A small experiment

[Mike Borgelt]

Would anyone like to carry out the following experiment?
Upon touchdown on a sealed runway, close the brakes, don't use the
wheel brake and see how far the glider rolls.
If you feel like doing this please let me know the results and include
glider type, approximate weight, wind, altitude, temperature, slope.
I'm trying to find out the frictional forces acting on the glider on
the ground as part of the ongoing jet project. Some statistics would
be nice.
Thanks.
Progress seems to be rapid amongst the jet engine manufacturers in the
last few months with one 22Kg thrust engine available and two 25 Kg
engines in development including one with a really neat 11 stage axial
flow compressor.
I'm convinced these micro turbines are a breakthrough, disruptive
technology for soaring.
We have a small group in SE Queensland working on applying these
engines to gliders.

Mike Borgelt

[BTIZ]

"Mike Borgelt" > wrote in message
...
<snip> Would anyone like to carry out the following experiment?> We have a
small group in SE Queensland working on applying these
> engines to gliders.
<snip>

I believe someone already did .. with the "Silent"

BT

[Marc Ramsey]

BTIZ wrote:
> I believe someone already did .. with the "Silent"

You mean the "Not So Silent" 8^)

Marc

[BTIZ]

yes... I believe you can here it whine on the video..

BT

"Marc Ramsey" > wrote in message
. com...
> BTIZ wrote:
> > I believe someone already did .. with the "Silent"
>
> You mean the "Not So Silent" 8^)
>
> Marc

[Leon McAtee]

Mike Borgelt > wrote in message >...

> Progress seems to be rapid amongst the jet engine manufacturers in the
> last few months with one 22Kg thrust engine available and two 25 Kg
> engines in development including one with a really neat 11 stage axial
> flow compressor.
> I'm convinced these micro turbines are a breakthrough, disruptive
> technology for soaring.

> Mike Borgelt

Is there a web site where one could get an update?

I also think that small jets have lots of potential for self-launch
use but rather than increase the efficency of the small turbines with
multi stage compressors (fuel use is rather unimportant IMHO)I'd like
to see one of the micro turbine manufactures develop a high bypass
version. What we need for glider use is higher mass flow at low
speeds.
======================
Leon McAtee

[Mike Borgelt]

On 21 May 2004 21:12:14 -0700, (Leon McAtee)
wrote:

>Mike Borgelt > wrote in message >...
>
>> Progress seems to be rapid amongst the jet engine manufacturers in the
>> last few months with one 22Kg thrust engine available and two 25 Kg
>> engines in development including one with a really neat 11 stage axial
>> flow compressor.
>> I'm convinced these micro turbines are a breakthrough, disruptive
>> technology for soaring.
>
>> Mike Borgelt

If you go to www.airtoi.com and click on the turbine specs you will
get to most of the known manufacturers.

Also check www.nybro.com.au for the axial compressor.

Also www.jet-rpm.com
>
>Is there a web site where one could get an update?
>
>I also think that small jets have lots of potential for self-launch
>use but rather than increase the efficency of the small turbines with
>multi stage compressors (fuel use is rather unimportant IMHO)I'd like
>to see one of the micro turbine manufactures develop a high bypass
>version. What we need for glider use is higher mass flow at low
>speeds.

Not necessarily. Higher thrust for the same fuel consumption isn't bad
either.
The turbofan is likely much more complicated and expensive. Most
turbofans are two shaft engines which basically means one engine built
inside the other or an aft fan/turbine(see the original Whittle
inventions).
Fuel consumption is OK for our use as is and turbojets have a slower
drop off in thrust with airspeed.

I'm aware of the jet Silent but it isn't that relevant as it is a
lightweight glider. Our interest is in retrofits of existing 15/18m
motorless sailplanes.

Towing to measure the drag forces on the ground will be done by
members of the group.

Measuring ground roll is actually very neat and elegant as the drag
forces are integrated over the length of roll.

As for regulatory requirements in the US and Australia we have
Experimental Air racing/exhibition.

There is a Caproni A21(non powered) jet conversion project going on in
Australia already. I saw it fly a couple of years ago. This has a
single engine similar to the one in the A21SJ but an allegedly
improved installation. I have some time in the original Caproni built
jet.

I've heard the small turbines run and they aren't that bad, confirmed
by consulting some of the model airplane jet people.

The crash loads design the mount for the engines but unlike propellor
motor gliders the moments are low and the crash loads are only about
twice the normal thrust loads. The sort of structural margin you would
need anyway.

