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

[Nomad]

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

Sigh... I guess I'll give up on trying to have you figure it out and just explain.

 

Look, when you have a digital readout of a variable that's normally continuous from, say, DCS infobar it will be rounded, in case of our infobar the Mach number is rounder to the nearest hundreth, and the load factor to the nearest tenth. This means that a reading of M 0.65 for example is in fact anything between 0.6450... and 0.65499.... Same applies for the G number. Now if you plug in the min and max possible values in the formula you can see the interval in which the end result (your turn rate) can vary.

 

ϵ_1 = 4.6499999 * 9.81 / (0.645 * 340) = 11.9 deg/s

 

ϵ_2 = 4.55 * 9.81 / (0.6549999 *340) = 11.5 deg/s

 

As you can see, the final result can vary by about 0.4 deg/s. You can write it as 11.7 ± 0.2 deg/s, or ≈ 12 deg/s, rounding to two significant figures as your Mach and G numbers. And this is just the measurement uncertainty, and doesn't include user error, such as failing to stay in desired flight parameters, and will likely lead to even bigger errors in the end result. This is something you can't ensure properly, which is why you were told to use the turn rate check mission, which not only provides you with assistance to maintain a good turn, but also calculates the turn rate directly from the change of your direction. If you want to have the G load logged, it is easy to modify the script, it's sitting inside the mission file.

 

That said, there's still going to be some errors since the limits you have to stay in have some leeway (otherwise it would be way to difficult to do it) so ideally you should do a bunch of experiments around the same speed/g load, record the results, calculate averages, confidence intervals etc. Some work, but if one cares as much as you do, then why not? ;)

 

P.S. There are better ways to do the above math, this is just more instructive. You can read more about that here:

https://en.wikipedia.org/wiki/Propagation_of_uncertainty

https://en.wikipedia.org/wiki/Significance_arithmetic

[Bearfoot]

Can someone link to the referenced turn rate test mission? Seems to have been lost in the squabble

[Figaro9]

Can someone link to the referenced turn rate test mission? Seems to have been lost in the squabble

 

 

here you go.

 

 

 

https://forums.eagle.ru/showpost.php?p=2692721&postcount=15

[Hummingbird]

Sigh... I guess I'll give up on trying to have you figure it out and just explain.

 

Look, when you have a digital readout of a variable that's normally continuous from, say, DCS infobar it will be rounded, in case of our infobar the Mach number is rounder to the nearest hundreth, and the load factor to the nearest tenth. This means that a reading of M 0.65 for example is in fact anything between 0.6450... and 0.65499.... Same applies for the G number. Now if you plug in the min and max possible values in the formula you can see the interval in which the end result (your turn rate) can vary.

 

ϵ_1 = 4.6499999 * 9.81 / (0.645 * 340) = 11.9 deg/s

 

ϵ_2 = 4.55 * 9.81 / (0.6549999 *340) = 11.5 deg/s

 

As you can see, the final result can vary by about 0.4 deg/s. You can write it as 11.7 ± 0.2 deg/s, or ≈ 12 deg/s, rounding to two significant figures as your Mach and G numbers. And this is just the measurement uncertainty, and doesn't include user error, such as failing to stay in desired flight parameters, and will likely lead to even bigger errors in the end result. This is something you can't ensure properly, which is why you were told to use the turn rate check mission, which not only provides you with assistance to maintain a good turn, but also calculates the turn rate directly from the change of your direction. If you want to have the G load logged, it is easy to modify the script, it's sitting inside the mission file.

 

That said, there's still going to be some errors since the limits you have to stay in have some leeway (otherwise it would be way to difficult to do it) so ideally you should do a bunch of experiments around the same speed/g load, record the results, calculate averages, confidence intervals etc. Some work, but if one cares as much as you do, then why not? ;)

 

P.S. There are better ways to do the above math, this is just more instructive. You can read more about that here:

https://en.wikipedia.org/wiki/Propagation_of_uncertainty

https://en.wikipedia.org/wiki/Significance_arithmetic

 

If you go by Mach alone you would have a point Nomad, but why on earth would you ever do that? You should ofcourse go by the TAS reading, which is in either kts or km/h, and not the HUD mach number. My infobar readings are in km/h (I'm Danish, so I like it that way) before I converted it to kts. So for a SL Mach 0.65 reading I would aim for 796 km/h at SL. So the speed readings are plenty accurate.

