The Famous "Downwind Turn"

[PTKay]

Recently a nice read:

http://www.avweb.com./news/columns/191034-1.html

;)

(You still remember our discussions?)

[Alan Coats]

That was interesting. I'm glad to know I can make downwind turns over giant conveyor belts with no worry.

Alan

[John Stahl]

SOOOOOOOOOO
We don’t need 2000’ of runway to take off.
All we need is a conveyer belt, with a Segway type of balancing gyro in front of the weal’s to control the conveyers speed.

A set of rollers instead of a conveyer may be more practical.

This may not be such a far fetched idea.

[Paul_in_Ohio]

The article about the plane on the treadmill has been getting some attention on another forum I am on. Sure is great timing you posted your article now and I read the whole page.

Thanks!

[scottessex]

I'm going to stay out of this one...................................

[PTKay]

http://www.rotaryforum.com/forum/showthread.php?t=1953&highlight=Downwind+Turn

[PTKay]

"Birdy - what Chuck and Doug were trying to tell you is that, it doesn't matter what maneuver you are making - coordinated or not, accelerated or not - will have the same outcome in terms of loss or airspeed and/or altitude is you make it exactly the same – start to end - into downwind or into upwind. - Udi"

[Harry_S.]

ME too.

This could be used on Carriers...in place of the steam launch...eh, David Holmes?!


Cheers :)

[Low'nSlow]

I’m always amazed that pilots continue to believe the two oldest myths in aviation, the ‘dangerous’ downwind turn and flying on the ‘step’. Even after having it logically explained, some doggedly continue to ‘believe’. I suppose you have to add to this group, those who sing the praises of the RAF and are offended when told otherwise.

[Harry_S.]

AHhhh...another basher emerges?!


Cheers :)

[Brent Drake]

THe wind crossing the wind creates lift. not the speed at which the ground passes. Since the airplane is a tractor design, with enough air past the wings from the prop, it would fly. nothing about ground speed counts, only the air passing the wings is going to create the lift or vacuum on the wings top trailing edge to create lift. Most aircraft designs loose lift when turning. This could be the anology that makes most sense.
Brent

[ventana7]

Tom,

I'm a sea plane pilot and don't even know the second myth- so what is this about flying on the step?

Rob

[Low'nSlow]

Originally Posted by ventana7;
I'm a sea plane pilot and don't even know the second myth- so what is this about flying on the step?

Rob,

The ‘step' I’m referring to isn’t the ‘step’ sea plane pilots use.

Even one of my personal aviation heroes, Ernest Gann, bought into this one. Usually they would climb a few hundred feet above cruise altitude then ‘dive’ down to it, this somehow put it on the ‘step’.

Barry Schiff and many other aviation personalities have tried to ‘bust’ this myth.

http://www.avweb.com/news/airman/184274-1.html

Myth #1 — Getting It "On The Step"

I must admit, this confused me for quite a while. The old timers would swear by this technique for getting a little extra performance out of their Cessna/Cherokee/Mooney and looked down on us "kids" who didn't subscribe to the technique. For the uninitiated, the story goes that you can get a couple of extra miles per hour (airspeed indicators were in MPH then. I'm convinced that this was a marketing thing — 115 mph just sounds faster than 100 knots.) cruise performance if you get the airplane "on the step." The "step" was alleged to be a mythical "just-right" angle of attack which minimized drag and allowed an airplane to cruise at a higher airspeed than normal on the same power. "Just put it on the step" the ol' timers admonished. "It's amazing. You won't believe the increase."

Well, I didn't believe it. Seemed to me that if such a phenomena existed, the airplane manufacturers would have seized upon it and you would see advertising along the lines of "Our step is easier to find!" and "Take the big step up to..." and "Only a step to faster..." and the like. Never happened. If the marketing types don't exploit it, it probably doesn't exist, I reasoned, so I asked for a demonstration. Joe — one of the good ol' boys — consented to educate the kid and so we headed for the flight line.

