reported Hornets Max R/Max E AOA Performance

[Swift.]

I have long suspected that the hornets AOA numbers are not accurate to real life for different phases of flight, in particular the AOA for maximum range and maximum endurance. NATOPS provides us with the concept that Max R and Max E can be flown approximately by flying at 4.2 or 5.6 AOA respectively. To test this in DCS I conducted the following test:

 

 

 

 

 

Intent:

To investigate the validity of using real world AOA numbers to fly maximum endurance or maximum range profiles in DCS

 

Setup:

-Default weather and TOD on Caucasus map

-Infinite fuel

-Loadout and Gross weight as described

 

Results:

All Altitudes +- 50ft

All AOA +-0.1

All Weights +-100lbs

 

Two test cases: 2x9M with Single tank. 2x9M 6x120C with 2 tanks.

 

Analysis:

It is apparent from these results that the DCS hornets AOA numbers are significantly different to the expected values. The only consistent value between real and simulated is the Max E for 2Wx1. Additionally we can see the AOAs 'closing together' at the extreme high altitude test, this may be a behaviour replicated in real hornets so I shall ignore that.

 

As you can see also, there is little consistency between loadouts and gross weights, WRT to best performance AOA.

 

The main crux of the issue is that we cannot use a known AOA to fly best performance, even if that AOA is different from RL.

 

 

 

Ideally we would have the same AOA numbers as real life so that we can use the same ROT as real life. However a compromise that I believe is necessary is that the AOAs are at least consistent so that we can learn a DCS number and use that for approximating Max E and R.

 

Using AOA to fly the best performance is a technique used IRL. Not having this ability in DCS is, in my opinion, a significant oversight.

[BIGNEWY]

I will mention it to the team, but you should really add your track replays from the testing. 

 

thanks

[Swift.]

10 hours ago, BIGNEWY said:

I will mention it to the team, but you should really add your track replays from the testing. 

 

thanks

I'll try, I refrained at first because of how many different replays there would be. But if thats needed then so be it.

[BIGNEWY]

Only reason I ask is the team are pretty busy at the moment and to have them look at this is in detail will take time away from development, they are bound to ask me your testing environment and for track replays. 

 

thanks

[Machalot]

On 11/28/2020 at 6:21 AM, Swiftwin9s said:

NATOPS provides us with the concept that Max R and Max E can be flown approximately by flying at 4.2 or 5.6 AOA respectively.

Is the NATOPS publicly available? I am still curious about the assumptions behind these AoA approximations. 

[Swift.]

8 minutes ago, Machalot said:

Is the NATOPS publicly available? I am still curious about the assumptions behind these AoA approximations. 

Yes and no. 4.2/5.6 were also provided by an SME, ED just like hard numbers better than hearsay. 

 

There are no assumptions provided in the book about these numbers other than 4.2AOA up to 0.85 Mach. The performance charts supplement makes no mention of AOA other than 'dash AOA <2.5' 'cruise AOA >2.5' 

 

It's important to be aware that these numbers don't have to have assumptions or specific circumstances where they apply. AFAIK AOA is the important value when determining cruise performance, look to something like tomcat for example, and that the FPAS values are just driving you towards a given AOA.

 

I've had it described to me as such: You will fly the jet to the AOA approximations provided, because if you fly to what the computer tells you and you run short of fuel then it's still your fault. Computer is just to back you up.

 

Edited April 6, 2021 by Swiftwin9s

[Machalot]

4 minutes ago, Swiftwin9s said:

Yes and no. 4.2/5.6 were also provided by an SME, ED just like hard numbers better than hearsay. 

 

There are no assumptions provided in the book about these numbers other than 4.2AOA up to 0.85 Mach. The performance charts supplement makes no mention of AOA other than 'dash AOA <2.5' 'cruise AOA >2.5' 

 

What I'm stuck on is that to fly a particular AoA in general you will need to change the thrust setting, which also means change altitude and/or airspeed.  And that depends on weight, drag index, and atmospheric conditions.  So what combination of thrust, altitude, and airspeed gives max range or endurance at 4.2 and 5.6 deg, respectively, for a particular weight and drag index? 

Edited April 6, 2021 by Machalot

[Swift.]

5 minutes ago, Machalot said:

What I'm stuck on is that to fly a particular AoA in general you will need to change the thrust setting, which also means change altitude and/or airspeed.  And that depends on weight, drag index, and atmospheric conditions.  So what combination of thrust, altitude, and airspeed gives max range or endurance at 4.2 and 5.6 deg, respectively, for a particular weight and drag index? 

 

That's the point, it's every altitude and weight. You set thrust to fly 4.2/5.6 and that is the optimal drag/thrust ratio

[BIGNEWY]

The team will be reviewing the flight model in general soon, they will include a review of the AOA, thanks for the report.

[Swift.]

To augment this existing thread:

I will provide some additional data points to improve the modelling of hornets AOA performance.
 

Spoiler

Sample1
5000ft MSL
30,000 lbs GWT
50 Drag Index (single centreline)
25@052_16@065@8000pph.trk

Expected AOA@M0.65 = 2.5
Test AOA@M0.65 = 1.6
Mach required for 2.5 AOA = M0.52

Sample2
20,000t MSL
42,000lbs GWT
75 Drag Index ('double bubble')
25@080@8000_20@090@11200pph.trk

Expected AOA@M0.90 = 2.5
Test AOA@M0.90 = 2.0
Mach required for 2.5 AOA = M0.80

It can be observed that for the majority of hornets flight regime, the AOA shown is too low, however there exist situations where the AOA shown is too high. So the conclusion may be that the problem is more complicated than a simple absolute shift in AOA reading.

[NineLine]

Hi, what are you basing your tests on?

[Swift.]

33 minutes ago, NineLine said:

Hi, what are you basing your tests on?

Hi 9L,
For this report, I was basing it off the definition of 'Cruise AOA' and 'Dash AOA' which are above and below about 2.5 degrees AOA respectively (as per page 30-2 of NFM-210).

On the specific range charts there is a marker that separates two regimes, with cruise AOA being to the Slower side and Dash AOA to the faster side. Inferring that the approx 2.5 AOA point is where these areas divide.