L-19 Leaf spring installation

How to keep the Cessna 170 flying and airworthy.

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cfzxo
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Re: L-19 Leaf spring installation

Post by cfzxo »

Ryan Smith wrote:
DWood wrote:
Honestly, I don't know.
If you don't know then why say it?
Because he thinks we're all idiots.
Ryan, The saying goes something like this, If you learn from your mistakes, and I have made a few, that would put me in the geneius category. But with an open mind to make more. :lol:
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cessna170bdriver
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Re: L-19 Leaf spring installation

Post by cessna170bdriver »

Ryan Smith wrote:
DWood wrote:
Honestly, I don't know.
If you don't know then why say it?
Because he thinks we're all idiots.
VERY un-called for comment, Ryan. Not at all how we want the Association to be represented.
Miles

“I envy no man that knows more than myself, but pity them that know less.”
— Thomas Browne
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Ryan Smith
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Re: L-19 Leaf spring installation

Post by Ryan Smith »

cessna170bdriver wrote: VERY un-called for comment, Ryan. Not at all how we want the Association to be represented.
You're right, Miles. To Joshua and the Association - please accept my sincere apologies for my poor attitude and comments. It's not consistent with the respect I've been given by Association members and is not representative of what the Association embodies. I'm ashamed that I've been immature, disrespectful and petulant to others on this forum over the past week. I'm truly sorry.
flyingredyeti
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Re: L-19 Leaf spring installation

Post by flyingredyeti »

I would like to learn more about the "heavy duty" L19 leaf. I've not seen one yet.
Del, in cross referencing Univair's part numbers with TM55-1510-202-35P, the 170IPC, and the emails from Univair, the so called "heavy duty" L-19 leaf set(listed as L19TWS), is simply Univair's nomenclature for the L-19 spring set, which is nearly identical to the Cessna 170(A/B) leaf Sets, except for the main leaf. The top three springs are reportedly identical(disregarding the early models' fifth spring), but the main leaf for the L-19 is 1/16" thicker (I know you read this earlier, I'm just summing up my thoughts).

The misleading information, which I referred to earlier in the thread, is that while Univair lists the L-19 as exclusively applicable to the L-19 (because of the larger main spring), they list the 0642101 CESSNA MAIN LEAF SPRING by itself as applicable to both the 170 & the L-19, even though it does not match the 170 P/N, and is in fact has no PMA/FAA approval for either the L-19 or the 170.

Regarding Bruce's post earlier in the thread about how many owners may unknowingly have the L-19 spring installed, I would guess this is a contributing factor.
First time aircraft owner: '26C A gleaming Cessna 170B with 180 horsepower: the perfect mechanical bird.
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ghostflyer
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Re: L-19 Leaf spring installation

Post by ghostflyer »

A reality check has to be done here , it sounds like every body has been running around in circles in the hot sun drinking tequila. It's nice to have a PMA supplier but what does Mr Cessna say about all this after all he did design both aircraft . We had a couple of Bird dogs in our fleet a number of years ago and they broke all sorts of things due to different missions . Consulting Mr Cessna to come up for a fix was often a reply was "you tells what you want and and if you have any ideas see if it works and then tell us . ". This was under a military situation . So when I,found my 170a with a bottom Spring broken [due to the sharp edge of a corresponding Spring ] I looked at all my options . Due to experience and some common sense I made a choice . Now fly with a tail wheel Spring that's going to last me for a long time . And believe me I have put it into places that when I go to take off ,I shake my head and wonder how and the hell did I get in here. But it's FUN.
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Bruce Fenstermacher
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Re: L-19 Leaf spring installation

Post by Bruce Fenstermacher »

That is very interesting info Joshua, and it enforces my earlier point. A fact seems to be that even those that are supplying PMA'd parts don't know or have the specs just right. And after having done so and being the only supplier of parts for the last 40 years, no one knows exactly what came from the factory. And BTW I'd bet my airplane Cessna doesn't know or could not find the info buried in the salt mines.

Most interesting to me is that Univair says there is no known spring tension for these springs. And so apparently Univair is making them to what ever tension they think is appropriate. Could be weaker, could be stiffer than original. And we are worried about using an actual L-19 spring which they are happy to sell you formed but not under PMA as it is only raw material. Heck, seems to me all the springs they are making are only raw material.

As I was at convention and had a ready fleet of 21 170s of all models I looked at each and every one to see what springs and spring configuration they seemed to have. Out of the 21 all of them had what I would call a L-19 main spring. Not one had a main spring the same thickness as the others as has been reported at this forum in previous threads. In fact there was very little consistency in the thickness of the other springs. Many aircraft had second springs as thick or nearly as thick as the main spring. One reason I've always tried to say L-19 type spring when talking about a thick main spring is I've seen very few thin main springs. As I've just looked at an actual L-19 spring I own I'm sure I've seen at least one on the field at convention but not all 21 though most of us would call all of them L-19 springs. Really it seems no one has a good grasp of what is really suppose to be there.

