Cessna Flap Track Slot Dimensions

timwinters

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My Google fu is failing me. I'm trying to find the dimension of a NEW Cessna flap track slot. I found the maximum go/no go limit. It's 0.6035 but I can't find any data on what the original slot size is. Anyone have this?

Each year at annual I try to do one extra upgrade or preventative mx item on my plane. This year I'm pulling the flaps, having them reskinned, and installing trailing edge stiffeners/wedges from McFarlane and then we're going to re-rig all flight controls in accordance with the CPA guidelines.

I'm also considering installing flap gap seals but I want to make sure we don't find any "gotchas" in the base project first before committing to the extra $$$ for flap gap seals, painting and installation labor, hence the reason for my above question. Without knowing the new dimension, I don't know to what percentage the tracks are worn and what percentage remains.

As an aside, I found a guy in Alabama, Stephan Schomp, who was highly spoken of on some Cessna Type Forums. He reskins Cessna components. That's all he does. And he does it far more reasonably than other places I spoke with. We'll see...

And here's the crate I built for shipping (before I added the bump outs for the flap tracks). It's completely lined with 1" foam and another sheet of foam will slide 'twixt the two flaps. I don't think even FedEx Freight can destroy this. Okay, forget I said that... ;)

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And here's the crate I built for shipping (before I added the bump outs for the flap tracks). It's completely lined with 1" foam and another sheet of foam will slide 'twixt the two flaps. I don't think even FedEx Freight can destroy this. Okay, forget I said that... ;)[snip]

Oh man! That's throwing the gauntlet down for Murphy and FedEx!

John
 
...I found the maximum go/no go limit. It's 0.6035 but I can't find any data on what the original slot size is. Anyone have this?...

...Without knowing the new dimension, I don't know to what percentage the tracks are worn and what percentage remains...

You have the limits and you have your current measurement, I don't see why a percentage calculation would serve any real purpose. FWIW, barring some serious neglect, the flap tracks are not an item that would be expected to be replaced in normal use over the life of the airframe. There are Cessnas with tens of thousands of training hours on them, which would constitute abnormal over use of the flaps, that have never worn to the limits. If the rollers are kept properly lubricated and maintained there will be very little, if any, wear on the tracks.
 
And here's the crate I built for shipping (before I added the bump outs for the flap tracks). It's completely lined with 1" foam and another sheet of foam will slide 'twixt the two flaps. I don't think even FedEx Freight can destroy this. Okay, forget I said that... ;)



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Any idiot can stick a forklift tine through it. ;)

(And I saw UPS, not FedEx actually attempt to deliver hundreds of thousands worth of router fear that someone had obviously put a tine through. But I'm sure FedEx has forklifts too.)

;)
 
You have the limits and you have your current measurement, I don't see why a percentage calculation would serve any real purpose.

Well, it may be flawed, but my reasoning was that if the tracks are 50% worn, then there's no reason to consider replacement but, if they're > 85% to 90% worn, then maybe now's the time to replace them since things are already partially disassembled.

But, as it turns out, they're not even 25% worn. I measured the slots yesterday with a micrometer after removing the flaps and they're right at what McFarlane's data shows for new tracks.
 
And to document for anyone searching for this information in the future.

New flap track slot dimension, per McFarlane:

0.565 to 0.574

Go, no go wear limit:

0.6035
 
As a side note, on Monday an A&P showed me a flap linkage from a 182 that had broken during operation. I didn't measure anything but it looked like about 3/16" diameter cold roll snapped off about an 1/8" from the end fitting. No corrosion was apparent but I did not examine it under a lense.

Since the link bent prior to breaking, something jammed the flap pretty tight. How could that happen if the track slots were not warn? Trash in the slots? maybe but I'm thinking the track slots were worn and that led to misalignment and jamming. The A&P said the aircraft appeared poorly maintained.

Long story made short, maintain the equipment. Good job inspecting, Tim.
 
Curious. What leads you to re-skin the flaps? Corrosion? Are they bent? I can't imagine flaps re-skinned being a maintenance priority. Thus the question.

Don't your flaps have the trailing edge bulb? To keep you from getting that cookie cutter pattern in your forehead when you walk into them? How and MacFarlane's trailing edges different?
 
Curious. What leads you to re-skin the flaps? Corrosion? Are they bent? I can't imagine flaps re-skinned being a maintenance priority. Thus the question.

