HpH 304S JET Videos now on Youtube!

Bob Kuykendall wrote:
On Dec 7, 8:41 am, wrote:

I guess that the heat problem on the tail will clearly appear with the
new engine (twice the thrust of the actual one)-

Ah, and is this idle speculation, or can you demonstrate it?

If, as claimed, the engine burns the same amount of fuel, and it's a
high bypass engine, then my idle speculation is the air temperature at
the tail will be significantly lower.

A turbofan would make the jets much more appealing for glider use,
perhaps at the cost of wider opening in the fuselage.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Oct 29, 10:31*am, "Tim Mara" wrote:
The Jet is a sustainer..not intended as a self launcher in spite of the fact
that nearly all test flights from short 50 foot auto tows..hence the
temperature at the tail is actually no higher than that of a recip engine on
other sustainers and self launch gliders... remember the engine is a
jet...not a rocket....
tim

"Michael Henry" wrote in message

...



How does the vertical fin not get melted by the exhaust?- Hide quoted text -

- Show quoted text -

What is the appeal of a 'sustainer'? They seem to be almost as
expensive as a self-launcher, without the ability to self launch.
It's great not to have to land out, but it seems like an awful lot of
money to spend and still need a tug to get airborne.

In message
,
Uncle Fuzzy writes
snip

What is the appeal of a 'sustainer'? They seem to be almost as
expensive as a self-launcher, without the ability to self launch.
It's great not to have to land out, but it seems like an awful lot of
money to spend and still need a tug to get airborne.

In the UK they can be flown without a PPL or NPPL which saves lots and
lots and lots of money. Also many sites (in the UK if not the US) do
winch launching, which is a lot cheaper than a tow, so you launch, start
the motor (or land back if there's a problem) and motor off to the lift.

BTW the BGA accident database contains plenty of sustainer accidents,
where the P1 was concentrating on trying to get it started for far too
long instead of switching to doing a field landing when they could not
get the engine started.

--
Surfer!
Email to: ramwater at uk2 dot net

On Dec 7, 8:41*am, wrote:

I guess that the heat problem on the tail will clearly appear with the
new engine (twice the thrust of the actual one)

Not necessarily. I'd guess most of the additional static thrust comes
from the fan, rather than a bigger core. This would be likely since
the absolute fuel consumption supposedly is unchanged, which means the
amount of heat energy produced in combustion is more or less
unchanged. With the bigger fan (does the original engine even have a
fan, or is it a straight turbojet?) you might actually get lower temps
due to the mixing of cooler bypass air after the turbine section. In
any event I'm guessing the Hph engineers are aware of what the
temperature parameters are as a melty-tail sailplane would not likely
pass certification. It would be fun to watch though...

9B

keep in mind Jet engines move a LOT of air....a LOT of air and only a very
small amount of the air being moved is actually used in combustion so what
you have is a lot of air....and a small % of (fire) combustion...
tim

wrote in message
...
On Dec 7, 8:41 am, wrote:

I guess that the heat problem on the tail will clearly appear with the
new engine (twice the thrust of the actual one)

Not necessarily. I'd guess most of the additional static thrust comes
from the fan, rather than a bigger core. This would be likely since
the absolute fuel consumption supposedly is unchanged, which means the
amount of heat energy produced in combustion is more or less
unchanged. With the bigger fan (does the original engine even have a
fan, or is it a straight turbojet?) you might actually get lower temps
due to the mixing of cooler bypass air after the turbine section. In
any event I'm guessing the Hph engineers are aware of what the
temperature parameters are as a melty-tail sailplane would not likely
pass certification. It would be fun to watch though...

9B

On Dec 8, 2:30*pm, "Tim Mara" wrote:
keep in mind Jet engines move a LOT of air....a LOT of air and only a very
small amount of the air being moved is actually used in combustion so what
you have is a lot of air....and a small % of (fire) combustion...
tim

Tim already knows this, but just to clarify -- the above description
is true for turbofans, but not for turbojets, the difference being
that a turbofan has (ready for this?) a big fan on the front that
bypasses the compressor, combustor and turbine sections. It is
normally driven by an additional turbine section at the very end of
the engine. The higher the "bypass ratio" the more air goes around the
hot section of the engine. Generally the higher the bypass, the more
static thrust and better specific fuel consumption (lbs of fuel per lb
of thrust per hour) you get, particularly at low speeds and lower
altitudes. Most of these smaller engines are simple turbojets because
you can get away with a single stage compressor and a single turbine.
Lots cheaper to build. I don't have the specs for what Hph is using,
but from Tim's comment perhaps they are already using a turbofan - the
self-launch capable engine certainly is fan with a high(er) bypass.
In any event the simple fact that they have something flying is proof
that you don't need a titanium vertical fin for this to work.

