F/A-18 turn radius - 3k, 6k and 9k

[vctpil]

Hi,

 

In the CNATRA book 1289, it is wrote that the average turn radius for the T-45 is 6,000ft in diameter. That why offensive/defensive BFM start with 3,000ft, 6,000ft and 9,000ft apart.

 

What about the F/A-18C ? In the NAVMC 3500, 3k, 6k and 9k are still use, but the turn radius of the F/A-18 is less according the A1-F18AC-NFM-200 - NATOPS Flight Manual Performance Charts.

 

I have a try in DCS, and it seems more logical to use 1,5k, 3k and 4,5k.

 

So, can anyone clarify ? Thanks.

[Yoda967]

I'm not sure what they mean when they say "average turn radius for the T-45". The radius of an aircraft's turn is not a function of the aircraft's design, but of bank angle and velocity. (If you want to see the math for that, look here.)

 

It's important to note that bank angle and G are not tied together. You can bank your jet at 60 degrees and pull 0 G, but in doing so, you'll lose altitude. You've probably noticed that you have to pull back on the stick to maintain altitude when your wings aren't level, and that's what we're talking about here. It doesn't matter what airplane you're flying, bank the wings at 45 degrees and pull the stick back to maintain altitude, you're "pulling" about 1.4Gs. At 60 degrees and constant altitude, you're "pulling" 2Gs. At 80 degrees of bank and a constant altitude, you're pulling 5.8Gs.

 

A level turn with 60 degrees angle-of-bank at 400 knots and a given altitude is the same for an FA-18C as it is for a T-45 or a MiG-29. That's why NAVMC 3500 gives the same separation distances for BFM that you find in the CNATRA 1289.

[Switch625]

I'm not sure what they mean when they say "average turn radius for the T-45". The radius of an aircraft's turn is not a function of the aircraft's design, but of bank angle and velocity. (If you want to see the math for that, look here.)

 

It's important to note that bank angle and G are not tied together. You can bank your jet at 60 degrees and pull 0 G, but in doing so, you'll lose altitude. You've probably noticed that you have to pull back on the stick to maintain altitude when your wings aren't level, and that's what we're talking about here. It doesn't matter what airplane you're flying, bank the wings at 45 degrees and pull the stick back to maintain altitude, you're "pulling" about 1.4Gs. At 60 degrees and constant altitude, you're "pulling" 2Gs. At 80 degrees of bank and a constant altitude, you're pulling 5.8Gs.

 

A level turn with 60 degrees angle-of-bank at 400 knots and a given altitude is the same for an FA-18C as it is for a T-45 or a MiG-29. That's why NAVMC 3500 gives the same separation distances for BFM that you find in the CNATRA 1289.

 

 

Interesting. So what IS affected by the aircraft design?

 

 

I'm just now starting to get into all the technical BFM theory: rate vs radius fight, Corner speed etc. So i'm still trying to internalize some basic concepts, and this post was quite helpful. Just looking for some more enlightenment!:smilewink:

[Yoda967]

Thanks, Switch. A good many books have been written to answer that question.

 

The first thing that comes to mind in answer to your question is thrust, which is what determines the aircraft's ability to overcome total drag, and for the purposes of our radius discussion, the induced drag that comes with high G maneuvering. The more thrust available, the greater a fighter's ability to sustain a turn.

 

As you "pull" Gs, the induced drag from the increased angle of attack will slow the airplane, forcing you to increase thrust to maintain the airspeed (and thus the generated lift that is producing both the turn and the constant altitude). At some point, You'll reach the limits of the available thrust, and you won't be able to pull any harder without decelerating. Once that happens, you're limited by the thrust and not by the structural G limitation of the airframe.

 

Corner speed is also design dependent. I'd define corner speed as the speed at which maximum control surface deflection produces a G loading equal to the airframe G limitation. Any faster, and maximum deflection produces excess stress on the airframe. Any slower, and you can't produce enough of an angle of attack to generate G at the limit.

 

I'm not an expert here...there are certainly folks here who are, and I'll defer to them, if they choose to chime in.

Edited October 2, 2019 by Yoda967

[Ironhand]

Switch625 said:

Interesting. So what IS affected by the aircraft design?

Maximum rate, minimum radius, and corner speed. Here’s an old video that explains corner speed in basic terms. Perhaps it’ll be helpful:

 

 

 

Edited December 4, 2020 by Ironhand

[sk000tch]

OP- Not sure what your reading but sounds like BFM exercises, and if It's in a t-45 those drills are setup to teach specific concepts and skills. If you're copying drills to improve in Hornet, like off/def perch sets or something, not necessary to perform exactly as specified. Probably better to have some variety. Most DCS guys just pass head on, in a sim minimum sep, hard deck, knock it off calls, etc are all Kinda pointless.

 

Your second question is more intersting. I can't post anything here, but if you've got t-45 syllabuses presumably you can find 18c performance charts. Look for chart with turn radius or rate on Y axis, Mach number on x axis. Charts will be available for different altitudes. Good to know these well enough to predict radius at high speeds to calculate lateral separation on intercepts, but I suspect more general knowledge of which fighters are turn vs rate for DACM will be fine. Otherwise you'll be spending a lot of time Memorizing charts for adversarial aircraft.

[majapahit]

Real Life (AIM-9X) 'shoot around the corner' missiles as the new worldwide standard, are a universe separated from DCS (or maybe ‘RL’ Nevada) 'guns only, heads-on-merge' jet fighter duels,

 

where such seem to be rooted in antiquated (WWI) training setups to demonstrate and mark a pilot's command of the apparatus, as are f.i. parading exercises and 'flying by the numbers'.

 

I'd say in RL hot theatres, the Black Sea or China sea these days, maximum corner speed is the number in the back of the mind of any intercepting jet pilot send out to investigate or flying CAP, to be on the safe side of error.

Edited October 3, 2019 by majapahit

[Hummingbird]

Sadly there are no publically available EM charts for this bird, otherwise it would've been an easy question to answer.