 

Thus your biggest rounding error will be with the G reading, and the infobar seems to only round down, i.e. it will only show for example 6.1 G when 6.1 G is reached, not when at 6.06 or 6.09 G. And it will continue to read 6.1 G until 6.2 G is reached and so on. Hence G readings have up to a negative 0.09 G possible rounding error.

 

Also like I pointed out earlier I ran these tests over and over again to get an accurate average, I didn't just run it twice or three times. I did at least 10 to 15 of these runs.

 

Either way like I said I don't mind a 0.2 deg/sec discrepancy, what I do mind is when we hit 0.5 deg/sec or more, and at 15 kft I'm getting over 1 deg/sec more in the F/A-18 than what the GAO report lists as the max STR at that altitude, and at at SL its the same if you use the paddle, and as a result the F/A-18 is outrating everything.

Edited November 22, 2019 by Hummingbird

[Figaro9]

If you go by Mach alone you would have a point Nomad, but why on earth would you ever do that? You should ofcourse go by the TAS reading, which is in either kts or km/h, and not the HUD mach number. My infobar readings are in km/h (I'm Danish, so I like it that way) before I converted it to kts. So for a SL Mach 0.65 reading I would aim for 796 km/h at SL. So the speed readings are plenty accurate.

 

 

 

Well, we took you by your own words. Our fault, we should not do that, sorry.

 

Please, show your math, then we do not have to take you by your unprecise wording.

Anyway, Devs will not take your on flight observations and simplified maths as a proof, I assume. No log, no tacview, no proof.

 

 

 

Any news on your math on hornet turn rate at sea level (DI=0, 60%fuel) ? All we could see till now are some formulas, no maths…. Thanks

[Nomad]

If you go by Mach alone you would have a point Nomad, but why on earth would you ever do that? You should ofcourse go by the TAS reading, which is in either kts or km/h, and not the HUD mach number. My infobar readings are in km/h (I'm Danish, so I like it that way) before I converted it to kts. So for a SL Mach 0.65 reading I would aim for 796 km/h at SL. So the speed readings are plenty accurate.

 

Thus your biggest rounding error will be with the G reading, and the infobar seems to only round down, i.e. it will only show for example 6.1 G when 6.1 G is reached, not when at 6.06 or 6.09 G. And it will continue to read 6.1 G until 6.2 G is reached and so on. Hence G readings have up to a negative 0.09 G possible rounding error.

 

Also like I pointed out earlier I ran these tests over and over again to get an accurate average, I didn't just run it twice or three times. I did at least 10 to 15 of these runs.

 

Either way like I said I don't mind a 0.2 deg/sec discrepancy, what I do mind is when we hit 0.5 deg/sec or more, and at 15 kft I'm getting over 1 deg/sec more in the F/A-18 than what the GAO report lists as the max STR at that altitude, and at at SL its the same if you use the paddle, and as a result the F/A-18 is outrating everything.

There is another thing as well. For any non-90 degree bank angle your G readout will have a vertical component due to gravity, which will result in a higher readout than you'd get from just the turn acceleration. This will make it seem like the turn rate is higher, so you want to correct for that too.

Edited November 22, 2019 by Nomad

[Hummingbird]

Well, we took you by your own words. Our fault, we should not do that, sorry.

 

Please, show your math, then we do not have to take you by your unprecise wording.

Anyway, Devs will not take your on flight observations and simplified maths as a proof, I assume. No log, no tacview, no proof.

 

1) Never claimed to rely purely on a Mach reading, infact I very clearly specified that I used infobar readings for all measurements. So that really isn't an excuse.

 

2) I already showed you the math...

[BuzzU]

I never dreamed this thread would go this far. I created a monster.

[Hummingbird]

There is another thing as well. For any non-90 degree bank angle your G readout will have a vertical component due to gravity, which will result in a higher readout than you'd get from just the turn acceleration. This will make it seem like the turn rate is higher, so you want to correct for that too.

 

Err... the infobar G reading doesn't work like that, it only shows the G about the centripetal axis, i.e. toward the center of rotation. You can check that yourself by doing for example 90 deg climb or dive. If it didn't work like this it would be useless for our tests. Same deal for the HUD reading.

