investigating Hornet's Slow-State Energy Bleed?

[wilbur81]

Question about the Hornet and energy-bleed/general performance between 225(ish)-300kts:

 

I was watching (again) the brilliant Jetstream documentary about Canadian Hornet pilot training. In episode 5, the "BFM" episode, I was struck with how well the CF-18 could maintain knots and even accelerate when pulling 3-5 g's in the 250-300 kts range. I've done quite a bit of testing at the altitudes, airspeeds, g-loading, and a/c configuration to compare, and with our current DCS Hornet FM/Engine model, pulls of 2.5 to 4 g's when at or below around 240-300 kts (and b/w sea level and 16000K) just instantly bleed (even when descending). I'm not using max stick deflection pulls and most all maneuvers are in full AB. I'll create some of my own tracks and post them when I get the chance. But here are some time-stamps for the HUD footage so you can see what I mean: basically watch/assess starting at 08:19 through 10:42. (Do yourself a favor if you haven't and watch the whole series. )

 

Note especially that he can, multiple times, achieve 25+ Alpha at speeds between 290 and 300 kts without 'cashing it all in.' In DCS, the only way I can see those Alpha's is if I'm slower than 250(ish) kts and drain the knots out...in which case you can see Alpha's get VERY high, but you have limited to no real maneuverability. In the video, at 20+ Alpha he still has knots and solid maneuvering options and hasn't 'cashed it all in.'

 

Keep in mind that it appears from takeoff and landing footage that these CF-18s are carrying one centerline bag and have all pylons, though unloaded...and of course are two-seaters with the instructor in the back. Also, I'm keeping in mind that I don't know the air temperatures for the flight. I'm just wondering if anyone else can achieve the AOA/and energy sustainment with 2.5-4 g pulls between 240ish - 300ish kts with our DCS Hornet like the real CF-18s in this video?

Edited August 6, 2021 by wilbur81

[Oozler]

I think they (ED) made the F/A-18 module poopier then it (the actual F/A-18) really is in an effort to keep the high alpha low speed bread and butter of the hornet secret as some aspects are still classified.... If one wants to hide what an airframe can really do one needs to make it either better or worse then the real thing. Looks like we, unfortunately, got the latter. The flight model seems to me to have improved a bit since initial release but it would be great to see more realistic performance in the high alpha slow speed regime(s). As it is, the F/A-18 is my favourite module and what I have the most time in.

PS: That is a really good show (Jetstream) and anyone in to military aviation and/or the F/A-18 would really enjoy it I am sure.

[wilbur81]

Here's a quick demo of the bleed: EnergyBleed.trk

Air temp: -1.3 Deg C.

 

Note the loss of energy as speed decreases below 300 KTS with 3 g's in a descending turn. Never thought much of this before viewing the real life BFM HUD footage from my original post... just seems like the real jet has better performance in terms of maintaining energy/AoA at low G and below 300kts than we are currently seeing in DCS... But I'll readily admit that ED's model may be pretty much spot-on and my testing not thorough enough, FWIW. Here was the airframe configuration. 

Edited August 6, 2021 by wilbur81

[HWasp]

I could not open your track for some reason, but for me the F-18 can sustain 4,6 G in horizontal flight at 10000 feet easily with a center tank (total fuel between 7000 and 6000)  (and around 3,8 Gs at 20000 feet horizontal ...)

What altitude did you try that?

 

Also comparing the DCS AoA vs G and the video's AoA vs G, it turns out they get less Gs for the AoA compared to DCS:

 

Video: 

290 kts at 13800 feet  ---- AoA 22,4 degrees ----> 4.6 G (or 4,8 its blurred)

 

DCS:

290 kts at 13700 feet ---- AoA 20,4 degrees ------> 5,3 G

 

This can vary with weight a lot of course, but they can't be too heavy in the video since they have 7.3 as max G on the hud

 

 

Edited August 6, 2021 by HWasp

[wilbur81]

13 minutes ago, HWasp said:

I could not open your track for some reason, but for me the F-18 can sustain 4,6 G in horizontal flight at 10000 feet easily with a center tank (total fuel between 7000 and 6000)  (and around 3,8 Gs at 20000 feet horizontal ...)

 

At what airspeed? What I'm getting at is the question of airspeed bleed at or below 300 knots with 2-4 g's loaded. You're saying you can sustain 4.6 g's in horizontal flight at 10k feet with an airspeed between 250 and 300 kts?

