9
$\begingroup$

My CFI (PPL) has on a few occasions pointed out that I need to apply back-pressure during taxi, even if we're taxiing on the apron at ~5 knots.

While I can understand the benefits of doing so during takeoff rolls and expedient backtracks, surely the effects of applying back-pressure on anything below 10-15 knots must be negligible?

I fly a C172 and I've heard that they have notoriously sensitive nose wheels, but still.

Am I misunderstanding something or is my CFI just trying to make me develop good habits (for when rolling faster)?

$\endgroup$
1
  • $\begingroup$ @757toga I did ask him if it mattered during slow speeds and he agreed that the effect isn't much although not negligible. He then mentioned something about reducing the risk of a prop strike, which I didn't understand at the time (for the same reasons explained in my post). In retrospect, his explanation now sounds very much like what GdD said below. $\endgroup$
    – Chris
    May 30, 2022 at 14:43

3 Answers 3

17
$\begingroup$

Back pressure is not negligible at taxi speeds, the prop is still running and even at idle will give you some elevator authority. While it's not that much with the elevator fully back you will lift the nose a bit, and if you hit a rut that can make the difference between getting over it or having prop strike.

The ground handling of a c172 is also better with a bit of weight off the nose.

$\endgroup$
6
  • 2
    $\begingroup$ I see. So the elevator authority is almost entirely due to the prop wash, correct? $\endgroup$
    – Chris
    May 30, 2022 at 14:38
  • 3
    $\begingroup$ At taxi speeds that's correct @Chris. You can feel the difference, next time hold the brakes and keep the RPM at 1200, then pull the yoke back to your lap and the nose will lift a bit. $\endgroup$
    – GdD
    May 30, 2022 at 14:47
  • 1
    $\begingroup$ Thanks. Would be interesting to one day test pulling back with full power and with the breaks applied. I suppose it would be visibly noticeable on the nose wheel suspension. Just a thought. Edit: Saw your edit after I posted this. $\endgroup$
    – Chris
    May 30, 2022 at 14:56
  • 2
    $\begingroup$ Tell your CFI you want to try that, I can't see why they'd say no. Maybe at power check RPM not full throttle. $\endgroup$
    – GdD
    May 30, 2022 at 15:03
  • 2
    $\begingroup$ You may want to review pages 2-19 and 2-20 in the FAA' Airplane Flying Handbook. faa.gov/sites/faa.gov/files/regulations_policies/… Taxing with quartering tailwinds requires some consideration as to what position your elevator should be in during taxi $\endgroup$
    – user22445
    May 30, 2022 at 15:55
5
$\begingroup$

It just reduces the load/wear-and-tear on the nose gear a bit, and keeps prop a little farther away from the ground. Even smooth looking paved taxiways and ramp areas usually have all kinds of small stones and gravel fragments, and propellers love to suck them up and create all those little dings on the prop leading edge.

This is especially important during run up, and at the start of the takeoff roll where thrust wants to pull the nose down and the propeller tips get to only a few inches from the surface, but it's also a good habit to do all the time in a plane like a 172. It's also a good practice, if you own your own plane and have to pay for the repairs, to do your runups on grass if that is at all possible. That is a huge propeller saver.

If there is a strong tailwind component however, holding the elevator up does nothing, or actually increases the nose wheel load if there is a net tailwind that overcomes the prop blast, so in those cases, you generally taxi with the elevator neutral. You will notice the effect if you are paying attention and the winds are strong enough.

$\endgroup$
1
$\begingroup$

I would get another opinion, my 141 school did not teach this. They only taught to hold full aft whenever taxiing/takeoff on soft fields, and short field takeoff.

Just because the instructor told you doesn't mean it's right... I was taught a wrong procedure before, and have heard of egregious stuff not taught like not leaning at altitude, etc.

From AFH 2-19 to 2-20:

When taxiing at appropriate speeds in no-wind conditions, the aileron and elevator control surfaces have little or no effect on directional control of the airplane. These controls should not be considered steering devices and should be held in a neutral position.

When taxiing with a quartering headwind, the wing on the upwind side (the side that the wind is coming from) tends to be lifted by the wind unless the aileron control is held in that direction (upwind aileron UP). Moving the aileron into the UP position reduces the effect of the wind striking that wing, thus reducing the lifting action. This control movement also causes the downwind aileron to be placed in the DOWN position, thus a small amount of lift and drag on the downwind wing, further reducing the tendency of the upwind wing to rise. [Figure 2-15]

When taxiing with a quartering tailwind, the elevator should be held in the DOWN position, and the upwind aileron, DOWN. Since the wind is striking the airplane from behind, these control positions reduce the tendency of the wind to get under the tail and the wing and to nose the airplane over. The application of these crosswind taxi corrections helps to minimize the weathervaning tendency and ultimately results in easier steering. [Figure 2-15]

The presence of moderate to strong headwinds and/or a strong propeller slipstream creates lift on the horizontal tail surfaces and makes it necessary to control the pitch attitude while taxiing. The elevator control in nosewheel-type airplanes should be held in the neutral position, while in tailwheel-type airplanes, it should be held in the full aft position to hold the tail down unless the headwind gets very strong, which allows for an elevator position closer to neutral.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .