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Stores drag too high?


Vladinsky
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Its been feeling really slow to fly around with some of the larger stores so I decided to compare it to the expected top speeds and acceleration times listed in SFI AJ37 Del 3 using the supplied loadouts.

 

Clean acceleration and speed is pretty close but as soon as stuff goes under the wings performance is greatly reduced which leads me to believe that drag is the main culprit.

Bomb drag is most certainly too high.

 

All tests are started at M0.55 and flown 20-40m above the black sea in altitude hold.

Max dry thrust.

Weight: Starting weight -275kg

ISA 15C 1013mbar.

Time and speed verified in tacview.

 

 

Clean

Target speed: M0.89 in 2:15 minutes.

Result: M0.85 in 2:15 minutes. Top speed of M0.88 took 3 minutes.

 

hC5s2wX.png?1DNTUUDU.png?1

 

Loadout 1(2 RB24 + KA(U22)/KB + XT)

Target speed: M0.85, in 2:30 minutes.

Result: M0.75 in 2:30 minutes, would not accelerate further.

 

DGBaRBk.png?1uywcjxW.png?1

 

Loadout 2(1 RB04 + 1 RB24 + KA(U22) + XT)

Target speed: M0.83 in 2:30 minutes.

Result: M0.74 in 3:10 minutes, would not accelerate further.

 

WzzeXkN.png?1wgd5hie.png?1

 

Loadout 3(3 Rocket pods + KB + XT)

Target speed: M0.77 in 2:40 minutes.

Result: M0.75 in 3:30 minutes, would not accelerate further.

 

3DkF0OL.png?1mmCwb0x.png?1

 

Loadout 4(16 HE bombs + XT)

Target speed: M0.77 in ~3:00 minutes.

This was the worst one by far, the plane was not capable of sustaining the minimum speed required to actually start the test.

Not even max zone 2 was enough to reach M0.77

 

8KLvin8.png?15pdBxZm.png?1

 

 

 

 

I've no doubt messed up somewhere though, don't hesitate to double check.

(No, I really didnt have anything better to do last night:helpsmilie:)

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Good effort!

 

I know that having the automatic fuel regulator on has had negative impact on speeds during high altitude flying, but I'm wondering if it has played a part here as well... Would you care to double-check any of these with the fuel regulator turned to manual?

I don't necessarily see how that bug could play into this scenario, but it's the only issue that manifests in lower speed that we know of (AFAIK).

 

593c3Ai.png

 

(I absolutely would do this myself, but I'm going to bed. I'll do it in 8 hours or so, if no one else has)


Edited by scaflight
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edit: there was something here that was wrong, below is correct:

 

Vladinsky, takeoff weight minus 275 kg is correct for the acceleration graphs, but the level flight envelope graphs I just now discovered use the term "flygvikt", which is defined as 70% fuel for an aircraft without the drop tank and 100% for an aircraft with the drop tank. 100% is defined as 4200 kg.

 

Great work, by the way!


Edited by renhanxue
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Thanks for checking guys, I did do a run with manual fuel regulation but there was no change. That seems to be a non ISA/high alt issue only.

 

E: I flew a top speed only test with adjusted "flygvikt" and saw a consistent increase of about M0.01 across the board.


Edited by Vladinsky
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Seems like bombs create massive drag. We struggeled to stay in fornation during an MP mission.

AJS37s with XT and 4 rocket pods+Rb24 had no issues. But AJS37s with XT, 8 bombs on two racks and 4xRB24 had problems keeping the speed over 500-600km/h in level flight and on full military power. There was a bit of wind that might have added to the issues we had. But the general feeling was that the drag for bombs was very high. Or is it standard procedure to always fly in afterburner when carrying bombs?

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Seems like bombs create massive drag. We struggeled to stay in fornation during an MP mission.

AJS37s with XT and 4 rocket pods+Rb24 had no issues. But AJS37s with XT, 8 bombs on two racks and 4xRB24 had problems keeping the speed over 500-600km/h in level flight and on full military power. There was a bit of wind that might have added to the issues we had. But the general feeling was that the drag for bombs was very high. Or is it standard procedure to always fly in afterburner when carrying bombs?

 

Yep bombs seem to create far too much drag barely able to hold her level without the AB

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Loadout 4 acceleration timing and top speed seems much more consistent with the other loadouts now, reaching M0.7 in 3 minutes and not accelerating further.

I've not tried any of the other yet but I'd expect a small time reduction and top speed increase from the fuel tank change. Well done:thumbup:

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