F/A-18 vs F-16 Turn rate?

Hello,

Threads regarding aircraft performance, like turn-rate, turn radius, thrust to weight ratio, acceleration, wingloading, etc. are one of my favorites.

And indeed I've been learning even more stuf about this with several of you here... however, it never ceases to amaze me how quickly you turn these threads into hostile conversations between you.

By the way Hummingbird,

I've re-edited your diagram from thread below, post #608 (remember?), to put the last merge in the same colours.

Thank you again, as "a picture is worth a thousand words".

http://forums.eagle.ru:8080/showthread.php?t=140030&page=61

Just curious, does ED recognize your skills?

Thank you for the flattering words, but it doesn't take much skill to check wether an aircraft matches the real life performamce charts or not. It takes willingness/dedication to keep testing however, and a good understanding of aerodynamics helps a great deal in uncovering the source of an observed discrepancy.

Do you mean in terms of some kind of rpg GLOC fitness training for playing a certain number of hours regularly? I don't think so. But you can do g warmups that will give you X seconds to reach and sustain <8g without instantly blacking out.

Or turn off G-loc entirely ;)

By the way Hummingbird,

 

I've re-edited your diagram from thread below, post #608 (remember?), to put the last merge in the same colours.

Thank you again, as "a picture is worth a thousand words".

 

http://forums.eagle.ru:8080/showthread.php?t=140030&page=61

Nice, yeah that illustration shows how to take advantage of a smaller radius at max STR in a horizontal turn fight, all else being equal. What it doesn't show due to its two dimensional nature is the options the faster flying aircraft has to counter this, which lies in taking advantage of the extra speed by going vertical.

And thus starts the ballet with each pilot trying to lure the other into the flight regime where his/her aircraft is better off than that of the other.

When I used that test mission and looked at some of the other tracks people were posting in support of certain outcomes I had the following observations.

 

 

1. The test mission is the same for everyone and enforces some flight discipline as it won't record outside of it's parameters for sustained turn. It's a very narrow focused tool we can use.

2. Using infobar or tacview might be accurate or not, either way it does NOT enforce any parameters for a sustained turn. We have to take their word for it.

3. Outcomes using the test mission seem to be close to the GAO document.

4. Some of the posted tracks that were being cited as evidence would not have produced an output from the test mission, nowhere even close.

 

I pointed all of this out previously and was largely ignored by a certain posters almost completely, but was challenged to provide a track. I did so and there was no further comment on that either.

 

My numbers for the Hornet were quite close to the GAO document, like yours, and they showed the F-16 becoming superior at higher speeds at 15,000ft or higher, all measurements taken using the test mission file script output.

 

So, I gave up arguing. They'll use whatever 'evidence' they have that fits their narrative and seem to have a wind source that far exceeds my own.

 

Lastly, to be clear, I am not saying that the current state is correct, I would have *expected* more of a difference, but I can't definitively say that something is not well modeled.

^^^^ this.

Thanks for your testing.

All (RentedAndDented, Robin Hood, Nomad and myself) but one got all the same figures for the dcs f18 turn performance. (ED nailed the GAO figures at sea level and the hornet is slightly overperforming at 15kft by approx 0.4dps)

The acceleration figures in the GAO are slightly better than those we see in dcs. I also checked the roll rate at moderate to high alphas (approx 4 seconds to 90°), and ED nailed it.

As far as we can compare dcs and gao rw, FM is not yet perfect, but close. They did a great job so far.

RentedAndDented, keep on arguing with facts, correct the guys doing their own simplified maths (and not providing them), making oversimplified guesstimations on aircraft-performance. It is exhausting, but we must remind them providing sources and facts, showing their math and logs.

@Hummingbird, would you please share your math on 19.4dps hornet turn rate at sea level, di=0, 60% fuel?

By the way, can you give us a source on the sop regarding rw turn rate measurement?

Thanks.

I didn't realize using actual flight test data was considered "simplified maths". You guys are really digging deep.