Edited November 22, 2019 by Hummingbird

[Oceandar]

I never dreamed this thread would go this far. I created a monster.

Well you should know by now sir, any kind of A vs B thread basically just open pandora box lol.

[BuzzU]

Yes, what was I thinking?

[Nomad]

Err... the infobar G reading doesn't work like that, it only shows the G about the centripetal axis, i.e. toward the center of rotation. You can check that yourself by doing for example 90 deg climb or dive. If it didn't work like this it would be useless for our tests. Same deal for the HUD reading.

Incorrect, what it shows is the vertical component of the force that acts on the sensor in aircraft's coordinate system. In simple terms it show how hard the seat is pushing up on the pilot's butt (but not his sides or back). When you are in a vertical climb, he is resting on his back instead while his butt takes zero pressure, hence you get 0G. Be in a climb that is anything else than 90 and you will see numbers on the G-meter. Same applies for bank.

 

Hey, you can do a simple problem: find out what turn rate your plane is doing in a straight and level flight. First answer that using common sense, and then use the formula and see what you get.

[Syndrome]

I never dreamed this thread would go this far. I created a monster.

 

Well to be fair to everyone, it's a fascinating question about the physics of flight and this kind of passionate interest would exist about this topic whether there was a thread or not. I was certainly curious about it and was hence drawn to this thread despite the apparent land mines.

 

For the people who are still interested in the physics, the basic force diagram behind the formula are as follows: (see attached).

 

The G that we see our HUD is by definition the ratio of the Lift (the force you feel through your seat) and the force of gravity. Or equivalently the ratio of the accelerations of the two forces.

 

G ≡ LIFT/mg = LIFT/[L*Cos(θ)] = 1/Cos(θ)

 

To clarify, since there appears to be some confusion on this point, the centrifugal force (shown in orange) is horizontal in a flat circle turn. The red arrow (not labeled) is the resultant force which is equal and opposite of the Lift force.

 

There also seemed to be some confusion about which g was being measured in the HUD, and that is of course the G defined above by the LIFT (blue vector), and the resultant opposing force (red vector) that feels like apparent extra gravity.

 

So some of the above equations regarding bank angle, velocity, and ratios of the Lift to gravity are in fact correctly taking into account the bank angles and component forces. However, the derived formula for G = (Fcpt/Fg) = (mv^2/rmg)= vϵ/g was also missing a sinθ term since L= (Fcpt/sinθ): ergo G = Fcpt/(sinθ*Fg) = (mv^2/rmg*sinθ)= vϵ/(g*sinθ), and hence ϵ = Gg*sinθ/v. However I didn't notice because we used θ=82 and sin(82deg)= 0.99, so it didn't make a big enough difference in this case to catch the error. My apologies if I added to any confusion. Hopefully this post clears things up a bit, and provides an example of why it is always a good idea to verify engineering formulas posted on the internet that aren't backed up by a derivation, and a force diagram.

Edited November 23, 2019 by Syndrome

[Dee-Jay]

Hi!

There also seemed to be some confusion about which g was being measured in the HUD, and that is of course the G defined above by the LIFT (blue vector), and the resultant opposing force (red vector) that feels like apparent extra gravity.

 

 

G meter seems to be not 100% reliable yet. One can indeed have some fluctuation on taxi/takeoff roll:

 

 

... but not that much:

 

 

(up to 3.8!)

 

Maybe a matter of position of G meter relative to CG (?)

 

Regards.

Edited November 23, 2019 by Dee-Jay

[Nomad]

Hopefully this post clears things up a bit, and provides an example of why it is always a good idea to verify engineering formulas posted on the internet that aren't backed up by a derivation, and a force diagram.

The real lesson here is that it is always better to measure things as directly as possible if one can. You want to argue about turn rates? Measure the turn rate. Yes, they might be using the g load in rl, but it is most likely because it is much easier to just record data from an accelerometer than to determine an aircraft's exact position and velocity vector 10 times per second. But since DCS is a computer program, and we have full control over what happens and what information we receive, there is no reason to not do things in the most convenient way possible.

 

TL;DR: use the goddamn rate mission.

[Syndrome]

Hi!

