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Old 01-11-2020, 03:22 PM   #1
Deano87
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Default Acceleration & AoA - Some Observations.

Hey All.

----------------
I don't want this post to be taken as me slamming on EDs representation of the F-16, I understand that its WIP and subject to change. I truly love the work that ED have done so far on the Viper, Flying it in VR is basically a dream come true for me, so I'm only interested in improving the sim as best I can. The intention of this post is to try and incite mature conversation about the topic from people more knowledgeable than I, that is all.
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I was recently browsing Youtube and found this fun F-16 HUD tape of an F-16N which includes a Mach 2 run. 11min to 14mins



This piqued my interest and I thought I'd have a go at flying a similar profile in the DCS F-16 and see how it compares. Now I fully understand that this isn't an apples to apples comparison because the F-16N is a different beast to a Block 50 Jet, BUT still I figured that any weight or thrust difference between the two wouldn't produce that big of a difference, at the very least it would produce some interesting results that might be worth discussing. The Jet in DCS was setup clean with no pylons and full internal fuel.



Well... thats interesting.

My non-perfect flying aside, You can see that the DCS version keeps up pretty well until about Mach 1.35 at which point the IRL jet starts to pull away... and keeps pulling away.

By the time the simulated jet is at mach 1.6 the real jet is at 1.83.
By the time the real jet gets to mach 2, I've just passed 1.75.
But what is really telling is how long the real jet takes to go from mach 1.80 to 1.90, which only takes 16 seconds. The DCS jet does the same in 1 minute and 4 seconds!

So I think there is some high mach drag issue here, although the F-16N is lighter it should also have less thrust then the Block-50, And I wouldn't think that any of the airframe additions (IFF interrogators , big intake, bulged gear doors etc) to the Block-50 would increase drag this much? But perhaps I am wrong?

Also While I was editing the video together another thing I noticed was the difference in apparent AoA between the two aircraft. I calibrated the two hud images using the pitch ladder (actually pitching up in both cases as it was easier to get a clear image of the Pitch Ladder, but not shown in the image below) so I could attempt to get a readout of the AoA between the two videos. Here is what I found.

IMAGE UPDATED TO V2 - ERROR WITH G LOADING CORRECTED - ORIGINAL IMAGE STILL ATTACHED BELOW


I found the fact that in both cases the sim jet had an AoA 133% of whats shown in the F-16N video very interesting.

- EDIT -
Pointed out to me that my G loading in the top and bottom images were not 1G, Corrected that issue, now the AoA numbers are 133% and 126% of IRL respectively.
- EDIT -

Could that be accounted by the weight difference between the two aircraft? Or does it point to the DCS F-16 being down on lift in general? These are questions I don't know the answer to. But are interesting to discuss, for sure.

I have subsequently noticed that the CAS displayed in my sim footage is a fair chunk lower then in the F-16N video, This is no doubt due to me not adjusting the temperature to better represent the conditions of the real HUD tape. I intend to re-do the speed test with corrected conditions to see if it makes any difference. I don't imagine it will change the lack of acceleration at high mach, but at least it's another variable to disregard.

Anyway, apologies for the long and rambling post. Hopefully some of you have found this interesting. Anybody who has more intimate knowledge of how lift relates to Aoa in regards to the F-16, I'd be interested to hear your thoughts.

Cheers
D
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Last edited by Deano87; 01-13-2020 at 01:01 PM.
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Old 01-11-2020, 03:34 PM   #2
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I have nothing to add, other than I wish I had this much time on my hands.
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Old 01-11-2020, 03:58 PM   #3
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This is what happens when you get the flu. Lol.
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Old 01-11-2020, 03:58 PM   #4
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Very interesting

Last edited by The Falcon; 01-11-2020 at 06:55 PM.
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Old 01-11-2020, 05:03 PM   #5
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That's the spirit.
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Old 01-11-2020, 05:10 PM   #6
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I believe the naval variant has titanium wings. IIRC the FADEC in the later-model is a reason why there's a time difference

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Old 01-11-2020, 05:13 PM   #7
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Quote:
Originally Posted by jcdata View Post
I believe the naval variant has titanium wings. IIRC the FADEC in the later-model is a reason why there's a time difference

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The F-16N has titainium wing mounting plates, not complete ti wings. Afaik.
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Old 01-11-2020, 06:13 PM   #8
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In the last picture you are flying 4000ft lower than the F-16N. Also did you remove the pylons underneath the wing and centerline? Did you set 1013Mbar or 29.92Hg in the altimeter? If you want to compare you really need to have more info than you have...
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Old 01-11-2020, 07:39 PM   #9
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Quote:
Originally Posted by Bouli306 View Post
In the last picture you are flying 4000ft lower than the F-16N. Also did you remove the pylons underneath the wing and centerline? Did you set 1013Mbar or 29.92Hg in the altimeter? If you want to compare you really need to have more info than you have...
Yes I did remove all the pylons.

Altimeter was set to 29.92, yes.

I was 4000 ft lower because if you watch the video I was holding the same dive angle as the IRL pilot did, but because it took a lot longer to get to the same to the same speed I ended up much lower. I can try and recreate it more accurately in the future though.
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Last edited by Deano87; 01-11-2020 at 08:27 PM.
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Old 01-12-2020, 12:06 AM   #10
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Gross weight can make a significant difference in cruise AOA. I would be curious what are the AOAs for DCS in matching conditions at a wide range of GWs. The video might be a lightweight condition.
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