Airplanes / Too low speeds at high altitude

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AKar
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Airplanes / Too low speeds at high altitude

Post by AKar »

Cheers everyone!

New to the forums, though been following for some time, I was a big fan of Harpoon series and only lately I've found CMANO which I'm learning and becoming a big fan of as well! [:)]

Playing through different scenarios (and mostly getting my ass kicked up [:D]), I'd like to ask about an "issue" I've noticed that affects multiple aircraft. It appears that thinner upper atmosphere has no negative effects on aircraft speed envelope. This becomes very noticeable with loitering units such as, say, tankers. For instance, the loiter speed of KC-10 is 230 kTAS (Mach .4) regardless of the altitude band. Similar performance data is found on many other units as well. This is clearly out of the performance capability of the aircraft. Not to mention of the high-speed airplanes that may be in the queue. The minimum speeds should be much higher at altitude.

Any thoughts on this? [:)]







ComDev
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RE: Airplanes / Too low speeds at high altitude

Post by ComDev »

Yeah okay this should probably be looked at.

What should the speeds be, you think?

Remember that for tankers, the loiter speed is also the refueling speed.
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AKar
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RE: Airplanes / Too low speeds at high altitude

Post by AKar »

Is there any minimum speed in the database, per unit? Would it make sense to include a calculation to the database values that would keep the minimum IAS constant over altitudes? It would be rather rough, but still a reasonable estimate.

I can figure it would be pretty laborious to search out for actual minimum speeds for every unit, not least because it varies quite a bit and is a function of weight, among the other factors.

As an example, the KC-10 performance data quotes a minimum refuel speed, which would be (without the wing pods) 1.2 g buffet onset speed plus 5 KIAS. For the sake of this example, if we assumed 500 klbs mass at station, that would be roughly Mach 0.68 or 400 kTAS.

Stall boundary speed at 30000 ft and 500 klbs is about 218 kIAS, or Mach 0.59 approximately, that is 346 kTAS.

I think the refueling in real life is usually performed at lower altitudes (?), but the topic would still apply to loiter speeds. In CMANO, airplanes that loiter at high altitude fly at significantly low speeds at times.

Cheers!
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Randomizer
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RE: Airplanes / Too low speeds at high altitude

Post by Randomizer »

My sense is that this is nonsense on a grand scale. Aerodynamic stalls at altitude are related to indicated airspeed (KIAS) or mach number with the latter based on temperature rather than velocity. There are so many variables involved that accounting for any means accounting for all otherwise the average values that we see are fine for CMANO's needs.

True airspeed (KTIS) is irrelevant to stalling and it has been stated elsewhere by the developers that CMANO uses KTAS so the above seems like a solution desperately searching for a problem. Reworking the entire flight envelope of every aerial platform for a few knots here or there would probably be a massive effort for little or no substantive gain in simulation value.

CMANO is not intended to be a flight simulator, please let's keep it that way.

-C
AKar
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RE: Airplanes / Too low speeds at high altitude

Post by AKar »

And I, obviously, disagree. [:)]

No, my intention is not simulating stall or anything else in lines of making CMANO a flight simulator. Just to suggest an increase of aircraft minimum speed to be affected by altitude. Without that, we get unrealistically slow loiter/refuel speeds, easily by a factor of two in many cases. It doesn't affect only the refueling, I used that simply as an example. Many other assets capable of high altitudes can be made essentially to hover in comparison to their real life speed over ground.

Edit: Just to push the point...in the game, U-2 seems to be able to hold 150 kTAS at 85000 ft...that would put its equivalent airspeed down to 25 kts. Not going to happen. More...real specs I'd figure would maybe be Mach 0.65 at 75000 ft. That would put it just above 80 knots of equivalent airspeed, perhaps able to hang up there due to low Mach number. But she would be doing some 375 knots over ground with no wind, instead of that 150. Just to give an example of the order of the error we are potentially having with this one. [:)]

Cheers!
ComDev
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RE: Airplanes / Too low speeds at high altitude

Post by ComDev »

Thanks for your feedback guys.

I've opened a new feature request on this, and added it to the queue. It will be looked into when resources become free [8D]
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ComDev
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RE: Airplanes / Too low speeds at high altitude

Post by ComDev »

Also...

If you have any useful sources or links to data that we should look at, feel free to put it here. That'd be extremely helpful [:)]

Thanks!
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AKar
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RE: Airplanes / Too low speeds at high altitude

Post by AKar »

Thank you for considering this improvement! [:)]

I'll post here if I can figure out any simple way to make any reasonable estimate based on what already is in the database. Obviously, only a fraction of the airplanes in the database have their performance data readily available in public domain, and even if they did, it would be PITA to go through all the graphs one-by-one. As the current speeds and altitudes are somewhat generic in nature for the most of the included units, and that is perfectly adequate for the purposes and the scope of the sim, I'd figure a rather generic approach to this problem would suffice as well.

This doesn't answer directly to this problem, but while at airplanes and their performance, I wonder if you have checked if the following source can be of any use to you? Can't post links yet, but if you google "eurocontrol aircraft performance database", you get a comprehensive listing of many aircraft types, and their approximate performance figures for different phases of flight for air traffic control purposes.
c3k
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RE: Airplanes / Too low speeds at high altitude

Post by c3k »

As someone who has refueled hundreds of times, I'll look at this in-game at some point. The big picture? It's done in the mid-20s. (25,000' and thereabouts) There are lots of reasons for that. I'll see if I can find some info. It's been a bunch of years since I've done it, and I've forgotten some details.
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