[HWasp]

Managed to get a screen at exactly AoA= 22,4 in DCS (3 kts slower though)   config : 2x AiM-9s + 1 center tank, no pylons, total fuel : 7000 lbs

 

Video : 4,6 G

 

DCS :  5,5 G

 

(with the pylons it is only 5,4G at 293 btw)

 

 

[HWasp]

15 minutes ago, wilbur81 said:

At what airspeed? What I'm getting at is the question of airspeed bleed at or below 300 knots with 2-4 g's loaded. You're saying you can sustain 4.6 g's in horizontal flight at 10k feet with an airspeed between 250 and 300 kts?

 

at 300 kts 4,6 Gs horizontal 

at 250 kts 3,4 Gs horizontal

 

that it what the 18 sustains for me with 2x aim9s center tank and pylons on with total fuel of 7000 - 6000 lbs in horizontal flight at 10000 feet

Edited August 6, 2021 by HWasp

[Jenson]

Maybe try to press pinky switch to increase instant G limit? 

[wilbur81]

1 minute ago, Jenson said:

Maybe try to press pinky switch to increase instant G limit? 

Nah, I don't ever pull the pinky switch... nor do the real Hornet pilots.

4 minutes ago, HWasp said:

 

at 300 kts 4,6 Gs horizontal 

at 250 kts 3,4 Gs horizontal

 

that it what the 18 sustains for me with 2x aim9s center tank and pylons on with total fuel of 7000 - 6000 lbs in horizontal flight at 10000 feet

 

NIce... so you're maintaining those airspeeds at those G loadings, correct? I am carrying a bit more fuel for my tests (8,000 to 10,000 lbs) so maybe that's the difference? I guess ED has got it pretty spot-on, then. 

[Jenson]

Just now, wilbur81 said:

Nah, I don't ever pull the pinky switch... nor do the real Hornet pilots.

I recalled in Chuck's manual, it says when you are pulling a high G turn, press it will instruct the onboard computer to increase limit (of G or alpha) for about 3 second. Why this isn't used with real pilots? 

[HWasp]

11 minutes ago, wilbur81 said:

 

NIce... so you're maintaining those airspeeds at those G loadings, correct? I am carrying a bit more fuel for my tests (8,000 to 10,000 lbs) so maybe that's the difference? I guess ED has got it pretty spot-on, then. 

 

I checked with your fuel values, then its is 3Gs at 250 kts horizontal at 10k feet

 

With that much fuel max G is limited to 6.5, but in the video they have max G of 7.3, so they must be lighter

 

We really can't measure speed loss form those vids, but what we can see, is that they certainly get less Gs for a given AoA, so there is a clear difference between DCS and the videos, but in this case DCS is clearly overperforming not under.

 

this certainly depends on weight, but they can't be too heavy if max G shows 7.3

[wilbur81]

1 hour ago, HWasp said:

 so there is a clear difference between DCS and the videos, but in this case DCS is clearly overperforming not under.

 

 

Clear? No, not hardly. Too many unknown variables. In fact, performance could be considered relative here as a pilot might desire higher AoA under less G than higher G with less AoA. Also, that 7.3 g isn't indicative of the FCS's max allowable at the time as you can (in real life and DCS) exceed the FCS limiter for a split second quite easily and it will register as max g pulled. I appreciate your screenshots for sure, but it would be more helpful to upload a track and do the flight with the controls indicator on. I find it pretty hard to believe that you were sustaining 287 knots at 5.5 G like in your pic below.  

Edited August 6, 2021 by wilbur81

[HWasp]

30 minutes ago, wilbur81 said:

Clear? No, not hardly. Too many unknown variables. Also, that 7.3 g isn't indicative of the FCS's max allowable at the time as you can (in real life and DCS) exceed the FCS limiter for a split second quite easily and it will register as max g pulled.

 

 

IRL if an aircraft registers an exceedance, there is usually some explaining to do by the crew later on, and people tend to try to avoid that. Are you sure, that it is a common occurance that F-18 pilots exceed the FCS limiter by accident? Do you have any source on that? 

 

 

[Harker]

1 hour ago, HWasp said:

 

I checked with your fuel values, then its is 3Gs at 250 kts horizontal at 10k feet

 

With that much fuel max G is limited to 6.5, but in the video they have max G of 7.3, so they must be lighter

 

We really can't measure speed loss form those vids, but what we can see, is that they certainly get less Gs for a given AoA, so there is a clear difference between DCS and the videos, but in this case DCS is clearly overperforming not under.

 

this certainly depends on weight, but they can't be too heavy if max G shows 7.3

In the HUD, the number below the current G value doesn't show the max allowable G, it shows max G that was registered, if it' above 4.0 G. i.e., your FCS could allow for 7.5 G, but if the max G you pulled was 5.2, the HUD will display 5.2 under the current G value.