[ventana7]

OK - I was never fooled by the downwind turn but I'll bite on this one.
I think my confusion stems from the mechanical setup of the conveyor not the aerodynamics. If I run ever faster on a treadmill and I keep increasing the treadmill speed to match my pace I do not feel an increase in wind in my face.

The prop spinning does not create the airflow over the wings to create lift. So how does any air movement relative to the wings take place if the conveyor spins against the wheels like a person on a treadmill.

[ventana7]

Tom thanks for the step clarifiction. Kind of reminds me of fishing with my Dad when I was a kid. If he caught fish and I didn't he told me it was becaue I wasn't holding my mouth right.

[Chuck_Ellsworth]

Well low and slow I'm one of those ignorant ones such as Ernest Gann who just happens to understand the advantages of "On the Step " to get optimum cruise speed.

So you tell me where I have gone astray here believing in accerelating to cruise speed after level off either by using power or lowering the nose to gain airspeed, rather than just fly along at a high angle of attack and remain behind the power to lift curve?

Here is a hint for you...If an aircraft with high aerodynamic and parasitic drag is cruising in equalibrium (sp?) at optimum angle of attack and power setting for best cruise speed encounters turbulence which ends up with the airplane in a higher attack angle than that previous to the upset of angle of attack how would you regain the optimum cruise speed for the power you had set previous to the upset of angle of attack?

Chuck E.

[Doug Riley]

Chuck, I think the "step" thing involves something more voodoo-ish than merely picking your most efficient cruise speed vs. lugging it along at best rate of climb. I think the "theory" is that you will NEVER get as efficient a cruise by merely levelling off and trimming for cruise speed. I believe that THEY believe that somehow diving to reach cruise speed carries some advantage -- gets the wings wetter with air or some such thing.

But maybe I've got the story wrong. Certainly there IS a best cruise and it's faster than best rate of climb. It won't matter how you get to that speed, however.

A slightly related phenomenon does exist -- once you hit stalling AOA with a wing and stall it, it won't un-stall if you bring it back just below that AOA. You have to go a ways below stalling AOA to get the flow to re-attach itself. Airflows do have a bit of "memory" in some cases...

[Udi]

I'll bite.

Chuck - I think you are referring to travel at MPRS where, any increase in AOA or reduction in airspeed places you behind the power curve . Planes normally don't cruise at MPRS, and don't need to go on the step. Not so?

Udi
p.s. After some more thinking I take back what said above. The only sustainable condition I know of that you HAVE TO come from the top is a minimum S/L airspeed. The only direction out of a minimum S/L airspeed is down, and the only way back is from the top. But who wants to cruise there?

[GyroRon]

This flying on the step thing.... never really thought about it before but I do this myself and it seems to work. Not that it produces a faster cruise speed, but by going a few hundred feet higher in climb and then diving down to the desired altitude and leveling off I seem to get to my best cruise speed faster....

[Chuck_Ellsworth]

Doug and Udi :

Almost all fixed wing aircraft ( at least certified aircraft ) will not generally give problems with loss of airspeed during flight in turbulence and not recover on their own...

..however the PBY when at or near gross weight will " Fall off the step " so to speak if disturbed in pitch attitude enough to get back of the power to lift equasion that it was previously maintaining and trimmed to.

The reason that this occurs is because of the high aerodynamic and parasitic drag factors inherrent in its design...

..We are very concious of this phenomena when flying at over gross weights on long over ocean flights. It can become rather annoying having to regain airspeed after an angle of attack upset, generally we can regain airspeed by increasing power and then resetting it after the airspeed is recovered...however the best method is to gain about two hundred feet with power, then lower the nose to regain the desired angle of attack and resultant airspeed.

A loss of ten knots that is not recovered can mean a loss of one hundred miles during ten hours of flight...so we do use the "on the step "method of flying them

Incidentally if really in danger of not enough range we can decend to the ocean level and fly in the T effect...which is another word for ground effect and get a slight increase of airspeed and also a more stable pitch zone.

