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  #1  
Old 04-05-2010, 02:28 PM
pierre smith's Avatar
pierre smith pierre smith is offline
 
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Location: Louisville, Ga
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Default High Key approach in a -10..

...I've been chomping at the bit to do this since Doug Rozendahl mentioned it on here.

I arrived from a XC this afternoon and guessed that 1000' AGL in my -10 might be close. Over the end of the runway at 100 MPH and 1000' AGL, I closed the throttle and started turning onto left downwind...man this thing sinks with the prop forward but a continuous turn and a landing with full flaps touched down just short of the 1000' marker with 4000' remaining.

I don't suppose that bringing the prop control all the way back to coarse pitch will overload the engine at idle...I'd like to try this to see how much the glide improves.

This is a maneuver I'd highly recommend all of us getting used to in the event of an engine-out situation....just more familiarity with our airplanes.

Stay tuned..

Best,
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  #2  
Old 04-05-2010, 05:04 PM
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AlexPeterson AlexPeterson is offline
 
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Pierre, I do this frequently. I try to be upwind directly over the touchdown point at about 2000' agl. I pull the throttle to idle and pull the mixture all the way back (I do keep my hand on it the whole time until short final, so that I don't forget it is out in case I need power!). I trim for about 90 knots IAS, and immediately start a 360 degree continuous turn to final. I keep the prop forward for no special reason. When I'm going through the 180 degree portion of the glide, I check position and altitude, verifying that I'm higher than half the altitude (1000 agl in this case). Also, on the 180 (downwind heading) degree point, I try to be about a half mile away from the TD point.

In my 6A, it would be a fairly tight 360 turn if started only from 1000' agl.

I've been exploring the final touchdown phase on our mile long runway. Specifically, I am keeping the flaps up all the way to TD to learn the trade-offs of a slightly (only a couple knots) higher TD speed vs much better control over just where the TD spot is. I'm sure some will think this is heresy, but if one puts in full flaps on short final, it greatly limit the range of actual TD points. With no flaps, one can float a fair ways or not in ground effect to move the TD point.

I've not concluded anything yet, as I need to make a few dozen more without flaps to get a better feel. The ability to arrest the final descent without flaps is significantly improved. With full flaps, one needs to nail the flare as well.
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  #3  
Old 04-05-2010, 07:18 PM
Rick S. Rick S. is offline
 
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I was under the impression that in order for the prop to move from flat to coarse the engine had to be turning at least 1700 rpm to generate enough oil pressure to move the blades. I really don't know, just what I had picked up during hangar flying tales and seemed to fit since we run up to 1700 to cycle to cycle the prop prior to takeoff.
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  #4  
Old 04-05-2010, 09:27 PM
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L.Adamson L.Adamson is offline
 
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Quote:
Originally Posted by Rick S. View Post
I was under the impression that in order for the prop to move from flat to coarse the engine had to be turning at least 1700 rpm to generate enough oil pressure to move the blades. I really don't know, just what I had picked up during hangar flying tales and seemed to fit since we run up to 1700 to cycle to cycle the prop prior to takeoff.
Somebody may correct me if I'm wrong,

But you should have a lot more than 1700 rpm if the mixture has just been pulled back and the prop is windmilling. Aircraft is still moving right along, and the governor attempts to maintain it's set rpm. It takes quite a bit to stop the prop.

L.Adamson --- RV6A
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  #5  
Old 04-05-2010, 11:19 PM
Finley Atherton Finley Atherton is offline
 
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Quote:
Originally Posted by pierre smith View Post
I don't suppose that bringing the prop control all the way back to coarse pitch will overload the engine at idle...I'd like to try this to see how much the glide improves.
I am no expert, but I can't see how it would overload the engine at idle power??
I did glide tests some time ago and found that the prop will go coarse to the extent that it has a significant effect on the sink rate even with the mixture at idle cutoff.

At 70 kts with the mixture at idle cut-off (dead engine) and prop control full in:
Sink rate on the VSI 1,200 fpm
Oil pressure 55 psi
RPM 1350

At 70 kts with the mixture at idle cut-off (dead engine) and the prop control fully out (coarse):
Sink rate on the VSI 800 fpm
Oil pressure 50 psi
RPM 900

I also found that the sink rate with the engine dead and the prop control set at full coarse is very similar to the sink rate with the prop stopped.

