Elevator Deflection

[Bruce Fenstermacher]

Jim, I see you've pulled out all the tricks trying to increase your airspeed by leaving red traces on your controls. Very sneaky.

[c170b53]

Ah..Thks Bruce, there's no fooling you
I guess in search of the solution to this puzzle, we may want to know the incidence of the stab if there were major tail repairs.

[56alpha]

Another thought is that the holes in the support bracket that mounts the bellcrank are worn and elongated. This could be caused by a seized bearing, causing the bolt to rotate in the bracket. As the holes elongate, the bellcrank would shift forward. The effect of this would be less up elevator deflection and more down.

-Jay

[n2582d]

... Just wondering to me-self and I hadn't thought of it ever before, whether the stops are physically different in their dimensions? ... .

The upper and lower blocks are nearly identical. The bottom block is slightly longer than the top one. As you all know the hole in the block is drilled off center. The maximum one can adjust the stop is around 0.10".

Click to Enlarge

[FredMa]

well tim, found out anything new on your elevator problem?

[c170b53]

I had a look at mine trying to come up with something. It's been a few years since I put the plane together and so I've forgotten how I came up with my adjustments. On the weekend using a inclinometer, I measured the horizontal stab angle but as it has an elliptical shape, laying the meter on the stabs skin really doesn't work very well. The elevator skins taper from the elevator spar to the trailing edge so even with the elevator in neutral there's at least a 5 Deg diff between the two top surfaces at neutral. So what I believed I did way back when, is aligned the leading edges (Stab&Elevator) and then simply measured the displacement at the elevator trailing edge from neutral when at the stops and as I believe hand grenades are effective getting close is good enough for me. Although you could play around with the stops if you we're a deg out, I don't think it would be discernible in flight characteristics. Any way I know I did rotate things around a few times and now rechecking things years later, it appears I had better principles back then as using the above reasoning the elevator meets the travel specs.
Fred I'm kinda more than interested in these kind of things as well. I also tried to measure the stab's incidence angle but I'm not confident with my guesstimate that by measuring the fuselage levelling point angle and comparing it to the (what I perceive to be the horizontal Stab's centre plane) stab angle, that zero incidence is correct, but roughly that's what I came up with. I could easily be out by a couple of degs.
Things that make you go....humm

[FredMa]

I am not sure what the incidence is supposed to be either or what the difference is between the 170, 170A and 170B. I am more interested in making an accurate comparison between tim's plane and another 170B with normal elevator deflection. An easy way to do this is to pick a fairly flat rib location near the base of the stab and mark it front to back with a piece of masking tape. Tape two drill bits perpendicular to that crossing the tape on the front edge and also one on the aft edge. Lay your level across the two drill bits to measure the angle. This is how the curved surface of prop blades are measured. As long as you duplicate the location on another aircraft for comparison, you should get a pretty accurate reading.

[FredMa]

for measuring the deflection it doesn't really matter what the centerline angle if the elevator is. You place the elevator in it's neutral position with the horn faired. Place the protractor on the surface at a place you have marked and zero the protractor in that position. Then measure the new angle from that same spot with elevator full up and full down.

[c170b53]

I'm sure there's more than one way; some will be more precise than others, I'm just offering what I did. The only problem with my quick method is the neutral ref.point would be off if the tips had been improperly replaced. I keep thinking that Tim's observations of his elevator's movement were the beginning of this thread. If he can see a physical difference and has measured the difference I got to think the wrong part is installed somewhere beginning with the aft crank, the rod (now ruled out), the control horn and the attachment points of that horn. After that what's left? other than the elevators themselves. dimensional checks of these parts would help steer the thread.

[GAHorn]

Level the aircraft using the top of the door frames, both longtitudinally and laterally using corresponding points on each door-sill.

With the aircraft levelled: Angle of incidence – stabilizer ... . . . – 2 deg. 48 min.

Stabilizer angles listed are measured as the difference between a line across the top of the front and rear spar and the top edge of the fuselage splice plate. When measuring across the top edge of the spars it will be necessary to push the skin down slightly close to the centerline of the airplane to get an accurate measurement.

