Aileron spar lightening holes

[voorheesh]

1950 170 A SN 19225 27 holes on both sides.

[ron74887]

1953 170B sn 25853--- 8 holes on both sides. Ron

[hilltop170]

John my logs didn't show any wings being replaced with L-19 wings on my airplane until 2000.

Bruce-
So what does that mean? Did you get the logs up to date after you bought the plane or was that when the L-19 wings were installed, or what? Just curious if the subject is not too sensitive.

[Bruce Fenstermacher]

It was "discovered" by an IA in 2000 just before I bought the plane. The IA thought they were 17OB wings and so sought and received an approval for 170B wings which essentially they are. We can by the books substantiate that the plane flew in this configuration at least 10 years since it was painted in 1990 and in reality probably flew like that since the first log entry I have from 1955.

There is no mention in the logs anywhere till 2000 of a wing, strut or elevator change yet they are there.

So either I have the only A model with L-19 wings complete with rocket hard points, B model flaps, struts and elevator that Cessna ever produced and didn't document or some maintenance didn't get recorded in the log book.

My point is that unfortunately, specially with older planes, lots of maintenance from yesteryear didn't get documented and it is naive of someone to think that lack of a documented change alone means that is the way the aircraft came from the factory.

[Bruce Fenstermacher]

A friend has an A model serial 18837 with 27 holes. We need a few newer A models later than serial 19225 to report in with what they have as well a early 52 B models.

[hilltop170]

Bruce-
Interesting story about your wings and tail. I would guess maybe unrecorded maintenance?

My 1951 A model is s/n 20158 with 27 hole ailerons on both sides. Looks like '52 might have been the changeover year.

[Bruce Fenstermacher]

52 B models started at serial 20267 so we are looking for examples of A models close to that and B models just after. The Beyers aircraft with the mixed ailerons that started this thread is serial 20472.

[wingnut]

SN# 20968 in my hangar has 8 holes.
The main things to be mindful of when swapping ailerons from any 100 series to another are balance weights; they are different from model to model, and the sweep-up at the outboard end; 170A wings and 150 series have less because 1 degree wing twist versus 3 degrees on other models

[Bruce Fenstermacher]

Del I was waiting for you to chime in.

Interesting that you say the ailerons would be different for the A model because of the different degree of twist yet the part numbers are the same for all years.

I'm not familiar with how or where the Cessna wings twist. If they twist on the leading edge and the trailing spar remained straight then the result would be that only the wing tip trailing edge would not line up to the aileron in neutral. This is exactly the way I see many of them with the aileron trailing edge lower than the wing tip trailing point.

I don't mean to question your expertise Del, you have inspected many more of these than I have. I'm just thinking out loud.

And if the ailerons are different as you say Del despite the same part number, then I'll bet that is when the 8 hole aileron spare was used.

We will just have to keep looking and noting which serial numbers have what holes and see if we can prove anything out.

[wingnut]

The parts numbers may not have changed because the same parts are used, just the assembly technique at the outboard end was different.
The aft wing spar is angled upward more on the 3 degree wings, so the aileron was also angled up more (starting approx 16" from the outboard end) so the aileron would line up with the tip. If you installed B model ailerons on an A model wing, the aileron trailing edge would be about 3/4" higher than the aft end of the wing tip (assuming the ailerons were built correctly).
Beech has the same part numbers for left and right ailerons. You can swap tham left to right, but the trailing edge rivets would be uside down. Their IPC says to specify left or right when ordering because they have the same PN#. Just an example

[Bruce Fenstermacher]

Interesting Del. So the twist is all in the aft spar and not in the leading edge of the wing. I will have to inspect my ailerons and compare with the A model my friend has to see this.

Hmmm now you got me thinking I wonder if L-19 wings had 1 or 3 degrees of twist? As noted above my wings are actually L-19.

[Bruce Fenstermacher]

Well sorta answered my own question. The L-19 wing was a modified 170 wing with dihedral which later became the 170B wing.

[GAHorn]

I'm not the expert which Del is, and I don't have a wing-jig and don't repair wings. But recalling the reading in my documentation-library, leads me to make the following comments with a certain degree of confidence.

The wings of A and B models are identical (except for flaps) as far as twist is concerned. The additional twist of a B-model (and L-19) wing takes place outboard of the upper strut attachement. This is why the same aileron part numbers can be used on both aircraft, because the ailerons only follow the twist which is set by the rear spar outboard of the ailerons.

