back to article Spirit of Steve Fosset lives on as glider is poised to soar to 90,000ft

The Perlan 2 unpowered glider is on course to soar to a record-breaking 90,000ft (27,400m) next year, following a successful first test flight last week at a more modest 5,000ft (1,500m). With pilots Jim Payne and Morgan Sandercock of The Perlan Project at the controls, the aircraft lifted off from Redmond Municipal Airport in …

It's very pretty and I want one.

Presumably they have done loads of tests on this, but I am surprised how conventionally sized the control surfaces are. What happens if it pops out of the Perlan wave zone regarding stability and control?

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If it pops out of the wave zone, then it comes back down again. There is nothing mystical about the lift - it's just air which happens to be going upwards, so if you're in that area, you also go upwards with it. In fact, this is the only way to get back down again - even with air-brakes open, you often carry on climbing when you're in lift that good.

As far as I can see, there is no reason for the glider to have anything particularly unusual, except for a pressurised cabin. Which I suppose leads to funny-shaped windows, which must be a nightmare to see out of. I certainly wouldn't want to be sharing a thermal with any of these things!

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Which I suppose leads to funny-shaped window

I suspect primary view is a front-facing camera, same as in Virgin galactic and its Scaled Composites predecessor. The windows are more for belt-n-braces, just in case the camera fails and for side view.

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Wave lift

I've been in it, a couple of times, and it's incredible. We left the ground and, 10 minutes later, were pushing at (and past) the legal limit of 10,000 feet - a vertical climb rate of over 11 miles per hour (incidentally in a DG500 - the precursor to the DG505 mentioned in the article).

I've often wondered how high wave lift goes - I guess these guys are aiming to find the answer. Good for them.

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Re: Wave lift

"I've been in it, a couple of times,"

God, you could hate some people, sometimes

(but still give them a upvote)

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Re: Wave lift

"I've been in it, a couple of times"...

Never managed to do that - and now I stopped flying :( this makes me want to go back to it. A lot. I mostly flew LS planes (LS4, LS6 and the then-in-testing LS8-18). Sadly bad management decisions (I can only assume since the planes were very nice) sent Rolladen Schneider bankrupt. It was bought by Glaser-Dirks - linking back to the article nicely... (who continue to build the LS8 and I think LS10).

Good luck to all fellow glider pilots out there!

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Re: Wave lift

AndyS, NASA satellites indicate the circumpolar wave that this glider is to ride may exceed 120,000 feet AMSL. That is awesome. However at that height atmosphere is so thin even Mach 3 aircraft don't go there. However, for the techheads, the next glider to go to 100,000 feet is going to be the really interesting one. Rumour has it that the wings will have supersonic airflow as getting that last 10,000 feet requires way more engineering and advanced high speed design. As it is, AFAIK, the current model will have a true airspeed of 500 knots at 90,000 feet. Not what one will see on ASI but very fast for a glider. No idea of flight envelope but suspect computer control to keep airframe flying and together.

Wave is great. Nothing like 17000 feet in afternoon sun at 50 knots indicated and 2 knots climb happening, while still miles from controlled airspace with 2 hours before last light. Rapid descents from altitude are very cold when one is trying to be over airfield before last light. Prefer a good seabreeze front. Not as high, but 80 knots plus straight line (almost) cruise for 40 minutes at 10,000 feet is hard to beat. Then you turn around and repeat to go home.

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Total non-sequitur

This tidbit:

The knowledge gained from this project will impact how the world understands and addresses climate change.

What? How is it supposed to impact how we understand climate change of all things??? It reminds me of Soviet propaganda, when the press release would read: The knowledge gained from this project will impact how the world understands and addresses Marxism and Leninism.

I mean, I have nothing against the project, and backing it just for the kicks and bragging rights, but be honest about it!

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Re: Total non-sequitur

"What? How is it supposed to impact how we understand climate change of all things???"

Precisely.

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Re: Total non-sequitur

It will impact the way we write funding pitches.

