737 Aileron Roll rate / Effectiveness

[matta757]

Hey guys,

Scott I don't mean to hijack your topic (there seems to be a lot of that going around doesn't there?) but I have a related question for those of you who know more about aircraft dynamics than I do...

Problem: it takes WAY too much thrust to taxi. By that, I mean that compared to what I have seen in real aircraft (though videos and such, since I'm not actually a pilot), it does not take that much thrust to get a real airplane to roll for taxi. Generally it seems that pilots apply a bit of movement to the levers and the airplane easily rolls. I have to advance my throttles MUCH further forward than what it seems real aircraft require.

Question: is there a certain entry in the dynamics that can fix this issue? Maybe something that has to do with how easily the aircraft rolls on the ground? Force necessary to overcome weight and friction of the tires? Something? Anything?

I digress- if anyone knows how I can fix this problem (and what needs to be changed) I would greatly appreciate the help!

Thanks,
Matt

P.S.- Aircraft is PSS/POSKY merged 757. Posky model with the PSS flight dynamics (.air and .cfg), using the modified dynamics posted on Avsim a few years ago.

[MLeavy737]

A fully loaded 737 will take about 35-40%N1 on 2 engines to get moving from a standstill to get the airplane moving at a normal acceleration. Sometimes a little more depending on the type of pavement your on. . We try to taxi out with 1 engine to conserve fuel. When thats the case that loaded airplane will sometimes take about 45%plus. Were only allowed up to 45% in the ramp area. More than that and you start hurting people behind you. Usually you also need to initially turn the nosewheel into the inop engine to get it going single engine as well. And if your in a small rut or something after pushback you may not even be able to get the airplane moving on one engine. Have to start the other
  Not sure about 757 but it does take a little bit to get these things moving. Once moving you dont need much. Little over idle is ok. I always noticed how easy it was in FS to get the airplane moving from standstill. Totally wrong. Maybe the model you have is accurate?

Mike Leavy

[matta757]

Mike,

That makes me feel a little better about my dynamics... altho what is idle N1 on a 737? It's about 22% on my 757, to get the plane rolling I usually need around 40% depending on weights. But to keep it rolling in FS, I find that I need to keep the thrust up around 40%, which is why I assuming something is not right. What is normal taxi speed? Isn't it between 20-30 knots? I usually try to keep that, but like I said it takes a substantial amount of thrust.

I have also noticed that taxi fuel burn is a lot higher in the game than in reality, but read somewhere that FS is just that way and there really isn't a way to fix it...

Matt

[MLeavy737]

I dont remember the exact idle speed but its somewhere in that range mid 20's or so.  The 40% initial to get it rolling sounds right but generally once rolling its closer to idle with some occasional blits of throttle in turns and such. Safe taxi speed is closer to a person fast walking or jogging. 20-30 kts is too fast. Unless your Southwest of course
  Im sure if you can do anything about the fuel burn adjustment.
While im thinking about it do you know where the setting is in the config file so you can bring up a different window and not have FS go to pause mode? Been working on my own software and just remembered there is a setting for it. Thanks.

Mike Leavy

[matta757]

I don't know what the setting is but would love to know... would make takeoff speed calculations much easier!

[Kennair]

While im thinking about it do you know where the setting is in the config file so you can bring up a different window and not have FS go to pause mode? Been working on my own software and just remembered there is a setting for it. Thanks.

Mike Leavy

Mike, its in the General Settings section and called "Pause on task switch"  If it's ticked the sim will pause when it loses focus i.e. another window opened.

Ken.

[matta757]

Is that only for FSX? Or is there a similar setting in FS9?

[Kennair]

Yes Matt exactly the same in FS9 & FSX: Options - Settings - General - 'Pause on task switch'.  Untick and the sim won't pause when you fiddle in another application.

Ken.

[matta757]

Awesome, thanks Ken!

[markuspilot]

Aileron force is controlled by the "aileron feel and centering unit". What ever "spring" tension is in there determines the resistance / force + cable tension - resistance etc.
The Captain's control wheel is connected by cables to the aileron power control units (PCUs) through the aileron feel and centering unit. The First Officer's control wheel is connected by cables to the spoiler PCUs through the spoiler mixer. The two control wheels are connected by a cable drive system which allows actuation of both ailerons and spoilers by either control wheel.
With total hydraulic power failure the ailerons can be mechanically positioned by rotating the pilots' control wheels. Control forces are higher due to friction and aerodynamic loads


HYD= off -> driving the '73 is just that... driving like a truck with no power steering, really stiff & heavy - you need to anticipate and lead with rudder to help the ailerons. pitch is also really heavy - use trim.
Having said  that the aircraft is still 'flyable' and dare i say still 'enjoyable'. ( real a/c easier to fly with HYD off than the simulator )
Thats all with the HYDraulics off. - loss of sys A & B.

HYD = ON -> flying the 73 is smooth and light. the classic is heavier on ailerons. I prefer the classic at max crosswind than the NG. The NG aileron is lighter and more responsive but easier to "over" control with gusts and crosswinds etc.
pitch control is the same for both however the longer the fuselage the better it flys. I'm guessing the -600 is very different to the -900. - I only fly the -400 & -800.