That should answer most of the point raised.

Thanks for the roll data so far.

Mike Borgelt

[bsquared]

See www.silentwingsairshows.com. I saw it fly at Turf. Wasn't a really
impressive climb rate, but it did climb.

"BTIZ" > wrote in message
news:_Burc.5849$7y5.5751@fed1read03...
>
> "Mike Borgelt" > wrote in message
> ...
> <snip> Would anyone like to carry out the following experiment?> We have a
> small group in SE Queensland working on applying these
> > engines to gliders.
> <snip>
>
> I believe someone already did .. with the "Silent"
>
> BT
>
>

[Michael Stringfellow]

This would probably be easy to measure with a spring balance and a tow rope.

The forces you need once airborne can readily be calculated - for instance,
an 800 pound glider with a 40:1 L/D has 20 pounds of drag. If you assume
this increases 50% with a deployed engine, this increases to 30 pounds of
drag. So a single engine with 40 to 45 pounds of thrust would probably be a
minimal sustainer. Two such engines would give you a climb rate in the
hundred feet a minute range.

Watching the jet-powered Silent on its recent visit to Arizona, the problem
appeared to be more the energy needed to accelerate and climb with the
glider's mass than to overcome friction. (The noise wasn't objectionable,
by the way. Certainly nothing like a pulse jet!)

On the other hand, I know of a Nimbus 3DM that operates from a grass strip
and sometimes uses auto tow to get it airborne to reduce the take-off roll,
so friction on the ground is not negligible.

Mike ASW 20 WA


"Mike Borgelt" > wrote in message
...
> Would anyone like to carry out the following experiment?
> Upon touchdown on a sealed runway, close the brakes, don't use the
> wheel brake and see how far the glider rolls.
> If you feel like doing this please let me know the results and include
> glider type, approximate weight, wind, altitude, temperature, slope.
> I'm trying to find out the frictional forces acting on the glider on
> the ground as part of the ongoing jet project. Some statistics would
> be nice.
> Thanks.
> Progress seems to be rapid amongst the jet engine manufacturers in the
> last few months with one 22Kg thrust engine available and two 25 Kg
> engines in development including one with a really neat 11 stage axial
> flow compressor.
> I'm convinced these micro turbines are a breakthrough, disruptive
> technology for soaring.
> We have a small group in SE Queensland working on applying these
> engines to gliders.
>
> Mike Borgelt

[Mike Borgelt]

On Thu, 27 May 2004 08:59:42 -0700, "Michael Stringfellow"
> wrote:

>This would probably be easy to measure with a spring balance and a tow rope.

We'll do that too but getting a steady reading on rough ground will
likely be difficult.


>
>The forces you need once airborne can readily be calculated - for instance,
>an 800 pound glider with a 40:1 L/D has 20 pounds of drag. If you assume
>this increases 50% with a deployed engine, this increases to 30 pounds of
>drag. So a single engine with 40 to 45 pounds of thrust would probably be a
>minimal sustainer. Two such engines would give you a climb rate in the
>hundred feet a minute range.

Performance calculations for jet are pretty straightforward even
including the effect of thrust fall off with increasing airspeed. You
can calculate that from the mass flow of the engine and sea level
thrust.
>
>Watching the jet-powered Silent on its recent visit to Arizona, the problem
>appeared to be more the energy needed to accelerate and climb with the
>glider's mass than to overcome friction. (The noise wasn't objectionable,
>by the way. Certainly nothing like a pulse jet!)

The Silent has a max gross of 640 lbs according to their website. It
also is only a 31:1 glider. Jets have the interesting characteristic
that the power available increases with airspeed. Unlike propellor
aircraft the best rate of climb speed occurs at relatively high speed
which favors gliders with good performance at high speed.

With two 55lb thrust engines(which are going to be available soon) a
900lb glider will have a sea level climb rate of around 650 feet/min-
at 80 to 100 knots IAS. The takeoff run will be the big issue and the
rolling friction will play a large part in this. Preliminary estimates
are that it won't be all bad and will meet JAR22 in this regard. It
will also have single engine climb capability.

What altitude above sea level and what temperature when you saw the
Silent fly?
>
>On the other hand, I know of a Nimbus 3DM that operates from a grass strip
>and sometimes uses auto tow to get it airborne to reduce the take-off roll,
>so friction on the ground is not negligible.