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Re: Total non-sequitur

" How is it supposed to impact how we understand climate change of all things?"

It isn't.

This is a sop to throw to the ne’er-do-wells who want to shut down anything and everything unless it fits their agenda. ie something along the lines of:

"What an egotistical waste by the white male patriarchy. They could have spent this money on buying XBoxes for single mothers."

"But it will help us understand climate change."

"Ok then"

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Re: Total non-sequitur

Yeah. It should read "The knowledge gained from this project will impact how the world understands climate dynamics" - or possibly "atmospheric dynamics". Especially the interaction of the upper Troposphere with the Stratosphere is not that well known, and weather (and climate) models will indeed benefit from knowing the physics better.

Measurement flights with gliders are really an awesome thing, though. In my old home country they mapped thermals, which was (afaik) also used by the weather service to improve their forecasts and likely also fed back into model development. They are approaching a 1km scale resolution... just... wow.

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Re: Total non-sequitur

That announcement now counts as one of the 97% of papers supporting the concept of man-made dangerous climate change....

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Re: Total non-sequitur

"Especially the interaction of the upper Troposphere with the Stratosphere is not that well known, and weather (and climate) models will indeed benefit from knowing the physics better."

My grandfather was an engineer on the Skyhook sounding balloon project, which by 1948 had sent instruments as high as 105,000 feet. Sounding rockets went higher, and were active around the same time. It would seem downright odd to not have data on the area that you mention.

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Re: Total non-sequitur

Sounding rockets and balloons shoot up and decent through the atmosphere pretty quickly and have relatively short "dwell time". An aircraft might permit more focused research.

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There's a lot of it about

" first postulated by Perlan founder and NASA test pilot Einar Enevoldson back in the 1990s"

Wave exploration goes back a lot further than that - I think wave lift was discovered in the '30s and the Siera Wave Project in the early '50s got to 30,000+ ft IIRC.

Wave lift is actually quite common - even in the flat lands of Cambridgeshire when it's blowing hard from the general direction of the Welsh mountains.

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Spinning for 50,000?

Worryingly when this pops out of the lift, unless they do something extremely clever with the wing, it'll be straight into (way beyond) Coffin Corner and will probably end up spinning for several thousand feet until air density is enough to re-enter the normal polar curve behaviour of the wing and regain control.

Or until the wings rip off as it zooms past VNe

Hope they have lots of sick bags, AND the cockpit is jettisonable and parachuted, to cover both scenarios.

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Re: Spinning for 50,000?

"

Worryingly when this pops out of the lift, unless they do something extremely clever with the wing, it'll be straight into (way beyond) Coffin Corner"

You will have to explain why you think that the aerodynamics change when you fly out of lift. Lift is simply vertically moving air - air density remains the same in or out of the lift and the glider's rate of decent *relative to the air* will be the same. The less dense the air, the faster your actual flying speed (keeping the dynamic density the same) so the aerodynamics remains the same and the aircraft handles the same and the pilot won't feel any difference. Fortunately the pilot does not need to do any calculations, because the air-speed indicator is also affected by density and under-reads by the same amount, so all your *indicated* airspeeds remain the same. The big gotcha occurs when your *actual* speed increases to approach the speed of sound (note your airspeed indicator will still be indicating the same low speed you always fly at), because near supersonic speeds the aerodynamics *do* change significantly. The highest you can fly (the aircraft's aerodynamic "ceiling") occurs when your stall speed approaches the speed of sound - you cannot fly slower because you will stall, and you cannot fly faster because you would go supersonic. In that respect a glider has the advantage over an airliner, because its stall speed is lower so it can go higher before reaching the supersonic stall limit.

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Re: Spinning for 50,000?

