How do pilots maintain the taxi speed of the aircraft they're handling?

Question

i am just wondering why if i taxi manually without the Auto pilot, i go faster and faster eventhough i just moved the throttle a little bit??

Answer 1

Power is what moves the aircraft foreward, friction is what holds it back . you must increase power a lot more to get it rolling than you need to maintain that speed! Therefore you can control speed with throttle, - but this is a "hunt" and see what is best "juggle". Therefore you can apply brakes slowly to maintain the speed you want, as you "zero in" on the proper power setting. You will aslo find that the faster the plane is moving the smaller increment of RPM change is required (Throttle controls rpms). Once you get the plane rolling good, - you have inertia on your side, - but you also have it aginst you when wanting to slow down (because inertia wants to make "slow" changes in speed "mass will continue to propel plane some distance even with power shut off! However in air "altitude" will be down (to keep speed up).

This is also true in air to some extent, but when flying,-- power is regulated different if you have a "controllable pitch prop". In flight, you can control RPMs with "prop pitch", - and manifold pressure with throttle! This is a "interplay" adjustment between the two! But in the air you control your speed by the "pitch of aircraft" up or down pitch under power also controls speed). The "power" now maintains your altitude, -- as well as controlling speed (more evident going down - than up!) Note that the plane can still maintain speed going down - even with engine shut off,---this will depend on how fast you are going down (pitch of plane).

Your job as pilot is to manage power (thrust), and drag (friction) to get results you need! Of course you also want to navigate so that you can find place where you are going, maintain your altitude, communicate so that you don't hit anybody, - or get hit. Keep sharp eye out for other aircfraft for same reason. (and keep airplane right-side-up most of the time) also keep track of fuel left, and fuel consumption rate (to make sure you have enough to get to airport).. Otherwise there isn't much to do when you are flying!
Better to leave auto pilot "off" when taxiing! George (the auto-pilot) can't see what is going on in front of you! Autopilot is maintaining engine rpms, - not ground speed!

NOTE: Pilots get old by being cautious and careful!

Answer 2

Jude, I expect that you are talking about handling a simulator aircraft. In real life, ground handling is part of your training and check-out. No two aircraft handle the same way on the ground.
But simulator is another matter. I own a Kitfox taildragger aircraft that I fly every week-end when the weather permits. I modelled it in the X-Plane flight simulator. It took me the good part of one year to get it nearly correct. I had to tweak all aspects of the flight enveloppe, also ground handling, in order to get the correct ground loop (the fear of taildraggers!) etc. I had all the parameters to give tyres ground drag, side drag, etc. Even the spring that links the rudder to the tailwheel can be adjusted in the X-Plane flight simulator. Now, it behaves pretty much as in real life. I am still not happy how it starts spins but ... I'll get there.

Anyway, this is to say that simulators are not real-life. If an aircraft is highly praised in a simulator, it doesn't mean that it is behaving exactly in accordance to the real one. Think of this: How many have experienced a Dutch roll with a B-747? Yet, many do in in a flight sim. If the aircraft is praised, it is often for its 'eye candy' i.e. how nice the livery is reproduced, etc. and not its aerodynamic fidelity to the real one.

My father who was an airman in the Belgian air force, flew the Dakota and told me that to turn it in order to track back at the end of the runway (he did a lot of bush flying in the former Belgian Congo) he had to unlock first the tailwheel, press a pedal with toe brake added and rev up the opposite engine to induce the turn. Not an easy manoeuvre but a necessary one with those old taildraggers.

Answer 3

Essentially, with differential braking, ie, using one or both brakes to slow and/or turn the aircraft. Larger aircraft have nose gear steering.
Engine(s) are usually at idle during taxi and only used to initiate taxi. Idle thrust is generally enough to sustain taxi speed and if the aircraft is light or the taxiway slopes, the plane usually accelerates. Brakes are repeatedly used to check the speed.

Answer 4

A jet engine produces thrust even at idle power, unlike a propeller.

So at light weights the plane will be accelerating even at idle power, so the most brake-friendly technique is to allow speed to build up to about 25 knots then make one smooth brake application to bring the speed down to about 10-12 then let it go again.

Unless you work for a US commuter airline, in which case taxying at 40 knots seems normal!

Answer 5

If you are talking about a small aircraft, it's b/c it doesnt' take much to move that "small" aircraft. Just back off on the throttle, don't ride the brakes..... just like every other part of flight, it's a touch that you have to get used to.

Answer 6

Don't have all the engines operating, use zero thrust or reverse thrust, and brakes.

Plenty of planes can taxi with some engines off. These techniques are used on all kinds--propeller and turbojet. At any major airport you can see planes taxiing with a propeller stopped or a jet engine in reverse.