Pegasus a little bit too powerful / Drag miscalculated?

[myHelljumper]

I did not say that the turn rate for the Harrier will increase, I said the the aircraft will not loose as much energy when turning. That's really not the same thing.

[Bog9y]

Hi guys, I have just done another climb test with the latest flight model update. The results are very interesting! 

 

The original test was this and I have added the latest figures in BLUE: 

 

Reading in the NFM-400 performance manual you get the following data for a climb with these conditions:

 

Engine = 408

Drag Index               :  17.7

GW at start of climb : 22,000 lbs (7200 lbs of fuel)

CLB Speed : 300 KCAS / .75 M

Max thrust climb, this is 109% / 710 degrees C JPT for the -408 engine

Test carried out in ISA conditions, winds calm 

 

EXTRAPOLATED DATA FROM THE CLIMB CHARTS VS DCS :

 

                        TIME TO CLIMB  - DCS  - NEW FM /  FUEL REMAINING - DCS - NEW FM /   DISTANCE - DCS - NEW FM

SL to 10,000 ft = 0:48 mins  / 0:25   / 0:35             /    7040 lbs / 7094    / 7016                         /  3.5 nm    / 2.5   / 3.8 

SL to 20,000 ft = 1:42 mins   / 0:54   /1:27              /    6850 lbs / 7010    / 6855                         / 10.5 nm   /  5.1  / 9.1

SL to 25,000 ft = 2:30 mins   / 1:13   / 2:04             /    6770 lbs  / 6967   / 6771                         / 16 nm        / 7.1  / 13.2

SL to 30,000 ft = 3:24 mins   / 1:35   /2:57             /    6660 lbs / 6922    / 6671                         / 24 nm       / 9.6 / 19.8

SL to 35,000 ft = 5:00 mins   / 1:56   / 4:25            /   6580 lbs  / 6881    / 6545                         / 32.5 nm    / 12.0 / 30.1

SL to 40,000 ft = 7:34          / 2:24     / 7:46           /   6430 lbs  / 6836    / 6363                         /  53 nm      / 15.3 / 54.4

 

Comparing the BLACK figures to the BLUE figures Razbam have done a really good job at making the flight model more in line with what NFM-400 says is possible. The fuel burn in particular is very accurate as is the distance.   

 

Unfortunately I know the FM change may annoy some people out there that were enjoying the really powerful engine/low drag FM.  On the positive side, the overhead break has become more realistic and doing a VNSL is also much better now. 

Edited May 7, 2021 by Bog9y

[Fri13]

On 4/23/2021 at 9:55 PM, Wisky said:

so RAZBAM said on discord today that turn rate for the Harrier will increase with next patch.

Also engine thrust will decrease by ~10% at low altitude and ~50% at high altitude, to get closer to performance charts

Did the 5th May patch bring that change? I didn't notice it to be in patch notes....

[Fri13]

On 5/7/2021 at 7:57 PM, Bog9y said:

Hi guys, I have just done another climb test with the latest flight model update. The results are very interesting!

 

Comparing the BLACK figures to the BLUE figures Razbam have done a really good job at making the flight model more in line with what NFM-400 says is possible. The fuel burn in particular is very accurate as is the distance.   

 

Unfortunately I know the FM change may annoy some people out there that were enjoying the really powerful engine/low drag FM.  On the positive side, the overhead break has become more realistic and doing a VNSL is also much better now. 

 

Excellent testing. I think whole community should thank you for it.

 

Reading the values I think little more tweaking for the power reduction is required to get those low altitude climb times little longer.

 

They are already close ones, but I think there is enough speculation room to lower the thrust to get it more accurate.

 

Does these tests include the high altitude lower engine RPM requirement to have higher airflow? Someone who knows better might understand what I try to ask....

 

The pegasus engine should be powerful at low altitude (time-to-altitude records), but be slow to accelerate for higher speed.

 

Now it has been so easy to pull nose up and just climb to 20-30k ft in matter of seconds and same time just gain speed at low altitude without even noticing how quickly it does so.

 

 

 

[Bog9y]

10 hours ago, Fri13 said:

Did the 5th May patch bring that change? I didn't notice it to be in patch notes....

Yes

 

9 hours ago, Fri13 said:

 

Excellent testing. I think whole community should thank you for it.

 

Reading the values I think little more tweaking for the power reduction is required to get those low altitude climb times little longer.

 

They are already close ones, but I think there is enough speculation room to lower the thrust to get it more accurate.

 

Does these tests include the high altitude lower engine RPM requirement to have higher airflow? Someone who knows better might understand what I try to ask....

