Can ailerons control a broken cable on 1/3 flaps?

[macaman]

The stall progresses from the tip with a swept wing but with straight wing aircraft, the root is designed to stall first. Chances are I've missed something, it is late. Check out a classic Martha King video for an example:

http://youtu.be/sKzbeWwe0wM

In theory, the wing with the flap down would have the root stall before the root on the unaffected side. There is also the thought of slipping to reduce the airflow over the flapped wing but sirens are going off in my head talking about slow and uncoordinated flight in the same breath. I like the fast approach to a long runway if it cannot be fixed as in my mind, I've already given ownership of the plane to the insurance company at that point and do whatever gets me back on the ground safely.

Great thought provoking question.

[JimC]

Originally Posted by macaman

In theory, the wing with the flap down would have the root stall before the root on the unaffected side.

The wing with the flap UP would stall first, right? What am I missing here?

I honestly think the questions about higher speed, rudder for yaw, etc are academic. Based on Robert Rice's description of his incident, and other reports I've read, it seems you have two options with asymmetrical flaps in any Cessna:

1) get the unbroken flap up as quickly as possible and continue to a higher-speed, no flaps landing

2) crash.

The thought that you'd be able to maintain effective control for more than a few seconds, even with only 1/3 flap down, contradicts the evidence.

Let's say the ailerons could counteract the rolling moment of one flap at 1/3 (I think they can) - but now imagine the situation you're in. You've used all of your aileron authority and a lot of your rudder authority. You're struggling to keep it upright, let alone fly a straight line. You're an instant test pilot in an unfamiliar aircraft only a few seconds away from the ground. Your life expectancy is low, to say the least.

And the thought that they'll break at 1/3 deployment is also misleading - the pressure on the flaps (and therefore tension on the cable) is vastly increased at full deployment. They're just not going to break at 1/3 if you've had them at full any time in the last few flights.

I suggest two things if this problem makes you lose sleep:

1) Leave your hand on the flap switch for a bit any time you go to full flaps. The cables will break when stress is added. Real-world incidents in 336/337s (and other Cessnas*) show this problem is survivable if you get the flaps up IMMEDIATELY.

2) If you still can't sleep, REPLACE YOUR FLAP CABLES.


*
http://www.pprune.org/archive/index.php/t-260242.html
http://www.faa.gov/aircraft/safety/a...7_04_Alert.pdf
http://www.aero-news.net/index.cfm?d...9-48d422ca215a

[Ernie Martin]

Great info. Thanks all for contributing. I realize 1/3 flaps has lighter loads on the cables and the risk of a break is lessened, but it's good to know if the ailerons have enough authority to counteract. Key point is to keep your hand on the flap lever for a few seconds after lowering them -- not so much so your hand is closer, but more as a reminder of what you need to do instantly if a cable breaks. I also agree that if a cable is going to break, it's likely to do so when you first lower the flaps, not several minutes later when you are closer to the ground.

Ernie

[JimC]

Originally Posted by Ernie Martin

I also agree that if a cable is going to break, it's likely to do so when you first lower the flaps, not several minutes later when you are closer to the ground.

Ernie

Although lowering the flaps to full immediately upon reaching Vfe will generate a very high load, it *may* be higher during pattern turns (esp base->final, which is often steeper than dwnd->base) if your airspeed is higher than normal. Reading the accident and incident reports, breaks always seem to come at first deployment of full flaps (more likely) or base->final (less likely, but it happens.)

My first instructor in a 150 taught me to never deploy full flaps during the base-> final turn. If your inside flap cable breaks (it has less load than the outside flap, but who knows which cable is frayed?) you'll be inverted before you can react. Deploy before the turn, or after, but not during.

[bjherron]

Just curious, how many flap cable failures have been reported? Were any of them due to the flaps being extended above recommended range?

I read about Rob's flap cable failure in his 336, but didn't he also have a STOL kit installed? Wouldn't that add more stress to the cables and induce other variables?

I am curious how many reports there are of actual failures.

Brian

[JimC]

I've read of many failures (Maybe 10? - the problem affects most Cessna single models as well as the 336/337) but I have yet to read one where the airspeed at time of deployment is recorded or mentioned.

Here's an interesting link - it includes two descriptions of pilots successfully flying Cessna singles with asymmetric flap deployments. So it seems the answer to the OP's question is "Yes, it can be done." It also includes examples of flap failure on *retraction,* which I hadn't heard of earlier.

http://cessna170.com/forums/viewtopic.php?f=2&t=6608

[JimC]

This question interested me - I did a bit more investigating. I found plenty of anecdotal evidence that many pilots have survived a full asymmetrical flap deployment in many kinds of light aircraft. This makes sense - you have two ailerons counteracting one flap, and the center of pressure of each aileron is farther outboard by a factor of more than 2 (x3, if the flaps and ailerons are of equal span.) Every crash I read about came from a problem that occurred close to the ground. The only crash of a large airplane I found was AA 191 -the DC-10 at O'Hare that lost an engine. That flight was under control until it dropped below the slat-retracted stall speed.

A few people on the internet thought FAR 23 required that the airplane be controllable in an asymmetric condition - I could not find that explicitly, but I did find the FAR that says the wing must handle the load (and not snap in half.) FAR 23.701 implies that a possible asymmetric flap failure that results in an uncontrollable condition will pass certification if the failure is "extremely improbable."