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Spiral slip Stream is it real ?

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Spiral slip Stream is it real ?

Old 03-27-2013, 06:13 AM
  #76  
Top_Gunn
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Default RE: Spiral slip Stream is it real ?

How's this for a summary? Spiral slipstream is real. Its effects vary from plane to plane, and they are very hard to measure because they are similar to the effects of torque and P factor. The end.
Old 03-27-2013, 06:39 PM
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ARUP
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Default RE: Spiral slip Stream is it real ?

Stator vanes wouldn't be needed in wind tunnels if spiral slip stream wasn't a factor. This thread entry will replace the one that was removed (which I liked better!). I wonder if tip vortices coil....
Old 03-27-2013, 06:39 PM
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Default RE: Spiral slip Stream is it real ?


ORIGINAL: drac1


ORIGINAL: Quikturn

Some more evidence. Notice more soot on the right wing?
I can see how there would be more soot on the right wing, but wouldn't the wing act as stator and stop the airflow from spirallingfrom the wing back?
I don't think a wing will completely straighten out a spiraling airflow of a propeller. It likely does straighten it to some degree however.

Spiraling slipstream as one of the left turning tendencies is what is taught to everyone taking flying lessons. It was taught when I was a student and I taught it when I was a flight instructor and taught ground school. I'd like to see credible evidence that spiraling slipstream does not exist if this is in fact the case.

This is like me arguing with a doctor that aspirin doesn't work because it didn't cure my headache when in fact the doctor can explain to me scientifically why aspirin does work.
Old 05-19-2014, 07:32 AM
  #79  
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Hi, just thought I'd freshen up an old thread.

Anyone see any evidence of a spiral in this slipstream smoke in this video?

https://www.youtube.com/watch?v=thKg...layer_embedded

Thanks

Last edited by MajorTomski; 05-20-2014 at 01:44 PM.
Old 05-19-2014, 01:25 PM
  #80  
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Shore in free flight days. If you put the vertical stab on top or on the bottom it would turn one way
or the other.
Darryl
Old 05-19-2014, 03:50 PM
  #81  
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Originally Posted by MajorTomski
Hi, just thought I'd freshen up an old thread.

Anyone see any evidence of a spiral to this slipstream

https://www.youtube.com/watch?v=thKg...layer_embedded

Thanks
Great show there Maj. Tomski. I don't wish to get into the organizational portion of the subject. I just remember that rejoining up in the sky was much more rough than being in formation position, even when flying the slot. Holding onto a boom for refueling behind the KC-97 (prop job for you youngsters) was a real attention getter especially in the B-47!
When sliding into position in a banked C-123 (2-P&W R-2800s) it could get pretty shaky, especially when flying co-pilot for some old WW II or Korean recall that had never flown any formation to speak of. Was it prop stuff or just something else? Beats 'ELL out of me! To be proper, those old guys (I'm one real old guy now) quickly adjusted to letting us formation trained troops help them and they did learn fast.

For the younger crowd: Theory is great. Take it and use it. OTOH don't let theory overshadow your butt! When I was young, and knew it all, an old guy told me one day, "It isn't what you don't know that will hurt you nearly as much as that which you know for certain that ain't so."
Old 06-18-2014, 03:10 PM
  #82  
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I don't think that video disproves the spiraling slip stream theory. Are you expecting to see the smoke spiral like a cork screw? I've been flying professionally for 20 years; everything from a C152 to various turboprops to heavy MD-11s. I also instructed for several thousand hours in single/twin recips and turboprops. Many books and training manuals refer spiraling slip stream. I have a hard time believing they are all wrong. One video with no "obvious" spiral of smoke doesn't debunk the theory any more than than the video proves there is no gravity because the airplane flies away from the ground!
Old 06-19-2014, 08:38 PM
  #83  
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https://www.youtube.com/watch?v=PqewZDoOIuE

This isn't the usual "tip vortice" spiral pictures and there're plenty of youtube clips of boat propellors showing the spiral path of tip cavitation but this isn't one of them.

