Students' Experiments To Fly By Glider To the Edge of Space

techmage writes: In 2002 Steve Fossett and Einar Enevoldson set the altitude record for a glider climbing to 42,000 feet in the Perlan I. This year the Perlan II glider will attempt to reach over 90,000 feet. Carried aboard will be be 10 science experiments from students participating in a Teachers in Space contest. Some of these experiments push the boundaries of what can be done at the K-12 level. This news article has a lot more detail on what these kids are sending.

Comments

Where will the speed come from?

[Viol8]

I can't see from the article or the wonkypedia page where they expect to get enough speed from to retain that sort of altitude. They mention carried aloft by air currents (mountain waves). Err , even assuming those currents will get you to 90K feet (I doubt it) they're not going to get you to the 200-300 knots (heavier U-2 need to do 370 but it was "only" at 70K feet) you'll need to maintain that altitude without them guys. So unless by "gliding" they simply mean falling fast from height until they hit another updraft then to me this seems a bit of a non starter.

Re:Where will the speed come from?

[Tx]

You implied that you read the wikipedia article; well, it explains the specific weather phenomenon that is to be used to reach above 90k feet.

"Standing waves normally do not extend above the tropopause at temperate latitudes. A strong west wind usually decreases above the tropopause, which has been shown to cap or prevent the upward propagation of standing mountain waves. However, at the outer boundary of the polar vortex, in winter, the stratospheric polar night jet exists. Its wind field can join with the wind field of the polar jet stream. The result is a wind which increases with altitude through the tropopause and upward to 100,000 feet or above. When this conjunction of winds occurs over a barrier mountain, standing mountain waves will propagate through that entire altitude range."

And once that altitude is reached, presumably if the standing mountain wave can get you up to that altitude, it can also keep you up there, if you can ride it. Again, from the wiki page;

"A sailplane can maneuver precisely at very high altitudes to traverse or remain relatively stationary in a desired portion of the wave structure, as the structure is determined in flight."

Re:Where will the speed come from?

[Anonymous Coward]

Let's assume that somebody involved has done some sums, looked at previous comparable attempts, and deduced that it's at theoretically possible, shall we? Airbus and Windward Performance do actually know a thing or two about the subject, and it wouldn't have got this far if it was pointless, so I think I'll take their opinion over some random guy on the internet.

Saftey & Planning

[ebonum]

I'm a licensed pilot. If I was preparing to fly a glider twice as high as the previous record, I'm not sure I would want anything on my plane not 100% required for my flight. The first concern is weight. The second concern is that I really don't need anything extra to worry about. There are already enough risks involved. I'm not an expert on the flight envelops for gliders at this kind of altitude, but I'm going to guess that the plane will be at the knife edge between stalling and over speed. Gliders at 10,000 feet on a hot summer day get bounced around. A lot. They have shoulder straps for a reason. Storms have been known to remove their wings. Where there is powerful rising air, falling air can't be too far away. At 70, 80, 90,000 feet, a plane with huge, long wings might struggle to deal with the air currents.

An unmanned balloon can hit 90,000 feet and carry a small payload. There are other ways to get these experiments to the edge of space.

Re:Saftey & Planning

[vyvepe]

They do not want to catch a raising column of hot air (thermal). They want to catch a wave downwind of a mountain. The waves reach considerably higher than the mountain which generates them. Thermals are typically very bumpy. Waves are typically extremely steady. Only their middle part (the rotor) is bumpy but you can avoid that. This should be quite a steady flight.

Re:Saftey & Planning

[ebonum]

Good points. Not all wave flights are so smooth:
http://www.aviationtoday.com/r...
http://www.paul.moggach.yorkso...
No one knows how high these waves travel, much less the edges of the rising, mid and falling air. You can't see rising air. There might be a cloud at the top. If it is there at 90,000 feet, I doubt it will be of much help when you are 20,000 feet below it. Instruments (total energy compensated variometer) can tell you if you are going up or down. Bumping into the edges tells you where the edge is.

Re:Saftey & Planning

[techmage]

I understand the concern and yes, the experiments could fly on a balloon - as has been done many times. The advantage of the glider is level stable flight. You cannot effectively steer a balloon, it mus be carried by the winds. The glider gives us the advantage (to a better degree) of picking the direction to fly in. If an experiment picks up something interesting on its instruments, the glider can fly back. The balloon cannot.

The Perlan II was designed with the payload capability in mind. It is also why the glider and payloads are being tested in Minden Nevada before the actual 90k attempt.

Re:Saftey & Planning

[Viol8]

"Powerful" is relative. At 100K feet its virtually a vacuum so even the fastest winds would seem like little more than a gentle breeze if you were standing in it.

