Jet Glider Sparrowhawk

Bill Daniels wrote:

Have you math whizzes figured out how far the wing runner will have to run
before this dog whistle is going fast enough to have aileron control?

Well, we've got a name for the project!

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.

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.

In article 4004fb99$1@darkstar,
(Mark James Boyd) wrote:

Bill Daniels wrote:

Have you math whizzes figured out how far the wing runner will have to run
before this dog whistle is going fast enough to have aileron control?

Well, we've got a name for the project!

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...


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.


--
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."

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.

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."

"Mark James Boyd" wrote in message
news:4004fb99$1@darkstar...
Bill Daniels 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

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