We are above Venus’ clouds, 70 km altitude. Let’s take a ride on an aerofoil. I'm hoping the aerofoil can keep us stationary against the wind. Right now I'm exploring the ideal scenario with arbitrarily-energetic fans.
The acceleration down to Venus’ surface is, here, about 8.666 ms-2. The wind here is long visible to Earthlings: 100 ms-1. For air “fluid” density (ρ) at 70 km up, I'm working with Yeon Joo Lee's fig 4.12f, 90 gm-3.
For reference : NASA. Density of air at Earth sealevel and room temp: 1200 gm-3 : assuming 1013 millibars or 760 mmHg. Zubrin put 16 gm-3 on Mars; Yeon Joo Lee puts 65000 gm-3 on Venus' surface. M. Ballon Solaire is telling me Earth has 1.225 kgm-3; first with a decimal and next with a comma. I side with NASA. All moot here since we're over Venus.
We're going against steady wind at 100 ms-1, and tilting our wings up.
FL, Lift, = cL 1/2 ρ v2 A FD, Drag, = cD 1/2 ρ v2 A
Some of our constants are baked in, which reduces 1/2 ρ v2 to a nice 0.5 * 0.09 * (100 * 100) = 450. I don’t pretend to know coefficients; but a drag coëfficient of 0.015 and lift co-efficient at 0.5 seem fair, from what I see elsewhere on the cylinder-bourne-by-wing models.
Here we re-introduce my cylindrical fuselage 20 m long and 2 m radius. For wing area, I was careful with my fuselage: it’s not only 250 m3 volume but 250 m2 area. But it’s not aerodynamic so I must add to this area: say, two 12.5 m2 triangles, doublesided, 2 m wide at the innerside and 12.5 m long. 300 m2 area total.
Our first priority is drag, because that determines the turbine we need - which we’ll be carrying too. Our drag force is 450 * 0.015 * 300 = 2025 N.
How much weight can we carry? 450 * cL * A = 450 * 0.5 * 300. That is 67.5 kN. At 70 km altitude, this wing can bear mass about 7800 kg mass.
D’accord - voici: la turbine “GE90”. This turbine weighs 8300 kg and can do 512 kN thrust.
Note: our drag had inflicted barely two kN. We needn’t need tweak the design much to carry that turbine, the wing, and the fuselage. Heck, a much cheaper turbine alone doing 5 kN would get us there.
Over Venus, the 512 kN turbine can allow to our wing area, up to 75,851 m2; dragging aloft 17066475 N. Over Venus that is almost 2000 metric tonnes. For reference a Boeing 737 maxes out at 80 tonnes. Go ahead and deduct some of those 2000 tonnes for the turbine and the chassis. Deduct a spare turbine too. Sabotage the coefficients (within reason). We’re still looking pretty.
We have learnt elsewhere that carrying hot hydrogen in a hopefully-unreactive fuselage does offer some lift. Maybe 50 kg for 250 m2 / m3. But it doesn't offer much, compared to good ol’ aerodynamics. Which gets us 7800 kg for the same. And the latter lets us stay in the sunlight.
Now: GE90 as a turbine is, more exactly, a turbo-fan. The turbo part requires, still, a fuel-tank, whose weight I am not (here) considering. Other essays here handle my power needs, and how I propel the thing. The turbofan is not a permanent flier! It is, however, a very powerful flier; and Venus' atmo has all the elements required to refuel it between jumps.
CONFIRMATION 2/10/2020: I ran the drag coëf by an aeronaut on my 'phone. He was pretty busy, and didn't wholly understand what I was trying to do, but he gave the example of a greasy 737 at "Mach 0.8": 0.019 cD. Faster than that, the coëf rises - yay nonlinear equations. But ... as you see here: I am looking at Mach 0.3 and as you will see on my other pages, I am prepared to bargain down to Mach 0.15. That is in glider / kite territory, by contrast with a 737. 0.015 is to be considered validated for this project's purpose.
TEST FLIGHT 8/6/2020: the battery Cessna, May 2020. No fueltank!
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