Hello,
I realized I have a bit of trouble correctly trimming the C172 for take-off. Strangely, I never had this problem on the C152 type aircrafts that I trained on and that I fly these days. In the C152, I find that when I set the trim-tab for take-off, using the marker, I don’t feel any significant pressure on the control wheel during the take-off run. At 55 knots, I lift the nose slightly and watch the magic happen.
Whenever I fly C172 types, I find it more or less difficult to find the correct trim for take-off. I especially had this during the last week of flying the same airplane for several hours and take-offs. It just doesn’t feel quite right.
The difference between the types may have to do with the different loadings that are possible with the 172 that are not possible with a 152 (i.e. pax on the back seats or not). I generally feel pressure on the control wheel during the take-off running and I apply forward pressure to keep the nose wheel on the ground until Vr – and I don’t like doing that. It doesn’t feel right and it also makes it harder to find the correct control wheel position right after lift-off for the intitial climb.
I have no problem at all to more or less “intuitively” trim the aircraft in flight. When there is pressure on the control wheel, I just sort of “know” what to do with the trim wheel to find balance. I don’t consciously think about which way to move the trim wheel.
That doesn’t work on the ground, as you set the trim tab BEFORE the pressure comes on. And I know this might sound stupid, but when I’m on the ground in the aircraft, I tend to not “know” which way to adjust the trim tab away from the marked “take-off” position (which is often just carved into the panel) to have the right position for my so-and-so loaded aircraft. I also don’t “know” how far in that direction I should divert from the marked “take-off” position.
I realize this may sound a bit odd for someone who’s been flying for a bit now, but then again, the problem only came up with the transition to the C172 and I don’t fly them as often as the C152.
Any hints how to better handle this?
Trim serves to remove the control forces. Just put it in a position where you do not have to use a lot of force for takeoff (the “takeoff” position) and control it manually. It shouldn’t matter what the exact forces are.
I fly a heavier Cessna which requires flaps for takeoff and has a retractable gear. Both cause massive changes of momentum, far more than a turn of a trimwheel. I just put the trim wheel in neutral and I know that I have to push quite a bit when retracting the gear but I will have to pull again when retracting the flaps afterwards. Only when I’m configured for the climb, I trim it (or rather let the AP do that job).
IMO not so important.
IMO not so important
I disagree somewhat as I find it harder to get the aircraft off the ground in a stable and consistent way, when during the take-off roll, I have to increasingly push before lift-off.
I thought about aborting the take-off once, but then thought that was a bit “too much”.
Another option would be to retrim during the run, but that doesn’t seem to be a good idea, either.
As long as you have the strength to fly the plane, trim is secondary. Of course, trim out control forces as you can, but fly the plane first. The trim indicator on Cessna can be “out” a little, so take it as guidance only. Similarly, the loading of the plane will affect pitch control forces.
Single Cessnas don’t have a “Vr” speed. I suggest, for the sake of the rather delicate and expensive nosewheel, and to remove any possibility of wheelbarrowing the plane, apply lots if not full nose up pitch control at the beginning of the takeoff, and as the nose rises a little, relax some of the back pressure so the nosewheel stays light. If you hold this attitude with care, the plane will fly off when it is ready, with your doing nothing more than simply maintaining this attitude, and keeping it straight, then level. Trim out control forces as you can, but fly the plane first.
One day, while taking off on grass, apply 10 flap, and begin the takeoff with the controls full nose up, and try to get the nosewheel right off the ground early in the takeoff roll. Avoid banging the tail, which is why we do not practice this on a hard surface. The nosewheel will lift off easily, and the aircraft will be very controllable in pitch and yaw, at speeds as slow as 20 knots. Yes, you’ll use a bit more runway, but you’ll be amazed how controllable the plane is, and how eager it will be to fly. Be ready to control yaw and roll. This is really useful soft field takeoff technique.