The last trip I flew in Europe in September of this year as a crew member was in the Boeing 767-300ER and on the step was not a concern..;)

Chuck E.

[Low'nSlow]

Originally Posted by Chuck_Ellsworth
“…So you tell me where I have gone astray here believing in accerelating to cruise speed after level off either by using power or lowering the nose to gain airspeed, rather than just fly along at a high angle of attack and remain behind the power to lift curve?...”

Your right on target, but that’s not what I’m talking about. As Doug Riley put it, “the "theory" is that you will NEVER get as efficient a cruise by merely levelling off and trimming for cruise speed.” I agree that if you were to climb and when reaching target altitude you leveled off and immediately went to cruise power, it would take a while to reach cruise speed. But you’d get there eventually.


"...Here is a hint for you...If an aircraft with high aerodynamic and parasitic drag is cruising in equalibrium (sp?) at optimum angle of attack and power setting for best cruise speed encounters turbulence which ends up with the airplane in a higher attack angle than that previous to the upset of angle of attack how would you regain the optimum cruise speed for the power you had set previous to the upset of angle of attack?"

Lower the nose? I guess I don’t really understand the question. Compared to most ‘spam-cans’, my plane has one of the most ‘draggy’ airframes you’ll find in the GA fleet and having such light wing loading, turbulence has a huge effect on my attitude. So if I were to jockey the throttle every time my angle of attack was increased by turbulence, I’d have to replace my throttle cable every annual. I’ve never flown anything heavy, so maybe it’s an apples and oranges thing?

When I climb and reach target altitude, I keep it at full throttle until the speed comes up, then throttle back. I’ve tried the other method, but found that the extra time it takes (especially at high density alt) to get above cruise altitude negates any advantage.

[Chuck_Ellsworth]

Tom:

I think that maybe we are using the wrong term when we describe optimum angle of attack at a given power setting and maintaining altitude..or level flight...as on the step.

There is sometimes a large difference betweel level flight as in level attitude and maintaining a given altitude.

There are many factors that determine how any individual aircraft will behave when turbulence changes airspeed, attitude and altitude.

As well aircraft weight and its aerodynamic profile v/s its wing loading and many other factors will determine how any given airplane reacts...there is also the factor of inertia etiher the loss of inertia or the gain of inertia.

As I explained there are some aircraft that require very delicate handling of both attitude, speed and loss of inertia to maintain a given altitude.

When Ernest Gann and myself who have come from an earlier era of aviation describe getting and keeping an aircraft "on the step " we are describing the need to accelerate to a pre determined airspeed and attitude to maintain altitude at a given power setting determined by what cruise speed we need based on distance to be flown and changes in weight as fuel burns off..

If a loss of airspeed occurs due to increasing angle of attack to counter subsiding air you will either have to wait for rising air to lift the aircraft back to the desired altitude or climb the airplane by increasing your angle of attack which will further reduce airspeed or add power and increase angle of attack to regain altitude.

With some low performance heavy aircraft we will allow the airplane to climb a hunderd or more feet above the desired altitude and then lower the nose to use the increase in airspeed to hasten the change of inertia and thereby regain the desired attitude, power and airspeed that we had set prior to the upset of a trimmed steady cruise at a selected airspeed.

I knew Ernest Gann as a personal friend having met him many years ago through one of my employers and Ernest was using the expression "on the step " in the same context that I would use it.

Anyhow once again I find myself in a discussion that will probably change no ones minds about the art of flying, but for whatever it is worth my observations come from flying aircraft from the early biplanes to the most modern computer operated fly by wire heavy jet transports...

...anyhow that is about as good an explination as I can give on the subject.:D

by the way..lovely Champ, many, many moons ago I used to instruct on Champs both land and floats. :cool:

Chuck

[Chopper Reid]

Would love to had all you guys that believe the downwind turn isnt a problem flying with me this afternoon. I'm talking 100 ft AGL, hot, windy and extremely strong willy willys. ASI indicating 45 to 50 knots [usually 60knots] GPS speed into wind indicating 27 mph and a fuel flow of 18 litres per hour [usually 15.5 LPH] into wind and up to 30 LPH to do a down wind turn sucessfully !! All this and trying to work stock !!!

