HWasp
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Posts posted by HWasp
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22 minutes ago, Kercheiz said:
Just opened one of your tracks (full AA) and you're still starting at 10000ft
Here is a 40nm one with a center droptank full + 100% fuel
had to do S-turns on short final, because ended up high
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4 minutes ago, Kercheiz said:
Just opened one of your tracks (full AA) and you're still starting at 10000ft
"So the procedure goes as follows:
- 280 kt indicated should give you 14 nm for 10 000 ft. 280 is chosen because it's close to the best glide speed (~260 kt) and inside the engine relight domain. The slats should be forced in.
- Stabilize at 5000 ft to slow down to 230 kt minimum.
- Maintain 230 kt in final.
This procedure does not give fuel or configuration information but we can guess that in such emergency external stores would be jettisoned so the procedure must be possible with basically full fuel and no stores.
I'll record a track later."
This was the procedure given to me. I was testing this one.
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For this I have also disabled the slats, and made an S turn to simulate a 30 degree offset, so worst case scenario. I would consider this reasonably safe in this config
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1 minute ago, Kercheiz said:
Did you disable slats?Yes I did, but I have found something more interesting:
I just stumbled upon this combination : with 1 full center tank and 100% fuel, sustained rate at 340 kts is almost exactly 4,8G as per the video (that may or may not be relevant)
Also with the same configuration engine out procedure is fully safe (the previous loadout was really on the limit)
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2 hours ago, Kercheiz said:
Two wing tanks, it should start being able to dry cruise below 2T internal fuel
Thanks!
I checked that, really is on the limit as you say. I would not have thought, that the aircraft is capable of this (I don't think I ever flew that high with less than Mach 1,5
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On the other hand, regarding the possible effects of a 10% L/D reduction, I did fly the engine out profile now with full A/A loadout + a droptank at full fuel, and still made it. I have even made a small S turn around 5000 feet to simulate the effect of a 30 degrees offset.
I'm not sure, what the combined drag penalty of the 2x Magic2 + 2x 530D + droptank is, but I would guess it is a lot.
Please see the track attached.
I understand, that emergency procedures have tolerances built in, but this seems too much for me. Speed can be completely off of the optimum speed (demonstrated earlier), stores, droptanks can still be on, even with a turn.
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34 minutes ago, Kercheiz said:
About removing some L/D ratio artificially between 5 and 12 degrees AoA, besides giving the CL and CD an unrealistic shape, this has the effect of loosing the ability to dry cruise at FL500 where some loadouts that can do it and some can't. The margin is extremely tight there and this is an important feature. Plus giving a weird effect with the chevrons that seem to "fall" when smoothly increasing the load factor during a turn, which is also not observed IRL.
I can't describe the few hundredth hours spent at studying it, but we have thought all of this.
Also about the Jx... I think (but it would need a confirmation) the nominal values are not an average, but a decision minimum. Actual value vary on every engine. And, we are just at this value in the current module.
Could you please tell me a possible FL500 loadout? Thanks!
Regarding the chevrons: I think they don't follow the changes perfectly intantenously in the HUD footage. There seems to be a maximum speed, at which they move, so during a high G-onset rate they are a bit late. Looking carefully at the video you can see at high G-onset turns, that the speed is already decreasing while the chevrons still indicate an increase.
That was my main point, why the initially claimed G at Ps0 is not valid, because the chevrons are late and plane is already beyond Ps0 when they arrive at the FPM.
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6 minutes ago, myHelljumper said:
And you are ignoring all the other facts that indicates that this is a 2000B with a M53-5.
I'm not ingoring anything, I brought up points that might prove otherwise.
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7 minutes ago, Kercheiz said:
About removing some L/D ratio artificially between 5 and 12 degrees AoA, besides giving the CL and CD an unrealistic shape, this has the effect of loosing the ability to dry cruise at FL500 where some loadouts that can do it and some can't. The margin is extremely tight there and this is an important feature. Plus giving a weird effect with the chevrons that seem to "fall" when smoothly increasing the load factor during a turn, which is also not observed IRL.
I can't describe the few hundredth hours spent at studying it, but we have thought all of this.
I understand, it is complicated.
Are you sure, a Cd increase causing a 0,5-0,7 G sustained G drop at around 12 AoA would distort that much? Again I'm thinking about relatively minor differences.