Having owned one of them and operated off a sealed strip at 2100 feet
on warm days I can say it has no problem. At 5000AMSL it was
considerably less good. At high altiude on grass I can see the
problem.


Mike

[Robert Ehrlich]

Mike Borgelt wrote:
>
> Would anyone like to carry out the following experiment?
> Upon touchdown on a sealed runway, close the brakes, don't use the
> wheel brake and see how far the glider rolls.

If I do that with any glider in my club, it will become airborne
again when I close the brakes.

[Andy Durbin]

Robert Ehrlich > wrote in message >...
> Mike Borgelt wrote:
> >
> > Would anyone like to carry out the following experiment?
> > Upon touchdown on a sealed runway, close the brakes, don't use the
> > wheel brake and see how far the glider rolls.
>
> If I do that with any glider in my club, it will become airborne
> again when I close the brakes.

Land slower?

Andy

[Charles Yeates]

Do you always touch down at excessive speed?

Robert Ehrlich wrote:
> Mike Borgelt wrote:
>
>>Would anyone like to carry out the following experiment?
>>Upon touchdown on a sealed runway, close the brakes, don't use the
>>wheel brake and see how far the glider rolls.
>
>
> If I do that with any glider in my club, it will become airborne
> again when I close the brakes.

[Eric Greenwell]

In article >,
says...
>Do you always touch down at excessive speed?

I don't know about Robert's gliders, but all the ones I have flown
require more airspeed to stay up with the spoilers open (stall speed
about 3 to 4 knots higher) than with them closed. If I land with the
spoilers open, it will be at a higher speed than with them closed. For
this reason, and if the field is long enough, I try to land with the
spoilers closed during a field landing.

So, I think what Robert says is will happen, even for the best pilots.
The solution is to let the glider speed decay below the spoilers in
flying speed before closing them, or to land with them closed.

>Robert Ehrlich wrote:
>> Mike Borgelt wrote:
>>
>>>Would anyone like to carry out the following experiment?
>>>Upon touchdown on a sealed runway, close the brakes, don't use the
>>>wheel brake and see how far the glider rolls.
>>
>>
>> If I do that with any glider in my club, it will become airborne
>> again when I close the brakes.



--
-------
Eric Greenwell USA

[Jack]

Eric Greenwell wrote:

> ...let the glider speed decay below the spoilers-in
> flying speed before closing them, or to land with them closed.

Unless of course one reduces angle of attack while retracting spoilers,
or is that an advanced maneuver that should not be too widely discussed?



Jack

[Eric Greenwell]

In article >, baron58
@sbcglobal.net says...
>Eric Greenwell wrote:
>
>> ...let the glider speed decay below the spoilers-in
>> flying speed before closing them, or to land with them closed.
>
>Unless of course one reduces angle of attack while retracting spoilers,
>or is that an advanced maneuver that should not be too widely discussed?

I think it is, because there is no point to closing the spoilers
completely immediately after a normal touchdown. The reason for doing so
in this case was to measure the drag while rolling after landing.

But to discuss your suggestion: I usually land on the main and the tail
wheel (or just the tailwheel), and keep the tail on the ground with back
stick. To reduce the angle of attack, I would have to raise the tail off
the ground. I haven't tried it purposely (I sometimes did it
inadvertently on my ASW 20 C when braking hard), since I haven't
encountered any situation where it would be of value, but I think it
could be done on most gliders.

--
-------
Eric Greenwell USA

[Robert Ehrlich]

Andy Durbin wrote:
>
> Robert Ehrlich > wrote in message >...
> > Mike Borgelt wrote:
> > >
> > > Would anyone like to carry out the following experiment?
> > > Upon touchdown on a sealed runway, close the brakes, don't use the
> > > wheel brake and see how far the glider rolls.
> >
> > If I do that with any glider in my club, it will become airborne
> > again when I close the brakes.
>
> Land slower?
>
> Andy

With open airbrakes, I can't land slower. With closed airbrakes,
it would take more than the 1km runway to decrease the speed
at the point the glider is no more airborne, if the approach
was done with the standard safety speed margin (stall speed plus
30%) and with half airbrakes.

[justsoaring]

Mike.

Ventus 2cxt.
aprox 450m ground roll.
Bitumen (11/29 x strip int to 29 threshold)
No brakes (wheel or air)(slight drag on wheel disk)
Nil wind.
Tip dragged for 20m

:) Mark R


--
justsoaring
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