 

The pegasus engine should be powerful at low altitude (time-to-altitude records), but be slow to accelerate for higher speed.

 

Now it has been so easy to pull nose up and just climb to 20-30k ft in matter of seconds and same time just gain speed at low altitude without even noticing how quickly it does so.

 

 

 

You're welcome. Not sure if the changes are appreciated by all though....think some are getting the pitchforks and lynches ready!  

 

I think the performance factors are close enough now for a commercial sim, reducing it further is unnecessary in my opinion. One tweak that would be good is to somehow have the plane decelerate a bit quicker when going to hover stop because for RVLs and VLs the decel rate is too slow and you end up needing the braking stop to not overshoot or be too fast on an RVL. I am not talking about the decel rate for an overhead break, that is much better now than it was before. 

 

Are you talking about the RPM creep that happens at higher alts? I noticed it creeps up from 109% RPM at full power to something like 112-ish, and yes I did reduce the throttle to 109 when that happened. 

[ddwg72]

Takes awhile to get used to but interesting to fly now.  The current performance is well within the margin of error of an estimated performance chart. 

[Draken35]

I actually like it... Now you have to  really be mindful of you weight for vertical take off and landings... 

[Fri13]

9 hours ago, Bog9y said:

Yes

 

You're welcome. Not sure if the changes are appreciated by all though....think some are getting the pitchforks and lynches ready!  

 

I think the performance factors are close enough now for a commercial sim, reducing it further is unnecessary in my opinion. One tweak that would be good is to somehow have the plane decelerate a bit quicker when going to hover stop because for RVLs and VLs the decel rate is too slow and you end up needing the braking stop to not overshoot or be too fast on an RVL. I am not talking about the decel rate for an overhead break, that is much better now than it was before. 

 

IMHO what the couple pilots has said about the deceleration capability doesn't (talking before May update) feel to be right. As even pulling nozzles back and you still have difficulty's to slow to join another aircraft. 

 

9 hours ago, Bog9y said:

Are you talking about the RPM creep that happens at higher alts? I noticed it creeps up from 109% RPM at full power to something like 112-ish, and yes I did reduce the throttle to 109 when that happened. 

 

I don't know now. There is something about that maybe, as at higher altitude and higher speed you need to use low RPM to avoid overspending the engine or something. You don't get maximum speed or something with maximum RPM but need to bring it lower like 70% or something as it is after all a airbreathing engine.

 

Has anyone tried the performance maneuvers as mentioned here 

 

 

Like the 43:00 position about short takeoff etc?

[Fri13]

1 hour ago, ddwg72 said:

The current performance is well within the margin of error of an estimated performance chart. 

 

I disagree with that. 

 

SL to 10,000 ft = 0:48 mins / 0:25 / 0:35

A 48 seconds vs 35 seconds is a 34% difference.

3.5 nm / 2.5 / 3.8

That is only 9% difference.

 

SL to 25,000 ft = 2:30 mins / 1:13 / 2:04 

A 2:30 vs 2:04 is a 25% difference.

16 nm / 7.1 / 13.2 

A 13.2 vs 16 nmi is 17% in difference.

 

 

That is not a marginal ones IMHO.

 

I think that 5% would be more acceptable than almost 1/5-1/4th of the documented.

 

They went leaps better one, to more toward accurate one. But I still think that they could tweak the values more to get it closer of that interpolated data.

 

What comes to fuel consumption, that looks very good. But I am more looking the distance and the time that are still off. 

 

[Bog9y]

What he talks about at 43:00 is the 2 or 5 finger checks , carried out just before take off. I do it all the time. The Razbam module replicates the systems really nicely and gives the indications you would expect as far as I can tell. 

39 minutes ago, Fri13 said:

 

IMHO what the couple pilots has said about the deceleration capability doesn't (talking before May update) feel to be right. As even pulling nozzles back and you still have difficulty's to slow to join another aircraft. 

 

 

I don't know now. There is something about that maybe, as at higher altitude and higher speed you need to use low RPM to avoid overspending the engine or something. You don't get maximum speed or something with maximum RPM but need to bring it lower like 70% or something as it is after all a airbreathing engine.

 

Has anyone tried the performance maneuvers as mentioned here 

 

 

Like the 43:00 position about short takeoff etc?

 

Edited May 9, 2021 by Bog9y

[Fri13]

1 minute ago, Bog9y said:

What he talks about at 43:00 is the 2 or 5 finger checks , carried out just before take off. I do it all the time. The Razbam module replicates the systems really nicely and gives the indications you would expect as far as I can tell. 