The math for calculating the rate of an aircraft at differing weights is made simple when you have an EM diagram to go by, as the EM diagram basically hands you the Cl & Cd of the aircraft as established through flight testing.

The formula for calculating lift:

L = Cl * A * .5 * r * V^2

The formula for calculating drag:

D = Cd * A * .5 * r * V^2

The formula for calculating rate:

x = r ⋅ θ ⇒ (dx/dt) = v = r⋅(dθ/dt) = ϵ

G = (Fcpt/Fg) = (mv^2/rmg)= vϵ/g

ϵ = Gg/v.

As for the SOP regarding measuring real world turn performance, everything is recorded on an accelerometer measuring, you guessed it, acceleration aka G-force or load factor. Turn rate is then later calculated from the measured accelerations / load factors.

The point isn't whether calculating turn rate is complex or not - for horizontal, uniform circular motion it is not as you're showing. The point is that available sustained G for a given jet type - F18C Lot 20, F16C Block 50, you name it - can vary based on flight conditions and between different jets of the same type, by a significant margin.

That is why saying "The Hornet in DCS out-turns real Hornets by 0.2 deg/s!" is meaningless. Those measurements (both in game and in the real world) do not report error bars. If the real world measurement is 19.1 +- 0.2 deg/s, and the DCS turn rate is 19.4 +- 0.5 deg/s, then the performance of the DCS and real jet are by all intents and purposes identical.

The point isn't whether calculating turn rate is complex or not - for horizontal, uniform circular motion it is not as you're showing. The point is that available sustained G for a given jet type - F18C Lot 20, F16C Block 50, you name it - can vary based on flight conditions and between different jets of the same type, by a significant margin.

 

That is why saying "The Hornet in DCS out-turns real Hornets by 0.2 deg/s!" is meaningless. Those measurements (both in game and in the real world) do not report error bars. If the real world measurement is 19.1 +- 0.2 deg/s, and the DCS turn rate is 19.4 +- 0.5 deg/s, then the performance of the DCS and real jet are by all intents and purposes identical.

I'm not worried about 0.2 deg/sec, I only start to get worried when rate is anything over 0.5 deg/sec too high or too little. What's suspicious about the DCS F/A-18's performance is the sustainable load factors above 0.7-0.75 mach, esp. at altitude. At SL it is less noticable as you're quite simply G restricted down there, but go high and the odd performance starts to show. For example at 15 kft the F/A-18 is currently outrating the F-16 and F-15 at all speeds.

This in combination with the DCS F-16 underperforming in a number of areas adds up to a very noticable ingame advantage for the F/A-18 currently, esp. at what are considered normal ACM training altitudes.

I didn't realize using actual flight test data was considered "simplified maths". You guys are really digging deep.

 

The formula for calculating rate:

x = r ⋅ θ ⇒ (dx/dt) = v = r⋅(dθ/dt) = ϵ

G = (Fcpt/Fg) = (mv^2/rmg)= vϵ/g

ϵ = Gg/v.

Congrats, you managed to copy a formula from a page on the Internet. Now tell me, given the precision of the measurement results (G and M you get from the infobar) the game can provide, what would be the uncertainty in the result and how would you report the result correctly. E.g. given M=0.65, G=4.6 from the infobar, what is ϵ?

And the above is assuming you can actually manage to hold the flight parameters static enough without assistance, which I doubt because it isn't that easy. Using the rate check mission gives you that assistance.

Prancing Killer, I enjoy physics conversations when people work together to find an answer. Being humble is important. I mean, I have a degree in astrophysics, but I'm new to DCS and the physics of aviation, so even I'm scratching my head at the strange short hand of skipped derivation steps in the formulae above, and I'm quite used to highly abbreviated derivations in proofs.

That being said, the formulae do work, eg:

given the precision of the measurement results (G and M you get from the infobar) the game can provide, what would be the uncertainty in the result and how would you report the result correctly. E.g. given M=0.65, G=4.6 from the infobar, what is ϵ?

