cowl flaps won't stay closed in flight

[M Terry]

On my 69 F model the cowl flaps operate normally on the ground, but spontaneously open in flight. while in cruise the knob comes about half-way back out. If i push hard I can force it to remain closed, and see a 2-3 knot gain in speed. the cable is a straight push-pull, with no twist to lock mechanism. 

anyone know how to fix this?

[Shadrach]

Does the cable have a button? My 67 has a cable with a button in the middle of the knob.

[BobbyH]

42 minutes ago, Shadrach said:

Does the cable have a button? My 67 has a cable with a button in the middle of the knob.

Same with my 66' E, it should hold the cable in place whether open or closed.  

[N201MKTurbo]

If it has a button and the button doesn’t work, the ball probably fell out. You can put it back in.

Edited August 16, 2022 by N201MKTurbo

[Guest]

4 hours ago, N201MKTurbo said:

If it has a button and the button doesn’t work, the ball probably fell out. You can put it back in.

Only if it’s not in your vacuum cleaner.

[N201MKTurbo]

5 hours ago, M20Doc said:

Only if it’s not in your vacuum cleaner.

I had to buy a new one once, now I have 99 spares.

[Ragsf15e]

The reason for the jokes is that the “ball” is about .5mm diameter.  It’s tiny.  I found one once after my IA lost it.  He’d already ordered the 100 pack like @N201MKTurbo.  Probably smarter than looking for something  that small in an old cockpit.

[RobertGary1]

My F doesn’t have any type of a button. Just the resistance of the cable.  

[N201MKTurbo]

1 hour ago, Ragsf15e said:

The reason for the jokes is that the “ball” is about .5mm diameter.  It’s tiny.  I found one once after my IA lost it.  He’d already ordered the 100 pack like @N201MKTurbo.  Probably smarter than looking for something  that small in an old cockpit.

The balls are 1/8" so not that tiny. 

[Ragsf15e]

5 hours ago, N201MKTurbo said:

The balls are 1/8" so not that tiny. 

Maybe, but they seem much smaller when you’re digging through my faa approved shag carpets.

[Yetti]

10 hours ago, RobertGary1 said:

My F doesn’t have any type of a button. Just the resistance of the cable.  

Same, but I think it is more like some over link designed in the later models

[N201MKTurbo]

The OPs cowl flaps require the button to hold them open. The later Fs had the same arrangement as my early J it is some crazy double overcenter mechanism that has a stable position at both the open and closed position. It has no locking button but about twice the cable stroke. 

[M Terry]

Mine doesn't have a button, just the solid knob. Also not arranged for an "over center" position to hold them closed.

 

[M Terry]

I looks "original but does not have the button. In looking through the maint manual I dont see how the over center bit will work like the J model that N201MKTurbo describes

 

[brad]

See my new post re. cowl flaps cable.

[M Terry]

I see it, Yours is on the passenger side of the throttle quadrant, Mine is on the pilot side next to the ram air lever. I'm going to look again at how it is rigged, perhaps adjusting the length of the arms to the doors and the length to the cable adjustment point will allow it to over center, or at least give the sucking wind force less leverage when the doors are closed. I will probably have to work with my A&P to get a cable like yours

 

[LANCECASPER]

On 8/16/2022 at 11:14 PM, N201MKTurbo said:

I had to buy a new one once, now I have 99 spares.

It takes a lot of balls to make a purchase like that.

[M Terry]

Update.

Was working on getting the cable out to send to Mcfarlane when we came to understand how the linkage really works. The cable pushes and pulls on a lever inside the cockpit, which is directly connected to a shaft to a similar lever in the engine compartment, which is in turn connected to the rod that moves the cowl flap mechanism.  It is that second lever that is meant to go to an "over center" position and hold the cowl flaps closed. If one reaches in there you can move the lever to the over center position, but even pushed all the way to the stop, the inner lever cant make it go far enough. The two levers are held together by a split steel pin, secured with safety wire.

The flaw lies in the slop present between the two levers. The hole through the shaft was enlarged by years of use.

When we dug through the documentation from our last annual, it turns out they took it out, made note of the flaw and put it back in.

Now the trick will be finding some machinist to make me an owner provided part to replace it

[M Terry]

here are images showing the slop in the connection.

the first shows how far the cable and inner lever can push the outer lever and rod.

the second is how far it would go if firmly connected to the hole, if the hole was oriented correctly, to the over center poistion

[Joshua Blackh4t]

Nice fault finding. Looks like a clear case of drill/ream oversize and put a bolt in it.

You could even try just a bit of epoxy metal to build the hole back up. Worst case it just wears out again.

Seems like the wrong place for a split pin, I would have expected a cotter pin to hold it solid. 

[A64Pilot]

I’d just get me a new pin and drill it, or you could weld the old one and drill it

A split pin so long as it’s tight is the best, anything that has slop like a cotter pin will wear, it had to have play to begin with to wear.

I don’t think this justifies an OPP in my opinion, just a repair.

 

[Guest]

From the IPC, the pin, item 31 is a roll pin 094” diameter X .625” long.  I’d align as well as possible and drill it for an 1/8” roll pin.

[M Terry]

Yes it was a roll pin, rather than a "split pin"  I just didn't know the proper name for it.

I like the weld and re-drill idea

[GDGR]

6 hours ago, M Terry said:

Update.

Was working on getting the cable out to send to Mcfarlane when we came to understand how the linkage really works. The cable pushes and pulls on a lever inside the cockpit, which is directly connected to a shaft to a similar lever in the engine compartment, which is in turn connected to the rod that moves the cowl flap mechanism.  It is that second lever that is meant to go to an "over center" position and hold the cowl flaps closed. If one reaches in there you can move the lever to the over center position, but even pushed all the way to the stop, the inner lever cant make it go far enough. The two levers are held together by a split steel pin, secured with safety wire.

The flaw lies in the slop present between the two levers. The hole through the shaft was enlarged by years of use.

When we dug through the documentation from our last annual, it turns out they took it out, made note of the flaw and put it back in.

Now the trick will be finding some machinist to make me an owner provided part to replace it

I should’ve taken photos. My AME just fixed this issue on mine. Did some welding and fitting up. Don’t know the full details, but it stays closed now. 

[Ragsf15e]

Maybe the ones with the “tiny balls”weren’t so bad after all?!