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Induced drag


Hummingbird
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Not sure what the scientific definition of "that fast" is, but I suspect that regardless of the value chosen, the answer is "yes". At sea level, you can turn something hilarious like close to 30 degrees per second for a short time if you pull 8 G, but you can only sustain like 10-11 degrees per second at max zone 3. (Numbers from the JA 37 flight manual, the AJ 37 is marginally worse.)

 

The turn rate diagrams are missing from the AJ 37's flight manual but they are in the JA 37's corresponding part, and that part is the only part of the JA 37's flight manual that has been declassified. I'll see about getting it photographed and PDF-ified later this week.

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Not sure what the scientific definition of "that fast" is, but I suspect that regardless of the value chosen, the answer is "yes". At sea level, you can turn something hilarious like close to 30 degrees per second for a short time if you pull 8 G, but you can only sustain like 10-11 degrees per second at max zone 3. (Numbers from the JA 37 flight manual, the AJ 37 is marginally worse.)

 

The turn rate diagrams are missing from the AJ 37's flight manual but they are in the JA 37's corresponding part, and that part is the only part of the JA 37's flight manual that has been declassified. I'll see about getting it photographed and PDF-ified later this week.

 

I was just abit surprised by the fact that I couldn't sustain even 2 G without afterburner, and I struggle to sustain more than 5 G with the AB in zone 3, and that's going real fast.

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I get the feeling it underperforms on dry. I've seen a speed chart around here last week and it said she should be able to to .9 on the deck without AB. She doesn't even reach .75 right now... and it's impossible to climb more than like 5° angle without loosing speed at all. And it's practically impossible to take off at all without AB, as soon as you rotate before your gear gets broken due to the speed, the latter starts to fall back as soon as the plane starts to climb. I didn't manage to get her off the ground without payloads from Senaki-Kolkhi, 'cos I can't get her over the treetops without firewalling the throttle at least after lift off.

On the other hoof she gets insane acceleration and speeds on zone 3 above 10,000m altitude that even would make Rainbow Dash's jaw drop down to the deck in way less than ten seconds flat.

I guess the devs know about most issues and will work on them since it's all early access at the moment. The MiG-21bis also had lots of FM issues when it first came out.

dcsdashie-hb-ed.jpg

 

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I get the feeling it underperforms on dry. I've seen a speed chart around here last week and it said she should be able to to .9 on the deck without AB. She doesn't even reach .75 right now... and it's impossible to climb more than like 5° angle without loosing speed at all. And it's practically impossible to take off at all without AB, as soon as you rotate before your gear gets broken due to the speed, the latter starts to fall back as soon as the plane starts to climb. I didn't manage to get her off the ground without payloads from Senaki-Kolkhi, 'cos I can't get her over the treetops without firewalling the throttle at least after lift off.

On the other hoof she gets insane acceleration and speeds on zone 3 above 10,000m altitude that even would make Rainbow Dash's jaw drop down to the deck in way less than ten seconds flat.

I guess the devs know about most issues and will work on them since it's all early access at the moment. The MiG-21bis also had lots of FM issues when it first came out.

 

I don't know what you're doing wrong... I've taken off in zone 3 reliably without damaging the gear, about 60-70 times since release. At least 20 times since Friday's patch. Are you sure you set takeoff trim and let the aircraft take off mostly on its own? The gear doesn't get damaged by wind until somewhere between 550-600 km/h.

 

Mind you -- fuel regulator to MANUAL to achieve proper performance at altitude.

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I don't know what you're doing wrong... I've taken off in zone 3 reliably without damaging the gear, about 60-70 times since release. At least 20 times since Friday's patch. Are you sure you set takeoff trim and let the aircraft take off mostly on its own? The gear doesn't get damaged by wind until somewhere between 550-600 km/h.

 

Mind you -- fuel regulator to MANUAL to achieve proper performance at altitude.

 

Eldur meant dry, and I can confirm that.

 

If you try to takeoff with dry performance the tires blow up before you can lift.

[sIGPIC][/sIGPIC]

 

*unexpected flight behaviour* Oh shiii*** ! What ? Why ? What is happening ?