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12 minutes ago, myHelljumper said:
So you are now choosing to ignore direct pilot feedback that indicates that this is not a 2000C but rather a 2000B with a M53-5 engine to make the video align with your views ? Rather than concluding that we cannot use this video as a source for STR ?
No, I gave you some numbers, that seem to line up.
Is Jx value showing acceleration? Is the -5 engine is weaker, by 10%? How does a weaker engine affect acceleration? Does temperature affect thrust?
If -5 has 10% less thrust than P2, at 15C, Jx will be noticably lower.
You said 15C difference causes around 5% thrust difference for the engine--->> need a LOT of temperature correction to make up for the 10%, (-15C just going by your numbers )
I simply just used the information You have given me, and they seem plausible to me.
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22 minutes ago, myHelljumper said:
The Jx being similar does not mean anything temperature wise as we don't know the reference Jx for a M53-5 engine.
M53-5 has 8-10% less thrust than P2, right? This means acceleration will be less if T=15C, so Jx< 0.68
Previously you have mentioned, for this engine 15C temp increase is roughly -5% thrust
That means, that if you want to make up for the difference with temperature, then this should be a winter video, with temps around 0 Celsius at least.
So actually with that in mind, since foliage is visible in the vid, and it does not look like winter to me, this could still be a C model with non-standard B/W camera...
This would be best case scenario for everyone, since even though it means the necessity of another round of tuning, but finally there would be some really solid evidence for STR, and also probably this heavily debated subject about STR could be put to rest, and you guys could focus on my new MiG-23
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17 minutes ago, myHelljumper said:
As I said we are sure that the airbrakes efficiency is correct, then the only other variable is the aircraft drag with AoA.
That is certainly wrong, as this type of airbrake does disturb the airflow and may be even altering vortex forms and generation, so the whole system might act differently compared to clean.
Also, this is not even a precision manuever, it's just an overhead break. All kinds of variables there, great for testing against gross errors, but otherwise...
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24 minutes ago, myHelljumper said:
No, thrust is not static and changes with speed and altitude.
We know the M53-P2 thrust profile from publicly available information, we don't know about the M53-5 thrust profile.
Also, even though I understand now, what Kercheiz said about the signs, that show, it is a B, and while I trust his knowledge of course, that is not 100% evidence, although it could be very likely.
if Jx=0,68, what are the chances, that temperature there is just right for the B to match the C's acceleration exactly. Of course it can happen, but still...
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5 minutes ago, myHelljumper said:
No, thrust is not static and changes with speed and altitude.
We know the M53-P2 thrust profile from publicly available information, we don't know about the M53-5 thrust profile.
Ok, that is understandable, but given the comlete lack of data otherwise, it might still be better to assume, that it has similiar thrust profile, and use that, (I really wouldn't think, that a slightly improved version of the same, with the same intake, etc, would be that completely different...)
Again, I really can't see how the break procedure can help us with this +/-0,5-0,7G difference. Especially with the airbrakes involved. It works, of course, but my problem is with drag between 5 - 12-ish AoA clean. I can't test that with airbrakes out at all....
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46 minutes ago, myHelljumper said:
I know it's not hard data but in the previous FM where the STR was lower than it was now, holding above 14° AoA back then with a healthy engine was already not really a confortable situation so the reduced drag at high AoA and thus increased STR makes sense here.
I have on more point for the HUD tape video: The Jx=0,68 on take-off. If that matches exactly the value we need on take-off on this version, that means in the vid external conditions (lower temperature) compensate for the different engine.
If we could agree, that because Jx=0,68, ---> temperature is considerably lower than 15C ---> thrust in those conditions does actually match our version, because of the matching acceleration, that would mean, we only have to account for the possible weight difference of the B version (I know there are aerodynamic differences, but given the total lack of usable data...)
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15 minutes ago, myHelljumper said:
It's relevant that the Mirage does not suffer from a critical increase in drag from high AoA as the engine thrust was reduced enough to decelerate but the higher AoA did not increase the speed loss rate further.
That is a very big claim, given there is no info there about actual thrust.
Given, there are that many unknowns, it would be still better to try and interpolate data from the B-version video, because at least weight and thrust differences are known, so with those accounted for it might be less wrong, than vids like this.
