Sustained turn rate at 31.5 °/s with flaps on!? - Page 4 - ED Forums
 


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Old 02-12-2020, 01:59 AM   #31
Bunny Clark
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Originally Posted by Figaro9 View Post
But the f14 with 15 aoa, the f18 with only with 8.1...
To expand on what's been said above: the F-14 instrumentation measures AoA in "units" while the Hornet measures in degrees, so these numbers at least are not comparable.

I'm unsure how this translates to TacView.

Approach speed for both aircraft is going to vary by weight, to get a reasonable comparisons I suppose you could take the speed of a clean aircraft with an equal fuel load?
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Old 02-12-2020, 07:03 PM   #32
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Yep, thanks guys, f-14 aoa is units, not degree. Found two sources which says 15 untits is equal to 10.8 degrees. Tacview reading seems to be right then, makes sense now.

approach speeds according natops:

Empty: f14 (40) 118kts, F18 (24) 117kts
Fuel +1000: f14 (41) 119kts, F18 (25) 119kts
Fuel +2000: f14 (42) 121kts, F18 (26) 122kts
Fuel +3000: f14 (43) 123kts, F18 (27) 124kts
Fuel +4000: f14 (44) 124kts, F18 (2 126kts
Fuel +9’000: f14 (49) 132kts, F18 (33) 137kts

Angle of attack difference between f14 and f18 is 2.7 degrees.
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Old 02-14-2020, 12:02 AM   #33
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Originally Posted by captain_dalan View Post
Judging by the effect of full flaps on approach speeds (about 24% boost), with the full flaps down these 4.4 become 5.456.
I don’t understand the logic, where is the increased resistance from the flaps?
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Old 02-14-2020, 07:20 AM   #34
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Originally Posted by Yupi View Post
I don’t understand the logic, where is the increased resistance from the flaps?
https://en.wikipedia.org/wiki/Flap_%28aeronautics%29
Generally flaps change the wing profile so you get increased lift but at the cost of more drag.
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Old 02-14-2020, 09:24 AM   #35
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Originally Posted by draconus View Post
https://en.wikipedia.org/wiki/Flap_%28aeronautics%29
Generally flaps change the wing profile so you get increased lift but at the cost of more drag.
This is clear. The increase in drag from the flaps is not taken into account in the message above, and is unlikely to be an amazing 31 deg/s.
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Old 02-14-2020, 03:37 PM   #36
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Originally Posted by Yupi View Post
I don’t understand the logic, where is the increased resistance from the flaps?
You are right, this math is not very helpfull, I guess.

He most probably forgot to take drag of the flaps into account, as you say.

His read out of the flaps boost might be incorrect.
As far as I can see approach speed with flaps and 43000lbs is 122kts, 0-flaps approach speed is 142 kts. Difference is 14% instead of 24%.

I also think he over estimates the influence of drag index on str. It is mainly the weight of the missiles which has a big influence. But for weight he corrected elsewhere already.

Further more his aoa comment seams incorrect. As he likes to compare the f14 with a glider... a glider is capable of approx 15 degrees aoa. Higher AR , stall occurs at lower aoa. Higher sweep, less lift, higher aoa (delta wing).
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Old 02-14-2020, 04:29 PM   #37
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Originally Posted by Yupi View Post
This is clear. The increase in drag from the flaps is not taken into account in the message above, and is unlikely to be an amazing 31 deg/s.
The increased drag is mainly via the increased lift (Cdi), and not so much parasitic.
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Old 02-14-2020, 04:53 PM   #38
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Drag increase is very noticeable in the sim. So I dont know what you guys are flying...
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Old 02-14-2020, 10:26 PM   #39
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Quote:
Originally Posted by Yupi View Post
I don’t understand the logic, where is the increased resistance from the flaps?
Quote:
Originally Posted by Figaro9 View Post
You are right, this math is not very helpfull, I guess.

He most probably forgot to take drag of the flaps into account, as you say.

His read out of the flaps boost might be incorrect.
As far as I can see approach speed with flaps and 43000lbs is 122kts, 0-flaps approach speed is 142 kts. Difference is 14% instead of 24%.

I also think he over estimates the influence of drag index on str. It is mainly the weight of the missiles which has a big influence. But for weight he corrected elsewhere already.

Further more his aoa comment seams incorrect. As he likes to compare the f14 with a glider... a glider is capable of approx 15 degrees aoa. Higher AR , stall occurs at lower aoa. Higher sweep, less lift, higher aoa (delta wing).
Or maybe he did not.
L/D=g*W/T remember? I don't work with lift alone, but with lift-to-drag as a whole. At very low air speeds the increase in drag is much less then the increase in lift, which is why you have much lower approach and landing speeds with the flaps deployed then with the flaps retracted.

As for the AoA values, they come straight from the NASA's wind tunnel tests, so take that for what you will
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Old 02-15-2020, 09:31 AM   #40
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Quote:
Originally Posted by captain_dalan View Post
At very low air speeds the increase in drag is much less then the increase in lift, which is why you have much lower approach and landing speeds with the flaps deployed then with the flaps retracted.

As for the AoA values, they come straight from the NASA's wind tunnel tests, so take that for what you will
Well, 280kts is not low speed at all. Where in your math is increased drag of flaps?
You only computed lift increase due to weight and flaps (but wrong, 24% boost instead of 14%) and a too high boost due to drag index reduction.

Wings full spread, what is max. aoa according your tunnel test? Config? Thx.
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