The ailerons, as produced by Cessna, do NOT meet the wingtip fairings, their outer ends should rest equally, one-half inch BELOW the wingtip-fairing trailing edge. (While it may be pleasing to the eye for them to meet exactly, and while a diligent and careful re-builder may use a squeezer and add the aileron outer-twist while installed on the aircraft in order to achieve an exact match to the wingtip fairing trailing edge.... that is not the way Cessna did it. Cessna OEM ailerons do not match the wingtip fairing trailing edges because the fairings are interchangeable left/right and do not consider the "handed" left/right twist of the left/right wings.)

FYI- Aileron spars were mfr'd at various times and Cessna efforts at cost reduction and interchangeability between models led to simplified tooling, and that is why the aileron spars changed in the number of lightening-holes. (In a simplification move, certain later Cessna 150 and 170, 172, 182, L-19 ailerons are interchangeable.)

My rebuilt ailerons (B-model, SN 25713) has two 8-hole-spar ailerons.

[N2625U]

I was wondering about these holes when I was at the airport yesterday. I've got a '63 172D model and it has 27 holes on the right aileron and 8 on the left. According to the logs the wings were replaced in 1971 and the plane repainted then.

[wingnut]

I'm not the expert which Del is, and I don't have a wing-jig and don't repair wings. But recalling the reading in my documentation-library, leads me to make the following comments with a certain degree of confidence.

The wings of A and B models are identical (except for flaps) as far as twist is concerned. The additional twist of a B-model (and L-19) wing takes place outboard of the upper strut attachement. This is why the same aileron part numbers can be used on both aircraft, because the ailerons only follow the twist which is set by the rear spar outboard of the ailerons.

The ailerons, as produced by Cessna, do NOT meet the wingtip fairings, their outer ends should rest equally, one-half inch BELOW the wingtip-fairing trailing edge. (While it may be pleasing to the eye for them to meet exactly, and while a diligent and careful re-builder may use a squeezer and add the aileron outer-twist while installed on the aircraft in order to achieve an exact match to the wingtip fairing trailing edge.... that is not the way Cessna did it. Cessna OEM ailerons do not match the wingtip fairing trailing edges because the fairings are interchangeable left/right and do not consider the "handed" left/right twist of the left/right wings.)

FYI- Aileron spars were mfr'd at various times and Cessna efforts at cost reduction and interchangeability between models led to simplified tooling, and that is why the aileron spars changed in the number of lightening-holes. (In a simplification move, certain later Cessna 150 and 170, 172, 182, L-19 ailerons are interchangeable.)

My rebuilt ailerons (B-model, SN 25713) has two 8-hole-spar ailerons.

Both A and B wings have zero twist from the fuselage root rib to station 100 (strut attach point). The A wing has one degrees from sta 100 to tip rib and the B has three. It's hard to explain without being able to demonstrate in person. But the wing twist fulcrum is at the main spar, although it does not "rise or fall" from sta 100. The rear spar "twist" up from the main spar and the leading edge "twist" down, although the leading edge arm is shorter than the trailing edge from the main spar, so it's less noticable. Because the ailerons are rigged to the flaps, and the flaps are attached to the zero twist area of the wing, the position of the outboard end of the aileron will be different on A and B models, assuming you installed the same aileron on both an A and B just to see the difference.
I agree the ailerons are innerchangable between A and B models.
I have both A model and B model ailerons in the hangar, and there is a very noticeable visual difference in the sweep-up at the end; about 5/8" on the A and 1-3/8" on the B as measured by placing a straight edge on the trailing edge and measuring the sweep.
As for ailerons drooping below the wing tip, I know it's very common, but don't know that it's necessarily right, or wrong. I just know the 2 170's in my hangar line up within 1/8". That includes fuselage to flap, flap to ailerons, ailerons to tips. I also have a 182Q in house that the trailing edges are absolutely perfect everywhere.
I know, this is probably the exception rather than the rule, but I atribute the problem with trailing edges not lining up would be due to a combination of Cessna's fixtures being moved around how many times in 50 plus years? And how many improper repairs to these aircraft in 50 plus years? It's cumulative. And the lack of mechanics knowledge and/or motivation to rig properly