Numerous trailing edge cracks. The left one has a patch covering bout 7 ribs due to excessive cracks at the trailing edge. I think six cracks are allowed before they're considered in airworthy. Mine had far more. Too many years based on grass (and playing in other grass) taking off with 20 degrees.

Don't your flaps have the trailing edge bulb?

Nope, that's the problem

How are McFarlane's trailing edges different?

http://www.mcfarlane-aviation.com/Details.aspx?Article=398
 
I think one of the problems you get when they wear (and the rollers also) is that play that's normally there allows the flap to bang up and down when the aircraft is operating on rough surfaces, putting more force on everything than any of it was designed for.

Good job staying on top of it. It's a pretty significant problem in the aging Cessna fleet. Usually they crack and break at the rear attachment points.
 
...It's a pretty significant problem in the aging Cessna fleet. Usually they crack and break at the rear attachment points.

That's not a track wear problem, that's a problem caused by deploying the flaps at a speed greater than they are rated for. If they are properly maintained there should be little to no wear on the tracks or rollers.
 
That's not a track wear problem, that's a problem caused by deploying the flaps at a speed greater than they are rated for. If they are properly maintained there should be little to no wear on the tracks or rollers.

Maybe, but McFarlane sure sells the sh*t out of the flap tracks and roller kits that they mfgr.

:dunno:

As an aside, I lube everything on my plane after each wash. Typically that means at annual and at least two more times.
 
Goes back to "properly maintained" There are many that see neglect as well as improper operation (overspeed deployments) If they are taken care of the tracks should easily last the life of the airframe and never need to be replaced.
 
What I love is the people who argue that they don't deploy the flaps and check them during preflight because they believe that doing so effectively doubles the wear and tear on the system. Yeah right, like running your flaps down while the plane is sitting still in the hanger imposes the same stresses on the system as deploying them at 100 knots.

:rolleyes:
 
I fix flap stuff all the time on Cessnas. Cessna allows six trailing edge cracks per flap. We replace the skins rather than patch them. The big factor in cracks is the buffeting they take, and they'll crack even with the trailing edge bulb. There's an outfit selling STC'd thicker flap skins I've used and they fix the problem. http://www.airmetalfab.com/sites/product/skins.html

There's a Cessna SB on the flap rollers. That roller is a Torrington needle bearing with a thin steel sleeve pressed over it, and the sleeve can slip sideways and it starts cutting a circular groove into the flap support arms; after it gets so far thought the metal, that little disc punches out under air loads and the flap cocks and jams and bends the 1/4" push-pull rod and usually also ratches up the flap tracks and mounts and can ruin the rear wing spar. Cessna will sell you special washers for the front rollers, but only McFarlane has the stuff for the inboard rear roller: a narrower roller and special recessed washers. The outboard aft roller already has the alignment shims to protect the flap support.

Straightening a bent push-pull rod can crack it and cause failure later. Overtightening the jam nut against the rod end can crack it in the threads. Improper flap rigging or flap motor microswitch adjustments will overstress it and all the surrounding structure.

The flap track slot, when new, isn't much wider than the roller diameter. Paint in the slot will make it tight.

Dan
 
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Goes back to "properly maintained" There are many that see neglect as well as improper operation (overspeed deployments) If they are taken care of the tracks should easily last the life of the airframe and never need to be replaced.


What's the lifetime? 30 years? 40? 50? 100? ;)
 
Ha, ha I guess it is what it is. I don't imagine when they rolled a 170 out the door in 1946 that they ever thought it would still be flying 70 years later.
 
What's the lifetime? 30 years? 40? 50? 100? ;)

Years depends on the environment. Wet or salty, not long. Elsewhere, it's hours and flap cycles. Training airplanes might need new tracks at 12,000 hours, maybe a lot sooner if they don't maintain the rollers and they jam and slide instead of rolling. Even if they're rolling the aluminum track material slowly extrudes sideways. You can sometimes feel a burr along the edge of the slots.

Don't lube the rollers in place. Take them apart, clean them and use some Aeroshell 22 grease in them. The outsides should be dry. Some guys goop them up in place and it just attracts dust and dirt that abrades the tracks and flap arms at the rollers.


Dan
 
Wow...

Got the flaps back today. Nice, nice quality work.

Sent them to Schomp Aviation, Stephan Schomp, to have them reskinned. Total cost was less than $1500. Aircraft Components by Williams (who everyone says sets the industry standard) wanted $1750 each.

My mechanic said he's seen plenty of Williams' work and this work was just as good or better.

Full report later after everything is back together.
 
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