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Why does SS1 need the drag configuration?

Posted by: roygrif - Mon Aug 02, 2004 8:15 pm
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Why does SS1 need the drag configuration? 
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Post Why does SS1 need the drag configuration?   Posted on: Mon Aug 02, 2004 8:15 pm
The X-15 had no such ability and landed fine. Curious as to why SS1 needs the drag configuration.

Also, am i right in thinking that SS1 could never survive a re-entry from a true high orbit?

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Post    Posted on: Mon Aug 02, 2004 8:55 pm
Just for fun, I posed the question to Scaled. Of course, they may be way too busy to post a reply. But we'll see.

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Post    Posted on: Mon Aug 02, 2004 9:22 pm
JustMeKevin wrote:
Just for fun, I posed the question to Scaled. Of course, they may be way too busy to post a reply. But we'll see.

Suprised it's never been brought-up before. Thanks for emailing them.

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Post    Posted on: Mon Aug 02, 2004 9:44 pm
Some of these other guys may know the answer off-hand. But I'm certainly no real engineer. Just a software one :lol:

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Post Re: Why does SS1 need the drag configuration?   Posted on: Tue Aug 03, 2004 12:45 am
roygrif wrote:
The X-15 had no such ability and landed fine. Curious as to why SS1 needs the drag configuration.

Also, am i right in thinking that SS1 could never survive a re-entry from a true high orbit?


The only part that I know about the first bit is that the X-15 was meant to withstand much more than SpaceShipOne. The drag configuration on SS1 partially has to do with keeping the ship from overheating, because like you said in the 2nd bit, SS1 wouldn't be able to handle it. The forces that a ship would go through on reentry would propel the craft to such a high speed that SS1 would melt as it is now. The X-15 was designed (with the technology available then) to withstand those forces, and they still managed to just about burn the tail off of it at Mach 6.7... so now consider that after a full orbital reentry, the speed would be about Mach 18 and I think SS1 would have a little bit of a problem. :shock:

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Post    Posted on: Tue Aug 03, 2004 12:56 am
Doesn't answer the question about the X-15, but I though I'd post it anyway... from the Scaled Tier 1 Site:

Quote:
Why do you "fold" the wings to come back down?

In space, the wings are folded up to provide a shuttle-cock or "feather" effect to give the ship extremely high drag for reentry. This allows the reentry deceleration to occur at a higher altitude and greatly reduces the forces and heating on the structure. Also, the ship, in the feathered configuration, will align itself automatically such that the pilot has a less-critical flight control task. We refer to this as "care-free reentry". The atmosphere orients the vehicle to a belly-first attitude without pilot input. Another benefit is that, since the altitude is higher, the pilot can glide further after the entry deceleration. A SpaceShipOne pilot can glide more than 60 miles after he converts back to the non-feathered glider shape.

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Post    Posted on: Tue Aug 03, 2004 7:13 am
I myself a few weeks ago sent an e-mail to Scaeld too and I got an answer very quickly - less than one day. One of my questions were the physics behand the feather-technique.

The person responding said not to be a physicist and bacaus of this not to be able to answer this question. The other questions were sufficiently answered.

Hello, eraurocktchick87,

it's very nice that you are quoting Scaled.

I did so in a german fore and a german chemist annoyingly began to try to argue away Scaled's explanation. He seems to be quite ignorant. Perhaps here somebody might explain the physics working behind the feathering.



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Post    Posted on: Tue Aug 03, 2004 8:46 am
I'm not a physicist either, but I do have some knowledge of aerodynamics. I guess the feathered position is a controlled stall (the rudders and elevator-stabilators have still authority)

The feathered tail causes a nose-up pitching moment. However, the plane's natural behaviour is to pitch nose down; the center of aerodynamic forces acting on the plane lie behind the center of gravity.

As the plane slows down, the authority of the tail decreases, thus the pitching moment decreases. The forces acting on the plane will still cause pitching down moment. The plane will descend in an attitude where the moments cancel each other out.

F1A free flight gliders actually use a bit similar technique; at the set time (180 seconds) the horizontal stabilizer will rotate to a large negative angle, stalling the plane and bringing it down in a gentle, belly-first stall.


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Post    Posted on: Tue Aug 03, 2004 9:02 am
Which way does this cause the effect of high drag and deceleration at high altitude? As I am understanding Scaled's explanation without the feathering deceleration will occur later at lower alttitudes. The annoyingly arguing chemist didn't believe the high drag effect and the deceleration at higher altitude.



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Post    Posted on: Tue Aug 03, 2004 3:05 pm
Scaled's answer seems acceptable. However the "feathered drag" configuration would be useless for a true re-entry from a real geo orbit. I wonder if Scaled is working on a ship that can withstand a true re-entry?

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Post    Posted on: Tue Aug 03, 2004 5:24 pm
Ekkehard Augustin wrote:
The annoyingly arguing chemist didn't believe the high drag effect and the deceleration at higher altitude.


