Spiral slip Stream is it real ?
03-21-2013, 10:05 AM
#51
Senior Member
RE: Spiral slip Stream is it real ?
ORIGINAL: drac1
That's exactly what i was going to say Matt. You are spot on.
While there would be some spiraling of airflow as it comes directly off the prop, by the time it travells down the nose and over the wing (which would act like vanes and straighten the airflow), by the time it reaches the tail i can't see how the airflow would be still spiralling. Just as with contra rotating, how can the airflow be straight? The rear prop would still spiral the airflow albeit in the opposite direction. I think that torque is the biggest cause which is being confused with spiralling airflow. That's why contras don't need right thrust, props turning in the opposite direction cancel out the torque effect not spiralling airflow.
Of course this is just my opinion as i see it.
ORIGINAL: MTK
While there would be some spiraling of airflow as it comes directly off the prop, by the time it travells down the nose and over the wing (which would act like vanes and straighten the airflow), by the time it reaches the tail i can't see how the airflow would be still spiralling. Just as with contra rotating, how can the airflow be straight? The rear prop would still spiral the airflow albeit in the opposite direction. I think that torque is the biggest cause which is being confused with spiralling airflow. That's why contras don't need right thrust, props turning in the opposite direction cancel out the torque effect not spiralling airflow.
Of course this is just my opinion as i see it.
A contra cancels out a large portion of the tork and P forces attributed to the props. Motor or engine tork is still there.
Relax, crankshaft tork is relatively minor in models. Although the larger IMAC models can take advantage enough of crankshaft/prop tork to do real tork rolls (meaning aileron unassisted) at idle or a hair above. At idle, there is very little reactive tork from pulling in and throwingback air (or precession for that matter). Nowhere near as easy to do one of them Real Tork Rolls with a 2 meter Pattern model or smaller.
BTW- I do believe that the spiralling air coming from the prop is massive enough (meaning, carries force) far enough down the fuses of most models to cause significant trimming issues. I'm not sure if I mentioned it here (too lazy to go back and read my scribbles), but one experiment I have done is to add cannards immediately behind the prop. With the engine typical offset (right thrust), the model went right, following the thrust vector.
I have not reset the offset to zero and try the cannardexperiment again, but it is an experiment begging to be done. If it works as expected, cannards immediately behind the prop of a 2 meter pattern model can be a poor man's contra prop. I will do the experiment but will report in the Pattern column.....
03-22-2013, 01:52 AM
#54
RE: Spiral slip Stream is it real ?
[quote]ORIGINAL: Quikturn
This has been discussed in another thread so I thought I would copy and paste it here.
RE: Is left yaw induced by fore or aft force? - 10/16/2012
This is an interesting thread and I'd like to add to it by listing and talking about the 5 left turning tendencies in single engine airplanes.
1. P-Factor - is the asymmetrical thrust produced by the propeller. Every airplane needs some positive angle of attack (AOA) in order to fly and this AOA (angle of the wing vs relative wind that the airplane flies in) gives the propeller blade on the downstroke a higher AOA that the propeller blade on the upstroke. Since the propeller turns clockwise as seen from behind more thrust is produced on the right side causing the airplane to turn left. P-factor is pronounced at high AOA, low speed and high power settings. I doubt there is much p-factor during a perfectly vertical climb because AOA is minimal and gravity is at the tail. However, if you're at full power and pulling vertical you'll likely have p-factor.
A couple of questions.
1. How does the AOA of the wing change the AOA of the prop? (the AOA on the prop blade is the pitch).
2. How can the downward prop blade have a different AOA (pitch) than the upward blade?
03-22-2013, 01:20 PM
#55
RE: Spiral slip Stream is it real ?
drac1, first imagine the airflow as a perfectly horizontal component. Next, hold an airplane or even a propeller with a pencil through it at about a 45 degree angle (pitch up). Look at the propeller from each side and compare blade angles compared to the horizontal airflow. You will notice the propeller on the downstroke has a larger bite (higher AOA) and the propeller on the upstroke has a smaller (than normal) AOA.
If you have a flight sim you can play with this by practicing low/slow flybys. I like the P-51 with flaps lowered. During slow flight you need a touch of right rudder to keep the airplane flying straight. If you don't use rudder the airplane will want to veer off to the left or you could roll to the right slightly. As you add power you will need to increase right rudder to keep the airplane fling straight.
Now, how much is due to P-Factor and/or spiraling slipstream? Who knows, who cares. All you need to know is that right rudder is needed during slow (high AOA) flight.
Hope this helps.
If you have a flight sim you can play with this by practicing low/slow flybys. I like the P-51 with flaps lowered. During slow flight you need a touch of right rudder to keep the airplane flying straight. If you don't use rudder the airplane will want to veer off to the left or you could roll to the right slightly. As you add power you will need to increase right rudder to keep the airplane fling straight.
Now, how much is due to P-Factor and/or spiraling slipstream? Who knows, who cares. All you need to know is that right rudder is needed during slow (high AOA) flight.
Hope this helps.
03-22-2013, 06:43 PM
#56
Senior Member
RE: Spiral slip Stream is it real ?