On the viper you could use the HUD velocity switch toggle for true airspeed, and the G indicator in level flight. So for say a bank angle 82 deg G=7.3 and TAS = 564 knots = 290 m/s :

ϵ = Gg/v => ϵ = 7.3*9.8/290 = 0.247 rad/s = 13.75 deg/s.

You can also use the rate of turn formula ω=1,091tanθ/V and where θ is the bank angle and get the same result.

ω=1091 tan(82) / 564 = 13.76 deg/s

Congrats, you managed to copy a formula from a page on the Internet. Now tell me, given the precision of the measurement results (G and M you get from the infobar) the game can provide, what would be the uncertainty in the result and how would you report the result correctly. E.g. given M=0.65, G=4.6 from the infobar, what is ϵ?

 

And the above is assuming you can actually manage to hold the flight parameters static enough without assistance, which I doubt because it isn't that easy. Using the rate check mission gives you that assistance.

What do you mean a copy of a formula from the internet?? It is THE formula for calculating rate! Go look in your textbook please!

ϵ is rate, and if you follow the formula then for M = 0.65 & G =4.6 at SL that is 0.203 rad/s or 11.63 deg/sec.

What do you mean a copy of a formula from the internet?? It is THE formula for calculating rate! Go look in your textbook please!

 

ϵ is rate, and if you follow the formula then for M = 0.65 & G =4.6 at SL that is 0.203 rad/s or 11.63 deg/sec.

Yup, but just a heads up: that formula is for the true airspeed. So unless we know the altitude or assume you are 0 ft, then we need a direct reading of the true airspeed, which luckily the F-16 can provide in the HUD. For example at mach 0.65 & 15000ft the result would be 12.33 deg/s, since the TAS is 407.18 (as compared to 429.96 at sea level). Same G loading at a lower velocity requires a tighter turn, etc.

Just a heads up. That formula is for the true airspeed. So unless know the altitude or assume you are 0 ft, then you need a direct reading of the true airspeed, which luckily the F-16 can provide in the HUD. For example at mach 0.65 & 15000ft the result would be 12.33 deg/s.

Exacto mundo, and I always record TAS with the info bar (ctrl + y twice).

I use TAS as the EM charts list performance at true mach number.

Exacto mundo, and I always record TAS with the info bar (ctrl + y twice).

 

I use TAS as the EM charts list performance at true mach number.

You can double press ctrl+Y and get TAS? That's incredibly useful, thank you sir :thumbup:

You can double press ctrl+Y and get TAS? That's incredibly useful, thank you sir :thumbup:

You're most welcome :)

Prancing Killer, I enjoy physics conversations when people work together to find an answer. Being humble is important. I mean, I have a degree in astrophysics, but I'm new to DCS and the physics of aviation, so even I'm scratching my head at the strange short hand of skipped derivation steps in the formulae above, and I'm quite used to highly abbreviated derivations in proofs.

 

That being said, the formulae do work, eg:

 

 

 

On the viper you could use the HUD velocity switch toggle for true airspeed, and the G indicator in level flight. So for say a bank angle 82 deg G=7.3 and TAS = 564 knots = 290 m/s :

 

ϵ = Gg/v => ϵ = 7.3*9.8/290 = 0.247 rad/s = 13.75 deg/s.

 

You can also use the rate of turn formula ω=1,091tanθ/V and where θ is the bank angle and get the same result.

 

ω=1091 tan(82) / 564 = 13.76 deg/s

So the fact that you are getting a 4 figure result from an obviously rounded off 2 figure measurement does not bother you at all? You don't deal with experimental uncertainties in astrophysics or what?

What do you mean a copy of a formula from the internet?? It is THE formula for calculating rate! Go look in your textbook please!

No, the funny part was how you copied the derivation of the formula symbol for symbol from that website without any particular reason, you could've just said "ϵ = Gg/v".

