Pylons appear to cause zero or close to zero drag

[Default774]

The pylons on the JF-17 appear to be causing very little if not zero drag in some cases. 

Testing the top speed of the Jf-17 at 30000ft with a clean configuration resulted in a top speed of Mach 1.61 581kts indicated.
Testing the top speed with single SD-10 pylons and fuel tank pylons resulted in an identical top speed of Mach 1.61 581kts indicated.

As a reference, I have compared this to the F-16 with a similar set up. Completely clean the F-16 has a top speed of Mach 1.93 765kts indicated.
With wing pylons, this becomes Mach 1.83 726kts indicated.

Now I am aware this these are obviously different aircraft and different pylons, but what it looks like to me is that the pylons induce zero drag on the aircraft.

Another point I'd like to bring up is the SD-10 Dual pylon. Dual racks are notoriously draggy, yet, on the JF-17 they seem to be producing little to no drag at all.
Two SD-10 dual racks on the JF-17 cost you about 0.02 Mach and 5kts indicated of top speed, bringing your top speed down to Mach 1.59 and 576kts indicated.

Comparing this to the LAU-115+LAU-127(amraam dual rack) on the hornet, the difference is clear. Two amraam dual racks cost you 0.12Mach and 44kts indicated of top speed.
Furthermore, comparing to the BRU-57(JDAM dual rack) on the F-16, there is a clear difference again. Two jdam dual racks cost you .21Mach and 78kts indicated of top speed.

Now I'm no aerodynamicist, but this looks to me like the dual racks produce almost zero drag. Tracks are in tracks.zip. Enjoy the high quality summary image!

jf_drag.zip

[Mr_sukebe]

How does that compare to other aircraft?

Being fair, at 30,000’ air pressure is much lower, which will reduce the impact of drag

[Default774]

4 minutes ago, Mr_sukebe said:

How does that compare to other aircraft?

Being fair, at 30,000’ air pressure is much lower, which will reduce the impact of drag

The post details how it compares to other aircraft. In short, the pylons on the JF17 cause virtually no drag, and pylons on the 16/18 cause a lot of drag. All tests carried out in identical circumstances.

[Mr_sukebe]

2 hours ago, Default774 said:

The post details how it compares to other aircraft. In short, the pylons on the JF17 cause virtually no drag, and pylons on the 16/18 cause a lot of drag. All tests carried out in identical circumstances.

Sorry, missed that bit.

For the Jeff to have no additional drag doesn’t exactly seem right

[DSplayer]

Just doing math alone it does seem that the Cx_pil values seem a bit low when loaded with SD-10s and then basically become insignificant once the SD-10s are actually fired off. Cx_pil for the double racks of SD-10 is 0.00112629296 and then when the SD-10s are actually all fired off the pylon, the Cx_pil becomes 0.00014973046. Compare that to the AIM-120C double racks which has a Cx_pil of 0.00195976562 when loaded and the a Cx_pil of 0.00073906249 once the AMRAAMs are fired. Pretty significant that the double rack of AMRAAMs are basically double the Cx_pil value before the SD-10s are fired and then once all the missiles are fired from their associated pylons, the SD-10 double rack pylon still has basically 1/3 of the drag of the double rack AMRAAM pylons.

[AeriaGloria]

Interesting thoughts. I would say though don’t test in a place where you hit top speed. Since top speed is intake limited, there is a considerable amount of power still available before it can no longer maintain max speed

You see this with the pylons. The single pylon might not have enough drag, but it’s negligible enough to not make a impact on top speed. But in your tests, clearly the dual rack causes enough drag to use up the reserve power it has at top speed. 

That being said, I did always think the dual rack was a genius design to reduce weight, having large open spaces like that. But the same drag reduction structure obviously isn’t there for the single rack. If anything, I would expect the single rack drag to be most noticeable, and the dual rack to only be a little draggier. 
 

Perhaps the dual rack drag is close to reasonable, but the single rack drag is what’s lower then it “should” be. 

 

[uboats]

I got your point. i dont' know yet how loadout figures out cx_pil of each missile. In the lua, it seems to be only the total cx_pil of the loadout i.e. 120family lua under coremod aircraftweaponpack. can anyone try to comment out Weight_Empty line for aim120 single or dual, and see whether this affect the drag? Our FM engineer is now busy with his new baby daughter 

Edited December 22, 2022 by uboats

[DSplayer]

33 minutes ago, uboats said:

I got your point. i dont' know yet how loadout figures out cx_pil of each missile. In the lua, it seems to be only the total cx_pil of the loadout i.e. 120family lua under coremod aircraftweaponpack. can anyone try to comment out Weight_Empty line for aim120 single or dual, and see whether this affect the drag? Our FM engineer is now busy with his new baby daughter 

From my current understanding, the Cx_pil for empty pylons are the Cx_pil of the full weapon pylons minus the Cx_pil of the weapons that have been fired divided by 4096. 

 

So for the AIM-120C double racks, the full Cx_pil with 2 AMRAAMs would be 0.000739765625 + (2) * 0.00061 = 0.00195976562. To make get the empty Cx_pil, you would get the Cx_pil for the AIM-120C (which is 2.5) multiply it by the amount the rack carries and then divide it by 4096 (because for some reason the weapon and payload Cx_pils are different in this way). So it would be 0.00195976562 - ((2.5*2)/4096) = 0.00073906249 for the Cx_pil of just the pylons.

Edited December 22, 2022 by DSplayer

[Napillo]

How do you know it is too little drag and maybe its just too much drag - ie - if the drag of the dual missile rack is what is causing this even when there is no pylon there? So we should get less drag without the rack, but currently we're getting same drag as if we have both?

[Tiger-II]

Wow... people can't stop attacking the Jeff, can they? Anything to make it worse. Ever notice that?

Did you consider the drag is TOO HIGH on the F-18 or F-16? You can't even compare them like that.

I have a document for the Harrier that shows a TER has massively more drag empty that when loaded, because the gaps INDUCE DRAG, and the gaps are closed when loaded making them more streamlined!

I wish people would get a clue before mouthing off about "toO MuCh pErFormAncE! NERF IT!".

From just flying it, the double pylons induce a lot of drag. Thrust settings are higher, fuel burn is astronomical, and cruise climb is notably degraded.

Unless the drag was greatly reduced since the last time I flew, I actually question if the pylons induce too much drag.

Did you look at the pylons for the F-5? They are like flying with the speedbrake permanently extended. It has demonstrably too much drag, but they still haven't corrected it.

Edited January 6, 2023 by Tiger-II

[Mike_Romeo]

On 1/6/2023 at 9:59 PM, Tiger-II said:

Wow... people can't stop attacking the Jeff, can they? Anything to make it worse. Ever notice that?

We have a real bug here with evidence. Dunno what your point is.

On 1/6/2023 at 9:59 PM, Tiger-II said:

Did you consider the drag is TOO HIGH on the F-18 or F-16? You can't even compare them like that.

On 1/6/2023 at 9:59 PM, Tiger-II said:

Did you look at the pylons for the F-5? They are like flying with the speedbrake permanently extended. It has demonstrably too much drag, but they still haven't corrected it.

If there are issues with them, better report them in their forums with evidence. Regardes the F-18, a review and maybe rework of the flight model seems to be inbound
 

[Tiger-II]

Quote

If there are issues with them, better report them in their forums with evidence.

It has been posted multiple times over years, but it has never been corrected. It took 5 years for them to fix the bug with engines responding to ground speed.

[uboats]

the drag of pylon was set too small. will adjust