What you have in the above clip is the water that's being pushed back is also spinning around as evidenced by the action of the engines exhaust. Granted water is a bit more viscous than air, but as has been pointed out in previous posts, stator vanes are needed in axial flow turbines and compressors because the airflow does not leave the blade perpendicular to the shaft axis and needs to be straightend, and surfaces placed above/below the engine thrustline influence a plane in opposite ways.

Spiral slipstream is real, it exists, but an rc prop in air isn't going to create a spiral that wraps around a plane 4-5 times. It'd be lucky to be only a fraction of a full rotation over the length of the fuselage but a fraction of a degree can created ounces of force imbalance.



https://www.youtube.com/watch?v=N3WwQKZ05Uk

The above is a slo-mo of the spiral path of tip cavitation but is in no way "evidence" supporting spiral slipstream, it's just the path of the prop tip "drawn" in the moving water....

Last edited by bjr_93tz; 06-19-2014 at 08:48 PM.
Old 06-19-2014, 09:13 PM
  #84  
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A boat prop. does not have an Airfoil shape and is Pitched extremely.I can Imagine with those characteristics it would Have a Spiral stream behind it.Don't know if your reffering to my Prototype.But I use that Downward Airflow to control Axis!I changed direction of rotation.Allowing me to Run stock rotation on Both wing motors with stock ptops. If you Rotate it in differant directions.You will see that 1st had to counter 1 side to get equal and desired airflows.Changing Direction solved that problem!!
Old 06-20-2014, 12:30 AM
  #85  
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Hi Charlie111, I wasn't referring to your prototype.

You're right there's a huge difference between a boat prop in water and a airplane prop in air, but fluids are fluids and the airplane prop drags the air around with it as it's forced backwards just as a boat prop does. The free flight guys used bits sticking out into the propwash to effect trim changes between power on and glide such as wing pylon height, area and fin area above and below the fuse as starters.
Old 06-20-2014, 02:46 AM
  #86  
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I Hope to get some Backing behind My concept.I have increased the Surface Area of the Rotary wing.So that it will give More Lift at Lower r.p.m.s The props turn it plenty fast enough for it to lift a Small E.V. It is very simple and all energy is devoted to turning the wing.No tail rotor.Easier to operate!! An e.v. such as a Smart Car would make a Comfy Cockpit.See 1st working prototype on Twitter rotate1953.As a Unit the car could unplug and Drive off.Leaving the Unit at the Airfield.So many Features needed are allready in Todays Auto's.I think it could be Made Autonomous? A Google Craft of sorts!!! I use that Airstream for Axis control!!

Last edited by charlie111; 06-20-2014 at 02:50 AM.
Old 06-20-2014, 05:48 PM
  #87  
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I had an R/C Piper Cub Tail Dragger and I had to use Right rudder on Take off as in a Real Full Scale Aircraft.Made 2 Flights with it.Bringing it Home in 1 Piece both times.Used to be a Member of the 107 Flyers Club!!
Old 06-24-2014, 06:10 AM
  #88  
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Originally Posted by charlie111
A boat prop. does not have an Airfoil shape and is Pitched extremely.I can Imagine with those characteristics it would Have a Spiral stream behind it.Don't know if your reffering to my Prototype.But I use that Downward Airflow to control Axis!I changed direction of rotation.Allowing me to Run stock rotation on Both wing motors with stock ptops. If you Rotate it in differant directions.You will see that 1st had to counter 1 side to get equal and desired airflows.Changing Direction solved that problem!!
A boat prop has a "waterfoil" shape if it's a decent prop. Yet, some of the very efficient submarine propellers have a striking family resemblance to the multi-blade scimitar props used on some large turboprop A/C. Also interesting is that counter rotating props on twin engine A/C work better one way than another on particular A/C.
Old 06-27-2014, 08:13 AM
  #89  
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Originally Posted by MajorTomski
Ah another diciple drinks the coolaid.

