Operational Performance Comparison: Viper, Beagle and Stubby

johnwill · by **johnwill** » 06 May 2016, 05:40

Sorry to drag this out even more, but you are more correct than I gave you credit. The drag force from missiles is essentially the same for both airplanes, but when considered as percentage impact on performance, it is much less for the F-15 due to its greater mass and thrust.

eloise · by **eloise** » 06 May 2016, 11:43

summary

btw how come F-35A have better instantaneous turn rate than F-35C ? does it have higher wing loading ? , and why do some of them turn slower at their corner velocity ?

sprstdlyscottsmn · by **sprstdlyscottsmn** » 06 May 2016, 13:42

eloise wrote:summary

btw how come F-35A have better instantaneous turn rate than F-35C ? does it have higher wing loading ? , and why do some of them turn slower at their corner velocity ?

Huh, originally I had that information joined up like you see there but with the axis switched and it was too bloated and took up two charts. That looks much cleaner.

Anyway, on to your question. The Stubb-A is pulling 1.5G more than Stubb-C, albeit at a higher airspeed, putting more stress on the pilot. The Stubb-A is out rating the Stubb-C by less than 2%, Stubb-C is turning inside the Stubb-A by over 13%. Stubb-A is decelerating at 2.4G while Stubb-C is only decelerating at 1.5G. Who is really performing better at corner velocity? On the Sustained side Stubb-C is pulling lower G with faster rate and tighter radius.

As for "why do some of them turn slower at corner velocity?" I am not sure what you mean. Every one of them improves the instant turns at Corner (by definition) so you must mean sustained turn. Sustained turn rates tend to peak at .8-.9M for afterburning fighters at altitude as the dynamic thrust is increasing and the wave drag has not kicked in yet (or is greatly reduced compared to 1.0M+ anyway). So when you have a corner velocity down below 0.7M your engines are making less thrust than at 0.8M and you need a higher Cl, and thus higher AoA, for any given level of lift. So you are making less thrust and you have more drag for any given G, it becomes perfectly reasonable why sustained rates are going down at corner V relative to 0.8M. You will see though that while the rate go down a little the Radii drop a lot. You are flying a smaller circle, you are just doing it a tad slower.

basher54321 · by **basher54321** » 06 May 2016, 18:06

johnwill wrote:
Basher, the AMRAAMs on XL were strictly fake, being made of wooden bodies with sheet metal fins screwed on. The bodies were carved out to match the standard lower OML of the airplane and there were no..........

Great stuff thank you.

eloise · by **eloise** » 06 May 2016, 22:48

sprstdlyscottsmn wrote:Huh, originally I had that information joined up like you see there but with the axis switched and it was too bloated and took up two charts. That looks much cleaner.

Anyway, on to your question. The Stubb-A is pulling 1.5G more than Stubb-C, albeit at a higher airspeed, putting more stress on the pilot. The Stubb-A is out rating the Stubb-C by less than 2%, Stubb-C is turning inside the Stubb-A by over 13%. Stubb-A is decelerating at 2.4G while Stubb-C is only decelerating at 1.5G. Who is really performing better at corner velocity? On the Sustained side Stubb-C is pulling lower G with faster rate and tighter radius.

As for "why do some of them turn slower at corner velocity?" I am not sure what you mean. Every one of them improves the instant turns at Corner (by definition) so you must mean sustained turn. Sustained turn rates tend to peak at .8-.9M for afterburning fighters at altitude as the dynamic thrust is increasing and the wave drag has not kicked in yet (or is greatly reduced compared to 1.0M+ anyway). So when you have a corner velocity down below 0.7M your engines are making less thrust than at 0.8M and you need a higher Cl, and thus higher AoA, for any given level of lift. So you are making less thrust and you have more drag for any given G, it becomes perfectly reasonable why sustained rates are going down at corner V relative to 0.8M. You will see though that while the rate go down a little the Radii drop a lot. You are flying a smaller circle, you are just doing it a tad slower.

thanks spurt

sferrin · by **sferrin** » 06 May 2016, 23:13

basher54321 · by **basher54321** » 07 May 2016, 15:42

Great find that video thanks - shame that they got Benny Hill to provide the music!

mixelflick · by **mixelflick** » 08 May 2016, 00:19

basher54321 wrote:Great find that video thanks - shame that they got Benny Hill to provide the music!

Indeed

sprstdlyscottsmn · by **sprstdlyscottsmn** » 11 May 2016, 20:40

count_to_10 wrote:Something about the Tomcat vs. Super Hornet seems horribly wrong. Everything I've heard indicates that the TC vastly out ranges the SH. Is it the fact that it is basically carrying an extra 2000 lbs of missile, or is there something about optimal cruise speed?

