Ok, at the request of several people I merged the posts into a new thread. The scope is general (high-altitude flight), but for now I'll continue the discussion of a stratospheric powerplant. The view is one of the reasons to go up there... magic:
I recently found this thread again. I think the idea might have merit after all, with a rather different approach.
Let's imagine the Super Dimona or G109 Both have a MTOW of around 750 kg (1650 lbs) and a 100-ish engine in the front. Replace the passenger and engine with a PT6 which is roughly 500 lbs including prop and has a maximum power of roughly 1500 HP (usually thermally limited to lower ratings).
@ FL800 you have 3.55% of the sea level density. Thus speeds have to be 5.3 times higher. Both aircraft have their best L/D around 90 km/h. Times 5.3 that's 480 km/h (260 kts), far below the speed of sound. L/D max is roughly 25 on those aircraft, so we're talking 750*9,81/25*480/3,6=40 KW. Including losses and so on, that's roughly 60 HP.
Assuming a linear relation; the PT6 makes 53HP at those densities.
So that seems feasible. Apart from the obvious issues (pressure suits, vapor lock, PT6 cost, legal stuff, design for flutter), anything I'm missing? Can you linearly scale a turboprop, dependent on density, or are there issues at very low densities?
The current propeller records:
67,028 ft Boeind Condor (unmanned)
60,897 ft Grob Strato 2C (Manned, 2XTSIO-550)
47,530 ft Flyin Tiger (300HP RV4)
Some interesting links:
http://www.interglobal.org/sophron/high.html
http://www.faa.gov/pilots/training/airman_education/media/ac 61-107a.pdf
I recently found this thread again. I think the idea might have merit after all, with a rather different approach.
Let's imagine the Super Dimona or G109 Both have a MTOW of around 750 kg (1650 lbs) and a 100-ish engine in the front. Replace the passenger and engine with a PT6 which is roughly 500 lbs including prop and has a maximum power of roughly 1500 HP (usually thermally limited to lower ratings).
@ FL800 you have 3.55% of the sea level density. Thus speeds have to be 5.3 times higher. Both aircraft have their best L/D around 90 km/h. Times 5.3 that's 480 km/h (260 kts), far below the speed of sound. L/D max is roughly 25 on those aircraft, so we're talking 750*9,81/25*480/3,6=40 KW. Including losses and so on, that's roughly 60 HP.
Assuming a linear relation; the PT6 makes 53HP at those densities.
So that seems feasible. Apart from the obvious issues (pressure suits, vapor lock, PT6 cost, legal stuff, design for flutter), anything I'm missing? Can you linearly scale a turboprop, dependent on density, or are there issues at very low densities?
The current propeller records:
67,028 ft Boeind Condor (unmanned)
60,897 ft Grob Strato 2C (Manned, 2XTSIO-550)
47,530 ft Flyin Tiger (300HP RV4)
Some interesting links:
http://www.interglobal.org/sophron/high.html
http://www.faa.gov/pilots/training/airman_education/media/ac 61-107a.pdf
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