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F-15C turning performance App


PhoenixBvo
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Hi community,

 

as I recently revisited the Eagle to fly the excellent Red Flag campaign, I decided to look more closely at being a "good stick" in the F-15C. Turns out, you have to know your aircraft's performance limits for your current situation (altitude, gross weight) and be at corner velocity at the merge and in a few other critical points of a BFM engagement. (Pete Bonanni (Art of the Kill) talks in detail about it.)

 

As you can see in the "How to be a Good Stick in LOMAC" article, the Energy Maneuverability (EM) diagram nicely summarizes all you need to know about turn performance in a single graph. That is, for one altitude-weight combination. It turned out to be hard to find sources giving me EM diagrams covering the range of practical BFM situations.

 

Enter my EMDG app (for Energy Maneuverability Diagram Generator)!

mckXXWp.png

This application let's you check the EM diagram for any altitude - weight - drag index combination you need.

 

DOWNLOAD HERE: (http://www.digitalcombatsimulator.com/en/files/1787213/)

 

The flight dynamics driving it are real-world engineering methods from the aircraft performance field and the thrust model needed for the sustained performance curve is derived from the actual F-15C pilot operating manual appendix on level turn performance.

 

It's written using Matlab to make use of the powerful graphing tools and packaged as an executable app with Matlab Runtime dependency (will be downloaded and installed using the web installer).

You can also print a .pdf of the current graph by a single click of a button (will be stored in the directory from where you launch the application, look at the "start in:" field of the shortcut's properties).

 

Here's a screenshot:

mk1XFyH.png?1

 

EDIT: now with drag index input: drag index is an important variable for sustained turn performance as it reduces your sustained turn rate at higher velocities. You can find the drag index by adding together the values for each weapon/fuel tank from the table:

nYj9S6d.png

 

The default value of 12.1 includes all the pylons and launcher racks without stores attached.

 

Let me know if you like it and what I can do to improve it. Other aircraft might be add, pending available data (CLmax, CD, thrust curves, level turn performance graphs). If you have sources, please pass them on to me and I could maybe add Fulcrums and Flankers!

 

Cheers!


Edited by PhoenixBvo
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Nice work! This will improve my F15 flying. I would love to see this done for the F-86 and Mig-15, both real world values and values derived from testing in DCS for compairison.

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Thanks for the support guys!

 

Nice work! This will improve my F15 flying. I would love to see this done for the F-86 and Mig-15, both real world values and values derived from testing in DCS for comparison.

 

About "flight testing" in DCS World: it is quite possible to determine corner velocity in the sim with the help of Tacview. I only need to calibrate the model at a few points to determine the whole h,M,W dependency.

 

The hard part however is the thrust model, as you'd need to fly many, many sustained turns at different speeds and altitudes.

 

There, some real-world plots for sustained turn rate/load factor vs Mach and alt would be really helpful. That, or the model used in DCS itself...

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I can help you with DCS turn performance data but it will take some time. One thing I'd like to see is adjustable drag index as it will have noticeable effect at higher speeds. For what kind of loadout the current drag index is set up in your model?

DCS Finland: Suomalainen DCS yhteisö -- Finnish DCS community

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Thanks for the support guys!

 

 

 

About "flight testing" in DCS World: it is quite possible to determine corner velocity in the sim with the help of Tacview. I only need to calibrate the model at a few points to determine the whole h,M,W dependency.

 

The hard part however is the thrust model, as you'd need to fly many, many sustained turns at different speeds and altitudes.

 

There, some real-world plots for sustained turn rate/load factor vs Mach and alt would be really helpful. That, or the model used in DCS itself...

 

You mean the type of data found in Annex A, App 1 to this?

 

[ame=http://www.aceshighsquad.co.uk/DCS-F86F/F-86F_Flt_Manual.pdf][/ame]

I could do some testing against the tables if you tell me what points you need for calibration, we can come up with a test flight schedule

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I can help you with DCS turn performance data but it will take some time. One thing I'd like to see is adjustable drag index as it will have noticeable effect at higher speeds. For what kind of loadout the current drag index is set up in your model?

 

Thanks for the offer Bushmanni. What do you mean exactly? DCS sim "flight testing" or do you have access to the data itself?

 

Drag index is indeed an issue. Good that you noticed it and brought it up.

As this diagram is mostly useful for BFM, I took the clean config value.

 

In fact, I work with parasite drag coefficient (CD0), but that describes the same effect (only four decimal places shifted). I could easily add a slider for CD0, but the user would not be able to tell which value corresponds to which loadout. (Also, I need the realistic range of values for the slider.)

So, we need a table and incorporate that into the application somehow. Perhaps using discrete steps of the slider for all loadouts coupled with a text field telling you drag index and the loadout it applies to.

But I'd need the table first...

 

You mean the type of data found in Annex A, App 1 to this?

 

I could do some testing against the tables if you tell me what points you need for calibration, we can come up with a test flight schedule

 

Thanks Rob, great find!

The harder-to-come-by sustained turn performance (max thrust model) might be burried in that document. Give me some time to look into it.