This morning you could do any turn at cruise power just as the good book says !!! Absolutely not a problem and lovely delightfull flying !!

[Hognose]

Brian --

The downwind turn is a concern if you are flying by reference to ground, rather than air, speed. As Doolittle wrote in 1927 or whenever (Rick Durden quotes him in the original article), pilots flying with their heads outside the pit, flying by reference to ground, not air, speed, have a tendency to let [air] speed get too low in a downwind turn being executed by ground reference.

GPS speed is ground referenced even though the data comes to you from space!

With the sort of flying a musterer does, of course he is going to be 'heads out" and judging his speed by reference to the ground. But the airplane does not give a rat's arse what the airmass you are in is doing, except inasmuch as inertia effects it as it passes through changing winds.

cheers

-=K=-

[PTKay]

To the "on the step discussion".

I have never heard that term, but my CFI, flying a lot on the An-2
(sigle engine 1000 hp, double decker) during his military career and after,
claimed, that finding a "sweet" AoA for a certain cruise speed, would
reduce his fuel consumption from 220 l/h (standard) to 170.

I think, those slow and draggy STOL airframes (like the An-2) are very
sensitive to proper AoA, you can fly them with the same speed with
very different AoA, resulting in drastic difference in fuel consumption.

I could observe the same on my Socata Rallye STOL.
With my "feeling" for the machine I can fly it 100 mph cruise
with just 2150 revs on my O-320, but most of the other people
who fly it occasionally need 2250 revs for the same cruise.

It is again a very slow and draggy STOL.

[Chuck_Ellsworth]

PTkay :

Well I guess there are more people than myself and Ernest Gann who have learned that there is an advantage to "getting on the step " to increase range in level flight...

Here is part of my initial comments on this subject again.

" Almost all fixed wing aircraft ( at least certified aircraft ) will not generally give problems with loss of airspeed during flight in turbulence and not recover on their own...

..however the PBY when at or near gross weight will " Fall off the step " so to speak if disturbed in pitch attitude enough to get back of the power to lift equasion that it was previously maintaining and trimmed to.

The reason that this occurs is because of the high aerodynamic and parasitic drag factors inherrent in its design...

..We are very concious of this phenomena when flying at over gross weights on long over ocean flights. It can become rather annoying having to regain airspeed after an angle of attack upset, generally we can regain airspeed by increasing power and then resetting it after the airspeed is recovered...however the best method is to gain about two hundred feet with power, then lower the nose to regain the desired angle of attack and resultant airspeed.

A loss of ten knots that is not recovered can mean a loss of one hundred miles during ten hours of flight...so we do use the "on the step "method of flying them. "

Then again , what would we know after all there are many opinions on how things fly. All one needs to do is read this forum.

Chuck E.

[Low'nSlow]

Originally Posted by Chuck_Ellsworth;
“…I knew Ernest Gann as a personal friend having met him many years ago through one of my employers and Ernest was using the expression "on the step " in the same context that I would use it…”

Chuck,

Thx, I love my Champ.

I’m curious, did you get a chance to hang out and/or talk to Mr. Gann for any length of time and what were your impressions?

[Chuck_Ellsworth]

Yes, I did get to hang out with him and found him to be as facinating in person as he was as an author, as far as I am concerned he was without equal as an author of aviation stories....

..now comes the sad part, I had every book he wrote and lent them to a (friend?) about ten years ago...I can't find my friend nor my books.

The last time I was talking to Ernie was in his hangar in Friday Harbour just prior to his passing away. We were discussing the new Strike Finder he had installed in his Wing Derringer twin that he owned, I wish I had taped his description of the Strike Finder, it was priceless.

When he wrote "The Flying Circus " he wanted to include a story about some flying that I had done when I was water bombing for The Flying Fireman, but I managed to talk him out of it..