Since the HUD in the Jetstream video shows 7.3 G, this is the max G they pulled. So they are at least light enough to have 7.3 G allowed by the FCS (it's also safe to assume that they're even lighter than that, as the max allowable G by the FCS is 7.5, so they could be much lighter and still be limited to 7.5 G), assuming they didn't disable the limiter with the paddle switch (I really think they didn't).

[HWasp]

1 hour ago, wilbur81 said:

 I find it pretty hard to believe that you were sustaining 287 knots at 5.5 G like in your pic below.  

 

 

Where did I say I was sustaining it?? lol

 

These are 2 separate subjects.  The screens simply show the plane in a situation, that matches a screen from the video. Simple as that. 

 

 

 

Edited August 6, 2021 by HWasp

[wilbur81]

3 hours ago, HWasp said:

 

Where did I say I was sustaining it?? lol

 

These are 2 separate subjects.  The screens simply show the plane in a situation, that matches a screen from the video. Simple as that. 

 

 

 

 

Sheesh...that was the whole point of my original post. 

[nighthawk2174]

I mean we also don't know what their fuel state really was and it can be a big difference between near full and near empty.  Same thing for atmospheric conditions as well.

Edited August 7, 2021 by nighthawk2174

[Harker]

For the fuel state, a simple way to do it is to select the appropriate loadout and once you are at the desired altitude, start dumping fuel until the FCS allows at least 7.3 G. That would give you the max fuel state they could've had, assuming that the FCS G limiter in DCS is working with the same numbers.

[HWasp]

4 hours ago, wilbur81 said:

Sheesh...that was the whole point of my original post. 

 

Your original post is unfortunately quite pointless, because there is no way to accurately measure and test dynamic things like speed loss in a turn based on that couple of seconds of hud footage, where they fly with all kinds of attitudes, but the video is very good, thanks for posting that.

 

What we can easily match to DCS are values on the HUD in a given situation, and that shows that you get more Gs for the AoA in DCS

 

There is one point in the video at 7:50 where the instructor takes over and pulls 5.2 Gs max at 15 degrees pitch down at 310 kts, and ends up at 260 kts a bit later as he pulls on target.

You can certainly do better in DCS with around 7000 lbs of fuel on board.

 

You get 5.2 Gs in that situation in DCS just for little over 17 degrees AoA and you can almost sustain it. Track included this time

 

 

 

F-18min15degturn.trk

[Snappy]

6 hours ago, wilbur81 said:

Sheesh...that was the whole point of my original post. 

 

The entire thread is pointless.There are way too many variables (for starters OAT, air pressure ,exact aircraft specs and I don’t mean loadout and many more..)involved in the video/real world example which  you simply cannot know and therefore not replicate , plus others you may think you know but can’t replicate accurately enough .

All these affect aircraft performance and make these comparisons completely void for any meaningful performance assessment of the FM.

 

 

 

Edit: HWasp partly beat me to it while I was typing

Edited August 7, 2021 by Snappy

[Ahmed]

Agree with the last post by Snappy. The only thing related to this thread that holds up is common feedback by real hornet pilots that the DCS one doesn't have enough nose authority at low speed as the real. We will see when the FM update gets done what changes are made in this area, together with the announced on drag and rate.

[wilbur81]

3 hours ago, Ahmed said:

The only thing related to this thread that holds up is common feedback by real hornet pilots that the DCS one doesn't have enough nose authority at low speed as the real.

Which real Hornet pilots are saying this? Just curious.

[Andartu]

16 hours ago, Jenson said:

I recalled in Chuck's manual, it says when you are pulling a high G turn, press it will instruct the onboard computer to increase limit (of G or alpha) for about 3 second. Why this isn't used with real pilots? 

 Because it is too much stress for the airframe and it only would be used in an emergency situation like to prevent smashing into the ground.

 

Also the plane captain would kill you.

[HWasp]

5 hours ago, Ahmed said:

Agree with the last post by Snappy. The only thing related to this thread that holds up is common feedback by real hornet pilots that the DCS one doesn't have enough nose authority at low speed as the real. We will see when the FM update gets done what changes are made in this area, together with the announced on drag and rate.

 

My speculation is, that if the G vs AoA in DCS was closer to what is shown in the video (17,4 vs 23 AoA seems too much for me even with all the unknown variables), that would mean that both the lift vs aoa and the drag vs aoa curves would get a little flatter, and that would cause, I think, a decrease in sustained turn rates, but increased nose authority, and that would be in line with their feedback.

 

Do you have any links to where this was discussed?

[Jenson]

10 hours ago, Andartu said:

 Because it is too much stress for the airframe and it only would be used in an emergency situation like to prevent smashing into the ground.

 

Also the plane captain would kill you.

 

I see, I thought it was designed for dogfight...