Flap problems Why?

[FlyingMonkey]

I have not noticed Tom's "wheel barrow" effect per se, but my habit is to keep the stick full aft on roll out to get some aerobraking from the stabilator, that might mitigate somewhat.

[FastEddieB]

I think this is incorrect.  Full stall = insufficient lift to support the full weight of the aircraft, not NO lift. 

 

Interesting topic.

 

If a plane stalls at 39k, how much lift is there at 38k? 35k? 30k?

 

From the diagram, you are correct, and I overstated the case.

 

 

Still, lift falls off rapidly beyond the critical angle of attack. Hence the advantage to keeping the nose up - otherwise one can land at stall, but if the nose is allowed to drop, one may have reduced the angle of attack such that there is suddenly new lift. But my experience is that if I land with the stick all the way back, or nearly so, and hold it there, the plane is done flying - whether nosewheel or tailwheel.

 

Barring gusts, of course - which can lighten the wheels or even lift the plane back in the air. Which is why one refrains from full stall landings on gusty days.

[FlyingMonkey]

Interesting topic.

 

If a plane stalls at 39k, how much lift is there at 38k? 35k? 30k?

 

From the diagram, you are correct, and I overstated the case.

 

 

Still, lift falls off rapidly beyond the critical angle of attack. My experience is that if I land with the stick all the way back, or nearly so, the plane is done flying - whether nosewheel or tailwheel.

 

Barring gusts, of course - which can lighten the wheels or even lift the plane back in the air. Which is why one refrains from full stall landings on gusty days.

 

Yes, but "insufficient lift to fly" and "insufficient lift to get a pilot into trouble" are not the same.      Any lift can impart a force on the airplane, and especially with light airplanes in windy conditions, those forces can be hard to counter, even at below stall speed.

 

I think what we're seeing with the CT is that, because of whatever reasons, there is still plenty of lift to cause handling problems well after there is not enough to fly.  Using the flaps to minimize those effects seems to be a common technique, even if some don't think it's wise.

[FastEddieB]

Please note I slightly modified my post while you were typing.

[Ed Cesnalis]

Key is, full stall=no lift, and hence all the weight should be on the gear anyway. I guess if you fly it on well above stall speed, and there's a time and a place for that, I suppose getting rid of the flaps after landing may serve some purpose.

 

I'm a full stall landing guy and I retract for 1 reason, gusts.

 

Our airport was closed one summer to install a new runway and my CT spent a whole day flying on the ramp while tied down. Local winds and dust devils scoff at our CTs on the ground.  In the Eastern High Sierra dust devils aim first for paragliders, then hang gliders and if their favorite foods can't be found they will seek out light sport.

 

Rouge dust devils head for the runway when light planes are landing and their more sinister cousins, blue sky rotors wake up by 11:00AM this time of year. 

 

Is there really a time and place for flying it on?  I maintain that flying it on only postpones the vulnerable speed and ultimately the risk is increased by flying it on.

[Tom Baker]

Eddie, also of importance is that stall speeds are measured in the air, and not on the surface while landing. You need to remember that ground effect will change how the airplane behaves.

[FastEddieB]

Eddie, also of importance is that stall speeds are measured in the air, and not on the surface while landing. You need to remember that ground effect will change how the airplane behaves.

Of course.

 

But if you stall it down, that stall is obviously occuring in ground effect, so at that point I don't see any need to correct for that fact.

[gbigs]

CT gives a good description of landing the CT (and I know he has an SW which appears to be different in handling than the CT).  Most who have flown heavier aircraft like the Cessna 172 or even larger and then get into a CT find themselves starting all over again when it comes to stick and rudder technique and landing.

 

There are even tougher planes to land given their glider like characteristic, the Samba.  But the CT can do no flap landings on short runways and likewise takeoff in high density altitudes, say around 6500 feet in 1000 feet of runway easily.  And still climb at 400 to 600 fpm.

 

Lately I have been landing faster, say 70kts over the numbers (15 flaps), then leveling out and letting the airspeed bleed just above the runway, then around 60kts begin a slow flare pull on the stick.  The CT will quickly touchdown in that mode and rollout at a pretty rapid taxi rate.  Keeping the stick back is critical as the nose wheel, if allowed to take the full weight of the plane will wheelbarrow in a heartbeat, or start to catch the grooves in the runway and sidetrack.