So I don't know if I had said this yet, but I found a snippit of F-14A data for cruise. My drag model was way off for the Tomcat. I initially had no cruise data to compare against so I went back and found the initial assumption that was proven false (idle thrust during descent). This changed base drag area, trim drag, and turning efficiency. End result? Cruise fuel burn will get better, Sustained turn got a little worse, PS during max G turn got much worse (but I feel more accurate when I run it against the one turning chart out there). Also, I am re-doing the Tomcat loadout for Sparrows and Sidewinders only. This represents the capability available when the program was closed as the Phoenix was already retired. Comparing a 2005 Tomcat with a 2020 SHornet seems wrong though. I even up the Harrier to a "2020" spec with AIM-120D since it currently can carry AMRAAM. So what do I do here? Keep it 2005 spec or upgrade to 2020 spec with a missile it was never operationally cleared for (since the funds were diverted to LANTIRN integration)?

sprstdlyscottsmn · by **sprstdlyscottsmn** » 11 May 2016, 20:54

garrya wrote:Oh and since you talk about missiles range in your files it probably worth it to talk about their agility too
you can get the information from here

https://www.scribd.com/doc/12515933/Tactical-Missile-Design-Presentation-Fleeman

digital copy of "Tactical Missile Design : 2nd Edition"

http://www.mediafire.com/view/jeofkq9csiu7fss/%28AIAA_Education%29_E._Fleeman-Tactical_Missile_Design%2C_Second_Edition-AIAA_%282006%29.pdf

missiles agility can also be estimate by this spreadsheet :
http://www.mediafire.com/view/2uz1qmg2q ... ility.xlsx

So looking at the missile spreadsheet I started taking into account turn rates and radii of the missiles. with the assumptions I have made about best missile AoA (I perused the other docs looking for this but they are quite large and I found nothing) I assumed 2 deg for body and I think 5 deg for the steering fin I found that the corner velocity for an AIM-120C is at something nuts like 1.64M at FL360. I noted the G and the Turn Rate. I then thought I would see how the heavier Sparrow compared. The much bigger wings drop the corner V to ~1.05M for an even better rate and radius. Matching the Turn rates between the AIM-7M and the AIM-120C gives a lower speed for the AIM-7 still, 0.67M. So this got me thinking that in a head on intercept the AIM-7 can be allowed to slow down much much more than the AIM-120 to have the same turn rate to counter last ditch maneuvers by the target. The AIM-7 has a tighter turn radius as well. This means I could in theory extend the minimum speed for the AIM-7 to give it more flight range, but this also means the F-14 humming along at 1.88M would pass it's own missiles. And of course with the lower speed it has less energy to burn on these turns than the AMRAAM.

What would be the best parameter to use as the "end of missile flight"? Arbitrary speed? Speed of launching aircraft? Corner Velocity? Min velocity to achieve a given turn rate? Do I somehow take warhead size into account? I am rapidly wanting to expand the scope to include the lethality of the weapons the aircraft use.

count_to_10 · by **count_to_10** » 11 May 2016, 21:24

sprstdlyscottsmn wrote:
count_to_10 wrote:Something about the Tomcat vs. Super Hornet seems horribly wrong. Everything I've heard indicates that the TC vastly out ranges the SH. Is it the fact that it is basically carrying an extra 2000 lbs of missile, or is there something about optimal cruise speed?

So I don't know if I had said this yet, but I found a snippit of F-14A data for cruise. My drag model was way off for the Tomcat. I initially had no cruise data to compare against so I went back and found the initial assumption that was proven false (idle thrust during descent). This changed base drag area, trim drag, and turning efficiency. End result? Cruise fuel burn will get better, Sustained turn got a little worse, PS during max G turn got much worse (but I feel more accurate when I run it against the one turning chart out there). Also, I am re-doing the Tomcat loadout for Sparrows and Sidewinders only. This represents the capability available when the program was closed as the Phoenix was already retired. Comparing a 2005 Tomcat with a 2020 SHornet seems wrong though. I even up the Harrier to a "2020" spec with AIM-120D since it currently can carry AMRAAM. So what do I do here? Keep it 2005 spec or upgrade to 2020 spec with a missile it was never operationally cleared for (since the funds were diverted to LANTIRN integration)?

On the missile load out: it depends on what we are trying to compare. If it is the effectiveness of the underlying airframe, then the missiles should be the same. If we are looking at historical effectiveness, then the missile loadout should be "as was".
I think I'd rather see the former.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 11 May 2016, 21:44

count_to_10 wrote:
On the missile load out: it depends on what we are trying to compare. If it is the effectiveness of the underlying airframe, then the missiles should be the same. If we are looking at historical effectiveness, then the missile loadout should be "as was".
I think I'd rather see the former.

I think you are right. Otherwise I should compare a 2005 Tomcat with a 2005 SHornet. The rest of them simply ARE being replaced in the 2020 timeline. 2020 planes for all it is.

hornetfinn · by **hornetfinn** » 16 Jun 2016, 13:53

I have to bump this thread as I found this: Transonic Free-To-Roll Analysis of the F/A-18E and F-35 Configurations

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040110952.pdf

I know it's rather old but wondered if it would be useful for this performance comparison or otherwise interesting. I could not find this posted here, so this might be interesting to those who understand aerodynamics better than me. I find it interesting that this analysis seemed to be pretty spot on that F-35C has had some wing drop tendencies and F-35A doesn't.

spazsinbad · by **spazsinbad** » 16 Jun 2016, 16:14

PDF above mentioned here: viewtopic.php?f=60&t=24599&p=260048&hilit=transonic+analysis#p260048
&
Here: viewtopic.php?f=61&t=24999&p=264675&hilit=transonic+analysis#p264675
&
'LowObservable' used to post here?: viewtopic.php?f=55&t=10665&p=128722&hilit=transonic+analysis#p128722

hornetfinn · by **hornetfinn** » 17 Jun 2016, 13:15

LOL, thanks Spaz, should've known that it has already been posted. Tried to find if it was, but obviously failed to spell the magic words to do so.... :oops:

Anyway, I'm still interested if that document contains anything interesting for the performance comparisons as I don't have enough aerodynamics knowledge to do so and because the models and methods were obviously very accurate.