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Sustained turn rate at 31.5 °/s with flaps on!?


EvMstein

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dcs F15, configured as F14 above, same unrealistic 1000lbs fuel, sl, clean, turn rate ~ 24dgs

Dcs f18c l20, config as above: ~24.5 dgs

 

6.5 dgs advantage for the f14 (abusing flaps)

(All three with over-g)

 

That’s uhm, surprising.

 

This configuration is impossible in the Hornet as the FCS will not allow you to overspeed the flaps. With the flaps switch set to full, above 250knts the flaps will behave as if in auto.

 

The FC3 F-15C also has an auto flaps function, I'm not sure if that can be overridden or not. Even if the flaps can be forced to deploy, the F-15's flaps are way different than the Cat's.

 

And even still, as pointed out above, the Cat has very different wing geometry than either of these other aircraft, so I'm not sure the comparisons are useful.

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just look at landing speeds. The Cat on full flaps approaches at 90% of the speed a Hornet does.

 

We must look in different books then. Looking in natops f14 and f18 (400 engine), I see identical approach speeds. But the f14 with 15 aoa, the f18 with only with 8.1...

 

Since we talk about aoa ...

 

there is an other thing that is surprising me. The tacview shows the f14 pulling 7.7g at 280kts. LE and TE Flaps set (=landing config, but gear up). ~43’000lbs. Aoa at 11 - 11.5deg.

That pull must be very close to lift limit and accelerated stall (power approach stall speed 1g is 103kts at that weight). I would have expected higher aoa...

Is that tacview? Other theories?

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We must look in different books then. Looking in natops f14 and f18 (400 engine), I see identical approach speeds. But the f14 with 15 aoa, the f18 with only with 8.1...

 

Since we talk about aoa ...

 

there is an other thing that is surprising me. The tacview shows the f14 pulling 7.7g at 280kts. LE and TE Flaps set (=landing config, but gear up). ~43’000lbs. Aoa at 11 - 11.5deg.

That pull must be very close to lift limit and accelerated stall (power approach stall speed 1g is 103kts at that weight). I would have expected higher aoa...

Is that tacview? Other theories?

 

I don't know what Tacview and Hornet shows but Tomcat instrument shows units of AoA - not degrees.

 

What Draconus said. Also....it may be a tack view. IRL and in sim, it should be more like 14 degrees AoA. still nowhere near lift limit. That is above 30 (true) degrees.

Modules: FC3, Mirage 2000C, Harrier AV-8B NA, F-5, AJS-37 Viggen, F-14B, F-14A, Combined Arms, F/A-18C, F-16C, MiG-19P, F-86, MiG-15, FW-190A, Spitfire Mk IX, UH-1 Huey, Su-25, P-51PD, Caucasus map, Nevada map, Persian Gulf map, Marianas map, Syria Map, Super Carrier, Sinai map, Mosquito, P-51, AH-64 Apache

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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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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 (28) 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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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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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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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).

 

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 :thumbup:

Modules: FC3, Mirage 2000C, Harrier AV-8B NA, F-5, AJS-37 Viggen, F-14B, F-14A, Combined Arms, F/A-18C, F-16C, MiG-19P, F-86, MiG-15, FW-190A, Spitfire Mk IX, UH-1 Huey, Su-25, P-51PD, Caucasus map, Nevada map, Persian Gulf map, Marianas map, Syria Map, Super Carrier, Sinai map, Mosquito, P-51, AH-64 Apache

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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 :thumbup:

 

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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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.

 

It is slightly more then 225-250, so i decreased the effective L/D for an "arbitrary" value (IIRC about 5-10% - my calcs are at work, so i can't access them now).

 

What did you use to factor in the full flap effect? I used the decrease in approach speeds with the flaps down. For the same T/W ratio (a rough but plausible estimate considering the small air speed range we are working with here), the extra weight you can lift should be roughly equivalent to the increase in L/D.

 

Max AoA should be about 32-33 degrees true with wings at 22 degrees sweep.

Modules: FC3, Mirage 2000C, Harrier AV-8B NA, F-5, AJS-37 Viggen, F-14B, F-14A, Combined Arms, F/A-18C, F-16C, MiG-19P, F-86, MiG-15, FW-190A, Spitfire Mk IX, UH-1 Huey, Su-25, P-51PD, Caucasus map, Nevada map, Persian Gulf map, Marianas map, Syria Map, Super Carrier, Sinai map, Mosquito, P-51, AH-64 Apache

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I do not want to turn this in a math discussion. I am not a physician and not competent enough in aerodynamics to calculate such complicated things. That is fortunately Devs work. Your simplified math is not a proof that the fm is right nor are your (mis-) calculations a proof that it is wrong. It is still a black box and work in progress, as stated by hb.

I only checked your math and think there are probably mistakes in it. If you want to check/correct, check my post #36.

 

Natops state that at an oao greater than 25 units (=20 degrees true), lateral control inputs cause the aircraft to feint into the desired direction and then roll/yaw in the opposite direction.

Negativ directional instability at higher speeds occur at 20 units already.

