HTHL vs VTVL - Wheeled sled for landing?

Len wrote:
Charles Buckley wrote in message ...

Earl Colby Pottinger wrote:


snip

I favor either a skid or wheeled landing for a HL independant of
any ground mechanism. The way to improve glader landing characteristics
is to maximize L/D and reduce ground speed, then stick with landing
zones that have multiple vectored approaches to allow for better
crosswind options.


If the returning vehicle is light enough and slow enough,
then I think that air recovery--perhaps with a helicopter
--is more practical than trying to line up with a sled on
the ground. As a pilot, I am much happier with a couple
of minutes, rather than ten seconds, to match speeds and line
up with the recovery vehicle.



That makes sense. Capture is not that uncommon a method for
pulling items into aircraft.

Can see a few ways to do it depending on the size of the
respective vehicles. One is the basic parachute capture. The
other would be a modification of the boom where the vehicle
is pulled into the mother aircraft. If their relative speeds
are slow enough, a simple docking like they used in the 1930's
for LTA would also work. Someone pointed out an interesting idea
of a nuetrally bouyant return vehicle. I like that idea also.


Relative speeds are far more important than absolute speeds.
However, this seems to scare non-pilot types a bit. Military
pilots learn to fly in tight formation at high subsonic speeds
and in almost any attitude. It's fun.


Hmm. I'll point out that an unpowered glider with a very bad
L/D ratio is still going to have some very serious constraints on
it's absolute speed that will affect the timing of the capture. With
very low L/D, the ground is much easier to match velocities with..
(They'll end up doing that one way, or another...)

Len wrote:
Charles Buckley wrote in message ...

Earl Colby Pottinger wrote:


snip

I favor either a skid or wheeled landing for a HL independant of
any ground mechanism. The way to improve glader landing characteristics
is to maximize L/D and reduce ground speed, then stick with landing
zones that have multiple vectored approaches to allow for better
crosswind options.


If the returning vehicle is light enough and slow enough,
then I think that air recovery--perhaps with a helicopter
--is more practical than trying to line up with a sled on
the ground. As a pilot, I am much happier with a couple
of minutes, rather than ten seconds, to match speeds and line
up with the recovery vehicle.



That makes sense. Capture is not that uncommon a method for
pulling items into aircraft.

Can see a few ways to do it depending on the size of the
respective vehicles. One is the basic parachute capture. The
other would be a modification of the boom where the vehicle
is pulled into the mother aircraft. If their relative speeds
are slow enough, a simple docking like they used in the 1930's
for LTA would also work. Someone pointed out an interesting idea
of a nuetrally bouyant return vehicle. I like that idea also.


Relative speeds are far more important than absolute speeds.
However, this seems to scare non-pilot types a bit. Military
pilots learn to fly in tight formation at high subsonic speeds
and in almost any attitude. It's fun.


Hmm. I'll point out that an unpowered glider with a very bad
L/D ratio is still going to have some very serious constraints on
it's absolute speed that will affect the timing of the capture. With
very low L/D, the ground is much easier to match velocities with..
(They'll end up doing that one way, or another...)

Earl Colby Pottinger wrote in message ...
(Len) :

Earl Colby Pottinger wrote in message
...

In the case of a flying sled can they be brought together without the
airflow between the two crafts messing up the fine control needed?

With air recovery, a tow line is an option--and that can avoid
airflow intereactions.

But now the landing craft needs to carry it's landing gear, that is what I
was trying to avoid.

But now the landing gear can be quite simple and light.
Your air bag idea might even work--with the air bag
on the sled.

...snip...
The early Discover(?) satellite capsules were recovered
with a C-130. This sort of worked even though the capsule
was traveling vertically (from a parachute) and the C-130
was basically traveling horizontally.

Were they very heavy?

I think they were quite small.

Best regards,
Len (Cormier)
PanAero, Inc.
(replace x with len) ( http://www.tour2space.com )

Earl Colby Pottinger

Charles Buckley wrote in message ...
Len wrote:
Charles Buckley wrote in message ...

Earl Colby Pottinger wrote:


snip

I favor either a skid or wheeled landing for a HL independant of
any ground mechanism. The way to improve glader landing characteristics
is to maximize L/D and reduce ground speed, then stick with landing
zones that have multiple vectored approaches to allow for better
crosswind options.


If the returning vehicle is light enough and slow enough,
then I think that air recovery--perhaps with a helicopter
--is more practical than trying to line up with a sled on
the ground. As a pilot, I am much happier with a couple
of minutes, rather than ten seconds, to match speeds and line
up with the recovery vehicle.



