What would you do?

[coppercity]

Here is a scenario for discussion.

 

So lets say you have begun a descent from cruise altitude at reduced power, after a couple thousand foot descent the engine all of a sudden starts running extremely rough. And by rough I mean lots of vibration and reduced rpm. Pulling the power back makes it get worse, you increase power and things get better, and at full throttle the engine runs smooth again.

 

What do you think has happened, and what would you do to get down for landing?

[Roger Fane]

Sounds like carb icing to me. I'd apply carb heat with the throttles wide open for a bit to fully clear them. Then I'd fly back to the airport, throttle back and make a circling descent to test if it occurs again. If it doesn't, it was likely carb icing. If it does, check it out further after safely on the ground.

[Tony & Rose]

Eric:

Double check the air-box. The carb balance line running through the box. Or the balance lines at the carbs....

Tony

[Tip]

I'm with Tony. I have had a chronic problem with the balance tube coming off on my LS's left carb. The vibration was really bad from 4500 down to 3500 RPMs. I fixed it by replacing the nylon tie with a spring clamp from the auto store. The LS's balance tube has a sharp bend at the carb and the nipple is very short. When it happened to me, I increased power and got back to my airport. Then landed power off.

[Tom Baker]

Like others have said check the balance tubes not only for becoming disconected, but to make sure they have not slid in the airbox exposing one of the slits to cowling air. If you don't find a problem with that remove the intake hoses from the rear of the carbs. Reach in and check to make sure the slides are moving freely. If one feels sticky then this could be your problem. If the ignition check is OK it is most likely carb related. Tom

[Roger Lee]

Wrong answers because you are already in flight. You need to check for a fix right this minute. What to do while in flight? He kind of gave you the answer if you re-read it and know how carbs are set up. When it gets smooth at full throttle that should have said it all.

[Tom Baker]

Roger, you must already know what his problem was to say that we are wrong with our answers, but we are just wrong with his problem. I had an airplane that did just like he said, and the fix was as mentiond above. Sticking slides in the carb was my problem. Other things could be a broken or slippped throttle cable. With out being in the airplane to actually see what is happening it's hard to give an answer. Knowing what the problem was makes it easier to say our answers were wrong.

[Roger Lee]

He brought this problem up in the pattern, but it could happen anytime during a flight and has to some people.

 

Ok think of it this way.

First he said the engine started running extremely rough and your in flight so you aren't on the ground yet to fix it. Second he said when you pulled power back it got worse, but when you advanced the throttle to wide open it stopped shaking and became smooth.

Now think about how the carbs are set up. Is there anything on a carb that would influence the throttle position? He said when he went WOT it became smooth. What would happen to an engine if they were severely out of balance? What would cause such an acute event?

It would shake like a son of a gun and you would think the world was coming apart. What would happen if one carb was WOT and the other pulled back at idle?

 

Now answer his question. What happened and how would you handle it?

After a couple more answers if someone doesn't get it either Eric or I will give the answer. Even if you don't know the answer there is a right way to handle this problem in air.

 

This is an exercise to make you think about how to handle this emergency in flight and possibly help yourself if you ever get in this situation.

 

 

p.s.

This wouldn't be a balance tube that would act this particular way.

[Tom Baker]

Like I said earlier a slipped or broken throttle cable could do this since the throttles are spring loaded to WOT. A stuck slide would act the same way. If the engine runs extremely rough all the way dowm to idle then you would have to decide between landing with a rough running engine or landing dead stick.

[Roger Lee]

Like I said earlier a slipped or broken throttle cable could do this since the throttles are spring loaded to WOT.

 

 

Hi Tom,

 

You got it. The cable has either slipped through the cable lock or broken completely. The one carb would still be controlled by the throttle handle and the other being spring loaded would pop wide open. So the more you pulled back the throttle the out of panic the worse the shaking would get. When you go wide open then both carbs are back in balance and the plane is perfectly flyable any where you want or need to go. The only issue could be is if you have your wide open setting is 5600-5800 WOT then you have a 5 minute window. This was an issue just recently and it is why this subject was brought up as strictly an educational tool.

[airhound]

Thank you all for your experience and technically expertise. I am gratefull, but only feel partially informed. Please go a little further and splain why these cables slip, or break, and what the average Joe can reasonably do to reduce known causal factors contributing to the problem. Again much thanks all for contributing, us Joes want to know... Does it also happen with SWs?

[Roger Lee]

Hi All,

 

This was special issue and has not happened else where and we wanted people to share the knowledge if something did happen.

[coppercity]

Broken or slipped throttle cable was what I was looking for. This was not something that happened in flight, but after looking at how the system works I wanted to present a "what if" to the forum. So what if your throttle cable breaks or the cable nut holding it to the throttle arm loosens up and slips. As mentioned the throttles are spring loaded to wide open throttle, that's why in this scenario going back to full throttle with the connected carb makes the engine run smooth again. So what can we do, first of all keep flying even it means being at wide open throttle, you can start a climb to keep the engine within rpm limits if required. Find a nearby airport with services and head for it. Now for the uncomfortable part, in order to keep the engine from beating itself to death if you throttle back to idle, it might be best to just turn it off once over the airport and glide in, remember you could most likely start it back up and climb up again if needed, just like they did way back with ignition interrupters!