Not just 4300 but about performance values to get 250 knots at 700-800 ft runway.

[Bog9y]

Ah ok. Ehm, I haven't really paid attention to that during my take offs. 

[Bog9y]

25 minutes ago, Fri13 said:

 

I disagree with that. 

 

SL to 10,000 ft = 0:48 mins / 0:25 / 0:35

A 48 seconds vs 35 seconds is a 34% difference.

3.5 nm / 2.5 / 3.8

That is only 9% difference.

 

SL to 25,000 ft = 2:30 mins / 1:13 / 2:04 

A 2:30 vs 2:04 is a 25% difference.

16 nm / 7.1 / 13.2 

A 13.2 vs 16 nmi is 17% in difference.

 

 

That is not a marginal ones IMHO.

 

I think that 5% would be more acceptable than almost 1/5-1/4th of the documented.

 

They went leaps better one, to more toward accurate one. But I still think that they could tweak the values more to get it closer of that interpolated data.

 

What comes to fuel consumption, that looks very good. But I am more looking the distance and the time that are still off. 

 

I don't know dude, I personally think they did a great job changing the flight model and the numbers are close enough for me.  The -400 charts are not super easy to read accurately so the time/distance/fuel figures are all just approximations. I am not claiming that the numbers I posted are gospel, they are mere tests and interpolations of the graphs.

 

The SL to 10K is out by 34% which seems like a lot but it's only 13 seconds. And if I misread the time chart and over-read the graph the result would be much closer than that. 

[Torun]

3 hours ago, Fri13 said:

I think that 5% would be more acceptable than almost 1/5-1/4th of the documented.

I apologize if I seem like I'm grasping at straws here, but I really agree with @Bog9y in that what RAZBAM pulled was a great job. In fact, I dare say they can hardly do any better and let me offer a bit of context to that.

 

Error margins are acceptable depending on context: Even 20% is totally fine if it concerns small values and it's just a quick check of a measurement of something or a ballpark. That's somewhere where flight sims do and should operate; remember that while this is a sim, it's a commercial sim more slanted towards a gaming market.

 

Going down to 10% error, that's good enough for monitoring values and it's even acceptable in some sanity-check laboratory experiments. What you're hoping for is 5%, which is reserved for literal, actual laboratory experiments.

 

Most NFM-400 charts are made in anything but lab conditions, they were charted from flight tests. The specific one quoted here might not be, but I doubt it. If you wanted 5%, they'd have to be doing those in wind tunnels, accurate numerical physics models and simulations. The very source we're using here is way beyond 5%, and because of how minute some values are with the table in this thread, even the act of reading it off a graph with limited resolution and high clutter has an error beyond 5%, probably.

Edited May 9, 2021 by Torun
formatting

[Wisky]

the nfm-400 charts for our -408 engine are actually even further away from lab conditions as you might think.

because they are _E S T I M A T E D_

 

 

Zitat

SL to 10,000 ft = 0:48 mins / 0:25 / 0:35

A 48 seconds vs 35 seconds is a 34% difference.

3.5 nm / 2.5 / 3.8

That is only 9% difference.

 

this doesnt make any sense, if the climb would take longer we would also cover more ground. so if the time would get closer to the NFM-400 the distance covered would get further away.

so either someone guesstimated those numbers in the NFM400 very terribly, or we just defeated physics...

[Fri13]

10 hours ago, Wisky said:

the nfm-400 charts for our -408 engine are actually even further away from lab conditions as you might think.

because they are _E S T I M A T E D_

 

 

 

this doesnt make any sense, if the climb would take longer we would also cover more ground. so if the time would get closer to the NFM-400 the distance covered would get further away.

so either someone guesstimated those numbers in the NFM400 very terribly, or we just defeated physics...

That depends the angle. As lower your thrust, then lower your climb angle and so on more distance covered. More thrust means shorter distance and still same time.

 

As that was not about angle but maintaining the climb airspeed, right?

[Draken35]

I just did an empirical test for VTO

 

Caucasus: Harrier with 30% fuel, 2xMk83, 2xMk82, 2xMk81 for 20660Lbls.

Starting from the runway. VTO (wet), few seconds stable hover at 50'AGL, transition to wingborne fly.

Tested from Kobuleti (60'ASL), Tbilisi-Lochini (1574'ASL) and a couple of farps at 3000'ASL and 6000'ASL.

