BRU-33 Rack Negative Drag value

[raelias]

Hi, i have run into an odd observation

 

While flying around straight and level, at the terminal speed for current power seeting and 2 empty BRU-33 racks on each wing.

 

After uppon jettisoning the racks the speed actually starting to go down instead of going up due to reduced drag/weight, suggeting the rack actually have a negative drag value, did anyone else observe this? I will later post on bugs with track when able

Edited August 7, 2018 by raelias

[raelias]

BRU-33 Rack Negative Drag value

 

Hello,

 

I have observed in a variety of missions now how on jettisoning the BRU-33 Racks the drag of the aircraft actually increases

 

To showcase this i flew this simples missions as follows:

 

Loadout is 8x Mk-83 and 2x Mk-82

Take-off, fly straight and level at mil. power and wait for speed to stabilize (579Kt). Drop the 2 Mk-82 (Speed increases until stabilized at 584Kt). Drop all 8 Mk-83 (Speed increases to 614kt)

 

Then the weird part, after this later speed stabilizations i jettison the 5 empty BRU-33 Racks on the aircraft and speed starts to drop sharply, then stabilizes back on 585kt

 

It acts like the racks have a negative drag value

 

I've seen this same behaviour in a great variety of missions.

 

Version is current open beta 2.5.2.20143

 

Trk attatched (it won't let me post the mission and dxdiag because they are already attatched in the deck sliding thread, I used the same missions)

BRU-33 drag.trk

Edited August 7, 2018 by raelias

[Svend_Dellepude]

Seeing this too, as described above.

Bomb rack Drag.trk

[raelias]

the rack doesn't have a negative drag, the subtraction of drag from the overall Cd probably has an incorrect negative value.

 

If the rack had negative drag then by definition it would be a lifting body.

 

No it wouldnt, i said it had negative drag not negative weight.

 

Either way i used this term to clarify the way it acts, just like it has negative drag and getting rid of it adds to your total drag

[Druid_]

This issue has been reported and logged internally. Thanks.

[Svend_Dellepude]

I managed to reach 1.96 Mach at 35000ft with the racks still attached. :)

[raelias]

This issue has been reported and logged internally. Thanks.

 

You're welcome keep up the good job

[raelias]

One more funny addition

 

Today i was flying very high 40k feet+ with the empty racks on at close to supersonic speed, and at that altitude when i jetisoned them it seemed to behave normally (steep speed increase)

 

this is funny and indicates that the drag value is behaving badly only in low altitude

[Eldur]

Must be depending on the load. I tried that with 8x LAU-61 and 2x Mk-82, fired off the stores, dropped the pods but kept the BRUs. Unable to go supersonic. Max speed at 30k was like .88. Speed skyrocketed to 1.4+ quickly after dropping the 5 BRU-33s.

 

But well, witl that loadout unshot, the checklist gave me a weight excessive of 62k lbs (. Those LAU-61 are heavier than Mk-84s.

 

See screenshots attached. One was before getting the stores, tanks just fueled up completely. 25'340 lbs just for the stores which are 5 BRU-33s, 2 Mk-82 slick and 8 LAU-61 Mk. 5. Later I made shots after dropping the bombs and then after firing the pods empty, weight difference was 24'574 lbs, but I think the other two are enough to show something's seriously off here. I mean, just over 3'000 lbs each.

 

The real pod is 205 lbs empty, one rocket between 23 and 27 lbs. That makes 642 to 718 lbs for me. So they're more than 4 times the weight they should be...

[raelias]

Please note that ALL the cases i talked about in this thread is for EMPTY racks, the first case with jetisoning it decreasing your speed and the other way around in high altitude as well, all with empty racks

 

By the way i freaking love yourp posts haha

 

 

Must be depending on the load. I tried that with 8x LAU-61 and 2x Mk-82, fired off the stores, dropped the pods but kept the BRUs. Unable to go supersonic. Max speed at 30k was like .88. Speed skyrocketed to 1.4+ quickly after dropping the 5 BRU-33s.

 

But well, witl that loadout unshot, the checklist gave me a weight excessive of 62k lbs (. Those LAU-61 are heavier than Mk-84s.

 

See screenshots attached. One was before getting the stores, tanks just fueled up completely. 25'340 lbs just for the stores which are 5 BRU-33s, 2 Mk-82 slick and 8 LAU-61 Mk. 5. Later I made shots after dropping the bombs and then after firing the pods empty, weight difference was 24'574 lbs, but I think the other two are enough to show something's seriously off here. I mean, just over 3'000 lbs each.

 

The real pod is 205 lbs empty, one rocket between 23 and 27 lbs. That makes 642 to 718 lbs for me. So they're more than 4 times the weight they should be...

[Eldur]

My racks were empty, just dropped the bombs normally, fired the rockets, then I had all stations selected for jettison, rotated the selective jettison thing rightmost (Stores) and dumped the empty pods. I'll try the same with Mk. 83 instead and will check if it's behaving differently.

 

Edit: Did that test with completely different results. At 36.5k ft I was able to do 1.2 without AB and 1.5 with lowest AB setting. So probably it depends on what was on those racks since it didn't work with the rocket pods. More than that, those racks seemed to have inherited the utterly massive drag from the rocket pods (just another case that needs to be looked at) which on the other hoof would mean that maybe the bombs are the ones that might need a look at as well as the fact that the racks have different drag depending on what they carried. These are low drags after all, might be that their actual drag is "too low" internally which now shows with the racks.

 

I could provide tracks if needed... but they're 25MB in total and even a single one is in excess of 10MB (speed tests take time)... too much strain for the limited space a user gets here. Don't have a different place to put them up to at the moment, but I could just sign up for Dropbox and put them there.

Edited August 9, 2018 by Eldur

[Eldur]

Look here: https://forums.eagle.ru/showthread.php?t=217684

[raelias]

Look here: https://forums.eagle.ru/showthread.php?t=217684

 

Yes that's my own post i asked before reporting to see if anyone else observed this behavior

[fitness88]

Hi, i have run into an odd observation

 

While flying around straight and level, at the terminal speed for current power seeting and 2 empty BRU-33 racks on each wing.

 

After uppon jettisoning the racks the speed actually starting to go down instead of going up due to reduced drag/weight, suggeting the rack actually have a negative drag value, did anyone else observe this? I will later post on bugs with track when able

 

 

 

I've tried jettisoning the inboard/outboard racks but they don't drop...what did you do to drop them?

[Eldur]

Yes that's my own post i asked before reporting to see if anyone else observed this behavior

 

Silly me, didn't notice that

 

I've tried jettisoning the inboard/outboard racks but they don't drop...what did you do to drop them?

 

Select the stations left of the IFEI that you want to jettison and set the SELECT JETT selector to RACK LCHR (two times CW), go Master Arm on and push and hold that big red JETT button in the selector knob until everything selected is off. Set it to STORES (three times CW) to drop the stores, but keep the rack. Please note that only intermediate racks like the BRU-33 or LAU-115 mounted on the pylons can be ejected, you can't drop the big pylons.