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I finally walked my lazy ass back to the national archives and photographed the declassified aerodynamic performance part of the JA 37 flight manual (aka. the only part that's been declassified), soooo, turn rate chart:

 

RO1SEWK.png

 

Standard atmosphere (ISA), altitudes 0, 4, 8 and 12 km, clean configuration, 80% fuel remaining. Vertical axis is turn rate in degrees per second, horizontal axis is speed in Mach. The solid lines show both the maximum possible turn rate achievable by the airframe with regards to load factor limitations and control surface authority etc (so the max instant turn rate) and the turn rate at three given load factors (labeled as "Nz = x"). The dashed lines show the engine-limited turn rate at max dry thrust, max zone 2 and max zone 3 - that is, the sustained turn rate. Keep in mind though that the AJS 37 has slightly less thrust, is less resistant to compressor stalls at high alpha and has less control surface authority, so it's all around a bit worse at this.

 

I'm PDF-ifying the entire manual right now, will post in the documentation thread when done.


Edited by renhanxue
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Well judging from the charts it is evident that the Viggen should be capable of maintaining a 2 G turn at SL from around Mach 0.46 on max dry thrust, as well as just under 3 G's at M 0.78. However neither of these parameters can be met with a completely clean AJS-37 ingame atm.

 

As for wether 5 G's can be maintained in full AB from M 0.65 onwards, I will have to test that, but my guess is that can't be done either atm.


Edited by Hummingbird
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The ja37 from the dokumentation thread can sustain 2g turn up to 3km altitude on max dry.

 

So I dont know if 1.5 qualifies for cant even.

 

the RM8B gets roughly 15% more thrust with full AB, knowing the main difference is an additional compressor stage, most of the added thrust should come from there.

 

So terrible laymans guestimation bullshit is the AJS probably cant sustain more then 1.8G on full dry. Maybee even 1.7G. And thats with full air to air and X-Tank.

 

And BTW the charts are not engine limited load factor, but DPS turn rate.

So Even by that chart mach 0.3 on SL with a load factor of 2 gets roughly 8DPS, which cant even be sustained at SL.

 

So yeah, should be tested what can actually be sustained. anything around 1.5 sounds pretty believable looking at those charts.

 

The thing which is more definitely off are the stores parasite drags.

[sIGPIC][/sIGPIC]

 

*unexpected flight behaviour* Oh shiii*** ! What ? Why ? What is happening ?

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The charts also show the sustained load factor, which is what the DPS is derived from.

 

Also let's keep in mind that the AJS is also lighter than the JA, so I don't see the reason for a whole lot of difference in sustainable load factor, esp. not on dry thrust.

 

Now let's take this chart as an example:

 

g9Ay9js.png

 

 

As you can see the real aircraft can sustain 2 G's on max dry from M 0.46 with both a belly tank + 4 missiles, by comparison I can't even maintain 1.5 G with a clean aircraft at M 0.5 ingame. Something doesn't seem right here.


Edited by Hummingbird
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I just thought you mixed up load factor and DPS in the OP.

 

The weight doesnt play as much into the performance here, its more engine power vs the huge induced drag.

 

What can you sustain full dry btw ?

[sIGPIC][/sIGPIC]

 

*unexpected flight behaviour* Oh shiii*** ! What ? Why ? What is happening ?

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I just thought you mixed up load factor and DPS in the OP.

 

The weight doesnt play as much into the performance here, its more engine power vs the huge induced drag.

 

Well weight is rather heavily tied to the induced drag as less weight means less lift needed to pull the same load factor :)

 

What can you sustain full dry btw ?

 

IIRC around 1.2 G's, but I'll do a more thurough test this evening.

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As you can see the real aircraft can sustain 2 G's on max dry from M 0.46 with both a belly tank + 4 missiles, by comparison I can't even maintain 1.5 G with a clean aircraft at M 0.5 ingame. Something doesn't seem right here.

 

6 missiles. Full A2A loadout on the JA 37 is 2x rb 71/Skyflash + 4x rb 24J (later rb 74, but not when this manual was written). The difference between the RM8A and RM8B is (proportionally) bigger at max dry than at max zone 3, IIRC, but I don't have exact numbers (go look it up in the SFI yourself, there is a thrust diagram ;V)

 

Also, there's a tiny little load factor graph for the AJ 37 in the aerodynamics compendium, see https://forums.eagle.ru/showpost.php?p=2898721&postcount=2802


Edited by renhanxue
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Alright did some more testing and at SL I can maintain 1.8 G's on max dry holding completely level allowing for a +- 5 km/h fluctuation at 740 km/h TAS (M 0.6). Aircraft completely clean.

 

At M 0.46, or 568 km/h, I can maintain 1.5 G's.

 

This is achieved by trimming the aircraft into the turns btw so as to keep it as steady as possible.