If you get more into larger aircraft and IFR, you will start rotating by the numbers on the ASI. A C172 just starts to fly. A larger aircraft has to be pulled off the runway and then a specific attitude given in the POH/FMS has to be selected.
Your takeoff is visual, just keep it down until you have the required speed and then let it go up. The control forces on a C172 are next to nothing anyway. Fly a C210 and you will see that trim really isn’t an issue on the C172 
Rhino, the 172 just feels a bit heavier than 152 but you can easily control it when the trim wheel is anywhere close to the take-off mark. A bit of pressure on the controls can surely be compensated, do not worry about it too much. Please note that you should never push the controls forward when departing from a grass airfield ;) Just for the sake of reassurance – try another C172 and compare the feelings.
My view is that one should set the elevator trim so that the aircraft climbs at Vx.
That is consistent with the concept that you should be trimmed during all phases of flight, and the initial climb after takeoff should be at Vx, for obstacle clearance reasons.
It will still need to be deliberately pulled off the runway, if you are after a “max perf” takeoff.
As long as you have the strength to fly the plane, trim is secondary.
I know what you mean but I would not take that literally because it is certainly possible to trim back so far that two people pulling together cannot keep the aircraft on the runway and it just loops back. There is a well known 2x fatal Cessna crash ref1 ref2 where the autopilot is suspected of having got engaged accidentally at the start of the takeoff roll and it drove the elevator trim all the way back.
A larger aircraft has to be pulled off the runway and then a specific attitude given in the POH/FMS has to be selected.
Isn’t the need to do the specific pull due to bizjets and above having a negative AoA when the nosewheel is down – deliberately to ensure that when the nosewheel touches the runway, you are really not going to go up again, and you can really jump on the brakes. With light GA aircraft, the nosewheel down condition still has a positive AoA so you need to wait to lose airspeed before you are firmly down. This was explained in a great article by Mac McLellan formerly of the US Flying mag (he writes for some online mag now).
When learning to fly on the C172, I was instructed to set the trim at the “E” for Take Off (slightly nose down) rather than neutral – I once asked “why?” and my instructor said “let’s try it, shall we?”. So we did and the plane handled exactly as you described, it took pressure to keep the nose down. Could be that this was particular to that C172 but as part of the pre-checks, the trim is set to neutral and the pilot confirmed the tab was aligned with the elevator so I’m pretty sure the trim was set up correctly. Either way, with an Archer, I’ll set it neutral on take off, with the 172, at E. But as Achimha says, it’s no big deal as long as you’re not really wrestling with the controls……
Another option would be to retrim during the run, but that doesn’t seem to be a good idea, either.
One of my (nose wheel) planes has a stabilator which provides both powerful pitch control and powerful pitch trim control. Its impossible to trim accurately for take-off, by which I mean to preposition the trim setting so the plane will be perfectly trimmed on the upwind. I set it somewhere close and re-trim as I establish the climb at whatever speed I’m using that day. Typically I set trim a bit nose down before takeoff, which avoids the uncomfortable feeling of needing stick force to maintain flying speed. The out of trim forces are not high due to the powerful elevator control, so it works OK.
On takeoff in that plane I use PDAR’s technique of nursing the nose wheel into the air early, actually before the throttle is fully open, and then letting the plane fly off in due course. The plane has direct acting nose wheel steering and significant P-factor. The yaw control sensitivity mismatch between nose wheel steering and aerodynamic rudder control can cause some bobbling around in yaw if you rotate later.
Stick and Rudder pointed out that nose wheel aircraft are great for landing control but tail wheel aircraft aircraft are actually pretty well adapted for taking off. I find that to be exactly the case.
Have you ever looked over your shoulder during the run-up and checked if the trim tab was, in fact, in the takeoff position? The cables that control the trim tab can and do slip and I’ve flown more than one 172 where the trim tab was out of whack, quite a bit on some. In which case, re-trim visually.
