Approach Speed/AoA too high

[pngflyer]

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Edited August 23, 2022 by pngflyer
Posted in wrong section…

[Get_Lo]

2 hours ago, IvanK said:

Here is My effort. Weight 8684Kg based on Fuel weight added to Mission builder displayed Weight. Wanted 8718Kg to align with Flight Manual data. Fuel burn during the test dropped it by 34Kg.

Flight Manual 10deg Incidence Vref 151Knots at 8700Kg , Stable trimmed On speed hands off at 10deg Incidence I get 152K-153Kias ... close enough for me.

Level Flight tests outside of ground Effect at 13 Deg incidence are not valid imo. AOA v IAS in ground effect (where you will be during the flare) will bear very different value.

Trk attached

F1Vref_8718kg.trk 285.36 kB · 1 download

 

I ran your track and noticed a couple things:
1. Most of your track you were above 151 knots, often nearer to 160 knots when on the 10deg marker
2. There seems to be a wind in the mission, the F1 (at least) seems to be under-reporting the wind speed on the air speed indicator (tested with a 60+ knot headwind, only read as 45 knots)
3. The problem compounds more the lower in the speed range you get, it feels good at about 160knots but down to even 145 and it really starts to struggle with this problem, the lower you go, the worse.
 

[IvanK]

Just now, Get_Lo said:

2. There seems to be a wind in the mission, the F1 (at least) seems to be under-reporting the wind speed on the air speed indicator (tested with a 60+ knot headwind, only read

How does wind effect IAS once airborne ?

[Get_Lo]

1 minute ago, IvanK said:

How does wind effect IAS once airborne ?

Eh good question on that one, I just did a quick and dirty test while on the ground. a bit more to add to the track as well, at the end once you settled at near enough 151 knots at about 10 degree your decent rate was ~1000 feet per minute

However once speed increased to near 160knots the FPM lowered to a more gentle 500fpm, at the same AoA

[IvanK]

Wind has no effect on IAS once airborne. The aircraft moves with the airmass so the ASI doesnt care.

On the ground with the Pitot probe pointing into wind then yes Wind may register.

Not sure of the relevance of the Vertical speed either, we are simply looking at steady state Weight versus incidence to see what the resultant IAS is.

Edited August 23, 2022 by IvanK

[Get_Lo]

8 minutes ago, IvanK said:

Wind has no effect on IAS once airborne. The aircraft moves with the airmass so the ASI doesnt care.

regardless, you were over 151 knots for nearly the whole track, and not to mention on a rather high glideslope as well. at 2.5deg and 151knots you will be well over 10deg AoA

[Ripjawz]

Mirage F1 Landing Showcase at 20% Fuel 2.trk I did my best to fly at 151 knots on glideslope to see test AoA at that airspeed, I spawned with 20% fuel. So I'll be landing at <8700kg. AoA indicator shows 12 while holding 151 knots perfectly while following the glideslope. I also landed to showcase AoA in ground effect as well. There is no wind in this mission.

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Here's the AoA right before touchdown. I'm going 142-143 knots at 14.5 AoA and in ground effect.

Edited August 23, 2022 by Ripjawz
To mention the wind setting.

[Get_Lo]

16 minutes ago, IvanK said:

Wind has no effect on IAS once airborne. The aircraft moves with the airmass so the ASI doesnt care.

On the ground with the Pitot probe pointing into wind then yes Wind may register.

Not sure of the relevance of the Vertical speed either, we are simply looking at steady state Weight versus incidence to see what the resultant IAS is.

 

Because your glideslope was a very fast descent. I put it in tacview, you were flying at over 4-5degrees of descent at times because your speed and glideslope were unstable. Just look at the picture and track above, try to fly at 151 knots and hold the glideslope indicator on the gunsight. turn off wind to get rid of any extra variables we dont need.

[Ripjawz]

This is a live video of that landing for quick reference. Trimmed for convenience.
 

 

Edited August 23, 2022 by Ripjawz

[Kerosene]

Quote

turn off wind to get rid of any extra variables we dont need.

 

All comparative tests should probably be done in a standard atmosphere.

Atmospheric pressure and temperature variations in missions may, in part, explain variations from the documentation.

[Get_Lo]

11 minutes ago, Kerosene said:

 

All comparative tests should probably be done in a standard atmosphere.

