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#21
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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...) |
#22
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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...) |
#23
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HTHL vs VTVL - Wheeled sled for landing?
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 |
#24
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HTHL vs VTVL - Wheeled sled for landing?
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 ) |
#25
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HTHL vs VTVL - Powered wheeled sled for landing?
[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 |
#26
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HTHL vs VTVL - Wheeled sled for landing?
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 perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
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