 

Corner velocity can be tested in DCS as follows:

starting out with an accelerating level turn (low G, max throttle) at a set altitude and gross weight, you watch your IAS and when it reaches the test value you smoothly pull for max G. When you are able to reach the structural limit (9G in the F-15), you start a new test run, this time at a slightly lower IAS. At some point, you'll stall out when pulling for max G, before reaching the limit. Corner velocity will be a touch above that value.

Note down the IAS together with altitude and gross weight and repeat at other altitudes.

Basically, we want to determine the max lift coefficient for the accelerated stall boundary. This is just one value (save for high Mach regime), but having a few calibration points helps to pin it down more accurately.

 

Great input so far, thanks again!

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Thanks for the offer Bushmanni. What do you mean exactly? DCS sim "flight testing" or do you have access to the data itself?

 

Drag index is indeed an issue. Good that you noticed it and brought it up.

As this diagram is mostly useful for BFM, I took the clean config value.

 

In fact, I work with parasite drag coefficient (CD0), but that describes the same effect (only four decimal places shifted). I could easily add a slider for CD0, but the user would not be able to tell which value corresponds to which loadout. (Also, I need the realistic range of values for the slider.)

So, we need a table and incorporate that into the application somehow. Perhaps using discrete steps of the slider for all loadouts coupled with a text field telling you drag index and the loadout it applies to.

But I'd need the table first...

 

I have made scripts to get instantaneous and sustained turn-rate values from DCS test flights relatively easily. Turn performance is also important for BVR as time it takes to make quick or sustained 180 turns is important factor.

 

You could make the drag value slider match the drag index of the real life F-15C -1 charts. Don't know how hard it would be but that would be the most logical choice.

DCS Finland: Suomalainen DCS yhteisö -- Finnish DCS community

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I think a drag index slider will be the first thing I'll add. I found a table with drag index values for the F-15A/B/C/D here. For the F-15C, the range will run from zero to the loadout with max drag number (I'll have to sort that out). The user will need to apply the table to find the appropriate drag number then.

I won't have time to implement this till next week though, so check back then.

 

3704-p245-normal.jpg

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My TM Warthog Profile + Chart, F-15C EM Diagram Generator

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Oh, and as you might have noticed, there is no data for the AIM-120B/C... Can anyone point me to a source for that?

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I have made scripts to get instantaneous and sustained turn-rate values from DCS test flights relatively easily.

 

Would you mind sharing those scripts? If you do it'll make it easier for me to collect F-86 data and Mig-15 as well.

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I have put the scripts and missions using those scripts in the zip. You should be able to use the missions as is to make measurements. Instructions are in the mission briefing. If you want to inspect or modify the scripts I have included them besides the missions so you don't need to extract them from the mission file. Sustained turn script uses sound files included in the mission file to indicate when plane is is a sustained turn. I can also provide my sound effect files if necessary for some reason.

TurnRateMissions.zip

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Great find Bushmanni. Now it's a matter of adding the drag indices for the common configs and then I can add the drag slider control to the application.

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OK, the drag index has been implemented as input now. You will still have to sum up the drag index for your loadout from the operating manual, so I might add a dialog with per station loading later (spare time permitting :music_whistling:)

 

DOWNLOAD HERE (same link as in first post)

 

It turns out that mostly max velocity is affected, but optimal turn rate remains close to the value for a clean config.

 

mk1XFyH.png?1

 

EDIT:

 

BTW, the default drag index of 12.1 accounts for all the pylons without stores. That is: 2x SUU-59/A + LAU-128/A on the wings, 1x SUU-60/A on the centerline and 4x LAU-106A on the inlet ducts.

I think DCS does not let us jettison pylons, so this is the effective minimum DI in the sim. Just add the table values for stores.

 

nYj9S6d.png


Edited by PhoenixBvo
added table with DI and weight

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Small addition, AIM-120 has DI of 2.3 when loaded on the wing station and 1.3 when loaded on conformal fuselage station.

 

Thanks, table modified.

 

Where did you find that, if I may ask? It wasn't in the TO 1F-15E -1 versions mentioned earlier in this thread.

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My TM Warthog Profile + Chart, F-15C EM Diagram Generator

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OK, now I see it. I ignored the CFT columns as we don't have conformal fuel tanks in the sim.

Seems weird though, as "other stations" implies everything except "centerline"... But I have to admit the value looks plausible as the missile is much more exposed hanging on the wing launcher rack.

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Impressive work but I think the carts are off for the PS curves. I'll get you a track later but an example would be 5000ft at 37,000lbs, clean configuration. It states that the sustained turn speed for 8g is 474kts. I know this to not be true in the game, which has a sustained 8g turn rate of about 440kts for this speed at this altitude.

 

Edit: I am wrong, the charts are right, just goes to show much bias you can be despite all that experience.


Edited by IASGATG
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:) OK, thanks for the confirmation. :thumbup:

 

It actually shows that ED did a pretty good job as well, as the sustained turn performance curve is based on real-world engine performance. :geek: ;)

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My TM Warthog Profile + Chart, F-15C EM Diagram Generator

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