Atmospheric pressure and temperature variations in missions may, in part, explain variations from the documentation.

IAS is IAS no matter where you are or the temperature. 150knots IAS in Death Valley will yield the same flight performance as 150knots IAS flying over Mount Everest. Ground speed however... will be different, but that's irrelevant. we are working on an IAS only basis here. It wouldnt hurt to standardize but it shouldnt change anything. if it does thats a much different bug report.

Edited August 23, 2022 by Get_Lo

[sedenion]

It seem we are several to find this plane hard to land properly and smoothly while theoretical parameter from the manual are hard to reach.

Also, for comparison and explain why one shouldn't only compare with theoretical data: With the first Mirage 2000 flight model versions, it was able to land properly if you stayed a perfect equilibrium  position (AOA + speed + throttle) that exactly fitted the theoretical data but the airplane transforming into flying brick once a little outside this very specific configuration. the overall result is that the aircraft were hard to land, and had bad low speed behavior despit the perfect fit with theoretical data. I suspect that developpers took too many time and attention to manage to fit theoretical data without taking the problem in a more global aspect.

[=475FG= Dawger]

16 hours ago, IvanK said:

I used the Mission Builder weight dialog as a starting point to determine Empty weight +R550's. I then slowly increased fuel % and noted the litres this equated to. This revealed the DCS Jet Fuel Specific Gravity (SG) of 0.79. So knowing the weight and the DCS SG you can now determine the aircraft weight for any Fuel amount.

I then took the values from the Flight manual for 10 deg AOA (Chart in first post of this thread). I then made sure I had the weight the same in the chart (by varying fuel loading) and then jumped in DCS and flew the approach exactly at 10 deg AOA at exactly 2.5 degree flight path angle and noted the resultant IAS at both 8700kg and 11,000kg. The IAS in both cases was in very close agreement with Flight Manual chart. The next step was to extrapolate to obtain the IAS for each Weight/fuel remaining value. I have subsequently flown at random Fuel weights and noted the relationship between AOA/IAS and Fuel weight is in very close agreement with the extrapolations.

Given there is no real time weight indication in the F1 the only way to do it accurately is by Fuel remaining and adding that to your Basic wt. Of course to be super accurate you need to make allowance for other configurations or expended stores. Doing the numbers here shows that a 100Kg change in wt is a 1Kt change in Vref at 10deg AOA

I did not use the Arming/Loading window at all.

The only value really required is for 10 Deg AOA as thats what you fly final at and how the APP mode in the sight is set up. 13deg AOA is irrelevant imo in this case... its something you see in the flare and its relevance is simply Tail strike awareness.

From a practical point of view I have found that initially in setting up the approach going for the speed (for fuel remaining) is easier than chasing the AOA. Once pretty close then refine and continue with the AOA. The relationship between the orange VV and the site approach reticle works just like an E bracket.

 

I just tested the F1 at precisely determined weights and it matches closely to the published numbers. I don't see an issue.

 

IvanK looks to have resolved this, imo. 

Edited August 23, 2022 by =475FG= Dawger

[Torbernite]

Could anyone show a 136kts and 13deg AOA touchdown? The 10deg AOA speed matches the table in acceptable manner, but to make a 13deg touchdown I need more than 140kts at 8700kg.

[Get_Lo]

6 hours ago, =475FG= Dawger said:

I just tested the F1 at precisely determined weights and it matches closely to the published numbers. I don't see an issue.

 

IvanK looks to have resolved this, imo. 

 

IvanK never flew at a sustained 151knots in the whole track, he did a fairly good job at maintaining the 10deg AoA but if you look at his speed while doing so it was always over 151 knots, usuially around 155-159knots. Watch the track from Ripjawz where he does in fact fly the correct speed and glideslope for very extended periods of time and take note of the AoA meter. 

 

Edited August 23, 2022 by Get_Lo

[Koty]

and the touchdown in that was at just between 14-15° AoA at about 140 Kts

so my impression is either the indicator reads 2° too little or the aircraft with flaps out is generating 2° worth of lift too little.

