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Settling with Power
#41
Great point UH-60Pilot!
How many of us are worried about entering SWP at 100' in a vertical decent? Well, probably just one of us,---- that be me! Actually starting at about 120' on a 45 degree decent.
To stay out of DMC ( Dead Mans Curve ) I'll need to drop in fast ---> auto in?
To stay out of SWP decent needs to be slow.
Slow decent = slow forward speed => in DMC.

If engine is running good and I'm not super good at autos to the ground, it seems safer to come in very slow avoiding SWP than to botch an auto. Especially if dropping into an unknown area. But I would not be surprised that I'm wrong and the best would be to get more practice with autos until I'm good enough to auto in rather than risk SWP or engine failure. Or maybe best of all is to convince myself to not do it at all. I'm working on it.

OR ---- TurboEddy got me thinking.... , if SWP - auto-out, if DMZ - auto-out, if engine quits - auto-out, ... hey TEddy!
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#42
Yes you are right Larry the answer to anything amiss with a helicopter seems to be to auto out!
The first time it happened to me though, I was down at power line level, got myself inadvertantly downwind, and there was the sink, the shudder the random rolling and yawing----
I was too low to autorotate. I guess my aeroplane training kicked in as it felt very like an impending stall.
So: stick forward and fly it out. No question of power reduction: I was definitely into the wires if I tried that!
Rob1
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#43
Pfranc, Let me tweak your thoughts a little bit. Your decent can be fast you just need to keep forward airspeed above ETL. As you get to the bottom of the approach several things are culminating at once. First, you need to slow your vertical and horizontal speed to stop at a hover and the requirement to do this is coincidentally where you will be coming out of the dead man's curve. Keeping your forward speed up kills two birds with one stone. You are staying out of the dead man's curve and you are staying out of the SWP envelope. The L/Z you are going for will dictate how steep/shallow and how fast/slow your approach will be. A big L/Z will obviously allow you to make a shallow approach with a higher airspeed until you are in ground effect and then you can slow down therefore sidestepping SWP completely. If you are going into a more confined L/Z then make your approach steeper but keep your airspeed just above ETL and keep that speed/attitude constant. Keep in mind that once you go below the barriers (trees, buildings or whatever can act as a windbreak) your airspeed may decrease and put you into the SWP envelope. Just be aware of this and anticipate it. Keep in mind that you can have a pretty high decent rate and as long as you are above ETL your rotor system is still in clean air. After you make enough of these approaches you will be able to see you are doing it right without even looking at your airspeed indicator as long as you never break the cardinal rule (approach into the wind). This should be even easier for you to visualize since you are flying a Mosquito Air and your visibility is so good. Just keep your situational awareness about you and you should be just fine.
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#44
bryancobb - 9/24/2010 11:11 AM
Don't confuse that "Shudder" with the onset of SWP! You will feel shuddering with SWP, but the shuddering most folks are feeling during SWP demonstrations in an R-22 is caused by being right AT ETL airspeed during the descent!

Brian, I got to fly this evening. On the way over across the river not having flown in weeks I was fairly slow, about 60 feet coming in, flaring, and felt a little shudder, and loud rotor wap wap - not totally out of the ordinary --- but on the way home, - feeling more confident and in a bit of a hurry, and entering super familiar territory, I was faster, more direct, like a bee line to the LZ, and it seemed much smoother, quieter, and all-round better. Why I wonder? ... something you said about ELT. Question: Is being OGE (Out of Ground Effect) ... together with leaving ELT be the reason? I suppose, like everything else, there are a whole lot of variables here, ... temp. humidity, gross weight, relative air-speed, altitude AGL, the I imagine IGE and OGE are not fixed numbers, ... hell, ELT is probably not a fixed number? whew, no wonder this is soooooo much fun! Lots of science together with lots of art? Lots of knowledge, skill, experience, wisdom, some luck in order to get the experience and wisdom, - and then the folks on this fourm helping the little old low timer, me. Thanks everyone.
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#45
Rob1, I love it ....between you and TEddy I've got: "When in doubt, auto out. Can't auto? Fly baby, fly!". First priority: "Fly the airplane", sounds silly, but it makes a lot of sense to an experienced pilot. Autos are flying, - flying is flying, .... learn, learn, learn, then just do it.

