard had a
real high stall speed too. One of the reasons I LOVE gliders
is the generally low stall speed.

Some full size regional jets, and the RC models that use the
little turbines, have placed the twin turbines very close
together and near the rear with no blast towards surfaces.
It would be great to put turbine(s) on the tail of the Sparrowhawk,
but the CG would never, ever work...

Alas, back to the drawing board...

"Mark James Boyd" wrote in message
news:40057f22$1@darkstar...
Vaughn wrote:

One more reason why the twin Cri-cri version had it
right, with the two engines well ahead of the
CG, and with exhaust away from anything that might burn.

But introduces the possibility (certainty?) of asymmetric thrust! I
saw a Cri-cri (piston) lose power on TO one year at Oshkosh, it crashed
almost at the crowd line.

Vaughn

Probably because the Cri-cri is such a terrible glider...

Probably so, but I see I was not clear in my above post. The Cri-cri
apparently lost power in one engine only, the one towards the crowd. We
were sitting at the crowd line, but at the other end of the field, so we
were not among the menaced. Looking at the Cri-cri, the engines look close
enough together that you would think that asymmetric thrust would not be a
problem; apparently not so.

Vaughn

In article 40057c28$1@darkstar,
(Mark James Boyd) wrote:

Alan Baker wrote:

Project Dog Whistle. LOL

And Bill rightly points out that if the thrust
is behind the CG, any yaw at low speeds means
a ground loop on takeoff unless the tailwheel is
firmly tracking.

No it doesn't. The thrust is always directed through the centre of mass.

It's position of the main wheel with respect to the CM that matters for
a ground loop...

Alan Baker

Correct. I'm mixing apples and oranges. In our Sparrowhawk design,
the engine(s) thrust is through the center of mass, so this
doesn't matter.

I wonder about the Genesis mock-up, where this may not be the case.

How can it really be otherwise?

And what's more, a ground loop is cause when the main wheel -- ahead of
the CM -- develops a sideways force which causes further yaw, which
causes larger sideways force, etc.

Even mounted off the CM laterally, and engine would still be fixed to
the fuselage and hence the yaw force would be *constant*.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

On 13 Jan 2004 10:55:44 -0700, (Mark James Boyd)
wrote:



www.usamt.com

In the specifications I also see a AT1500 engine that delivers 670 N @
75,000 rpm.
Should be more than enough thrust to modify my DDT into a DDJ ?

"Ruud Holswilder" wrote in message
...
On 13 Jan 2004 10:55:44 -0700, (Mark James Boyd)
wrote:



www.usamt.com

In the specifications I also see a AT1500 engine that delivers 670 N @
75,000 rpm.
Should be more than enough thrust to modify my DDT into a DDJ ?

If not, you can add the afterburner! (re-heat)

Bill Daniels

Early models of the KC-135 tanker used water injection
on takeoff for added thrust. No idea how much additional
thrust could be gained by adding this to a 45Lb thrust
turbine but it wouldn't increase fuel consumption the
way an afterburner would. How about a cowling around
the jet and water could be sprayed or misted onto the
exhaust section. Could the steam then mix with the
exhaust well enough to increase thrust or would it
be a perpetual motion add on?

If not, you can add the afterburner! (re-heat)

Bill Daniels

The water was injected into the combustion chamber, not the exhaust.
Evaporation increased the pressure in the chamber without increasing
temperature too much. In the 70's, there has been a spectacular accident of
a Lockheed Tristar outbound Hamburg where the mechanics put fuel ino the
according tanks instead of water - resulting in all three engines failing
during the initial climb, and the aircraft passing underneath a bridge of a
local highway. Partially passing, that is :-(

--
Bert Willing

ASW20 "TW"


"Steve Davis" a écrit dans le message
de ...
Early models of the KC-135 tanker used water injection
on takeoff for added thrust. No idea how much additional
thrust could be gained by adding this to a 45Lb thrust
turbine but it wouldn't increase fuel consumption the
way an afterburner would. How about a cowling around
the jet and water could be sprayed or misted onto the
exhaust section. Could the steam then mix with the
exhaust well enough to increase thrust or would it
be a perpetual motion add on?

If not, you can add the afterburner! (re-heat)

Bill Daniels

I had no appreciation for how much water was injected until I saw the fire
go out in a KC-135 engine one day when they hit the water after throttle up.
Quite a splash.

Frank Whiteley

"Bert Willing" wrote in
message ...
The water was injected into the combustion chamber, not the exhaust.
Evaporation increased the pressure in the chamber without increasing
temperature too much. In the 70's, there has been a spectacular accident
of
a Lockheed Tristar outbound Hamburg where the mechanics put fuel ino the
according tanks instead of water - resulting in all three engines failing
during the initial climb, and the aircraft passing underneath a bridge of
a
local highway. Partially passing, that is :-(

--
Bert Willing

ASW20 "TW"


"Steve Davis" a écrit dans le
message
de ...
Early models of the KC-135 tanker used water injection
on takeoff for added thrust. No idea how much additional
thrust could be gained by adding this to a 45Lb thrust
turbine but it wouldn't increase fuel consumption the
way an afterburner would. How about a cowling around
the jet and water could be sprayed or misted onto the
exhaust section. Could the steam then mix with the
exhaust well enough to increase thrust or would it
be a perpetual motion add on?

If not, you can add the afterburner! (re-heat)

Bill Daniels

Water injection works but glowing shock diamonds in an afterburners exhaust
would be cool. Noisy, but cool.

Bill Daniels

"Steve Davis" wrote in message
...
Early models of the KC-135 tanker used water injection
on takeoff for added thrust. No idea how much additional
thrust could be gained by adding this to a 45Lb thrust
turbine but it wouldn't increase fuel consumption the
way an afterburner would. How about a cowling around
the jet and water could be sprayed or misted onto the
exhaust section. Could the steam then mix with the
exhaust well enough to increase thrust or would it
be a perpetual motion add on?

If not, you can add the afterburner! (re-heat)

Bill Daniels