[airhound]

I'm the below average Joe, there's always one in the crowd, thanks for belaboring.

 

These what if drills are very much appreciated.

 

Thank You!

[airhound]

How about brake and flap systems any what if drills along those lines?

[coppercity]

That's a great idea, I will try and post a new one occasionally, it's always good to keep ourselves thinking!

[207WF]

OK, so we think we might have diagnosed the problem, and are flying in the pattern at WOT where the engine is smooth. We can't land at WOT, unless you are happy going so far on the back side of the power curve that the nose seems straight up. So, what do we do? I think I would experiment with key on, key off at WOT a few times, then dead stick in with key off, knowing I could turn it back on and get WOT again if I needed it during the approach. WF

[FastEddieB]

I had a BMW motorcycle that used nearly identical Bing carbs.

 

Once it suddenly started running horribly at partial throttle - it idled OK and ran fine at high power settings. But inbetween it ran like it was on one cylinder (out of two).

 

In my case one of the screws that secured the rubber diaphragms to the slide had backed all the way out. At idle the idle circuit handled things. At full throttle there was apparently enough vacuum to overcome the leak.

 

Just another thing to consider.

[Ed Cesnalis]

the later you jump into this thread the smarter you sound, no applause please!

 

i hear 2 questions

 

1) what is the diagnosis (broken throttle cable)

2) what to do about it (dead stick landing)

 

seems to me #2 is the important question and i think the answer is a shift in mentality on how you rotate [deadstick vs with power].

 

there is a mentality that says your stick should be like a ratchet when flaring, it only moves back, if you move it to far it stays there while you add power.

 

when deadstick i change my mentality to where on flaring i will allow the nose to drop by relaxing back pressure to keep from ballooning.

[FastEddieB]

 

there is a mentality that says your stick should be like a ratchet when flaring...

 

On a calm day in a perfect world, well, maybe. And I've used the ratchet analogy before. But...

 

In the real world with gusts and human imperfection, sometimes the stick does need to go forward a bit. Watch a good pilot finesse the plane onto the ground on a gusty day and you'll see the stick "worked" quite a bit, both forward and back. But, ideally, the stick should be all the way back at touchdown for the lowest (and safest) landing speed possible (all things considered).

 

...if you move it too far it stays there while you add power.

 

Bear in mind I have zero time in a CT*, but...

 

...in general, in about every GA aircraft I've flown, no power is necessary on the landing.

 

In fact, I've come to see power as a "crutch", but one that complicates an already difficult maneuver (landing).

 

IOW, if you can have power at idle at about 100', its one less thing to worry about.

 

I find that pilots who are still "jockeying" the power into the flare have more difficulty landing than ones who glide in power off for the last bit of the approach.

 

 

 

 

 

*I'd still love to change that. If any CT owner in the SE needs a nice destination, try 1A3 (Copperhill, TN) and maybe we can swap rides!

[Runtoeat]

CT and Ed, I'm glad that you bring up the subject of pitch during landings. I've been curious how many CT pilots pull the power and use this method. My landing technique is to use pitch to maintain speed, providing that I've planned correctly and have some altitude to play with. If I haven't planned correctly with altitude, I use some power on short final but pull power during the round out. Observing the CFI's jockey the stick forward and back during the final stage to keep the plane flying until the moment of touchdown during those first landings I had in a CT was impressive and it gave me a "real time" lesson in how pitch controlled speed. Guess this technique stuck with me.

[Ed Cesnalis]

On a calm day in a perfect world, well, maybe. And I've used the ratchet analogy before. But...

 

 

we are not talking about flying in a perfect world we are talking about flying with a broken or slipped throttle cable. in this case it isn't a choice between using power and not it is forced upon you.

 

when forced to do a deadstick, especially if you normally use some power ( i don't ) it is a good idea to be prepared mentally.

 

i found wayn'es idea of key off and key on interesting but i think once i have the runway made i would let it die. on and off sounds lake a very unstable approach.

[airhound]

Anyone--I'm guessing the additional drag with the prop stopped has a significant impact on glide performance. Any war stories...?

[Tom Baker]

Anyone--I'm guessing the additional drag with the prop stopped has a significant impact on glide performance. Any war stories...?

 

Depending on idle RPM having the prop stopped might be less drag. The rotating prop disk at idle creates a whole bunch of drag. That is why they stop and feather the prop on a multi engine airplane. Coming up with a zero thrust RPM might be a little tough to do because of people having thier props pitched differently. Tom

[Roger Lee]

Hi Ranger,

 

Tom is right. A stopped prop on our (not all) plane is less drag than if it was free wheeling out there. I have flown some 503's-582's 2 stroke ultralights with the free wheel prop and clutch set up. If you shut down the engine with one of those the free wheeling prop fees like a parachute is attached. I have shut down my CT's engine in flight. First if you are going too fast the prop won't quit turning. When you slow down enough you can get it to stop and there is no difference in flight or feel. I can tell you also that I had a string taped on the front of the cowl at the edge of the window to see if my Dynon ball was reading right. Which it is not. People here said the string was being influenced by the prop wash and I said it wasn't. I turned the engine off to see if it made any difference and the string remained the same whether I was under cruise power or at a full dead stick no engine. The CT flys just fine at dead stick and handles well. There are no surprises. Keep your nose down to maintain speed and do what ever you need.