Trim Setting for Takeoff

[Mark A]

Is neutral (on the mark) the best takeoff trim position or is slightly nose up better? My 170A doesn’t appear to like the trim neutral position for takeoff. Thanks Mark

[cessna170bdriver]

I have a B-model, but I just use the mark as a reference; it just tells me when the trim tab is faired with the elevator. With just the front seats occupied, the neutral point is too nose-down, so I set the indicator about 1/8-1/4 inch behind the mark.

[N2625U]

I have a 172D model. The trim will vary depending upon loading. I find it is different between the back seat empty or full and depending upon how much baggage you have.

[dstates]

For my 170A I put the indicator about 1/8” behind the mark and that works out well for me.

[GAHorn]

Jack Nicholson said, “Heere’s the Deeal..!...”

Firstly, the Trim tab should be aligned (streamlined) with the elevator when the elevator is also streamlined with the horizontal-stabilizer. THEN... the cockpit indicator should indicate Neutral/Zero trim. (It’s important to first accomplish this relationship before proceeding with the excersize.)

NEXT... with the CG at the center of the fore/aft limits (each aircraft WT/BAl will differ but ALL should meet this description).... The takeoff should occur without pilot pitch-input under those conditions...as the airplane accelerates, the elevator will rise of its’ own-accord ... the tail will rise of its’ own.....and the airplane will lift off (and should be trimmed for climb) at ~67 mph.

Ain’t that Kool!!!? (Your pitch trim and aircraft elevator circuit is properly rigged.)

Hope that helps.

(It’s critical that the elevator Tab be streamlined with the elevator...and the elevator streamlined with the horiz-stab... and the cockpit indicator be exactly at the T.O. Index.). And, BTW.... that is what we should be CONFIRMING at each Pre-Flight Inspection. Set the cockpit wheel to put the index at the zero point... then during the walk-around... confirm the elevator raised to the streamlined position.... that the pitch-trim-Tab is also streamlined.)

Edited to clarify climb speed

[wabuchanan]

On my 170A I used to set mine for about 1/8th inch behind the neutral mark, until I started doing short field take-offs as a matter of course most of the time. Now I set mine 1/8th inch nose down on take-off.

I get the plane airborne at 40mph indicated and the nose down helps keep the plane in ground effect until I have the speed to climb out.

If I'm carrying a load or rear passengers I set for neutral or just barely nose down and lift off at 50-55.

I have found my plane likes to fly. It wants to start climbing immediately on take off, and frankly, it hates to come down....

[GAHorn]

On my 170A I used to set mine for about 1/8th inch behind the neutral mark, until I started doing short field take-offs as a matter of course most of the time. Now I set mine 1/8th inch nose down on take-off.

I get the plane airborne at 40mph indicated and the nose down helps keep the plane in ground effect until I have the speed to climb out.

If I'm carrying a load or rear passengers I set for neutral or just barely nose down and lift off at 50-55.

I have found my plane likes to fly. It wants to start climbing immediately on take off, and frankly, it hates to come down....

I wonder WHY your 170 LIKES to FLY..?

[cessna170bdriver]

Jack Nicholson said, “Heere’s the Deeal..!...”

Firstly, the Trim tab should be aligned (streamlined) with the elevator when the elevator is also streamlined with the horizontal-stabilizer. THEN... the cockpit indicator should indicate Neutral/Zero trim. (It’s important to first accomplish this relationship before proceeding with the excersize.)

<snip>

(It’s critical that the elevator Tab be streamlined with the elevator...and the elevator streamlined with the horiz-stab... and the cockpit indicator be exactly at the T.O. Index.). And, BTW.... that is what we should be CONFIRMING at each Pre-Flight Inspection. Set the cockpit wheel to put the index at the zero point... then during the walk-around... confirm the elevator raised to the streamlined position.... that the pitch-trim-Tab is also streamlined.)

Edited to clarify climb speed

Why the emphasis on the elevator being aligned with the stabilizer? On my B-model the trim tab doesn’t move relative to the elevator over the full range of movement of the elevator. Maybe it does on an A-model?

[GAHorn]

[

Why the emphasis on the elevator being aligned with the stabilizer? On my B-model the trim tab doesn’t move relative to the elevator over the full range of movement of the elevator. Maybe it does on an A-model?

I was afraid someone might notice this.... I should have known it would be you, Miles!