Fin
9A, 0-320, 9:1 CR, Hartzell CS prop, MT govenor.
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  #6  
Old 04-06-2010, 01:19 AM
Finley Atherton Finley Atherton is offline
 
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Quote:
Originally Posted by pierre smith View Post
I don't suppose that bringing the prop control all the way back to coarse pitch will overload the engine at idle.
I have been thinking about this some more since my earlier post (#5). Lets say your normal idle when on the ground is 600 rpm. I think you will find that in flight your full coarse idle rpm would be well above 600 rpm, so if anything there would be less load on the engine compared to normal idle on the ground?

Fin
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  #7  
Old 04-06-2010, 05:25 AM
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pierre smith pierre smith is offline
 
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Default Negative, Rick...

Quote:
Originally Posted by Rick S. View Post
I was under the impression that in order for the prop to move from flat to coarse the engine had to be turning at least 1700 rpm to generate enough oil pressure to move the blades. I really don't know, just what I had picked up during hangar flying tales and seemed to fit since we run up to 1700 to cycle to cycle the prop prior to takeoff.
...it'll go to coarse pitch as long as there's oil pressure and I've seen it do it at idle.

Alex, when I practise this maneuver, in my head, it's a forced landing and I've long ago made up my mind that I'll have full flaps by touchdown to greatly lessen forward impact forces...so for me, full flaps.

Best,
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  #8  
Old 04-06-2010, 06:57 AM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by pierre smith View Post
...it'll go to coarse pitch as long as there's oil pressure and I've seen it do it at idle.

Alex, when I practise this maneuver, in my head, it's a forced landing and I've long ago made up my mind that I'll have full flaps by touchdown to greatly lessen forward impact forces...so for me, full flaps.

Best,
Pierre, it the "greatly reduce impact forces" that I'm not so sure about. The vertical component cannot be ignored, and that is what is less under our control with full flaps. If the last 20 feet of descent rate is found to be too much, it is tough without power and with full flaps to arrest it. Especially if the "runway" is an undulating field. Or a diminishing headwind is in play. Additional factors are (at least my) inability to accurately judge the last 20 feet of altitude in a non-runway situation.

As one who buzzes fields at 6 feet for a living, you may not think about this for the rest of us runway type of guys.

I need to do a lot more tests with and without flaps and record actual ground speeds at TD. I am willing to add a few (and I don't think it is much more than that) knots TD speed to greatly increase my ability to extend the TD point if necessary, as well as dodging a cow or whatever.
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  #9  
Old 04-06-2010, 01:07 PM
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pierre smith pierre smith is offline
 
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Default Yeah, I do buzz at 6' for a living...

...but I meant forward impact forces....the slower the better. It may well be a ditch or the trees in a short field. My-10 has around a 57 MPH stall at light weight and that is a really slow landing for the size of the airplane,

Best,
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  #10  
Old 04-06-2010, 01:41 PM
gereed75 gereed75 is offline
 
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F=MA and E= 1/2 mv squared. The slower the better.

Pierre, the idea is that the Hi key/lo key pattern should be a comfortable glide, with plenty of room for adjustment - adjusting AOB primarily. We always used a bit more than a standard rate turn and a "wingtip" distance at low key. A wingtip distance was defined as rolling wings level and the intended point of landing should be visible on a line extended from the eyeballs , through the wingtip, to the intended point of landing. Obiviouslly this will vary with aircraft type but it is about 3 - 4000' abeam. Use a runway length to judge.

It sounds like 1000' AGL is a bit low to fly the pattern as designed. A standard rate turn will give you a 360 degree turn in two minutes. At 1000 fpm descent, that would require 2000' AGL. Using abit more than standard rate would require maybe about 8-900' per 180 degrees of turn. That is about what is taught in the military as the right AOB for the pattern. You can steepen it if low, extend it if high.

Flaps "when the field is made". That generally equate to about 150 - 200 feet on very short final. Flaps down and flair as necessary. You really have to hold the nose down to maintain AS on final and you are comitted to land when and where you flare. Yes a bit uncomfortable and a bit unforgiving of judgement errors but SPEED KILLS!!!
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