10 learn more, do more, go to 10.
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#46
UH-60Pilot, ... yeah, ETL, ETL, --- and IGE, ... I'm tweaked and I'm getting stoked. OK, I'm looking at 45 degree decent into a very confined LZ --- sooooooo, Mosquito DMZ (Dead Man Zone) is anything under 35mph at any altitude. One MPH = 88FPM. 35mph x 88 = 3000 FPM decent and I'm not in the DMZ, can't SWP, and am probably full down collective, ... that sounds scary. What are the numbers for a normal everyday auto?
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#47
Pfranc,

The shutter Bryan is referring to and that you are feeling is caused by transverse flow effect not effective translational lift. They do both occur at overlapping speeds but ETL doesn't cause the shutter even though it is often called the ETL shutter. Effective translational lift is an increased aerodynamic efficiency of the rotor disk because it is no longer recirculating it's own air in a circular pattern that keeps getting reintroduced to the rotor system in the form of vortices. Once through ETL (16-24 knots) the disk is moving through clean undisturbed air. The air is no longer being pulled down vertically through the disk but is coming into the disk at a much more horizontal angle which lowers the angle of attack and causes the increase in efficiency due to decreased induced drag. This increased lift efficiency also causes the disk to want to tilt back (blowback) and this is why the helicopter requires more forward cyclic the faster you go.

Transverse flow effect is a difference in the angle of attack between the front half and the rear half of the disk. When you tilt the disk forward and start to increase speed the front half of the disk is at a lower angle of attack and the rear half of the disk is at a higher angle of attack. Essentially the whole disk is moving at the same speed through the air but the local air flow patterns over the front and back halves vary greatly. The front half of the disk is flying and has a higher angle of attack and the back half of the disk is hovering and has a lower angle of attach. This occurs between 10-20knots. This difference in lift between the front half and the rear half of the disk is what makes the shutter. Gyroscopic precession or phase lag causes the disk to react 90 degrees later therefore causing the helicopter to want to tilt to the right and requires the pilot to move the cyclic to the left until the entire rotor system is flying. Transverse flow effect is what is causing the shutter and probably the blade popping you are hearing around this time. It will feel different depending on your horizontal and vertical speed in the many different takeoffs and approaches you will make. I would say that if your airspeed indicator is showing some kind of speed then you are out of the envelope for SWP and any shutters, vibrations and popping you are experiencing are related to Transverse flow effect. I didn't want to go into this much detail but I needed to so I could explain what you are experiencing instead of leaving you to think you are getting into the onset of SWP. I hope this is helping you and not confusing. I did my best to keep it watered down. It's actually somewhat more complicated. This should help you with a deeper understanding of what you are experiencing as you transition in and out of hover so fly that thing!



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#48
Thanks UH-60Pilot. Everything helps! I feel bad taking so much of your time. I think though that because this thread could be here for a time that it will not only help me as I reread it (sans beer) but will also help others who are a little slow on the uptake like me. Sometimes explaining the same thing in 10 different ways - is not a waist of time, and could save a little old low time wantabe helicopter pilot, me. Thanks again. OK, now, you mean I can't just hover at 120 feet and drop in at zero air speed? (just kidding, just kidding) Darn!
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#49
Larry, you can have your beer, mate. Just be sure the flying and driving is over for the day!
Seriously, numbers like 35mph do not mean a lot.
Centuries ago, I did the RHC Safety Course, and happenned to mention to the instructor that I had experienced the SWP, but could not be sure of being able to reproduce it for the student.
Instructor said " Oh yeah. This is how to get it everytime."
AT ALTITUDE, he slowed the Robbo, maintining height with power, until the airspeed went back to zero, still maintaining height with power.
He then reduced power to 16" and down we wobbled, totally in SWP.
At the thousands of feet that we were at, of course the recovery was to (as always) enter autorotation.
But to my delight, he used EXACTLY the same technique as I did when I was looking at the power lines!
Stick well forward, fly it away, just like an aeroplane (alright you win) airplane stall recovery. Just don't increase the power, is all. Reduce it if you can.
Rob1
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#50
Since it's a good idea to always land into the wind, what's a good way to tell which way the wind is coming from if you left home early before the wind started to pick up and there's no bodies of water to inspect? Typically when I take off it's 7 AM and 0 windspeed. After I'm up there for an hour the wind has picked up and I'm not sure which direction it's blowing. Any hints if you don't have a radio?
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