The previous FM might have had too much drag increase above 14-15 degrees AoA, certainly possible, but please keep in mind, I am talking about the 5-12 AoA range mainly.
I think the high AoA range is ok, since it was fixed, and increasing the rate of drag increase slightly between 5-14 does not have to affect that area seriously.
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12 minutes ago, myHelljumper said:
230 kt is chosen because it keeps the engine rotating at at least 10%, which gives enough hydraulic power for the control surfaces. I should add to the dead engine landing procedure that you should at 230 kt from 5000 ft you should be able to fly 4 nm to the runway.
Why would we change the FM to make it match with a data point that we know is incorrect (wrong airframe and engine) ?
The Mirage can really take some AoA without much drag increase thanks to the unstable design that reduces the elevon drag at AoA, the slats (not relevant in the dead engine landing case) and the strakes.
This this video where a 2000D with a malfunctioning engine keeps flying way past 14° AoA:
Yes, and also to stay reasonably close to the best glide speed and not end up with a whole lot of induced drag at low speed range of the drag curve.
Look, I can fly the whole thing between 170 and 180 kts easily. (And still have hydraulics in DCS, but this is a different subject then)
The video looks like a partial engine failure, someone in the description says it was a control unit malfunction, so it's not a complete loss off thrust. How is that relevant for glide ratio?
Here is the same slowing below 180 already at 10000
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13 hours ago, Kercheiz said:
It gives a very accurate value of the minimum required optimal lift/drag ratio. Then if you keep the exact same angle of attack, adjust the engine thrust carefully, and find the speed at which you can sustainably turn in these conditions, it gives a minimum point on the STR chart. We are basically at this point.
14 hours ago, myHelljumper said:So the procedure goes as follows:
- 280 kt indicated should give you 14 nm for 10 000 ft. 280 is chosen because it's close to the best glide speed (~260 kt) and inside the engine relight domain. The slats should be forced in.
- Stabilize at 5000 ft to slow down to 230 kt minimum.
- Maintain 230 kt in final.
This procedure does not give fuel or configuration information but we can guess that in such emergency external stores would be jettisoned so the procedure must be possible with basically full fuel and no stores.
I'll record a track later.
I think I have found a problem here, testing the procedure:
At 5000 feet I made an intentional error, and slowed down below 170 kts in level flight instead of the 230 minimum.
Problem is, I still made it easily, actually had to drop the gear at 2000 feet.
Also the flare is not a problem at all starting from this lower speed.
230 kts on final is a very high approach speed, there must be a good reason to keep it there. If I can do the same procedure with such an error, something must be off a bit.
I tested the glide ratios at speeds 240 - 160:
240 : 8,1 AoA 5,5
220: 7,4 AoA 7
200: 6,75 AoA 8
180: 6 AoA 10
160: 5,4 AoA 12
I'm sure the approx 8 L/D base given by this procedure must be ok, but I find it very strange, that plane could still have 5+ L/D at 160 kts where AoA is 12
I would be very interested to see, what would happen, if the drag curve would be steepened a bit to hit the 4,8G / 340 sustained according to the video (I think AoA around 12)
Please see track attached:
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3 minutes ago, myHelljumper said:
It's a straight in approach, you should be at less than 30° from runway heading when stabilizing at 5000 ft and should not have more than 45° roll angle.
Ok, thanks.
It works, tried it, but I think this test is a bit "low resulotion" regarding the +/- 0,5 or 0,7 Gs sustained at 340, we are looking for. This is a very good reality check for gross errors, but I don't think there is any.
I would call this whole discussion "performance tuning discussion", and for this matter a HUD video, like the one you posted, or things with similiar detail are suitable I think.
It's very unfortunate, that hud footage is a 2 seater with different engine.
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12 minutes ago, myHelljumper said:
So the procedure goes as follows:
- 280 kt indicated should give you 14 nm for 10 000 ft. 280 is chosen because it's close to the best glide speed (~260 kt) and inside the engine relight domain. The slats should be forced in.
- Stabilize at 5000 ft to slow down to 230 kt minimum.
- Maintain 230 kt in final.
This procedure does not give fuel or configuration information but we can guess that in such emergency external stores would be jettisoned so the procedure must be possible with basically full fuel and no stores.
I'll record a track later.
Thanks!
Is this a straight in procedure, or does it start over the airfield similiar to the MiG-21 for example? This would be quite important, as turns increase descent rate quite a lot.
