The International Cessna^® 170 Association

Wow, I thought we had this one figured out! Any chance the pylon assembly on the elevator is incorrect? By the bolt patterns in the IPC drawings it doesn't look like it would be possible to interchange these. For the B model it should be p/n 0534107. The earlier models have p/n 0310262.

I was kind of thinking the same thing. He could even have the wrong elevator installed, if that is even possible.

Perhaps there is an angular difference between the elevator and pylon horn on the 170B and 170A. I do believe the stabalizer is set at a different angle on the B models.

To confirm I just now had a elevator push rod measured from a 54 B model It is 29 1/8"th center to center. We also measured the forward control rod and it is 15 3/4 "center to center.

Fred it is not possible to mount an A model elevator to a B model horizontal stab and vice versa. The hinges are not in the same positions to start. It is suppose to be possible to replace the entire hor. stab./elevator combination between A and B model and that is what was suppose to have happened to my A model but I can't say that is actually what happened.

Thanks for the info bruce. Sounds like he needs to determine once and for all if the problem is aft of the bellcrank or the bellcrank itself not producing sufficient travel due to incorrect positioning of the stops. You can position the elevator in the neutral position and take an angular measurement of the aft bellcrank between bolt centers then do the same thing at full up elevator and full down elevator. Compare this to the same measurements of another B model with normal travel. If they are the same, you stops are correct and the problem is aft of the bellcrank. If the measurements are different your bellcrank is not acheiving proper travel due to the stops being installed wrong or previous repairs not done properly etc. Hope that makes sense.

Actually I just realized that you don't need another 170B for comparison. You can determine this mathematically by comparing the correct angular movements proportionally to the readings you get from your airplane. The readings don't have to be taken from the hole centers on the bellcrank either, any surface will do, like the forward flange of the bellcrank.

The correct angle of UP elevator travel is 26 deg and 22 deg down. 26/22 = 1.181818 deg of up travel for every 1deg of down travel. you have measured 20 deg of up travel and 28 deg down travel or 20/28 which equals .71428 degree of up travel for each deg of down travel. Measure the amount of angular change of your bellcrank for up movement and divide that by the amount of angular change for down movement (from neutral). If it equals 1.181818 your bellcrank and therefore stops are set correctly. If it equals .71428 your stops are incorrect and the reason for your travel problems.

I got my degrees of travel wrong it should be 26 and 20 for correct travel and 18 and 28 for what you are experiencing.

Let me try to answer some of the issues. Jim, my measurements were made with the bellcrank against the stops (up and down). My A&P and I rechecked the deflection measurements again with the same results. I don't see how the trim could affect the elevator throw when the bellcrank contacts both stops. I measured the length of the pylon assembly (part 5 in the sketches) and compared it to the 2 - 170A's on the field (there are no other B models). No difference in length. I see no way to install the elevators, bellcrank, pylon assembly, or push tube incorrectly. We haven't checked the forward control rod, etc. because it shouldn't matter since the bellcrank is hitting both stops at the rear. Fred, I've got to study your comments and draw a sketch or two in order make sense of what you are proposing. My search of the logs shows some old damage (1960's) in the tail area. The horizontal stabilizer, left elevator and bellcrank were replaced. The airplane has flown well and passed many inspections for 40 years since the repair. Any more suggestions would be welcome.
Tim

I doubt if you could install an A model elevator pylon (control horn) with the b model elevators. I have one of these pylons in my junk box and will take it to my A model tomorrow and compare it. Of course if it is the same it could be from an A model. Then we will have to find a B model to compare it to.

Let me explain it again so I don't confuse you or myself. The bellcrank drives the elevator directly through the pushrod and elevator horn. The amount of movement of the bellcrank is probably not the same as the amount of elevator movement it produces but is always proportional to it. By measuring the actual amount of movement of your bellcrank (from neutral) you will be able to tell if that corresponds to the correct elevator travel or the amount you are seeing on your plane. If it corresponds to the correct amount of travel your problem is aft of the bellcrank. If it does not correspond to the correct amount of travel (while hitting the stops) the stops are obviously wrong and preventing the correct amount of travel from occuring. It should be simple to make this determination in your case because you only have to determine if there is more travel in the up or down direction at the bellcrank.
Using whatever protractor you can find, measure how far your bellcrank moves in each direction. finding a good surface on the bellcrank will be the hard part due to accessibility.

There is so much lost in the verbage and imaginations.....
What you need is another airplane of the exact same model...side by side to compare.
There is no telling after 60s years what has been done.
You could have B model tail feathers on A model control system and no one logged it.
Find a B model with correct travel and compare.

From what I have read he is getting correct total travel just not correct in the up an down directions. That is what made me think initially it is the pylon and elevator combination/attachment that is the problem. He is for sure going stop to stop and has the correct total travel he just needs it reversed so to speak so he has more up travel then down travel.

Does it three point well? I don't see how it could with that little travel. I know I have seen similar problemw with the 180/185 series with the vertical spar rear attach bolts being installed backwards and contacting the torque tube limiting travel and not allowing for a three point landing. That would not be the case here but just a little thing can make a big change.

If hitting the stops and having enough travel it just seems that the problem is in the elevator and pylon area somehow. Darn wish I could be on site as do others on this forum I am sure. Might just have to disassemble everything and start from zero checking all lengths and travels.

Another thing hard to believe is that it went through all those years of annuals with no one checking control travels. That is the first thing I check along with control cable tension when I get a new to me airplane in for annual. 99.9 percent of the time something has to be corrected.

Marathonrunner, I am well aware that he has full range of travel. When I said "sounds like he needs to determine once and for all if the problem is aft of the bellcrank or the bellcrank itself not producing sufficient travel due to incorrect positioning of the stops" I was referring to the insufficient upward travel of 18 deg from neutral instead of the desired 26 deg. He has already looked at the pylon and hasn't seen a problem. I understand the bellcrank stops would seem less likely to be the cause but he needs to consider the less likely at this point. He did mention repairs to the tail being in the logbook. The only other thing I could think of to check that would cause tim's problem would be the angle of the elevator pylon relative to the elevator itself. I can't imagine how it could possibly be off but I guess anything is possible.

Well here's mine seen from above, and here's a closer look at the stops or at least you can see the top stop which is the one limiting elevator T/E up. You know its stuff like this that keeps people up at night Just wondering to me-self and I hadn't thought of it ever before, whether the stops are physically different in their dimensions? Can't believe it but I'll be looking at the components with at least the upstairs taking a different view.