Been arguing spiraling slipstream is a myth that was created when "Stick and Rudder" was published.

The true exsistance of a spiral has never been proven.

Folks love to explain P factor as the source of the yaw, but the same folks ignore that the physical manifestation of P factor is higher velocity air flowing down the right side of the fuselage, BUT the result of the force from that increased lift is a pitching UP moment on the prop shaft.

The high speed air from P factor will have EXACTLY the same effect as the suposed spiral.

But if the spiral truely existed the aircraft a low airspeed and high alpha would roll to the right almost uncontrollably, which it doesn't.
P factor is A result or an increased angle of attack thus increased pitch on the downward blade when at high angle of attack and high power setting. One side of the prop has more bite than the other.
Are you saying that the air is faster on the left side(assuming clockwise rotation pilots view) causes some bernoullli effect of some sort.
Old 06-27-2014, 10:12 AM
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A fair amount of downthrust on a Cessna 340A piston twin.

I should be more careful with those low passes (prop tips).
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Old 08-26-2014, 06:51 AM
  #91  
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Originally Posted by 417mack
P factor is A result or an increased angle of attack thus increased pitch on the downward blade when at high angle of attack and high power setting. One side of the prop has more bite than the other.
Are you saying that the air is faster on the left side(assuming clockwise rotation pilots view) causes some bernoullli effect of some sort.
Sorry to take so long to get back to this, It's been a very busy summer. Yes. Exactly.

The differential thrust on a propeller at high aircraft AOA can be computed and verified. There is more thrust happening on the right side of the plane. Every multi-engine pilot learns, sees and doesn't question this in their critical engine training. They DON'T attribute the yawing in this situation to the slipstream spiral. That extra thrust has to do something, it just doesn't disappear.

The next answer usually given is that the thrust off the right propeller blade is what is pushing the nose of the plane to the left. BUT that now violates the laws of physics! The thrust applied at the 90 degree point of the blade, due to gyroscopic precession the FORCE from that thrust reacts through the propeller at the 180 degree point; It causes the nose to pitch up, not yaw left.

Thanks for asking
Old 08-26-2014, 04:59 PM
  #92  
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The nagging question for me is my personal observations that seem to indicate that a plane with a symmetrical fore section (round cowl or box as in a stick) seem not to yaw much when going straight up (a condition where there is neutral angle of attack). Contrasting those, is the fore section that lacks symmetry in the horizontal plane with a prop shaft high. They seem to yaw left on vertical climb.

If horizontal asymmetry is the cause, then I'm thinking that pressures on the right fore section are greater than the left causing the plane to yaw. It seems quite reasonable that in close proximity that a spiral effect exist and that on the right side the spiral collides with the fore section and on the left side the spiral escapes to free space. The result is greater pressure on the right side and the plane yaws left.

It can be further noted, that as the plane slows its vertical climb, the yaw force increases. My thought is that the reason is because the spiral flow is washed less aft as the plane slows and thus has more pressure up front where the lever arm is then stronger to inflict yaw.

Edit note: On second thought... the greater yaw force as the plane slows could more likely be explained by less rudder control at slower speeds.

Last edited by AA5BY; 08-26-2014 at 06:50 PM. Reason: Additional thought
Old 08-27-2014, 06:07 AM
  #93  
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AA5BY you mention the condition that made me question everything that has ever been taught about the spiraling slipstream.

What is this spiral doing to the rest of the airplane In a vertical hover?

The spiral is always taught with one illustration from the side of the plane showing the spiral impinging on the vertical fin. Draw the same airplane from a top view and draw in the same spiral. No one ever shows that spiral doing the same thing to the wings and stabilizer. Where and why does this huge rolling force that is acting on the wings and tail plane go? No flight instruction manual OR engineering manual ever addresses it. It stops at stik and rudders simple explanaiton. Period.