Here’s why I wrote it as I did: ALL airplanes which have trim-tabs on elevators (and well as those which use trimmable-stabilators) should be checked during pre-flght inspections to confirm the trim-tabs match their indices for the take-off range and that flight controls move in the proper and full direction/deflection.

As Miles noticed, the 170 elevator trim remains stationary relative to the elevator movement, and although THIS is a C-170 Forum.... the pre-flight inspection process requirement applies to all makes/models aircraft. Since some aircraft have tabs which change** their relative motion to the flight control (such as servo-tabs and antiservo-tabs) ... it is common practice to ascertain the tabs’ relative position (and direction of motion or lack thereof) when the flight control surface is in it’s streamlined condition. In order to remain within that convention, I posted the “most correct” method of inspecting the tab positions, hoping to describe a method which readers might use as it applies to all aircraft. (Didn’t want to get into the discussion when some later 172 pilot Member points out that his tab actually changes relationship when he moves his elevator.... that obviously doesn’t work in a Forum which has highly-knowlegeable specific-model participants.).

**It is common design (especially with stabilators) that tabs are designed as “anti” tabs... as this will provide increased “feed-back” to the pilot if the pitch is moved away from the trimmed speed. This can be done to discourage speed departures as well as to prevent over-control when flying manually, ...and is also often used to prevent rudder-over-control... servo tabs which “assist” in movement are often used for roll control, especially common in high-speed aircraft. (Some aircraft pitch-trim indices may even change position when the flaps are deployed for take-off.)
When checking pitch-trim relative to take-off it is always correct to compare the tab to the indices if the primary pitch control surface (i.e. elevator) is streamlined.

[Ryan Smith]

In my airplane I have two trim settings: climb and everything else.

I prefer the slightly nose down trim setting for takeoff to train because most folks have a mental block on pushing the yoke forward on takeoff, and it also reduces the “spring” of the additional downforce on the tail keeping it down, lowering the effects of gyroscopic procession.

I taught myself to fly the airplane that way, and that’s the best method that works for me, and my students.

[cessna170bdriver]

In my airplane I have two trim settings: climb and everything else.

I prefer the slightly nose down trim setting for takeoff to train because most folks have a mental block on pushing the yoke forward on takeoff, and it also reduces the “spring” of the additional downforce on the tail keeping it down, lowering the effects of gyroscopic procession.

I taught myself to fly the airplane that way, and that’s the best method that works for me, and my students.

Ryan, are you saying that you have to trim nose down from the neutral point to get the tail to fly itself off? I don’t have any mental block about pushing the yoke forward on takeoff (I was trained that way in a J-3 & Stearman to acquire visibility down the runway), but I do like to let the tail fly itself off, then hold just enough back pressure to keep it low and let the airplane accelerate until it flys itself off. For most of my flying the back seat is empty, and it takes about 1/8” or so of nose up trim to make that happen. (My normal takeoff is with zero flaps. With 10 or 20 degrees of flaps it might require nose down trim to make it work as smoothly, but I do that so seldom that I don’t recall.)

[ghostflyer]

I always have the nose trimmed down for takeoff. The reason being is for some reason my hands leave the control wheel[seat sliding back or some other reason] the aircraft will pitch down and not climb and stall and if nose down it’s easily able to move that seat where you need it in a hurry. Accidents always happen for a number of reasons and very rare for a single reason. Eg. Motor dies on take off and seat slides back . It’s only when I reach 1000ft AGL that the flaps are retracted ,aircraft trimmed,and climb power selected.
It’s my belief that if things turn ugly at 300ft and aircraft is trimmed down slightly you have more time to rectify the situation than trying to regain control heading for a stall.

[Mark A]

Thanks for all of the comments. I think I will experiment with slightly nose down trim setting today for takeoff.

[counsellj]

I always have the nose trimmed down for takeoff. The reason being is for some reason my hands leave the control wheel[seat sliding back or some other reason] the aircraft will pitch down and not climb and stall and if nose down it’s easily able to move that seat where you need it in a hurry. Accidents always happen for a number of reasons and very rare for a single reason. Eg. Motor dies on take off and seat slides back . It’s only when I reach 1000ft AGL that the flaps are retracted ,aircraft trimmed,and climb power selected.
It’s my belief that if things turn ugly at 300ft and aircraft is trimmed down slightly you have more time to rectify the situation than trying to regain control heading for a stall.

Excellent reasoning and execution.

[GAHorn]

Just for fun.... sometime (with someone qualified in the right seat).... trim your airplane however you normally do.... then about 100’ let go of the yoke and slide your seat fully-back.... and see what happens.