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Taxi speed issues

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Still working through the new purchase kinks but I've definitely noticed an odd issue with taxi speed. Using FSUIPC's (paid version) friction LUA, with zero power I'll immediately begin rolling at 2-8 kts ground speed the moment I release the brakes. Yet if I apply power, I won't increase that speed until north of 35% torque.

 

I've found that if I have the propeller set to as little power as possible (definitely south of 10%) I can get it under control but it's very mysterious as none of my other turboprop Carenado aircraft do this.

 

Suggestions? Recommendations? Similar experiences?

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As the Do228 Taxis nicely without the friction LUA I don't understand why you are using it. Doesn't make sense to me.

BTW, if you have the propellers set a max RPM the Carenado Do228 is easier to taxi (and the Alabeo 441) because blade angle and torque are lower. 

Apparently Carenado uses the prop levers on their Do228 (and the Alabeo 441) only to adjust the blade angle while IRL fuel flow is being affected as well.    

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As the Do228 Taxis nicely without the friction LUA I don't understand why you are using it. Doesn't make sense to me.

BTW, if you have the propellers set a max RPM the Carenado Do228 is easier to taxi (and the Alabeo 441) because blade angle and torque are lower. 

Apparently Carenado uses the prop levers on their Do228 (and the Alabeo 441) only to adjust the blade angle while IRL fuel flow is being affected as well.    

 

Thanks. My understanding is the friction LUA is an "all or nothing" thing with FSUIPC. I have it enabled for the dozen or so other aircraft that pretty much require it to function reasonably well on the ground (Aerosoft's Twin Otter and Flight1's King Air are two aircraft in particular that have very different taxi characteristic with it disabled).

 

I'll have to give it a go without that LUA file, because if I set the props at max RPM, I can easily get north of 35kts with almost zero power during taxi and I've tipped the aircraft over a couple of different times when turning.

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Use high power setting only when you're ready for take off. Otherwise ground idle. Same thing after landing, ground idle can be set once below 35 kts. (if I remember correctly, if not use 30 kts :)

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30kts at idle isn't unrealistic at all IRL.  Normally you should taxi at 20-30kts on straight parts of the taxiway and 10-20 around wide corners.

Use of brakes and/or  reverse is usually required especially at low weights to keep taxi speed under control.

Hope you aren't trying to taxi at +30kts around corners ;) 

 

@Scarp I guess that with 'high power setting' you mean the prop levers. Again, this doesn't work with the Do228 and the C441 because on the Carenado/Alabeo versions the fuel flow and basic engine RPM remains the same.

This means that at low RPM blade angle and torque is higher than at high RPM.   

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30kts at idle isn't unrealistic at all IRL.  Normally you should taxi at 20-30kts on straight parts of the taxiway and 10-20 around wide corners.

Use of brakes and/or  reverse is usually required especially at low weights to keep taxi speed under control.

Hope you aren't trying to taxi at +30kts around corners ;) 

 

@Scarp I guess that with 'high power setting' you mean the prop levers. Again, this doesn't work with the Do228 and the C441 because on the Carenado/Alabeo versions the fuel flow and basic engine RPM remains the same.

This means that at low RPM blade angle and torque is higher than at high RPM.   

Taxiing at 30kts is not as a rule ("irl" as you say), done as a normal taxiing speed. It is too fast. At 30kts the control surfaces start to come alive and controlling the a/c can become difficult especially when there is a wind component of above 5kts. Most large airports have a speed restriction of 15kts. If you are on a long straight taxiway with no obstructions or "potential" obstructions then you might allow the a/c to get to 20-25kts. But around corners 7-10kts max. Because you are sitting at a desk you don't have the sensation that you do have in real life. It's uncomfortable for the pax and possibly dangerous for the undercarriage. You also have to think about brake temperatures. Particularly in large a/c having to stop suddenly from taxiing at 30kts usually means that the take-off has to be delayed until the brakes cool down as their temperature exceeds that allowed for a safe aborted take-off. Most heavies require a wait at the gate of at least 40 minutes to allow the brakes to cool just from a normal landing.

Taxi at 15kts and corner between 7 to 10kts.

 

Enac if it sees a pilot "habitually" taxiing to fast usually issues a reprimand. Not good for the pilot's career or the airline concerned.