If you do a complete free body diagram a plane should be rolling to the right, not just yawing to the left
Old 08-27-2014, 09:10 AM
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I hear ya and that is one of the reasons I think the yaw force is happening up front rather than aft. Another mental trap we get into sometimes is looking for singular cause. I bought a newly designed sailboat and went that route. I kept looking for the thing that was causing a handling issue and was buffaloed. Finally, it sunk in that the problem must involve more than one dynamic and that opened the door to taming the beast.
Old 08-27-2014, 09:47 AM
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The interesting thing is that if we look at the amount of aileron deflection to balance out the prop torque it's surprisingly little. And to me that suggests that the slip stream effect on the fixed portion of the wings is indeed considerable.

Keep in mind that when the folks that wrote "Stick and Rudder" were sketching their pretty pictures that they were trying to explain why the plane wants to YAW AND TURN when in a slow airspeed climb with lots of power and why some rudder is needed. The diagrams would have been considerably different and the students highly confused if they started listing and resolving all the effects and included prop hanging with the Cessna 150....

So simplicity is good to a degree. But all too often folks can walk away with the idea that what they were taught is the WHOLE picture.
Old 08-27-2014, 03:40 PM
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Picking six planes from my hanger and comparing their tendency to yaw left when going vertical.

Plane #1 is a Hanger Nine Ultra Stick Lite. Its fore section is horizontally symmetrical. It suffers almost no left yaw when going vertical.

Plane #2 is a Seagull Spacewalker II. Its fore section is significantly horizontally asymmetrical having a prop shaft near the top of the cowl and an inverted engine completely within the cowl. It suffers significant left yaw when going vertical.

Plane #3 is a Yak 54 (28cc powered). It of course has a round cowl and suffers hardly any left yaw when going vertical.

Plane #4 is an Akrobat II (33cc powered). Like the Spacewalker, it has a prop shaft at the top of the cowl that completely encloses and inverted engine. It suffers considerable left yaw when going vertical. Note: otherwise it is my best flying plane. It will knife edge from horizon to horizon with ease with very little in the way of roll or pitch couple.

Plane #5 is a self designed 35cc with a round cowl. It suffers little to no left yaw when going vertical.

Plane #6 is a Hanger 9 PT-19. It of course has a high engine shaft on a cowl that completely encloses an inverted engine. It as well suffers a good bit of yaw when going vertical.

I of course don't know if six planes are evidence for anything. Perhaps if others compared their planes and offer the observations relative to left yaw when going vertical and if the fore sections are horizontally symmetrical or asymmetrical.

I don't mean to imply that there is absolutely no left yaw on the three with horizontally symmetrical fore sections. Actually none are perfectly symmetrical. The stick has a jug that hangs down and the two others have spark plug cables that hang beneath the round cowls.
Old 09-01-2014, 04:11 PM
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I'm sitting here watching the Red Bull races on Fox Sports and I come to a realization. These airplanes are flying the course and the smoke trail follows a direct path on every airplane. During a high G turn the smoke trail may curve to about half span on a stab but that's it.
Old 09-01-2014, 05:40 PM
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Smoke is deceptive. It can be where it was blown by the exhaust and have the empennage pass through on it's own track. Any yaw and the smoke will be more one side than the other. Pylon turns can have the plane yawed for example. Skidding muddies the waters too.
Old 09-02-2014, 06:05 AM
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Well, as I am a guy who believes in what can be seen and felt. I have to honestly say that in 36 years of flying R/C I have never seen nor felt anything I could contribute to spiral slip stream. I will agree that it plays a part in full scale flying however I have always believed that because our models are smaller, lighter loaded and have much more power to weight that some things just don't affect the models as much. IMO if spiral slip stream does play a part on our models, is such a small affect as to not warrant any real consideration. I think that most guys don't ever fully trim their airplanes which would have a much larger adverse effect then what we are discussing here.

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