is it possible to stall the rudder?

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alexanderk
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is it possible to stall the rudder?

Post by alexanderk »

Was descending aggressively the other day needing to lose 3000 feet quickly. So setup a full forward slip (full rudder). Normally a slip is done at minimal airspeed - say 50-60 kias. But in this case I was going about 90 kias, and after a few seconds felt an unusual bump - very much same as if you are doing really steep turns at the edge of a stall and hit your own turbulence. This was not normal for a slip, so I did not wait for what would develop and recovered.

So I kept wondering - was it a fluke (like a hit of turbulence, but VERY unlikely). Or something to do with the higher speed aggressive slip? Perhaps somebody could shed some light.
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Steve
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Re: is it possible to stall the rudder?

Post by Steve »

I have done these on numerous occasions (I do full stalls, slips, steep turns, and a dive to within one or two knots of Vne as part of my PMCF after an annual inspection), never experienced what you describe. My aircraft does have the smaller rudder - not sure if that makes a difference.

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alexanderk
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Re: is it possible to stall the rudder?

Post by alexanderk »

I did not know the DA20s had different rudders. Mine is 2005, which model/years is yours?

Well, this is what caught my attention - I did not expect such thing to happen, but that got me thinking what I don't know about my airplane flying envelope. I'm sure that are other "interesting" things that I'd like to know about, stay away from or practice first :)

Would be great if the factory test pilot(s) added here. We have a few lurking around sometimes here.
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Re: is it possible to stall the rudder?

Post by Steve »

Sorry, I assumed you were flying a -40. Early DA40s had a slightly smaller rudder than the current version.

Steve
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ThomRiddle
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Re: is it possible to stall the rudder?

Post by ThomRiddle »

It is possible that in the cross-controlled attitude of a slip that the rudder could be blanked suddenly and temporarily during a bit of turbulence. If the rudder was blanked in smooth air then you could not get into a full rudder slip, so my guess is was a passing phenomenon.
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Re: is it possible to stall the rudder?

Post by Artiom »

I just checked DA40 AFM and didn't find anything that limits slips to any speed. The only limitation related to slips that I remember is on some Cessnas slips not allowed with full flaps. I usually slip DA40 at 75-90kts for two reasons:
- this is speed after turning final and I can clearly see I'm too high/too fast and need loose energy;
- at higher speed drag produced while slipping is higher causing faster energy lost;

Is there any slip related limitation in DA20 AFM?
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ThomRiddle
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Re: is it possible to stall the rudder?

Post by ThomRiddle »

I just checked the AFM for the DA20-A1 and there is no mention of slipping, whatsoever. The C model could be different. I assume this means any speed is okay as long as the Vfe limit is respected, with flaps extended. My typical approach is at idle power, a bit high deferring application of full flaps until stabilized on final and obviously high. At cruise if I want to get down fast, I follow the AFM recommendation which is idle power, set prop to 2400 rpm (max continuous), and nose down to attain Vno (top of green arc). I suppose if the air is smooth there would be nothing wrong with going up to near Vne.
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Re: is it possible to stall the rudder?

Post by BlackMammoth »

I have experienced serious rudder stalls, leading to loss of control and a crash... Luckily that has only happened to me while sailing under spinnaker ;)

I have never experienced anything approaching a stall with rudder in the DA40, and I personally doubt that it's possible without atmospheric intervention*.

*a 50 knot horizontal wind shear would probably do it.
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Re: is it possible to stall the rudder?

Post by alexanderk »

Yes, that was strange as I mentioned I did not experience this before. I use slips alot, but usually at lesser speed.

Artiom, it is actually better idea to slip at minimal speed. It is really hard to stall the DA20 (40 is similar) during slip, the nose up attitude needs to be ridiculously and simply unrealistically high which you would not do on final. I tried i t many times when up high. But the altitude loss when slipping at slow speed is A LOT more than slipping fast. I can do ~1500-2000fpm slip at 45kias. At 70 kias it will produce 500fpm at best.
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Re: is it possible to stall the rudder?

Post by alexanderk »

ThomRiddle wrote:I just checked the AFM for the DA20-A1 and there is no mention of slipping, whatsoever. The C model could be different. I assume this means any speed is okay as long as the Vfe limit is respected, with flaps extended. My typical approach is at idle power, a bit high deferring application of full flaps until stabilized on final and obviously high. At cruise if I want to get down fast, I follow the AFM recommendation which is idle power, set prop to 2400 rpm (max continuous), and nose down to attain Vno (top of green arc). I suppose if the air is smooth there would be nothing wrong with going up to near Vne.
Well, that's the way to do it but the C1 is a fixed prop airplane. So it dives real well, but goes fast quick as well. And it is pilot's repsonsibility to keep the tach under red. This is probably also no ideal for CHTs.

That's the reason I've been either doing a cruise decent with power, or a good slip if need to lose altitude quickly. I mean a spin is another great way to lose a couple of thousands, but not all my passengers like it :oops:
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