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@ vololiberista

Interesting observation as this is against everything e.g. Boeing recommends. BTW, I never wrote 30kts is the 'rule'. 

E.g. Boeing specifically recommends to let the taxi speed increase to 30kts to keep the brake temperature down.

If you start braking at 15 or 20kts brakes are used more often and heat up more. At least that's what Boeing says.

Never heared of a 15kts speed restriction either. 

Concerning turns in e.g. my company we use the Boeing recommendation for all fleets, max 30 straight, 20kts in shallow turns, 10kts for normal turns and 5 when turning into final parking.   

Never had any pax or FA complaints with this method...

Dangerous for the undercarriage? Seriuosly? This means that you could never land in a crosswind without taking out the crab angle first.

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Constantly braking certainly does raise the temperature bit by bit. But at 15-20 kts you will still have enough in the brakes to allow for an emergency stop during take-off. Constant braking to a stop from 30kts in a heavy will certainly stop you from taking-off. I think you would have in that scenario about 6 or so goes before the brake temperature is too high to allow for an aborted take-off.  London Heathrow and many other big airports have a blanket speed restriction of 15kts. For two reasons. 1. A lot of traffic so caution when taxiing. 2. The prevailing winds from the SW can be quite breezy so the additional wind component on control surfaces can cause wings to tip or dip unexpectedly. Or more embarassingly cause a ground loop!

 

Turning a corner at too high a speed during taxi can cause problems for the nosewheel. And with underslung engines it can cause them to touch the tarmac. That's quite different to a crosswind landing!!

 

Think about when you drive your car down hill. Constant pressure on the brakes reduces their efficiency to the point where they might be compromised if you need to do an emergency stop. The correct practice is to press the brake pedal from time to time to keep the speed from running away. Likewise when you turn a corner in a car. On the road you will always feel some centrifugal force because of your speed going round a bend. You rarely if ever feel that force as a passenger in an aircraft when they turn during taxi.

 

Aircraft brakes are designed to absorb very high temperatures and are rated so that there is sufficient braking potential for a high speed emergency stop. So it's up to the pilot in the end if he/she rides the brakes and taxis too fast then the margin of safety is much reduced.

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Nobody said to brake to a stop from 30kts. The normal procedure is to let the plane (heavies included!) to accelerate to a maximum of 30kts and then reduce the speed to 10-15kts and I'd guess that the engineers and test pilots at Boeing know what they are doing.

Haven't been to LHR since approx 1 1/2 years but can't remember to have ever seen a speed restriction.

If you taxi with 15kts at FRA you can be sure that ATC will ask you to expedite your maneuvers.

Never seen a 747 even remotely coming close to touching the ground with the engine nacelles in a turn and it sounds strange that Boeing would recommend SOPs that would be unsafe.

Riding the brakes is a no go in any plane.

A groundloop due to wind effects on planes the size of a Do228 or even bigger???

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I do know BA pilots are essentially told to taxi at 20 knots in a straight line and 10 knots max in a turn (this is in dry, good conditions), but then again, they have all the best stands at Heathrow, so they aren't looking at a 20 minute taxi to the runway lol.

 

As far as I'm aware, most airports I know would start getting snotty with you if you got much over 25 knots when taxying, particularly where there are a lot of aircraft movements, however, it's clearly not going to be a problem to let it get up near 30 on a long straight bit of taxiway where there's nothing else about (depending on the surface of course). Even though it hardly matters much in FS, I tend to impose my own 25 knot maximum speed limit on taxying and go fairly slowly around tight turns to avoid scrubbing damage, doing my best to follow the markings properly because again, even though I know FS doesn't have weight limits on the edges of its taxiways, in real life these things are an issue at quite a few airports where heavier aircraft can damage surfaces, and indeed their own tires if they get too near the edges.

 

Having said all that aircraft do often taxi very quickly at places like Kandahar and Basra, where there is a high risk of mortar attacks, and it's fairly standard practice in the Isreali Air Force to hammer it off the runway and get military aircraft in to a HAS as quickly as possible for the same reason, which often shocks visiting military pilots from other air forces when they see it, but it is born of experience, so they certainly have their reasons. I guess is why you see a fair few El Al airliners clanging it along at a fair old pace, given that many of their pilots are ex Israeli Air Force (I guess old habits die hard).

