Missile Drag: US vs Russia

[sprstdlyscottsmn]

Hello,

So something has been bugging me for a while and that is how draggy the Soviet missiles seem to be compared to their western counterparts. I dug through six flight manuals I have that give drag index of munitions and corrected them for wing area to get the drag area. I ended up with quite a range for most missiles so I listed the minimum drag and the maximum drag I found for each.

Weapon drag.PNG (27.23 KiB) Viewed 9467 times

Most amazing to me was the range for the AIM-9M, where even on a rail for the F-15 it has just over a quarter of the drag it has on an F-14. The only logic I can think of for this is that the large pylon on the F-15 holds the missiles "far" from the wing while under the F-14 missiles are held "tight" to the body or wing glove so there is interference drag involved. This is the only reason I can think why the Great White Hope under the wing of a Super Hornet has less drag than a Winder under a Tomcat.

As far as I know the Flankers use the same pylons as the Fulcrums, which would mean that the Drag Areas should be similar. The Flanker with 4 MRMs and 4 SRMs would then have a munitions drag area of 6.38ft^2 (DI 93) while it's contemporary F-15 and F-14 would have munitions drag areas of 1.61ft^2 (DI 26) and 2.72ft^2 (DI 48). This is a 50% increase to the base drag of a Flanker from the info I have!

Does anyone have anything on Soviet/Russian missiles/pylons to confirm/refute what this drag means to a Flanker?

[garrya]

Most amazing to me was the range for the AIM-9M, where even on a rail for the F-15 it has just over a quarter of the drag it has on an F-14. The only logic I can think of for this is that the large pylon on the F-15 holds the missiles "far" from the wing while under the F-14 missiles are held "tight" to the body or wing glove so there is interference drag involved. This is the only reason I can think why the Great White Hope under the wing of a Super Hornet has less drag than a Winder under a Tomcat.

Shouldn't there be less drag if the missiles is closer to the wing ?

[F-16ADF]

Cool comparison Spurts,

LOL, the Aim-9/Tomcat number in the supplement is very odd? But I guess a test is a test. Same number holds true for the A model.

[sprstdlyscottsmn]

Shouldn't there be less drag if the missiles is closer to the wing ?

Good question stemmed from "common knowledge".

Interference drag is the interaction of airflow trying to move around two objects at the same time and being 'squeezed' together causing an increase in local pressure. Conformal carry, as found on the F-15, F-4, F-14 (body mounted sparrow only) results in less drag because the two bodies in question, plane and munition, are actually touching so there is no air pressing between them. The closer the two bodies are the greater the pressure that can build up between them. Many manuals roughly approximate this by listing two drag indexes for an item based on what is on the next pylon.

If we look at the HAF F-16-1, which in my opinion is one of the easiest to read DI charts, we see that the centerline EFT has a DI of 15 (plus 7 more for the pylon), but it is 18 if there are stores on the inboard wing stations. The inboard wing EFTs have a DI of 27 if nothing is midboard or if AIM-9 is midboard. This rises to 35 if a single rack (bomb) is midboard and 39 if a multiple rack is midboard. If the Midboard station has a TER with low drag 500lb bombs then the pylon has a DI of 24. The Mk82 LDGP bomb has a DI of 5, but this raises to 9 if mounted on a TER.

So if we only looked at the base drag values of a centerline EFT, two wing EFTs, and two triple racks of 500 pounders (using base DI) we get a DI of 154. However, looking at the "if next to this" or "if carried on TER" DIs then we get 205. So this shows that the interference drag of the load is 51, or a third more than the original number.

The Hornet and SHornet manuals have such detailed and complex interference drag charts that they take up more room than the basic drag charts and trying to get through them can be an exercise in exploding your brain. Anyway, hope that helps.

[madrat]

The F-15 rail is mounted inline with the airflow. The F-14 cants the sidewinder nose slightly outwards. Wouldn't that make a difference?

[sprstdlyscottsmn]

The F-15 rail is mounted inline with the airflow. The F-14 cants the sidewinder nose slightly outwards. Wouldn't that make a difference?

That would make a huge difference. I can't payed attention to that. That the same reason the Hornet has less drag than a Super Hornet.