*heh* All we can say to that is, "Hey, it works". And of, course, I think I would trust Rutan and his team over and above a chemist :D

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Post    Posted on: Tue Aug 03, 2004 5:32 pm
roygrif wrote:
I wonder if Scaled is working on a ship that can withstand a true re-entry?


Well, the whole $20-million project is called "Tier One"...... Unless, of course, I'm the only one who thinks that name implies other "Tiers" are forthcoming.......

SSO flips its tail up for the same reason that the Shuttle zigzags on re-entry. The heat generated by moving through the atmosphere is related directly to two factors: how thick the atmosphere is, and how fast the vehicle is moving. Increase either factor, you increase the heat the vehicle has to withstand. Thus, the quick and dirty solution to this problem is to try and avoid both: slow down while you're still in the upper (thinner) atmosphere.

Considering that both SSO and the Shuttle are designed to fly (meaning that if you move them at a sufficient speed, they'll begin to drift upwards), slowing down is actually pretty hard: since they're falling, they want to pick up more speed. There are three effective (and therefore traditional) ways for a pilot to burn airspeed: one, to pull the aircraft into a steep climb; and two, to execute a scissors, which is defined as a series of jinks, which themselves are short, sharp jerks in any direction (old fighter pilot slang there). The third is to activate the craft's mechanical air- or dive-brakes, as appropriate (if they're equipped).

Now, a steep climb won't work in a reentry, because the vehicle isn't yet generating enough lift to do more than tilt a little bit. Besides that, as you descend, you'll gain most of your airspeed back again. Thus, the Shuttle executes a long, extended scissors maneuver, swerving back and forth to use up the extra airspeed.

[hypothesis]Rutan, realizing that extra airspeed would require extra shielding (which, in turn, weighs more), decided to build divebrakes into SSO. However, the divebrakes required would be so massive that he instead turned the entire rear portion of the wing/tail structure into super-sized divebrakes.[/hypothesis] By rotating up about 60 degrees, the rear wing portion effectively kills all lift created by the vehicle, causing the tail to drop, and turning the entire vehicle into a really big parachute. Also, because the design orients itself to the proper attitude (meaning SSO doesn't need to be controlled on reentry), this system allows the pilot to relax during the single most strenuous flight period.

All in all, SSO's re-entry system is truly a work of genius.

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Post    Posted on: Tue Aug 03, 2004 7:20 pm
Hey Hey :!:

Burt Rutan took time out of his very busy schedule to answer my question, along with some others. The following reply seems to be a combined answer of several questions RE the X-15...

Burt Rutan wrote:
The x-15 cannot be compared to SpaceShipOne directly since its goal was
not just to go to 100 KM, but to fly high-mach research out to mach 8
(actual max mach was 6.7). The x-15 flew only two flights above 100 km,
two consecutive flights by Joe Walker. I do not doubt that the price
per flight of x-15 was 3M$, since it was a government research program.
The price per flight during the research program of SS1 after 4 powered
flights is about 300k$, or 100k$ per seat (less than 4% of x-15 costs).

We chase with a donated Starship (for launch) and an Extra (small
aerobatic aircraft, used to chase landing). The Alpha jet is used by
our customer for video documentation. The White Knight is our B52.

Since the x-15 could not survive a steep descent into the atmosphere
after flying to 100 KM, it had to fly 300 miles away to allow a 40
degree climb and descent. SpaceShipOne can survive an vertical plunge,
thus its entire flight can be within 25 miles of the landing airport.

The hybrid motor developed for the SS1 is simple compared to the Liquid
motor on the X-15. It has one valve and redundant igniters. It has
never failed to start.

X-15 had to be very carefully flown during entry in order to survive.
SS1 will reenter safely even if the pilot is a spectator, i.e., it
reenters fine by itself without pilot control. The fatal accident that
killed Mike Adams in the x-15 would not have been an accident in SS1.

SS1 has no metal in its structure. It would need additional thermal
protection to survive the x-15's max speed of Mach 6.7.

White did not fly above 100km, only above 50 miles, then considered
space by the US Government. Only Walker flew above 100 Km. Walker was
killed when he ran his F-104 into the B-70 in 1966. The X-15 he flew
above 100km was the one that killed Adams. Thus there are no remaining
X-15s that have flown to space.

We will have expensive barnstorming with suborbital ships within the
next five years. Suborbital flights will become affordable (less than
30,000 $) within 12 to 15 years.

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Post    Posted on: Tue Aug 03, 2004 9:46 pm
I like answers that come from the horses mouth. I didn't know that SS1 had a non-mettalic body. I presume it must be some sort of carbon composite then?

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Post    Posted on: Tue Aug 03, 2004 10:40 pm
*heh* Yeah. Thus the company name Scaled Composites. I assume Voyager was made of the same (or similar) materials.

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