 

 

 

G meter seems to be not 100% reliable yet. One can indeed have some fluctuation on taxi/takeoff roll:

 

 

... but not that much:

 

 

(up to 3.8!)

 

Maybe a matter of position of G meter relative to CG (?)

 

Regards.

 

That's a good catch! I wonder if the g meter reading instability is related to the issues that cause other instability?

 

I can get this vibration at much lower speeds with lighter weight and enough to apparently cause blackouts from the instantaneous g forces, or maybe concussion?

[Syndrome]

You want to argue about turn rates?

 

Can't say that I do. I am still very new to DCS and learning at a break neck pace to try and keep up with most of the conversations here. I'm only chiming in with talk about physics and force diagrams because I like physics, and feel I have something to potentially contribute in that narrow regard.

 

As I said before, I am not overly worried about the turn rates of any particular plane so much as I am curious about the principles so I can know how to find the edges of the flight envelope vs the edges of my limited skill, and mostly so my practicing is more useful and not wasted on trying to push past actual physical barriers, or to know when I have stumbled upon a new trick or started to master some necessary & important level of fine control. I've been playing for a couple months and just did my first successful aerial refueling mission last night. Just so you know where I'm coming from.

[Nomad]

Can't say that I do. I am still very new to DCS and learning at a break neck pace to try and keep up with most of the conversations here. I'm only chiming in with talk about physics and force diagrams because I like physics, and feel I have something to potentially contribute in that narrow regard.

 

As I said before, I am not overly worried about the turn rates of any particular plane so much as I am curious about the principles so I can know how to find the edges of the flight envelope vs the edges of my limited skill, and mostly so my practicing is more useful and not wasted on trying to push past actual physical barriers, or to know when I have stumbled upon a new trick or started to master some necessary & important level of fine control. I've been playing for a couple months and just did my first successful aerial refueling mission last night. Just so you know where I'm coming from.

Oh but this was not aimed at you, but more in general, at an arbitrary forum poster who would find themselves unhappy about the performance of some aircraft and wants to let the public and developers know. If one wants to produce useful data, it is always best to stick to the most reliable measurement methods. That said, you contribution is welcome, although I kinda wanted to wait and let Hummingbird work it out on his own. ;)

[Hummingbird]

I think you guys should take the F-16 and F/A-18 and run STR tests at 15 kft.

 

According to the available documentation the clean F-16 has a higher max STR than the clean F/A-18 at 15 kft. Check wether this holds true in DCS, according to my tests it doesn't.

[Hummingbird]

Oh but this was not aimed at you, but more in general, at an arbitrary forum poster who would find themselves unhappy about the performance of some aircraft and wants to let the public and developers know. If one wants to produce useful data, it is always best to stick to the most reliable measurement methods. That said, you contribution is welcome, although I kinda wanted to wait and let Hummingbird work it out on his own. ;)

 

I knew what you were talking about Nomad, but Im still not sure the infobar G meter works like that. It would be more accurate if it only measures the centripetal force.

 

That said if it is measuring the sum of the vectors it won't make much of a difference. For example from 22,000 to 28,000 lbs a F-16 will hit 2.8-2.83 G at 12 dps due to the slightly different bank angle. (not the max rate btw, just chose 12 dps as an example)

Edited November 23, 2019 by Hummingbird

[Syndrome]

I think you guys should take the F-16 and F/A-18 and run STR tests at 15 kft.

 

According to the available documentation the clean F-16 has a higher max STR than the clean F/A-18 at 15 kft. Check wether this holds true in DCS, according to my tests it doesn't.

 

I suspect that the drag/lift model is a bit off in game. There are a few lines of evidence for this,

1) acceleration behaves as if the F-16 weighs about 7000 lbs more than the stated weight in game.

2) instability (violent oscillations) in level flight

3) inability to maintain higher bank angles (82-84deg) required for 9g turns unless the F-16 is ultra light and running on fumes.

 

The video provided in the OP gives information with regard to with the bank angle in level low altitude turns. Now to be clear, we can't assume too much accuracy since we aren't given a true horizontal/vertical line in the video. However we know they are flying at very low alt, so they can't be losing much alt in the turns, and if you average the angles entering and leaving the turns you can get rough idea of the kind of bank angles an F16 should be able capable of in game.

