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Taxi Speed


chardly38

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After the last update (is seems) on a cold start to get moving I having to apply alot more throttle 80% + to get moving and at least 60% throttle to keep a speed of 12 knots according to the HUD. And any thing below 50% and I stop. Not this way before. Also with my wingman his engine rpm is lower than my to keep the same speed. And yes my breaks are off.

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RAZBAM updated the engine power at the lower band of power. You may notice about a 10% increase in power needed to maneuver up to about mid RPM range. And slow switches.

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Which is pretty different from what described in documents and by RL pilots.

The Harrier is said to want to move forward and start rolling at idle, so much so that nozzle are kept rotated to avoid rolling forward, and it is even suggested that you control taxi speed just by nozzle roation.

 

From NATOPS A1-AV8BB-NFM-000 page 7-29

Idle thrust is high and will result in excessive taxi speed unless the brakes are used or nozzles deflected.

 

More on that, starting up the enigne without enough brake pressure is forbidden unless the aircraft is tied down with chains!

 

From NATOPS A1-AV8BB-NFM-000 page 7-12

CAUTION

Do not start aircraft if brake pressure is less than 1,500psi unless the aircraft is secured by at least two tiedown chains or chocked.

 

:mad:

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it is even suggested that you control taxi speed just by nozzle roation.

 

Not saying everything else is wrong, but this is mainly to avoid unnecessary use of the brakes. Same reason why wheeled helicopters use the rotor to primarily brake

 

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The performance at low power now matches that described in NATOPS. As for taxi this is a common problem - A-10 should also start rolling at idle (hence the biggest complaint of Hog drivers: lack of parking brake). So this has something to do with a different factor than just engine power.

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It feels like the Harrier is dragging on the ground. I dont think its right.

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I usually roll with 30 deg. nozzle. 60 when onboard ship. You could try less nozzle angle... but I'm finding more taxi control with this change. Also I'm not sure if the flaps getting cooked has been modled or not. Avoid lowering flaps with less than 25 deg. nozzle. I do know that chief doesn't mind R&R with 82 degrees. Lol!

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I usually roll with 30 deg. nozzle. 60 when onboard ship. You could try less nozzle angle... but I'm finding more taxi control with this change. Also I'm not sure if the flaps getting cooked has been modled or not. Avoid lowering flaps with less than 25 deg. nozzle. I do know that chief doesn't mind R&R with 82 degrees. Lol!

 

Flaps geting coocked as well as myriad of other things are not modeled unfortunately.

 

 

As for the rolling forward at idle, it could have something to do with wheel friction being too high (the M2000 has the same issue at one point), but it is definitely not right and I hope they'll look into it.

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As for taxi this is a common problem

Yup, I reckon it has something to do with friction of the airbase surfaces in DCS: lots of different modules need tweaking when it is apparent that there is an issue with distance needed when landing for example.

If what I heard is correct, the Mirage should also start rolling on idle power (and this seems to be confirmed by the start-up procedure, since the start-up training mission asks you to apply the parking brake before engine start).

 

I seem to remember that the friction is deliberately exaggerated to avoid unrealistically long landing distances.

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My nozzle setting for taxi is 10 deg.

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I seem to remember that the friction is deliberately exaggerated to avoid unrealistically long landing distances.

 

Exaggerating physics to obtain realistic physics, in a simulation??

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Exaggerating physics to obtain realistic physics, in a simulation??

 

Yeah, for all the claims of "realism" and DCS, I often find myself suspending disbelif far more than I should...

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  • 2 weeks later...
The performance at low power now matches that described in NATOPS. As for taxi this is a common problem - A-10 should also start rolling at idle (hence the biggest complaint of Hog drivers: lack of parking brake). So this has something to do with a different factor than just engine power.

 

That common problem is DCS's sticky ground, I've been wondering about that in practically every other module as well. Before the change, I could start taxiing at 42% RPM, now I need 55ish, with just 40% fuel and the gun pod.

 

Nevertheless even in midair the Harrier now feels like it has an airbrake deployed all the time. I couldn't even stay airborne at 50% RPM at all. This thing has lots of thrust, T/W over 1 (again, just 40% fuel + GAU-12, took off vertically). Before the update, she did like 380 @ that setting and 480 @70%. Now at 70% I'm somewhere below 370 knots.

 

Couldn't find exact speed figures in the NATOPS (000 and 400), but cruise speeds at low level for 18klb gross weight, 408 engine, 400 p. 153. Took a clean plane with 40% fuel to get there (a tad less than 18klb TO weight).

 

FF for given speed there vs. what I could achieve in a standard DCS Caucasus day, flying at ~750-800':

 

kcas - ffNAT. - ffDCS

300 - 64 - 96

330 - 73 - 106

360 - 83 - 116

390 - 94 - 126

420 - 107 - 135

450 - 121 - 149

580 - 138 - 160

510 - 157 - 172

540 - 181 - 196

570 - 230 - 268 (was at 100% / 640° JPT limit already attaining 567kts max)

 

Without having done that test before, I'd still say it was closer to these figures before the change... at least there it was possible to stay flying at ~60-65 ff which is not possible anymore.


Edited by Eldur

dcsdashie-hb-ed.jpg

 

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That common problem is DCS's sticky ground, I've been wondering about that in practically every other module as well. Before the change, I could start taxiing at 42% RPM, now I need 55ish, with just 40% fuel and the gun pod.

 

Nevertheless even in midair the Harrier now feels like it has an airbrake deployed all the time. I couldn't even stay airborne at 50% RPM at all. This thing has lots of thrust, T/W over 1 (again, just 40% fuel + GAU-12, took off vertically). Before the update, she did like 380 @ that setting and 480 @70%. Now at 70% I'm somewhere below 370 knots.

 

Couldn't find exact speed figures in the NATOPS (000 and 400), but cruise speeds at low level for 18klb gross weight, 408 engine, 400 p. 153. Took a clean plane with 40% fuel to get there (a tad less than 18klb TO weight).

 

FF for given speed there vs. what I could achieve in a standard DCS Caucasus day, flying at ~750-800':

 

kcas - ffNAT. - ffDCS

300 - 64 - 96

330 - 73 - 106

360 - 83 - 116

390 - 94 - 126

420 - 107 - 135

450 - 121 - 149

580 - 138 - 160

510 - 157 - 172

540 - 181 - 196

570 - 230 - 268 (was at 100% / 640° JPT limit already attaining 567kts max)

 

Without having done that test before, I'd still say it was closer to these figures before the change... at least there it was possible to stay flying at ~60-65 ff which is not possible anymore.

 

Thank you for doing these tests! Quite interesting. I'll see if I can do some tests tomorrow.

 

As for the lack of thrust in flight; that makes sense, I don't have any thrust curve graphs here, but the lack of an inlet might explain it. Besides the extra airflow when flying horizontally, the Harrier doesn't have a huge inlet to do work on the gas, Harrier doesn't seem to be very optimized for ram recovery at high speeds. And since inlet velocity is in the thrust equation, faster you go, smaller the difference between V1 (inlet) and V2 (exhaust) velocities so less thrust the engine produces.

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Maybe it has to be that way. I haven't dug this deep on other modules. Are their FF different as described above? I'm thinking like when RU annexed Crimea, the peninsula was revised to include.... nothing. Are devs required to use altered data? Since the NATOPS is public I imagine not, but Google Maps still shows the peninsula.

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