Anyhow Earnies passing was a true loss to aviation.

Chuck E.

[Mike Jackson]

I, too, was taught the "on the step" technique to leveling at a cruise altitude and speed way back in the 60s. Seems to work well enough compared to a level accel from best climb to a best range cruise speed. In the end game, the energy state of the prop driven aircraft is the same. So why do some guys like one technique over another? I suspect it is aircraft specific and may have to do with overall drag and prop efficiencies (maybe voodo).

If your aircraft has more excess power than your average autogyro, you might adopt a technique more in line with turbojet techniques - fly faster in the climb. For short climbs you are probably not burning much more fuel or taking up alot more time to altitude. What you are doing is getting there with more energy and the transition to cruise speed is smoother and quicker.

Turbo jets will try to approximate getting to altitude with the most total energy per time rather than best rate. The "Tommy Test Pilot" lingo is to climb on an energy curve where specific excess power is zero. Most will approximate this by climbing at a computed IAS (Boeing computers onboard)until picking up a computed climb mach. This climb mach is never less than cruise mach. Once at altitude you reduce to your cruise power setting. I still see some guys who'll let it accel slightly above cruise mach then throttle back to a compute power setting letting the machine settle to cruise mach - analogous to the step approach w/o the altitude change. We don't have auto throttles.

[Fleamer]

[QUOTE=Mike Jackson]I, too, was taught the "on the step" technique to leveling at a cruise altitude and speed way back in the 60s. Seems to work well

Sorry if this comes up twice - I haven't even gotten all the the "Post" protocol figured out yet...sighhh

I'm a little confused by the "on the step" thing. As this is agyro forum I keep looking for the link to gyros, but am a little to slow to find it....anybody help me out?

Down wind turns....I agree with the rat's arse thing about the air mass issue. It seems a pretty basic flying issue to fly with respect to the medium you are in rather than what you might hit if you don’t. What experienced pilot would fly using ground reference - except to watch for hard bits like barns or trees looming through the heat waves. Many pilots have taken an ambulance ride by using the ground as a reference……

I can see the downwind turn being an issue if close to the ground if one gets a sudden gust from behind (thereby lowing your airspeed) just as you are entering the turn. Of course if you got a sudden decrease in windspeed the opposite would occur wouldn’t it? Low flight is always fraught with challenges - which is probably why it is so much more fun…keeps us on our toes.

Cheers

GS

[Chopper Reid]

Kevin, the airspeed was reading low despite a high power setting and a straight and level attitude, the turns werent being attempted by using a ground reference as it was imposible to do a turn referenced to anything at times !! I'm an expereinced pilot and I know what I'm saying guys, with the conditions I stated, it was impossible to do a downwind turn at times !!

Yesterday, same place doing the same thing and any turn wasnt a problem, all of a sudden the theory of the airmass and any other theory you like to quote worked !! Never even had to apply power to compensate for the turn even !!.

My point is that despite excellent theory, some times it doesnt work. When flying close to the ground, you need to be aware that there are a lot of things that can cause big problems [under 200 feet] and the tricky thing is that inexpereinced pilots can be caught unawares. Even expereinced pilots can get caught as well.

[Chopper Reid]

Kevin, the airspeed was reading low despite a high power setting and a straight and level attitude, the turns werent being attempted by using a ground reference as it was imposible to do a turn referenced to anything at times !! I'm an expereinced pilot and I know what I'm saying guys, with the conditions I stated, it was impossible to do a downwind turn at times !!

Yesterday, same place doing the same thing and any turn wasnt a problem, all of a sudden the theory of the airmass and any other theory you like to quote worked !! Never even had to apply power to compensate for the turn even !!.

My point is that despite excellent theory, some times it doesnt work. When flying close to the ground, you need to be aware that there are a lot of things that can cause big problems [under 200 feet] and the tricky thing is that inexpereinced pilots can be caught unawares. Even expereinced pilots can get caught as well.