That makes sense. Capture is not that uncommon a method for
pulling items into aircraft.

Can see a few ways to do it depending on the size of the
respective vehicles. One is the basic parachute capture. The
other would be a modification of the boom where the vehicle
is pulled into the mother aircraft. If their relative speeds
are slow enough, a simple docking like they used in the 1930's
for LTA would also work. Someone pointed out an interesting idea
of a nuetrally bouyant return vehicle. I like that idea also.


Relative speeds are far more important than absolute speeds.
However, this seems to scare non-pilot types a bit. Military
pilots learn to fly in tight formation at high subsonic speeds
and in almost any attitude. It's fun.


Hmm. I'll point out that an unpowered glider with a very bad
L/D ratio is still going to have some very serious constraints on
it's absolute speed that will affect the timing of the capture. With
very low L/D, the ground is much easier to match velocities with..
(They'll end up doing that one way, or another...)

Most of the configurations that I would consider practical
will have an L/D of at least 7 or so--and some would have
an L/D of ten or so in the hookup configuration.

Best regards,
Len (Cormier)
PanAero,Inc.
(replace x with len) ( http://www.tour2space.com )

[Thought I'd sent this response a couple days ago, but it appears I
bobbled the buttons -d]

Earl Colby Pottinger wrote in message ...
(dave schneider) :

I suspect that at "reasonable" landing speeds, the lateral tracking of
the sled will be limited by how tight a turn it can make before it
starts tipping. Of course, a wide-and-low sled won't tip *over* very
easily, but it will probably tip enough to affect wheel loading, which
may feed into speed control as well as steering forces.

First, what do you consider reasonable? 100-200 KPH are easy speeds for a
wheeled platform to reach and maintain. Second, what tight turns? Where do
you see aircraft come in for a landing where they are not just basicly moving
in a straight line? So why would tracking be a problem? By the way don't
forget all-wheel steering.


At 200KPH, a turning radius can still be quite large relative to the
length of the vehicle (or your ordinary highway turn) and still be
"tight". A 100KPH landing sounds awfully slow except for quite
light-weight vehicles.

And I also suspect that the difference in speed between lander and
sled has to be *very* small to avoid in-track shear forces, and the
sled may have to be *very* heavy to avoid the lander's lift from
picking it up, which implies tensile strength for the capture.

I don't think you are thinking of the same thing/design as me. In the final
seconds of landing there would be *zero* land speed diffirence between the
sled and the landing craft. The lander is in affect is lowering itself onto
the sled.

To what precision are you measuring? I think +/- 1 KPH would be
extreme precision, and the masses involved mean that there would be
quite a bit of tensile and shear strains.


Why would the lander lift the sled? As soon as it lands it does the same
thing all airplanes do to stay on the runway and not take off again.


As most airline passengers can attest, airplanes tend to bounce
slightly whne they are making the transistion from flying to wheeling.
Even a little bounce would introduce tensile strains.

Then there's the length of the landing strip. It needs to be long
enough to be able to brake (w/wheels or drag (chutes)) without
exceeding that tensile strength. Add in the mile to get the sled up
to speed, and it looks like Bonneville *might* have enough room.

??? North America atleast has tons of flat open space to drive such a craft.
Also someone else has suggested making the sled a hovercraft which makes
every large lake a landing site.

The Bonneville reference means nothing to me. What is that in reference to?


Well, Bonneville Salt Flats are the most suitable such flat open
space, being unusually flat and open. That's why they are popular
with the land speed record people (dang, I can't remember anyone more
recent than Craig Breedlove, at least by name). Edwards has a
prepared strip used for shuttle landings which would be flat enough,
but it may not be long enough when you include the space to get the
sled up to speed.

I would guess that this is not impossible, but I do have doubts about
about it being practical.

I doubt it is practical but to me your objections did not seem well founded.
(Tight turns?)

Consider the difference in how controllable your car is when your
fingers twitch at 50 KPH vs 100 KPH. Now replace your car with
something the size of a convoy of 18-wheelers travelling twice as
fast, and consider the tipping moments and the reaction time and the
edge of the tread digging into the surface, and it doesn't take much
of a turn to be tight.

/dps

Earl Colby Pottinger writes:

How big and fast can skids go?

Much faster than wheels --- all high-speed rocket sleds use skids, not wheels.

The problem with skids is, skids are not nearly as re-usable as wheels are...


Is water cooling possible with them?

Lots of things are _possible_. The =REAL= question is, is this _PRACTICAL_
given engineering and mass constraints ???


-- Gordon D. Pusch

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