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6 minutes ago, Kercheiz said:
I don't know how to explain it better. There are several engine versions in the M2000, all variants of the Snecma M53.
M53-5 was the original engine of the first produced airframes, then M53-P2 was developped, installed on the later airframes. In the AdA, all M53-5 were gradually replaced by M53-P2 (retrofit) and the newer engine is now the only one for the whole french M2000 fleet. There are still M53-5 engines in service in other countries. The newer engine has significantly more thrust in both MIL and AB, for instance wikipedia states +8% in AB and +18% in MIL. All this info is publicly available if you search a bit.
Now the video : this is a pre-2007 video taken in Orange, France. This is likely a twin seater as B&W hudcam is typical (unless a color video was converted to B&W but unlikely). Twin seaters were still M53-5 in 2007 at Orange, so there is a significant chance this is video was recorded on an aircraft with a M53-5. This of course is, from my own source. It's not openly verifiable unless you have yours.
(I'm the FM author)
Thanks, now I understand better.
7 minutes ago, myHelljumper said:We can talk about the dead engine landing procedure if you want, this one was used to tune the aircraft drag and lift.
That would be great, sounds interesting!
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36 minutes ago, myHelljumper said:
@HWaspI wasn't aware that the aircraft was a twin-seat with a M53-5 engine, this makes this comparison not very pertinent except for rough estimate of where the STR should be as 10% trust can change it a lot.
Thank you again for the detailed analysis of the other parts of the video that showed a difference with our model.
I just want to clarify that this particular video was not used as a data-point to tune the Mirage FM, as said before the turns are not perfect sustained turns and are there are too few of them to build a coherent model. I just watched it again recently and spotted some near sustain turns that we could use to have an idea of the accuracy of the Mirage FM.
To be honest, I did not fully understand the points Kercheiz brought, on how exactly are we sure about what version this aircraft is. Information is very scarce, it's quite sad, if one of the only sources is not valid.
While I do really like the module and the FM overall now, it would be really important to back this up with some solid sources, because otherwise it will be constant debate without an end.
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For me this data point shows around +10%+ overperformance in STR at that speed.
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Considering the 4,8G at 340 kts in the vid at around +1000 feet/minute (Ps= +16,6 feet/sec), I think the realistic STR G based on the video is around 4,9 to 5 Gs. +16,6 feet/second is really not that much looking at other EM diagrams, so I would consider this much less of a problem compared to the chevron being late at a high g-onset rate.
The chart would look like this:
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2 minutes ago, Kercheiz said:
One important detail, the engine in the video is likely a M53-5 which has less thrust than the M53P2 modelled in DCS.
Source : pilots, terrain (orange), aircraft (B&W -> twin seater), date (<2007), and date of M53P2 introduction on twin seaters in Orange.
Ok, thanks, but how much is the difference?
The screen from the video was shown by myHelljumper to validate the current STR.
My point, to summarize is: When the pilot increases the G-load at a high rate (as it is the case with the 02:15 screenshot), the chevrons are lagging behind slightly, and at the point the screenshot was made, we are already beyond the G load for sustained turn at that speed.
We can see that happen in the other direction as well, when the pilot unloads at 02:13 and G is only 4,8 while chevrons indicate Ps0. That would also be an incorrect data point to the opposite direction.
The only moment I found in the video, where speed is reasonably stable for some time in a close to horizontal turn, is the turn at 02:03.
Please consider this turn as a data point instead of the one shown previously, even though there is a around 1000 feet per minute climb there, this might be the most accurate.
1 minute ago, Coxy_99 said:Youtube video's are not data.
How on Earth would a HUD footage with speed, g load, etc shown not be usable data???
This is usable, we just need to be careful about certain things, like lagging indicators.
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Should the M2KC be able to hold up against the Viper in a 2 circle fights?
in M-2000
Posted
Dropping the gear at 5000 is a pretty damn big difference! That should have been important to note really
What is the reason for that? If I'm flying to survive an engine out like that, I will drop the gear only when landing is assured, otherwise it will just ruin my glide.
I would never drop the gear unless a technical reason makes it necessary.
btw if that is the case, why was it so important to fly from 40nm at 260 if you can just start the scenario at 10k 260 14nm? It's the gear, what will ultimately decide the difference...