Re:Saftey & Planning

[vyvepe]

An experienced glider pilot has one more vairometer to use - his own posterior. One can feel speed changes in it :) Also one does not see how air moves, the pilot can feel whether the plane is nearing the turbulent region. This together with general knowledge about thermal ans waves helps a great deal.

No idea why Bigelow screwed up. Gliders are built for turbulent weather. When one is targeting thermals then it is the turbulent parts of the atmosphere the plane is heading to. Stall speed is typically about 40 knots and Vne (top speed) is about 120 knots at low altitudes. The range is quite big. And it is not a big deal to get below the stall speed if you have enough height. You just lose part of that height. I experienced stall in a glider myself a few times. Not a big deal. On the other side crossing your Vne is almost as good as trying to kill yourself real hard. It is not easy to fly when your wings break off :) Whatever Bigelow did, he should try not to cross his Vne. Crossing Vne was probably a consequence of something else though.

Re:Saftey & Planning

[BESTouff]

An experienced glider pilot has one more vairometer to use - his own posterior. One can feel speed changes in it :)

Nope. As you say it, own own posterior is an accelerometer, measuring the speed changes, NOT a variiometer, measuring the speed i.e. the position change. You're one derivative wrong.

Piloting without vario is easy to do when you have visual cues around to help assessing your vertical speed, but when higher up in the sky it's really difficult to tell the difference between a steady +1m/s and -1m/s. (World class paraglider competition pilot here, and from the few flights I did in sailplane it's not much different).

Re:The elephant in the room

[techmage]

The teams selected were not chosen with any race or gender elements in mind, only the science. But we have two teams predominately African American, one Latino team and the other teams are made up of blended groups. Some groups as you have correctly pointed out, have little to no minority presence (we are working on that). For the record, not all groups have posted photos, not were all the photos posted suitable for media use.

There are an almost even number of girls to boys with the girls edging out the boys. We have one team exclusively made up of young ladies. Three student leads and five teachers are women. The teams range from college to kindergarten.

Re:The only creed I need is

[camperdave]

The edge of space is 328,000 feet (100km). They're only going up 90,000 feet. That's less than a third of the way. "Oh, look! I'm on the second floor. I'm on the edge of space!"

some back of the envelope calculations

[bkmoore]

I'm no aeronautical engineer, only a pilot. [For cultural reasons glider pilots prefer the term sailplane, but I use glider here.] Gliders have a speed range. The minimum speed is the speed where the wings can produce enough lift to counteract gravity. The maximum speed is where flutter starts to occur, which can make the airplane uncontrollable and damage the airframe. In powered aircraft, this speed is usually expressed in terms of Mach. Most sport gliders that I am familiar with have a speed range between about 60 kmh and 200 kmh or 32 knots to 107 knots. I'm assuming that if you want to reach 90.000 feet in sustained flight, you would design a glider to have a much lower minimum speed than a standard sports glider, say 10 knots for arguments sake or 18.52 kmh. Lets also assume that the maximum speed remains at 200 kmh or 107 knots. At sea level the speed of sound is 665 knots. For a V_ne of 107 knots, your maximum speed can be expressed as Mach 0.16. At this point flutter begins.

Now take our glider to 90.000 feet. At that altitude, assuming standard atmosphere, the temperature is -49 C. Speed of sound is 583 knots. Your minimum true airspeed for sustained flight would be 111 knots or 10 indicated. At 90,000 feet, 111 Knots is Mach 0.19 which is greater than your maximum Mach number of 0.16. This theoretical glider cannot maintain level flight at 90.000 feet.

Solving this problem requires an airframe with a very large ratio between minimum and maximum airspeeds. Most conventional airplanes have a ratio of about three to one. Our example had a ratio of 11 to 1. This is where the U-2 reaches its limit and am told the min and max speed are very close at high altitude. The SR-71 solved this problem by increasing the maximum speed, but the tradeoff is a greater minumum airspeed due to the increased weight. It is critical that the tradeoff leads to a greater ratio of max to min airspeeds.

Doing it at the other end, reducing the minimum airspeed, would be much more challenging, because you would need to design a structure that can fly at very low speeds, but still have the aerodynamic stiffness and strength to be safe at higher speeds up to around Mach 0.2. It might be possible, but is definately not easy. I'm not aware of any manned fixed-wing aircraft that can fly as slowly as 10 knots and still have maximum speeds in the 100 kts range.

Critical mach number can be a problem in conventional sailplanes when they get above about 20,000 feet. The pilot needs to be aware that flutter will begin at lower indicated airspeeds than the red line on his airspeed indicator. I would leave 90.000 feet to either a U-2 or an unmanned model airplane. I do not think it is practical in an amateur-built experimental glider attempt to fly that high. But I am sure somebody will attempt it.