 

Going slow does have its uses though; I was once towing and aircraft with a tractor and the guy on the brakes in the aeroplane lost it and he let the aircraft run into the back of the tractor, fortunately the aircraft was rolling so slowly when the wing's leading edge touched the mudguard of the tractor, that no damage ensued (I flew it shortly after that incident, so I know it was okay), but I must admit it was a surprise to look around and see an aeroplane rolling up toward me with the tow rope slack lol.

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No way of doing 30kts if there's traffic around or in a congested area.  The 30kts example was mentioned to show that this is not an unrealistic taxi speed and that this is the best way to keep the brakes as cool as possible. 

I remember that at LHR it was sometimes really difficult with the A320 to keep the brake temperature below the T/O limit if you didn't have brake fans installed.   

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As the Do228 Taxis nicely without the friction LUA I don't understand why you are using it. Doesn't make sense to me.

BTW, if you have the propellers set a max RPM the Carenado Do228 is easier to taxi (and the Alabeo 441) because blade angle and torque are lower. 

Apparently Carenado uses the prop levers on their Do228 (and the Alabeo 441) only to adjust the blade angle while IRL fuel flow is being affected as well.    

 

I removed the Dynamic Friction LUA (verified it was removed after simulator start) and still have the same uncontrollable speed post breakaway. As soon as breakaway is established (usually less than 12% power) I'll immediately cut power and continue to coast from 4-6 kts all the up to 18 kts before starting to slow. The propeller is at 0% power the whole time.

 

So it's off to locally edit some config files because something is up with my system (I did a clean reinstall of the airplane as well, just in case).

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Again, I don't see any unrealistic behaviour if the Do accelerates to 18kts. (18kts is certainly not 'uncontrollable')

Have you tested with the props at max as well?

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Again, I don't see any unrealistic behaviour if the Do accelerates to 18kts. (18kts is certainly not 'uncontrollable')

Have you tested with the props at max as well?

 

Sure. I'll clarify what I mean by uncontrollable. It's controllable to steer, absolutely. But the plane is violating basic physics that other aircraft in the same environment do not (even from the same developer). I understand FSX is not a scientific program but it still has a physics engine.

 

Every other turboprop that I have (PMDG, A2A, Aerosoft, RealAir, Flight1 & Carenado) all generate ground friction. If I increase power to the throttle to breakaway, upon the reduction of that power the plane will begin to slow and ultimately stop.

 

My example scenario is always 16R/34L at KDEN (16,000 ft).

 

From cold & dark on one end (no weather injection) I'll put power to say 10% to breakaway at 3-4 kts ground speed. I'll cut power. The aircraft will continue to accelerate up to approximately 18 kts. It will then hold 18kts for anywhere from 3-10 seconds (varies every time) and then slowly return to 0 kts ground speed. In my 10 test cases last night (5 up and 5 down the runaway) the plane used up 90% of the total runway before coming to a stop. Again with zero power applied after maybe the first 100 feet.

 

I tried 5 tests with the props set to the lowest (0%) power setting and 5 tests with the props set to the max (99%) power setting. Near identical results. The props at max would require more power to breakaway but would still use 85-90% of the runway at zero power.

 

The furthest any other Turboprop got (and I tried 9 other aircraft in total) was 2100 feet from the start point with the identical situation. Power to breakaway and then immediately idle. But yeah the Dornier used up over 14,000 feet on the same test.

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That's really weird. Never observed anything even remotely similar on any turboprop in FSX.

All of them either maintain walking speed (especially at high weight) or accelerate up to e.g. 30-40kts at low weight.

None of them starts to slow down again, acceleration slows above 10-20kts but the acceleration never reverses into a deceleration.

Doesn't make any sense that the plane accelerates with from 0 to e.g. 20kts at idle and thereafter slows down again to 0kts.

Can't see anything wrong in my install with various planes but I don't have FDE disrupting add-ons like accufeel or friction scripts.

What's the OAT during your tests?

I'm always performing tests at S.L. and at ISA conditions. Suggest you do the same for troubleshooting.

If a plane accelerates or decelerates after reducing power to idle depends on factors like idle thrust, propeller blade angle, torque etc.