Very cool project. Nothing new, though, I'm afraid. All that is happening here is a glider is taking advantage of a massive amount of ridge lift. Obviously the altitude is a big deal and will require special consideration for the airframe and crew area. Beyond that, the same things that happen to the little RC gliders I used to fly on a local hill side will happen to them: They will fly aloft, probably back and forth across the pressure wave, gaining the altitude they want. When they get to their desired height, as has been done before, they will spin their way down to a more reasonable altitude prior to landing. Flight surfaces will continue to function as long as their is a pressure wave to fly upon. When that peters out, I would expect the aircraft to stall. If that is the case, just ease the elevator back until control is regained. If it spins, opposite rudder and stick forward. .

Still, very cool anyway. :)

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Re: Spinning for 50,000?

" air density remains the same in or out of the lift"

Errr, no, it doesn't. The change may not be major, but air movement of any kind requires pressure/density gradients.

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Re: Spinning for 50,000?

That is NOT how full size gliders work. At all. They are not using ridge lift, but wave lift (which is very different from ridge lift.

(Also, when stalling, you push the stick FORWARD, not back)

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It'll be jolly cold up there (approx. -50 deg. C?): in fact, much of the flight will probably take place in sub-zero conditions. I'd be concerned about control surfaces jamming, and degradation of the structure due to repeated cooling/heating cycles. Presumably there will be some kind of onboard powerpack to run things like instruments, oxygen supply and cabin pressurization. One plus point though: wave lift is usually smooth, unlike thermal lift which can be rough (usually the stronger, the rougher :-( ), so it should be a nice ride.

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I don't know for sure, but you know, maybe the aircraft's designers have thought of that?

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Happy

thermal cycling

@bucksboy. Yep, thats why aircraft lubricants are way more expensive than your cars/bike stuff. It cant freeze easily. As for control surface clearance, all carefully caluclated because it is an issue the designers cover before glass/carbon fiber is laid. Also something checked in annual airworthiness inspections.

As for rough, thermals can be bumpy, but nothing touches the rotor associated with wave for violence. Plus/negative 5 G sometimes appears on the G meter in one aircraft I fly. and not going fast either. Getting into the laminar flow of wave is a relief. OTOH, thermalling into wave is not rough, but an interesting challenge. Only did it for the first time this year.

Wind shear at altitude can also create some discomfort. Something like an invisible truck hitting your tail as you have uncommanded lurches. All part of the challenge to fly smoothly with minimal stress to airframe and pilot.

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Re: thermal cycling

@Denarius

Oh yes, I had forgotten to mention the rotor. On the hill we used to fly in, if your glider got stuck in the rotor during retrieval, it was a walk down the other side of the hill and hoping that it didn't hit too hard...But then again, 5 minute epoxy and masking tape do wonders. :)

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Robert Harris 1986, 49,009 in just woolies.

I remember reading about Robert Harris in Soaring (the SSA magazine). He made it to just over 49,000 in a standard Grob 102 without pressure suite, with just O2 and a shitload of clothing. If I remember the article correctly he starting to have problems with his Oxygen so he basically spun all the way down to a much more reasonable altitude and, going from hazy memory, he also may have set the record for number of consecutive spins. What he also did was piss off the FAA. Cant find the SSA article but found this.

"1986, a tow plane hauled Harris and the Grob 102 Standard Astir III aloft. He unhooked the towline and soon found weak lift that he worked to an altitude of 10,640 m (35,000 ft). Strong lift then pushed the glider up at 182-243 m (600-800 ft) per minute. By the time he had reached 11,552 m (38,000 ft), frost completely covered the canopy and Harris began to fly solely by reference to his instruments. At 12,768 m (42,000 ft), his eyes began to water but the teardrops froze and immediately formed ice cobwebs. Even five layers of clothing could not insulate him from temperatures that dropped to minus 65-70 degrees F (-50 degrees Centigrade) inside the cockpit. A failing oxygen system forced him to stop his record climb at 14,899 m (49,009 ft) and he returned triumphantly to earth using backup oxygen."

https://www.backcountrypilot.org/forum/hey-ez-heard-of-this-glider-pilot-9084

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Has anybody noticed...

...the Burt Rutan touch in the design? The project's website seems to be very careful not to mention who built the aircraft, but this certainly looks like a Scaled Composites job.

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