Temperatures from 0C to 50C in 10C increments

 

1) Kobuleti: success across all the the temp range (really struggling at 50C)

 

2) Tbilisi-Lochini: success at 0C and 10C ... I suspect 15C should work too but did not test

 

3) FARPs... Total failure at any temperature

[Bog9y]

55 minutes ago, Draken35 said:

I just did an empirical test for VTO

 

Caucasus: Harrier with 30% fuel, 2xMk83, 2xMk82, 2xMk81 for 20660Lbls.

Starting from the runway. VTO (wet), few seconds stable hover at 50'AGL, transition to wingborne fly.

Tested from Kobuleti (60'ASL), Tbilisi-Lochini (1574'ASL) and a couple of farps at 3000'ASL and 6000'ASL.

Temperatures from 0C to 50C in 10C increments

 

1) Kobuleti: success across all the the temp range (really struggling at 50C)

 

2) Tbilisi-Lochini: success at 0C and 10C ... I suspect 15C should work too but did not test

 

3) FARPs... Total failure at any temperature

I have played around with VTOs because I've seen several people complain about hover capability etc. 

So far, my findings have been pretty much exactly what the performance charts say to expect. DRY 19,400 lbs at sea level at 15 degr is no problem (you can probably squeeze it to 19800) and WET 20,400 lbs.  

 

Your FARPS are at 3000 & 6000 ft. For those elevations the graphs say your WET max weight should be:

 

+/- 18,400 Lbs for the 3,000 ft FARP

+/- 16,400 Lbs for the 6,000 ft FARP

 

At 50 degr , sealevel your max VTO weight should be +/- 17,500 Lbs. 

[Bog9y]

16 hours ago, Wisky said:

the nfm-400 charts for our -408 engine are actually even further away from lab conditions as you might think.

because they are _E S T I M A T E D_

 

 

 

this doesnt make any sense, if the climb would take longer we would also cover more ground. so if the time would get closer to the NFM-400 the distance covered would get further away.

so either someone guesstimated those numbers in the NFM400 very terribly, or we just defeated physics...

No necessarily, it comes down to best ANGLE of climb speed VS best RATE of climb speed, like Fri13 says. 300 kts may be the better rate of climb speed, so it may get there quicker but will cover more ground. 

 

In an Airbus for example your best angle of climb speed is what we call "green dot" , it's the best lift to drag ratio speed. Usually this is around 200 to  220-ish kts for your average A319/320.  The best rate of climb speed in an A320 (classic models) is around 250/275/M0.76 depending on your alttitude. 

[Draken35]

17 minutes ago, Bog9y said:

I have played around with VTOs because I've seen several people complain about hover capability etc. 

So far, my findings have been pretty much exactly what the performance charts say to expect. DRY 19,400 lbs at sea level at 15 degr is no problem (you can probably squeeze it to 19800) and WET 20,400 lbs.  

 

Your FARPS are at 3000 & 6000 ft. For those elevations the graphs say your WET max weight should be:

 

+/- 18,400 Lbs for the 3,000 ft FARP

+/- 16,400 Lbs for the 6,000 ft FARP

 

At 50 degr , sealevel your max VTO weight should be +/- 17,500 Lbs. 

I'll test those values when I get a chance...

Link for the charts (if rules allow it) please?

[Bog9y]

PM incoming

[Bog9y]

5 hours ago, Draken35 said:

I'll test those values when I get a chance...

Link for the charts (if rules allow it) please?

Just tested it and the numbers i quoted are pretty close to what's possible. 

[Draken35]

1 hour ago, Bog9y said:

Just tested it and the numbers i quoted are pretty close to what's possible. 

Just tested them too. They are very close indeed.

[Wisky]

vor 15 Stunden schrieb Bog9y:

No necessarily, it comes down to best ANGLE of climb speed VS best RATE of climb speed, like Fri13 says. 300 kts may be the better rate of climb speed, so it may get there quicker but will cover more ground. 

 

In an Airbus for example your best angle of climb speed is what we call "green dot" , it's the best lift to drag ratio speed. Usually this is around 200 to  220-ish kts for your average A319/320.  The best rate of climb speed in an A320 (classic models) is around 250/275/M0.76 depending on your alttitude. 

yes what you are saying is absolutely right, if we consiser your test and the chart used different speeds.

 

but the idea of this chart is to have a common ground (300 kcas)

 

if we climb longer the angle will have to be more narrow, and as such we will cover more distance

 

if the climb is faster the angle is higher and we cover less ground.

 

climbing slower without changing your airspeed is not gonna reduce distance covered.

 

well maybe if you factor in windspeed

[kengou]

Thanks everyone for testing!

 

Looks so far like this is a great change. Much closer to reality. Looking forward to trying it out.