Univair per their response feels that 170 springs other than the main spring are the same as the L-19. They claim, or at least they make all their 170 spring parts 1.5" wide by .312". This would lead one to believe that all the springs should be the same width and thickness. Maybe that is where we came up with the notion that all the springs should be the same but they where not. I asked this question of George this week and he indicated it was an interesting idea.

So I actually own a L-19 spring set. All 4 springs where made at different times. Three of them are marked as being made by Cessna, the oldest being made in 1952 and the latest on dated 1966. All where accepted by the USAF and later sold as surplus. They are the real deal.

main spring 0642101 1.498" x .36"
Second 0642102 1.522" x .262"
Third 0642103 1.151" x .196"
Third 0642159 1.498" x .25"

Note my "kit" included two third springs and no forth. I've also relearned there where two L-19 tail bracket assemblies and the parts numbers changed for at least the springs in that assembly. This is why each of my third springs have different part numbers.

The point of showing the actual L-19 measurements is to show that Univair, the only supplier of these parts, under PMA sells parts that are likely not like the original. The thickness of the second and third springs I listed is typical of what you see on a 170. Many of these 170 springs seen are original as those never break. Univair makes these at .312" likely thicker than the original.

As for the original 170 main spring thickness. I'd be surprised if it is .312" as Univair sells it. Univair does not appear to me to have the other spring thickness right. They quoted the L-19 main at .375" when mine is .36" . Of course I will allow that I have the original first L-19 part number, maybe the later part was .375"

None of this actually answers what thickness the 170 main spring should be. It does cement in my mind that probably most of what I'd call a L-19 spring are not actually L-19 springs. I did not have a mic on the convention field but I'd say all but maybe one spring was thinner than my L-19 spring yet they were all thicker than the other springs in the pack.

Like so many things in a 65 year old airplane, the details are likely lost forever. It can be ominous in today's exact precious environment. One thing to keep in mind is this. There are mounds of evidence that airplane manufactures of the time used a bit more eye ball engineering. They bought parts from the cheapest source and often times just what was available. If their truck spring source ran out they bought a spring that was close and available or cheaper. After all the original spring was overkill, a thinner or slightly thicker part that fit wouldn't make a difference. Likely Cessna themselves sold springs of different thickness over the years.
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flyingredyeti
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Re: L-19 Leaf spring installation

Post by flyingredyeti »

That is certainly food for thought Bruce- a lot of it. I did notice the L-19 has two main spring options listed in the IPC; could that account for the difference in sizes (i.e. 0.36" vs. 0.375")? Now I am curious about the basis of approval under which Univair was able to get the 170 springs PMAd. They did not supply the requested PMA number, but even if they had, many PMAs listed by the FAA include no reference data, while others might refer to a drawing number that is not included in the listing. Ultimately, I would like to know their basis for claiming a direct replacement for the above-mentioned springs.
First time aircraft owner: '26C A gleaming Cessna 170B with 180 horsepower: the perfect mechanical bird.
hilltop170
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Re: L-19 Leaf spring installation

Post by hilltop170 »

flyingredyeti wrote:........ Ultimately, I would like to know their basis for claiming a direct replacement for the above-mentioned springs.
Their basis could be nothing more than their springs are the size that fits the airplane, who knows?, they are not saying. They have admitted there is no PMA on the L-19 bottom spring so if someone is that concerned about absolute legality, there is nothing to stop them from obtaining a Field Approval for the installation. Might open a giant can of worms though.
Richard Pulley
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1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
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c170b53
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Re: L-19 Leaf spring installation

Post by c170b53 »

Ghost flyer wrote
consulting Mr Cessna to come up for a fix was often a reply was "you tells what you want and and if you have any ideas see if it works and then tell us
Even the big boys use this technique, which just shows to go ya, different perspectives count.
Richard sounds like someone could spend a lot of time, getting to the bottom of the bottom of this. :D time of which might be better used to just go flying.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
flyingredyeti
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Re: L-19 Leaf spring installation

Post by flyingredyeti »

hilltop170 wrote:
flyingredyeti wrote:........ Ultimately, I would like to know their basis for claiming a direct replacement for the above-mentioned springs.
Their basis could be nothing more than their springs are the size that fits the airplane, who knows?, they are not saying. They have admitted there is no PMA on the L-19 bottom spring so if someone is that concerned about absolute legality, there is nothing to stop them from obtaining a Field Approval for the installation. Might open a giant can of worms though.
Can of worms = my thought as well, specifically regarding the L-19 springs. However, regarding the 170 springs- the representative does offer the alloy of the spring steel used: 5160h/9260. So, hypothetically, if one were to produce a leaf from the same alloy, dimensions, & heat treatment as the manufacturer, it could be safe to presume the same spring tension is achieved, couldn't it?
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Bruce Fenstermacher
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Re: L-19 Leaf spring installation