 

Once taxiing down around 20kts. the plane will roll nicely, even with 15 degree flaps on.  But if there is anything like 10kts or more cross or headwind on the runway, those flaps will cause the plane to squirrel and lift up.  So in wind, the no flaps landing is not just easier in the air, but also on the ground.

[Anticept]

Eddie:

 

I have two instructors that also fly a Cirrus at a flight school. These guys say the techniques are the same for the CTs as are the Cirrus. Basically, both planes exhibit the same symptom, where if you overestimate the point where the plane "stops flying", they will rapidly drop out from under you, but will just keep on floating otherwise. Things like cessnas and pipers don't have that "cliff" as I call it.

 

We've all adapted the handling technique that they use with landing a Cirrus. We don't land to the point of "can't fly anymore". We'll bleed off the energy until a couple knots before it gives up, characterized by the increasing and increasing AoA, and just let it settle at that point. We could hold it off a little longer, but we've found it's so much GENTLER on the CTs to not let them drop out. It still encourages a student to be aware of when it's about to give up too.

[Tom Baker]

Of course.

 

But if you stall it down, that stall is obviously occuring in ground effect, so at that point I don't see any need to correct for that fact.

 

My point was that because ground effect excess lift at the slower speeds will have a greater impact. How much does aircraft design play into ground effect handling of an airplane? I know high wing verses low wing has an impact. Does the airfoil choice have an effect?

[Doug G.]

I learned in a Skycatcher and it seems to me the sense of ground effect was much more noticeable in it than it is in my LS. Anyone else find this true?

[johnr]

353

Not been back to this page since I posted the original question. ( buiiding a new home & its at a critical stage). The reversed motor problem first occurred before I replaced the relays, I checked for loose connections but could not find any cause that would make the orientation & operation of the flaps reverse.  Since replacing the relays & have only had on instance when the operation reversed. Immediatly prior when I was waiting on the taxiway  I shut the engine down without switching off all the power first. (naughty, naughty)

From a large number of replies there have only been 3 that suggested testing or a possible cause. Although the fuse/relays are designed to protect a circuit, I believe overcurrent operation can cause early failure of components without tripping a relay.

 

I posted my experiences to alert other owners so they might just look at the flap operation during there pre flight checks & not go beyond 15 degrees with the motor reversed which is what I believe caused an overload. Relays are usually chosen based on reliability tests of 1/2 million or so operations. There have been a number of relay & board  failures that would seem to reflect a much higher rate of failure than should be acceptable. Flaps do not have a high useage rate. To date I have not read any post that I believe caused my problem.

 

With reference to my closing remarks , there is no point in appologiseing, it was intended only in jest. Our media in Australia made much of the changes your Judges made & it was very topical in Australia . I have no idea how the democratic process operates in the US. I was however interested in Mac's reply where there was a public vote with a very decisive outcome in Ireland.

Finally as a boy 60+ years ago I played Robin hood & merry men games with my young friends, we were (at that time) happy to be merry & gay. I have no problem with any ones orientation & have amongst my friends, both. I just wish new words could be found instead of stuffing up (sorry) redefining  the meaning of existing ones.

John R

[Anticept]

The relays are controlled by a computer, johnr. If they ran in the wrong direction, it is because the computer thought you needed to go in that direction to set the flaps in the correct place.

 

There is a potentiometer connected to the flap system on a swing arm on the jack screw in the cargo bay area that acts as a position sensor. If the pot goes bad and reports the wrong resistance, it WILL cause the flaps to move in unintended and unexpected ways. This is actually quite common for that part to go bad. It acts as a voltage divider, and has relatively little movement on the swing arm (less than 1/4 movement), which translates into pretty small voltage changes and can mess up somewhat easy. It is the first thing I recommend to people to check and replace if the flaps move unpredictably.

 

I suggest you focus on that. It's not possible to run a brush motor backwards without reversing the polarity, and the relays will not move on their own as they default to an off state, and require the computer to provide the control signal, which again, relies on correct reporting of pot positioning.

 

In my opinion, since the pot is a common failure item and is in a relatively harsh environment (temperature), FD engineers really should use hall effect position sensing instead of a voltage divider.

[johnr]

31

Thanks for the reply Anticept, I will certainly concentrate on the potentiomete, however it is difficult for me to understand how the potentiomete would cause a wrong signal that would correct its self on shut down & restart. Have you had experience of a situation where the reverse will correct its self after shut down & restart. Electronics do not like power interruptions, have you had any problems after shutting down the engine with out turning powere off?. Most pilots would not admit it, Its only happened to me on 1 occsion that I can recall.