ϵ is rate, and if you follow the formula then for M = 0.65 & G =4.6 at SL that is 0.203 rad/s or 11.63 deg/sec.

This answer is not complete (and incorrect), you should check what I wanted you to do again.

Would love to just discuss numbers, but it is difficult to do so without occasionally having to question the competence of people who don't know how to work with experimental data properly and use arguments such as "my 13 ± 0.5 result is clearly larger than 12.9 on the chart, so the flight model must be changed!" I mean, how else is one supposed to explain? Thanks for cleaning the thread up though.

So the fact that you are getting a 4 figure result from an obviously rounded off 2 figure measurement does not bother you at all?

That's a fair point, and I considered it before posting, understanding that part of your point is about the small reported turn rate delta could fall under "uncertainty" of a low sig fig inputs. Just fyi, I don't necessarily disagree with you. However, given that the 2 angular speeds above are calculated from different figures according to diffently derived formulae using different physical properties, and are off by only 0.01 deg/s, it's a bit more likely that there are implied zeroes after each of those 2 digit numbers because DCS has to quantize steps between variable g force and bank angles at some figure. Why not the same values shown both in game and in tacview?

This answer is not complete (and incorrect), you should check what I wanted you to do again.

There's nothing incorrect about the calculation. Again refer to your textbook.

That's a fair point, and I considered it before posting, understanding that part of your point is about the small reported turn rate delta could fall under "uncertainty" of a low sig fig inputs. Just fyi, I don't necessarily disagree with you. However, given that the 2 angular speeds above are calculated from different figures according to diffently derived formulae using different physical properties, and are off by only 0.01 deg/s

You need to be careful with stuff like this, sometimes it could appear to match but only due to luck with the numbers you are given. Let's say you added a bit of extra thrust in your example and are now pulling 7.5G instead of 7.3, with the rest being the same (TAS = 564 knots = 290 m/s). What bank angle would you have?

ϵ = Gg/v => ϵ = 7.5*9.8/290 = 0.253 rad/s = 14.52 deg/s (old turn rate = 13.75)

bank angle = arctan(14.52 * 564 / 1091) = 82.4 degrees, which on the digital readout that rounds to the nearest integer (like the DCS infobar does) would still show "82".

, it's a bit more likely that there are implied zeroes after each of those 2 digit numbers because DCS has to quantize steps between variable g force and bank angles at some figure. Why not the same values shown both in game and in tacview?

No, the numbers are just rounded off. While the steps are indeed "quantized", just like anything digital, those steps are nowhere near 0.1G or 0.01M (you'd feel very noticeable "bumps" if it was like that). Check for example this picture of the modified turn rate mission output, the really long numbers at the bottom are coordinates from which most other things are calculated, and I have the M number show 6 digits:

You need to be careful with stuff like this, sometimes it could appear to match but only due to luck with the numbers you are given. Let's say you added a bit of extra thrust in your example and are now pulling 7.5G instead of 7.3, with the rest being the same (TAS = 564 knots = 290 m/s). What bank angle would you have?

 

ϵ = Gg/v => ϵ = 7.5*9.8/290 = 0.253 rad/s = 14.52 deg/s (old turn rate = 13.75)

 

bank angle = arctan(14.52 * 564 / 1091) = 82.4 degrees, which on the digital readout that rounds to the nearest integer (like the DCS infobar does) would still show "82".

As I said above, we agree on being cautious, and we don't have the data to make any conclusions. The tangent function close to 90 degrees can give wildly different results with even slightly different bank angles. Caution is indeed important. Imo, before we worry about turn rate too much, I think we should wait until we see the changes regarding early onset of GLOC and possibly issues with the drag/lift/FLCS model which could be limiting both the turn rate and the sustained turn rate.

I think we should wait until we see the changes regarding early onset of GLOC

Indeed, if this ends up being close to what real pilots say about g-tolerance, it's going to be great and probably the biggest "buff" the Viper can get. If on top of that they also let it sustain 9.3g as some people claim it should, it will certainly be quite competitive.