============================= From the Rigging Instructions for this airplane=============
Tail group:

To check the symmetry of the tail:
A symmetry check is an inspection to see how the aircraft’s individual components are positioned to each other.

The first step is to level the aircraft. An upper door sill maybe used to level the aircraft longitudinally, and corresponding points on both upper door sill may be used to level the aircraft laterally. With the aircraft level place a beam beneath the horizontal stabilizer and level the beam. With the aircraft level and the beam level, measure from identical points on the left and right tips of the horizontal stabilizer down to the beam. The distance should be equal to within ¼”. If the distances are not equal, we don’t know if the stabilizer is not straight or the aft fuselage is crooked.
Next place a beam vertically along one side of the main spar of the vertical stabilizer using a level to make sure that the beam is vertical. With the beam against the base of the main spar and vertical, measure from a point at the top of the stabilizer to the beam. Do the same thing on the opposite side of the vertical stabilizer, taking care to measure from the same point. These measurements should be equal, if they are not then the vertical stabilizer is not vertical.
Next, measure from identical points on the left and right horizontal stabilizer to an identical point on the top of the vertical stabilizer, again looking for equal distances.
To determine if the horizontal stabilizer is mounted correctly in regard to the centerline of the aircraft, measure from the same point on the tips of the left and right stabilizer to either the front mounting bolt of the dorsal fin or a rivet head in the top center of the fuselage bulkhead at Sta. 108.00. If these distances are not equal then the shims at the bulkhead at Sta. 205.812 are not correct.
With these measurements it is possible to determine the mounting of the entire tail assembly. If the horizontal stabilizer is parallel but the vertical stabilizer isn’t vertical then the vertical stabilizer isn’t on straight. If the horizontal stabilizer isn’t parallel, the vertical stabilizer measures vertical and the distances from the tips of the horizontal stabilizer to the vertical stabilizer are not equal, then the horizontal stabilizer is not on straight. If the horizontal stabilizer is not parallel and the vertical stabilizer is not vertical, but the distances from the tips of the horizontal stabilizer to the tip of the vertical stabilizer are equal, then the whole tail cone of the aircraft is crooked.

[marathonrunner]

Any more developments on this problem?

[swixtt]

I've run into a similar issue.. I'm 20 up and 20 down. Curious if this was resolved?

[n2582d]

Depending on where you look there are differing numbers for the degrees of elevator travel. The TCDS says 26 up and 20 down, The 1952 C-170B owners manual adds some tolerance by stating on page 52: 26 degrees up +1, -0, and 20 degrees down +1, -0. But take a look at the illustration. This must be a cut and paste from the 170A manual which slipped by the proofreader.

1952 170B illustration

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Swixtt, As your down travel is OK but your up travel is 6 degrees short I would start by confirming that the elevator rear bellcrank (fig. 67-36, p/n 0510108) in the tail is hitting the up stop. If it is not, it could be that the forward elevator bellcrank (fig. 67-1, p/n 0510159) is hitting the forward elevator stop (fig. 21-86, p/n 0713497-1 now revised to p/n 0713497-3) located on the gearbox cover. The stop bolt, fig. 21-87, p/n 0431141-1 has been revised to NAS428H3A12. This bolt is unusual in that it has UNJF threads.

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I was perplexed as to the purpose of this second up stop. The answer is found in the 100 series service manual on page 8-6:

This stop bracket is missing on my '52 rebuild project and there is no evidence of rivet holes on the landing gear box cover where one would have been. I may have a cover from a 170A or maybe Cessna didn't add this stop until later serial number 170B's.

[n2582d]

Could someone compare the shape of the elevator pylon assembly, p/n 0534107, on my '52 170B with one from a 170A? This still seems to me to be the most likely problem that Tim has experienced. Does the bolt hole pattern match between the two models? 4 squares=1 inch.

C-170B elevator pylon

Pylon.pdf

PDF Version of pylon

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[Bruce Fenstermacher]

I could but not for a few days. Perhaps someone else can quicker. But the A model and prior is # 0310262 and the B model IPC lists that part as 0534107. Do you expect them to be the same or different?