9B

On Dec 8, 4:15*pm, wrote:
On Dec 8, 2:30*pm, "Tim Mara" wrote: keep in mind Jet engines move a LOT of air....a LOT of air and only a very
small amount of the air being moved is actually used in combustion so what
you have is a lot of air....and a small % of (fire) combustion...
tim

Tim already knows this, but just to clarify -- the above description
is true for turbofans, but not for turbojets, the difference being
that a turbofan has (ready for this?) a big fan on the front that
bypasses the compressor, combustor and turbine sections. It is
normally driven by an additional turbine section at the very end of
the engine. The higher the "bypass ratio" the more air goes around the
hot section of the engine. Generally the higher the bypass, the more
static thrust and better specific fuel consumption (lbs of fuel per lb
of thrust per hour) you get, particularly at low speeds and lower
altitudes. *Most of these smaller engines are simple turbojets because
you can get away with a single stage compressor and a single turbine.
Lots cheaper to build. I don't have the specs for what Hph is using,
but from Tim's comment perhaps they are already using a turbofan - the
self-launch capable engine certainly is fan with a high(er) bypass.
In any event the simple fact that they have something flying is proof
that you don't need a titanium vertical fin for this to work.

9B

According to the spec sheet from Turbinenbau Schuberth for the
TBS-400, the engine uses a single compressor and a single-stage
turbine with no fan. The maximum EGT is 720 degrees C. I'm sure things
cool down sufficiently by the time you get to the fin, but I wouldn't
put my hand behind directly behind the engine to see if it's running.

I think in the end jets will replace props for sailplane self-launch,
the greater simplicity and lower weight, plus more favorable
operational considerations count in their favor and the efficiency
tradeoff isn't much of a concern unless you want to go significant
distances.

9B

Uncle Fuzzy wrote:


What is the appeal of a 'sustainer'? They seem to be almost as
expensive as a self-launcher, without the ability to self launch.
It's great not to have to land out, but it seems like an awful lot of
money to spend and still need a tug to get airborne.

Most pilots think they are significantly cheaper to purchase, to
maintain, and to insure. They are lighter, so easier to assemble and
manhandle; they have a wider wing loading, often with both higher *and*
lower wing loadings; and typically, simpler to operate, and more
reliable. In the USA, you don't need a self-launching endorsement to fly
one.

If you can get a tow when and where you want, and don't fly in high
density altitude locations, they are a more attractive alternative to a
self-launcher. They are much more popular in Europe than the USA, in
part because launches are so much easier to get, and because many glider
ports have noise restrictions that prohibit gas powered self-launching.

A sustainer gives you what some of us think is the "best half" of a
powered glider: the ability to fly or explore aggressively without the
worry of an outlanding and a long retrieve. Pilots that haven't flown
motorgliders often underestimate this major feature because it's not an
obvious one, while it's easy for everyone to see the advantage of
self-launching.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Dec 9, 7:23*pm, Eric Greenwell wrote:
Uncle Fuzzy wrote:

What is the appeal of a 'sustainer'? *They seem to be almost as
expensive as a self-launcher, without the ability to self launch.
It's great not to have to land out, but it seems like an awful lot of
money to spend and still need a tug to get airborne.

Most pilots think they are significantly cheaper to purchase, to
maintain, and to insure. They are lighter, so easier to assemble and
manhandle; they have a wider wing loading, often with both higher *and*
lower wing loadings; and typically, simpler to operate, and more
reliable. In the USA, you don't need a self-launching endorsement to fly
one.

If you can get a tow when and where you want, and don't fly in high
density altitude locations, they are a more attractive alternative to a
self-launcher. They are much more popular in Europe than the USA, in
part because launches are so much easier to get, and because many glider
* ports have noise restrictions that prohibit gas powered self-launching.

A sustainer gives you what some of us think is the "best half" of a
powered glider: the ability to fly or explore aggressively without the
worry of an outlanding and a long retrieve. Pilots that haven't flown
motorgliders often underestimate this major feature because it's not an
obvious one, while it's easy for everyone to see the advantage of
self-launching.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes"http://tinyurl.com/y739x4
* * * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

Thanks Eric,
That puts it into a perspective I can understand.