Higher aoa are possible at slow speeds if lift is replaced by engine power... But in a turn we are talking about, critical aoa (lift limit) should be at ~25 units.

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Dude, i just gave you the equation, you can do the math yourself wit the data you have in the manual :)

 

And, lift limit is by no means at 20 degrees, for any wing sweep angle. Not in the sim, not in the wind tunnel data, not in the high AoA study that you can find on google.

Modules: FC3, Mirage 2000C, Harrier AV-8B NA, F-5, AJS-37 Viggen, F-14B, F-14A, Combined Arms, F/A-18C, F-16C, MiG-19P, F-86, MiG-15, FW-190A, Spitfire Mk IX, UH-1 Huey, Su-25, P-51PD, Caucasus map, Nevada map, Persian Gulf map, Marianas map, Syria Map, Super Carrier, Sinai map, Mosquito, P-51, AH-64 Apache

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Dude, i just gave you the equation, you can do the math yourself wit the data you have in the manual :)

 

And, lift limit is by no means at 20 degrees, for any wing sweep angle. Not in the sim, not in the wind tunnel data, not in the high AoA study that you can find on google.

 

Yeah , guestimations and false, simplified math like you did (forgetting drag for flaps and aoa, false readouts, false estimations), that could do just everybody, me too. But it does not help at all. Doing your math gives me ~1g less, dude.

 

But serious calculations like engineers do , and that is what I was talking about, thats an other story, sorry.

 

If critical aoa in the sim is above ~25-27units, then I am surprised again, since that is the critical angle for f14a and f14d according natops. Just search for f14 accelerated stall and critical aoa. Search for F14 aoa indexer too. Lot of good reads, have fun.

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Do you even know what the quotes you posted mean?

The natops figures that is.

 

Extra points for:

 

If a plane has approach speed of 150 knots at 50000pds of weight with no flaps, and 150 knots at 55000pds of weight with flaps, then what is the effect of the flaps on the L/D? ;)


Edited by captain_dalan

Modules: FC3, Mirage 2000C, Harrier AV-8B NA, F-5, AJS-37 Viggen, F-14B, F-14A, Combined Arms, F/A-18C, F-16C, MiG-19P, F-86, MiG-15, FW-190A, Spitfire Mk IX, UH-1 Huey, Su-25, P-51PD, Caucasus map, Nevada map, Persian Gulf map, Marianas map, Syria Map, Super Carrier, Sinai map, Mosquito, P-51, AH-64 Apache

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Do you even know what the quotes you posted mean?

The natops figures that is.

 

Extra points for:

 

If a plane has approach speed of 150 knots at 50000pds of weight with no flaps, and 150 knots at 55000pds of weight with flaps, then what is the effect of the flaps on the L/D? ;)

 

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Edited by FWind
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...

Judging by the effect of full flaps on approach speeds (about 24% boost), with the full flaps down these 4.4 become 5.456...

 

Nice last ditch dude.

 

Nope, I am IMC, please make a talk down. ????

Entire quick math, all read outs with reference to natops flight manual pages.

 

Thanks for your kind help.

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Nice last ditch dude.

 

Nope, I am IMC, please make a talk down. ????

Entire quick math, all read outs with reference to natops flight manual pages.

 

Thanks for your kind help.

 

Then enlighten us all, what do roll reversal and negative directional stability have to do with maximum lift? ;)

 

i wonder if they modeled different penalities for different flaps positions.... sinced the flaps are analgoue in positioning

 

They said they will increase the drag values for deployed flaps at higher speeds, but i don't know if it made into the latest patch, nor did i had do chance to test the new flight model (apparently changes in the high and low air speed parts of the envelope)


Edited by captain_dalan

Modules: FC3, Mirage 2000C, Harrier AV-8B NA, F-5, AJS-37 Viggen, F-14B, F-14A, Combined Arms, F/A-18C, F-16C, MiG-19P, F-86, MiG-15, FW-190A, Spitfire Mk IX, UH-1 Huey, Su-25, P-51PD, Caucasus map, Nevada map, Persian Gulf map, Marianas map, Syria Map, Super Carrier, Sinai map, Mosquito, P-51, AH-64 Apache

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Then enlighten us all, what do roll reversal and negative directional stability have to do with maximum lift? ;)

 

Accelerated stall lines, or lines of maximum lift, represent the maximum load factor that an airplane can produce based on airspeed. The accelerated stall lines are determined by CLmax AOA. They are the curving lines on the left side of the V-n diagram. If one tries to maintain a constant airspeed and increase lift beyond the accelerated stall lines, the airplane will stall because we have exceeded the stalling angle of attack.

 

At high load factors, the sudden loss of lift from one wing (whichever stalls first ) creates a much larger rolling moment than with a 1-g stall. The result is a violent departure that resembles a snap roll.

Some aircraft tend to roll rapidly toward the outside of the turn, because the the outside wing stalls before the inside wing.

During a rapid departure from controlled flight, the normal CLmax may be momentarily exceeded and as a result, the aircraft could be overstressed or damaged below the corner speed.

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