[Get_Lo]

1 minute ago, Koty said:

and the touchdown in that was at just between 14-15° AoA at about 140 Kts

so my impression is either the indicator reads 2° too little or the aircraft with flaps out is generating 2° worth of lift too little.

well we use tacview to look at the true AoAs as well, and its not 1:1 with the gauge but its very close, still easily over 11 degrees of true AoA for the whole glide slope. And for the touchdown it should be 12.5-13 indicated AoA and the wheels on ground speed should be 136 at this weight. not 145knots at 15 deg. It might be the flaps not producing enough lift but I havent tested the no-flap lift and I dont really want to.

Edited August 23, 2022 by Get_Lo

[Koty]

i meant the on-gauge AoA in both cases

[IvanK]

Ok knock yourselves out , I can fly the aeroplane down final at very close to the book numbers. I have stated the exact criteria/parameters and refrences I used and provided a TRK. If you dont like it thats fine by me. I am not sure what you consider acceptable tolerances between IAS v Incidence V weight.

Perhaps the real argument is how accurately Ground effect is modeled ?  Seems to me , most are hung up on the 13 degree touchdown IAS.

Now  TACVIEW is into the equation implying its a better source of AOA 

2 minutes ago, Get_Lo said:

well we use tacview to look at the true AoAs as well, and its not 1:1 with the gauge but its very close, still easily over 11 degrees of true AoA for the whole glide slope.

Give me a break ! I will move on from this thread.... dont expect any further discussion from me.

[Get_Lo]

2 minutes ago, IvanK said:

Ok knock yourselves out , I can fly the aeroplane down final at very close to the book numbers. I have stated the exact criteria/parameters and refrences I used and provided a TRK. If you dont like it thats fine by me. I am not sure what you consider acceptable tolerances between IAS v Incidence V weight.

Perhaps the real argument is how accurately Ground effect is modeled ?  Seems to me , most are hung up on the 13 degree touchdown IAS.

Now  TACVIEW is into the equation implying its a better source of AOA 

Give me a break ! I will move on from this thread.... dont expect any further discussion from me.

I havent even gotten into ground effect and I havent looked into it, a different bug report for a different day. I just go off of what the manual says I should be able to do, and I cant do it. And as for Tacview im not saying its the "better source for AoA" but I use it in addition to all the sources I can possibly get, that includes the gauge, that includes the F2 view, and that includes Tacview. The above videos speak for themselves, every result repeatable when the tests are done ACCURATELY.

[Koty]

23 minutes ago, IvanK said:

Ok knock yourselves out , I can fly the aeroplane down final at very close to the book numbers. I have stated the exact criteria/parameters and refrences I used and provided a TRK. If you dont like it thats fine by me. I am not sure what you consider acceptable tolerances between IAS v Incidence V weight.

I can fly it down without even knowing the numbers, doesn't prove anything. Yes you have provided a track file - and you had issues pointed out.

And I would definitely consider a 10 knot discrepancy with constant AoA and wieght as too much. I could maybe live with a 2 knot difference.

23 minutes ago, IvanK said:

Perhaps the real argument is how accurately Ground effect is modeled ?  Seems to me , most are hung up on the 13 degree touchdown IAS.

No, most of us are hung up on discrepancy in IAS-indicated AoA-lift equation in free air, with full flaps down. As the opening post clearly states anyway.

23 minutes ago, IvanK said:

Now  TACVIEW is into the equation implying its a better source of AOA 

No, it's just been mentioned as "by the way".

Edited August 23, 2022 by Koty

[=475FG= Dawger]

I flew the F1 around at 151 KIAS at 10 units at 9000 kg. 
 

The numbers match the published data, indicating there is no issue. 

[Get_Lo]

4 minutes ago, =475FG= Dawger said:

I flew the F1 around at 151 KIAS at 10 units at 9000 kg. 
 

The numbers match the published data, indicating there is no issue. 

Track please, because if you watched the above video where Ripjawz was less than 8700kg you will have noticed he needed over 11.5 deg AoA to fly the glideslope at 151knots, so im curious. Because im getting a bit tired of having people explain to me what their own personal definition of "close enough" is and why we should all be using it.

Edited August 23, 2022 by Get_Lo

[Ripjawz]

Just tested this again and the AoA at 151 knots is still 2 units too high. Same results as in the video I posted above.

 

 

Edited October 24, 2022 by Ripjawz

[Ripjawz]

Good news! The flight model is closer to the numbers! 11 units AoA at 151 knots at 8700kg. It's still one unit high but I love to see the improvement!