Post by Bruce Fenstermacher »

Joshua, you could be right. The later spring could be thicker and it could be .375". And the second version could have been made thicker in response to the main spring breaking. We, the 170 community know all about that. As there is some evidence even Univair doesn't know much about these parts I can only put their info of .375" in the plausible category. However there is a limit to how thick the total spring pack can be in the spring bracket.

Swaging a measure of the early bracket I have in hand reveals an opening of .945" This bracket has a space riveted to the bottom, The later bracket may not have this rendering an opening .0075" larger or .9525". Between the spring retainer and the bottom spring block there is an opening .962"±2.5". Using Univair's thicknesses of the spring pack they sell for the 170 having 4 - .312" springs for a total of 1.248" which will not fit properly in the bracket. No way either thicker L-19 spring will fit. This is also why folks who might buy Univairs spring pack can't get them to fit. Of course adding up the spring pack I have on hand for the L-19 comes to 1.068" and that won't fit either. Is there any wonder we find the top spring retainer cracked?

The second version of the tail wheel spring retainer 0642151 item 23 on page 2-66 of the IPC no longer has the tab at the end that the U bolt clamped down as the original 0642136 did. This is likely because, as some 170 owners know as our part is the same as the original, the tab cracks at it's attach point and breaks off. The military services and Cessna probably made note of this and realized it was not needed. The 170 community did not benefit from Cessna's continued support of the military L-19. I've seen a few of these later spring retainers in 170s but I've also seen 170s with the tab missing, the cracked edge dressed.

I've never had an owner who I pointed out discrepancies admit to knowing. They trust their A&P to install the correct part and as far as they are concerned it works well and is correct.
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Bruce Fenstermacher
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Re: L-19 Leaf spring installation

Post by Bruce Fenstermacher »

flyingredyeti wrote:Can of worms = my thought as well, specifically regarding the L-19 springs. However, regarding the 170 springs- the representative does offer the alloy of the spring steel used: 5160h/9260. So, hypothetically, if one were to produce a leaf from the same alloy, dimensions, & heat treatment as the manufacturer, it could be safe to presume the same spring tension is achieved, couldn't it?
Joshua, we know Univair uses 5160h/9260 cause they said so. Does not mean that is what Cessna used or specified.

I would guess that Univair probably showed that a spring made out of 5160h/9260 would reasonably withstand the forces placed upon it. And that is about it.

And to be honest, I wouldn't be surprised to find they didn't even do that. In the old days PMA's and STCs where easier to get. And many of them are still in force today even though today the owners could not show the required evidence to receive such documents if they applied now.
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Bruce Fenstermacher
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Re: L-19 Leaf spring installation

Post by Bruce Fenstermacher »

Just measured a broken main spring I had in the garage. I'd always identified this spring as an L-19 spring. It measures .312±1. Probably from Univair.

After holding this in my hand I can say there is no way a pack of 4 of these would fit in the bracket and I've never seen a 170, and I've seen a lot, with 4 springs this thick installed.
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GAHorn
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Re: L-19 Leaf spring installation

Post by GAHorn »

flyingredyeti wrote:..., nor is the substitution of the stock bolt for the L-19 eyebolt. Why? Because, per Part 43 appendix A, any alteration to landing gear is a major alteration. ...
You are incorrect. Substituting one piece of AN hardware (a standard part) with another, albeit slightly longer but still within ordinary fitment guidelines, is not an alteration of a landing gear. It's a replacement of standard hardware. Minor activity.
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flyingredyeti
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Re: L-19 Leaf spring installation

Post by flyingredyeti »

Thanks to all who posted relevant replies, especially to those of you with real data & experience to contribute. It's a lot of information to get into for such a seemingly little, albeit important detail. In the end, it seems that a combination of real-world experience in proper aircraft maintenance as well as some hard digging and a fair amount of seasoning would all be required to figure this one out. I don't think that anyone on here has presented a conclusive ending to this post, myself included, but you have to admit there was a lot of thinking going on for a bit there.

Cheers all! I'm now the proud owner of N2826C (bought and paid for as of November), and look forward to consulting & debating you all in the future while enjoying the privilege of keeping her airworthy and airborne.

-joshua
First time aircraft owner: '26C A gleaming Cessna 170B with 180 horsepower: the perfect mechanical bird.
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