 

The video shows the F16 entering the turn at a relative angle of 82° and leaving the turn at a relative angle of 86°. Averaging these to account for an unknown true horizon, you get a bank angle of 84°, which is possible in game at high speeds for an extremely light weight F-16, though testing it is nearly impossible atm because we black out way too soon. The g-force experienced in such a level turn would be 1/cos(84) = 9.6g. And we can only sustain consciousness under 8g with warmups.

 

So yes, the F-16 is probably under-performing in terms of lift generated in high bank angles. This could be caused by the early access version of the FLCS which seems to be causing other issues as well such as moderately high speed instability. However we can't even really know this yet because we can't stay awake during such a turn at the speeds and weight ranges possible in game.

Edited November 24, 2019 by Syndrome

[Hummingbird]

Good findings Syndrome.

 

Should note that F-16 pilots have mentioned that 9.3 G's can be held in the horizontal, which is also supported by the information available regarding the DFLCS limit. More than this can be hit momentarily however, with as much as 10 G's being reported briefly in a pull out.

 

PS: In the mission editor turn off G-effects, then you wont black out nomatter the G's. Also turn on unlimited fuel so that you can continue testing the same weight :)

Edited November 24, 2019 by Hummingbird

[Top Jockey]

By the way, one doubt for whoever wants to share their opinion on BFM performance.

 

Which would be the most "equitable" way of comparing BFM performance between 2 different aircraft - regarding internal fuel:

- giving both the same percentage ( % ) of fuel - which can greatly differ the fuel quantity from aircraft to aircraft;

- or the exact same fuel quantity ( lbs ) for both ?

 

Example:

- giving both a MiG-29 and JF-17, 50% internal fuel, one will feel increased difficulty while BFM in the MiG;

- giving both of them some (for instance) 3500 lbs of fuel, one will notice easier BFM in the MiG.

 

Essentialy it's the question I've posted at port #7 htread below.

https://forums.eagle.ru/showthread.php?t=257423

[Exorcet]

By the way, one doubt for whoever wants to share their opinion on BFM performance.

 

Which would be the most "equitable" way of comparing BFM performance between 2 different aircraft - regarding internal fuel:

- giving both the same percentage ( % ) of fuel - which can greatly differ the fuel quantity from aircraft to aircraft;

- or the exact same fuel quantity ( lbs ) for both ?

It depends on what you're trying to determine.

 

 

I like to use fuel fraction (fuel mass/aircraft mass) because it's roughly proportional to range.

 

 

Range doesn't have to be equal though, for example a point defense interceptor may take off and go into combat at nearly full fuel while the long range fighter it's flying to intercept has already burned half its fuel.

 

 

Really, anything is fair and if you want to be thorough, you'd need to do multiple tests with different fuel loadouts.

[Top Jockey]

It depends on what you're trying to determine.

 

 

I like to use fuel fraction (fuel mass/aircraft mass) because it's roughly proportional to range.

 

 

Range doesn't have to be equal though, for example a point defense interceptor may take off and go into combat at nearly full fuel while the long range fighter it's flying to intercept has already burned half its fuel.

 

 

Really, anything is fair and if you want to be thorough, you'd need to do multiple tests with different fuel loadouts.

 

Yeah, I know this really is more of a specific technical comparison between dissimilar aircraft type.

But my curiosity is essentialy to ascertain which fighter has best / better BFM capabilities in a pure machine vs machine comparison.

 

The fuel mass / aircraft mass, also does make sense.

Although I'm not thinking in therms of range, but in therms of pure physics capability analysis of both fighters, which is in internal fuel:

 

- 50 % fuel for both an F-14 and an JF-17 (F-16, MiG, whatever):

Would be a disadvantageous comparison for the F-14, as it would represent a lot of weight in internal fuel in aircraft that is already much heavier than a JF-17.

 

- some 3500 lbs (for instance) of fuel for both:

Would be a disadvantageous comparison for the JF-17, as for this one this would be roughly 70 % of its internal capacity, whereas for the F-14 it would be roughly 22 % - therefore not hindering its BFM performance so much as for the JF-17.

 

So I've guessed: would it be more equitable instead, to give (for instance) the fuel for 5 minutes in full afterburner for both aircraft ?