 

I am fortunate in having a friend who designs circuits & programs them. Is there any where I can get some technical information to get him going in the right direction, such as circuit diagrams & specs. If the expected outputs were known & wireing could be identified it would make for a much easier & accurate diagnosis.

 

Substituition is a great way to test but not at the prices of Flight Design components. To further increase the dificulty it has only occured twice  in the last 18 months

John R

[Roger Lee]

You can reset circuits at times with a full disconnection of power. Remove both the negative and positive wires off the battery. Not just one.

Some cars now days that have computers that present glitches can be reset with a full power disconnect and then allowing it to power back up, just like a computer.

Possibly a low power situation. The power can be increased on the relay board.

 

I don't know for sure if this will work, but It's worth a try and will only take a few minutes.

[FastEddieB]

Remove both the negative and positive wires off the battery. Not just one.

 

Color me puzzled.

 

Please explain. Sure seems like a battery with one terminal removed is 100% out of the circuit and removing the second terminal would do nothing, since no voltage/current can flow.

 

I'm open to being educated, but this goes against whatever electrical knowledge I do have!

[Doug G.]

Yes, an open circuit is an open circuit no matter how many disconnects there are. Although, it doesn't hurt to disconnect both sides of the battery and may make accidental powering of the circuitry by mistake a little less likely. (I tape over the battery terminals to avoid things like a dropped tool or an accidental touch by a disconnected wire.)

[Doug G.]

Yes, an open circuit is an open circuit no matter how many disconnects there are. Although, it doesn't hurt to disconnect both sides of the battery and may make accidental powering of the circuitry by mistake a little less likely. (I tape over the battery terminals to avoid things like a dropped tool or an accidental touch by a disconnected wire.)

[Roger Lee]

Hi Eddie,

 

New to me too. I just spent a few days with Sandpiper (John Horn CT owner from Oregon). He had a car that had some odd issues. I can't recall the exact issues. He may read this and chime in. He was told by a dealer to remove both cables to reset the entire computer system. He to tried just one cable which did no good. It has to be both cables. As soon as he did this the car system was back online and normalised. 

 

Computer systems aren't like our lightbulbs where disconnecting one leg makes the light go out. Our systems are becoming more intricate and complex.

 

I don't know if the rest on the CT will help, but it for sure wouldn't hurt to try.

 

My guess is because his issue was intermittent it is a loose wire connection and vibration is affecting it. 

[Roger Lee]

Hi Doug,

 

"Yes, an open circuit is an open circuit no matter how many disconnects there are."

 

Not in the new cars with some computer systems. Wait till John comes online to explain. I was enlightened by this as anyone.

Times are changing.

[FastEddieB]

Hi Doug,

 

"Yes, an open circuit is an open circuit no matter how many disconnects there are."

 

Not in the new cars with some computer systems. Wait till John comes online to explain. I was enlightened by this as anyone.

Times are changing.

I'm waiting to be convinced.

 

New car or not, ya canna change the laws of physics!

[Tom Baker]

I'm not sure about this, but a quick Google search does seam to indicate that this is required for some vehicles. Some require touching the cables together. Maybe it is possible for some potential electrical energy to be stored in the computer with the electrical flow requiring a path to ground, and by removing the pathway to ground it will clear the code.

[Anticept]

There is no such thing as a truely open circuit on earth. The air is just really high resistance.

 

There are electronic circuits these days that are so sensitive, that just waiving them around generates a voltage. That's why things like audio cables must be shielded or they sound like crap. Cheap digital meters can register extraneous fields just by walking room to room.

 

A lot of systems these days do need you to touch ends together to bleed off any residual charges. Some electronic circuits with volatile memory will integrate a high resistance resistor right on board to bleed off the charges when the power supply is dropped as a shortcut for resetting. Different volatile memory stores information in different ways, but many are charge based.

 

DRAM, which is very common, uses charges. "Dynamic random-access memory (DRAM) is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1." https://en.m.wikipedia.org/wiki/Dynamic_random_access_memory

[FastEddieB]

A lot of systems these days do need you to touch ends together to bleed off any residual charges.

That I can sort of see.

 

But that's quite different from just disconnecting both battery cables. And if touching the cables was necessary, you could still leave one cable attached, and just touch the other to it.

 

Right?

[Anticept]

In theory that would work. There's still some exotic circuit designs that this wouldn't work on, and to be honest, because of murphy, I would not let positive and negative terminals get anywhere near their opposites on a power source.