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I have been reading the discussion and find it a little funny. :)

 

I have been reading a document from 1975 on the development of the Viggen, and it's aerodynamic qualities (Swedish only, sadly.)

 

It seems to confirm the behaviour of the DCS Viggen described in this thread.

 

It describes that the Viggen did not have an excessive amount of dry thrust.

In fact, on a warm day, a medium to heavily loaded Viggen would have difficulty taking off on dry trust alone.(!)

 

It is emphasized that on dry thrust alone, one would need a long runway (1200m) and would need to be cautious to not over-rotate, since the combination of high induced drag and lowered thrust due to disturbed airflow at the intakes could make it impossible to even maintain level flight.

 

For the same reasons, take off using EBK was recommended procedure, together with strong caution in case the EBK should flame out or fail to ignite.

 

It also states that the turn performance was limited on dry thrust.

At sea level a maximum of 3G at 800 km/h is suggested ( if I understand it right) and only ~2G at 450 km/h.

This is with a totally clean aircraft.

To me this is not that far from Hummingsbird's tests.

 

I have found, that the best way to fly the Viggen is to get her up to speed using level flight and/or EBK, then you can keep the speed high on dry thrust.

However, if you let the speed drop, you need one of these methods to get over the high AoA/high drag area again. Otherwise she will stay slow.

 

Turn chart here:

r1NpzrO.png

 

IAS on X-axis

Drag = D, Thrust = T on Y-axis.

 

Tänd (On) = Wet thrust

Släckt (Off) = Dry thrust

 

Sväng = Turn

Planflykt = Level flight.

 

The text box (and the shaded areas) says:

" OBS! Thrust deficiency "

" A: D - TDry ~9 ton "

" B: D - TWet ~10 ton "

 

The original document can be downloaded here:

Aerodynamik fpl 37 kompendium.pdf

 

Found in renhaxue's post here:

https://forums.eagle.ru/showthread.php?t=168144


Edited by Sporg
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It also states that the turn performance was limited on dry thrust.

At sea level a maximum of 3G at 800 km/h is suggested ( if I understand it right) and only ~2G at 450 km/h.

This is with a totally clean aircraft.

To me this is not that far from Hummingsbird's tests.

 

Isn't it quite far off, though? Cf.

 

Alright did some more testing and at SL I can maintain 1.8 G's on max dry holding completely level allowing for a +- 5 km/h fluctuation at 740 km/h TAS (M 0.6). Aircraft completely clean.

 

At M 0.46, or 568 km/h, I can maintain 1.5 G's.

 

This is achieved by trimming the aircraft into the turns btw so as to keep it as steady as possible.

 

Sustaining 1.5 g at 570 km/h seems very different from "~2 g at 450 km/h". Although now that I look, and if I understand that graph correctly, isn't it more like 550 km/h for 2 g at max släckt?

 

 

I still think, as per this thread, that dry thrust is lower than it should be; definitely, indisputably at altitude but probably also a bit at sea level.


Edited by Corrigan

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Isn't it quite far off, though? Cf.

 

Sustaining 1.5 g at 570 km/h seems very different from "~2 g at 450 km/h". Although now that I look, and if I understand that graph correctly, isn't it more like 550 km/h for 2 g at max släckt?

 

I still think, as per this thread, that dry thrust is lower than it should be; definitely, indisputably at altitude but probably also a bit at sea level.

I am not saying it is necessarily totally correct, just that it is also not that far off either.

 

My point was more about the general tendencies of the aircraft.

The thrust of the engine as well as the drag is very dependent on how you fly her.

Fly her too slow and at high AoA, she behaves like a brick.

Get her up to speed, and she behaves much nicer.

And, dry thrust is not high for take off or at slow speeds.

 

The thrust and other values might be somewhat off here in the beginning, but I guess LN will need to be adjusting these a bit over the coming weeks and months.

After all it is still an early access release, so not polished yet. smile.gif

 

By the way: Hummingbird, did you test at W=13 ton?

Would be good to know for comparison.

 

As for the document, it is dated 1975.

Since the JA was released some years after that, my guess is that this document must be covering the performance of the AJ version here.

That's why I thought it might be good to look at this one.

System specs:

 

Gigabyte Aorus Master, i7 9700K@std, GTX 1080TI OC, 32 GB 3000 MHz RAM, NVMe M.2 SSD, Oculus Quest VR (2x1600x1440)

Warthog HOTAS w/150mm extension, Slaw pedals, Gametrix Jetseat, TrackIR for monitor use

 

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