How stiff should the ailerons be? difficult without the use of a strain gauge. and i'm not about to go and buy one of those.

just try and get the controls smooth, with some resistance thats comfortable and noticeable - not heavy.

if you see a good "driver" at work he ( she ) moves the control wheel with quick smooth short/small movements - like the autopilot. someone new on type will be slower to correct and input correction later and generally larger or too much.

trying to get the sim to behave like the real deal is difficult.
adjusting the config will be necessary as different a/c types plus different yokes/ columns etc will all vary the force/feel/response.
after ablout 18months off I'm back into the garage next month to replace my saitek controls with made up thrust quad and columns. what is necessary is that when any force is released the controls go back to zero position - not near zero. otherwise you start chasing the aircraft/sim.
so yes I'll be thinking of control response and feel  - more trial by error

Elevator Feel System
The elevator feel computer provides simulated aerodynamic forces using airspeed (from the elevator pitot system) and stabiliser position. Feel is transmitted to the control columns by the elevator feel and centering unit.

As speed varies so with the elevator resistance vary. well I'm not going to get a ELEV feel system in my sim - would be nice but time & $ are factors.
control loading maybe one day...if time permits.

M

[jackpilot]

Thank you for your "input"here
Much appreciated
..anytime Mark

[MLeavy737]

Hey Marcus who are you flying for? Just curious..

   Ill tell ya having flown the 3, and currently flying the 5,7,8,9,9ER i would say the 300 certainly flew the best. Was just all around nice. Im not sure what the first model 737 that came out was,  however my guess is that it was based on the 300 length or somewhere in that size. I think when they just start stretching the hell out the thing to fit more people on it your kinda deviating from the original plan. Only reason your landing that 800 at a 164kts sometimes i because it too damn long! Lol.
  800 is my favorite to fly however. 900 is just a different animal. Flys and lands completely different than the others.  Also feels different in the bumps. Little more stable obviously because of the lenght,  like you said.
  For builders its probably one of the tougher things to get right. Soo much depends on the sim, the control setup, springs, dampers, hydraulics, flight model etc. I also see alot of talk about control forces and how many pounds it takes to go full fwd/aft and turn the yoke. Thats great and all when the plane is sitting there on the ground but i dont see that info usefull for building a sim that is meant to fly.. to me you just modelling  the control feel with hydraulics on at the gate good enough for a start i guess.
  Not really sure where im going with this but my best advice for control setup  is have as many people who fly them real life come over and fly your sim and listen to what they say. Maybe even video it. Then watch the video and compare it to a youtube video of someone landing a real one. Can prob tell alot by that.

Mike Leavy
 

[XOrionFE]

ok Mike...so when are you coming to Chicago?   

[MLeavy737]

ok Mike...so when are you coming to Chicago?   

Im up there all the time. Usually just heading through KORD. Ill let ya know if i have a descent overnight there with some time.

Mike Leavy

[XOrionFE]

sounds good Mike.   i could pick you up at the airport.   i am about a 45 minute drive west of there.

Scott

[jskibo]

sounds good Mike.   i could pick you up at the airport.   i am about a 45 minute drive west of there.

Scott

Send a Limo! 

[fsaviator]

something like this?  all three surfaces

Oh Mr Mad Hatter...  what is that?  It really looks good....  I'm staring at it and seeing all sorts of good ideas, but it all looks like rudder assemblies.  Please elaborate.

[Garys]

Fantastic Art work from Northern Flightsim. Pun Intended 

[MLeavy737]

Yes that is a great setup.. Happens to be the setup I have Heres a better pic from my pit.
from www.Northernflightsim.com

Mike Leavy

[fsaviator]

Well, you all may have sold me here...

I looked at NFS a while back (when I first started my build) but then I guess this wasn't available.  I've asked for a quote, as this looks like it will make my new build a tad easier on me, to say the least.

I just hope it comes back as something I might be able to afford.

Warren

[fsaviator]

I hear ya, Bernard....

I have been trying to build something like that myself, and just can't get it right...  I never did put two and two together on the NFS setup, and prior looks at Mike Leavy's setup.  The selling point here is that Mike is a 737-800 driver and this is his preferred setup.  I would imagine that it can be adjusted to be pretty darn close then.

Warren

[MLeavy737]

I hear ya, Bernard....

I have been trying to build something like that myself, and just can't get it right...  I never did put two and two together on the NFS setup, and prior looks at Mike Leavy's setup.  The selling point here is that Mike is a 737-800 driver and this is his preferred setup.  I would imagine that it can be adjusted to be pretty darn close then.

Warren

  To be honest i have not flown the sim with the controls yet. I had a different setup before i moved and rebuilt (rebuilding).  I can say that the roll is very nice. Seems like just the right feel of an 800. When you pass through center there is a little bit of a clunk as the system transfers to the opposite side springs but then again i do not have the floor sealed up. That i believe can also be quieted down pretty easily. Most importantly, Feel is correct. I need to do some tweaking with the pitch on mine. Need to adjust for the forward tilt and when i get the MIP in place adjust the stops. During the move a small centering spring was knocked out of position so i need to mess with that as well before i get a good feel about the pitch.  Seems great so far.
   To me it was also about strength. You can literally slam these things around and nothing will happen. No plastic and PVC parts here my friends. Also probably the easist system to install. I build the base structure based on the design of the controls. ( have better pics if you need them )
  One thing i will try to incorporate is some type of HYD feel device to them. Some type of damper. Had VW steering damper on last control setup that worked great. Prob something like. Well see.
  Also i know Art personally. Awesome guy and will Never screw you. He has gone out of his was many times for me to make sure something was spot on.
  Let me know if you have any questions.

Mike Leavy