Friction is the same for all planes in FSX/P3D if you (or the developer) doesn't alter the base code.. 

 

edit:

just tried KDEN, ISA conditions, pilot only, 50% fuel.  

 

speed levers LOW > NO power required at all to start taxiing, speed builds up to around 20kts, above that acceleration slows and stops at 28ias/31tas and the speeds stays there.

speed levers HIGH> 10% torque required to start taxiing, speed builds slowly up to 7kias/tas and stays there.

 

btw I love the links below your sig!

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edit:

just tried KDEN, ISA conditions, pilot only, 50% fuel.  

 

speed levers LOW > NO power required at all to start taxiing, speed builds up to around 20kts, above that acceleration slows and stops at 28ias/31tas and the speeds stays there.

speed levers HIGH> 10% torque required to start taxiing, speed builds slowly up to 7kias/tas and stays there.

 

btw I love the links below your sig!

 

Alright, replicated. KDEN, ISA, pilot only, 50% fuel (split evenly).

 

Speed levers LOW > I needed a little power but not much, speed builds to around 20kts (23 in my case) and acceleration slowed/stopped at the same range 28/30 IAS and stayed there.

 

Speed levers HIGH > similar torque to start taxing, speed built to about 13 kias and stayed there.

 

So I'm able to replicate that scenario with the same weight. That's good.

 

Really, what it sounds like, is that my performance expectation is misinformed. The Dornier is performing correctly, what I need to adjust is my expectation of how it should perform.

 

Thanks for your response and for sticking with the thread. :)

 

Yeah, I make sure to check the Eaglesoft forums daily. Love the Citation X, it's an incredible add-on that has aged extremely well. But man, some of the stuff that's said in that forum is... well... perhaps also like a fine aged wine.  :dance:

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I'd say 50% perfect. It really shouldn't be the case that the Do is faster with the speedlevers at HIGH than with the speedlevers at LOW. But at least there's an easy workaround.

As the Do is still rather new Carenado might be able and willing to fix this problem.  Sent them an e-mail with a detailed report for the Do 228 and C441 problem and at least they said that they are planning to fix this issue soon.

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I'd say 50% perfect. It really shouldn't be the case that the Do is faster with the speedlevers at HIGH than with the speedlevers at LOW. But at least there's an easy workaround.

As the Do is still rather new Carenado might be able and willing to fix this problem.  Sent them an e-mail with a detailed report for the Do 228 and C441 problem and at least they said that they are planning to fix this issue soon.

 

Works for me. I'll ping Carenado as well regarding the unexpected taxi behavior.

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Ooops, serious mixup in my above post.  Should of course be the other way round:

 

It really shouldn't be the case that the Do228 is SLOWER with the speedlevers at HIGH than with the speedlevers at LOW.

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Understood. I've reached out to Carenado and they've indicated that this is the first report they've received. I also reached out to a couple of YouTube simmers that have filmed the Dornier. In all of the videos, it's impossible to determine their taxi speed and engine speed lever position.

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Made a video showing what i'm experiencing as Carenado support has requested it.

 

- Engine Speed Levers at 0% 

- Engine Speed Levers at 100% 

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Heard back from Carenado (Ticket #25435) that they'll investigate for revision in the future.

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Was this ever fixed ?

My do228 in P3D v4.3 just wants to turn left on take off roll.

I need to fight the rudder pedals to keep it straight.

There are no settings that I can find that allow me to adjust Rudder effectiveness or P factor.... nada !

But daft thing is, there is no turning tendency in air.

So wrong on both counts. Bad behaviour in air and on ground.

 

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1 hour ago, Gabe777 said:

1. My do228 in P3D v4.3 just wants to turn left on take off roll.

2. I need to fight the rudder pedals to keep it straight.

3. There are no settings that I can find that allow me to adjust Rudder effectiveness or P factor.... nada !

4. But daft thing is, there is no turning tendency in air.

5. So wrong on both counts. Bad behaviour in air and on ground.

 

1. That's correct since the props are not counter rotating.

2. You shouldn't fight the rudder pedals, you should simply use them.

3. Check the aircraft.cfg file and the P3D realism menu.

4. Of course not, due to e.g. the higher speed.

5. You are wrong on both accounts. See above.

Edited by J35OE

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