ORIGINAL: Quikturn
drac1, first imagine the airflow as a perfectly horizontal component. Next, hold an airplane or even a propeller with a pencil through it at about a 45 degree angle (pitch up). Look at the propeller from each side and compare blade angles compared to the horizontal airflow. You will notice the propeller on the downstroke has a larger bite (higher AOA) and the propeller on the upstroke has a smaller (than normal) AOA.
If you have a flight sim you can play with this by practicing low/slow flybys. I like the P-51 with flaps lowered. During slow flight you need a touch of right rudder to keep the airplane flying straight. If you don't use rudder the airplane will want to veer off to the left or you could roll to the right slightly. As you add power you will need to increase right rudder to keep the airplane fling straight.
Now, how much is due to P-Factor and/or spiraling slipstream? Who knows, who cares. All you need to know is that right rudder is needed during slow (high AOA) flight.
Hope this helps.
drac1, first imagine the airflow as a perfectly horizontal component. Next, hold an airplane or even a propeller with a pencil through it at about a 45 degree angle (pitch up). Look at the propeller from each side and compare blade angles compared to the horizontal airflow. You will notice the propeller on the downstroke has a larger bite (higher AOA) and the propeller on the upstroke has a smaller (than normal) AOA.
If you have a flight sim you can play with this by practicing low/slow flybys. I like the P-51 with flaps lowered. During slow flight you need a touch of right rudder to keep the airplane flying straight. If you don't use rudder the airplane will want to veer off to the left or you could roll to the right slightly. As you add power you will need to increase right rudder to keep the airplane fling straight.
Now, how much is due to P-Factor and/or spiraling slipstream? Who knows, who cares. All you need to know is that right rudder is needed during slow (high AOA) flight.
Hope this helps.
I'll see your bucketopropwash and raise you a bucketofbovinescat
03-22-2013, 09:01 PM
#58
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RE: Spiral slip Stream is it real ?
Just about everything's been said, for those who want to review the thread.
For the rest, talk amongst yerselves. [:@]
[:@]
03-23-2013, 03:36 AM
#59
RE: Spiral slip Stream is it real ?
ORIGINAL: Quikturn
drac1, first imagine the airflow as a perfectly horizontal component. Next, hold an airplane or even a propeller with a pencil through it at about a 45 degree angle (pitch up). Look at the propeller from each side and compare blade angles compared to the horizontal airflow. You will notice the propeller on the downstroke has a larger bite (higher AOA) and the propeller on the upstroke has a smaller (than normal) AOA.
If you have a flight sim you can play with this by practicing low/slow flybys. I like the P-51 with flaps lowered. During slow flight you need a touch of right rudder to keep the airplane flying straight. If you don't use rudder the airplane will want to veer off to the left or you could roll to the right slightly. As you add power you will need to increase right rudder to keep the airplane fling straight.
Now, how much is due to P-Factor and/or spiraling slipstream? Who knows, who cares. All you need to know is that right rudder is needed during slow (high AOA) flight.
Hope this helps.
drac1, first imagine the airflow as a perfectly horizontal component. Next, hold an airplane or even a propeller with a pencil through it at about a 45 degree angle (pitch up). Look at the propeller from each side and compare blade angles compared to the horizontal airflow. You will notice the propeller on the downstroke has a larger bite (higher AOA) and the propeller on the upstroke has a smaller (than normal) AOA.
If you have a flight sim you can play with this by practicing low/slow flybys. I like the P-51 with flaps lowered. During slow flight you need a touch of right rudder to keep the airplane flying straight. If you don't use rudder the airplane will want to veer off to the left or you could roll to the right slightly. As you add power you will need to increase right rudder to keep the airplane fling straight.
Now, how much is due to P-Factor and/or spiraling slipstream? Who knows, who cares. All you need to know is that right rudder is needed during slow (high AOA) flight.
Hope this helps.
While performing a high alpha 3D manouvre when the aeroplane is not moving forward very much, i can see how the AOA of the prop blades would be different left side to right in relation to airflow. But when the plane is moving forward during normal flight, wouldn't the airflow be flowing directly down the airframes thrust line, making the left and right side blades AOA pretty much equal?
I have a Hangar 9 P 47 with a DA 50. On a slow fly by with full flaps and the Dunlops dangling, the aeroplane tracks straight down the strip with no rudder input. Even when accelerating i have not noticed the need for rudder input.
03-23-2013, 06:18 AM
#60
Senior Member
RE: Spiral slip Stream is it real ?
ORIGINAL: drac1
I have a Hangar 9 P 47 with a DA 50. On a slow fly by with full flaps and the Dunlops dangling, the aeroplane tracks straight down the strip with no rudder input.
I have a Hangar 9 P 47 with a DA 50. On a slow fly by with full flaps and the Dunlops dangling, the aeroplane tracks straight down the strip with no rudder input.
Remember when you mounted that engine on the firewall? If I remember correctly, all my H9 warbirds had downthrust and right thrust designed into the firewall.
There are usually more details than one or two to most aerodynamic conundrums very often.
03-23-2013, 09:36 AM
#61
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RE: Spiral slip Stream is it real ?
While performing a high alpha 3D manouvre when the aeroplane is not moving forward very much, i can see how the AOA of the prop blades would be different left side to right in relation to airflow. But when the plane is moving forward during normal flight, wouldn't the airflow be flowing directly down the airframes thrust line, making the left and right side blades AOA pretty much equal?
Only in straight-and-level flight is the prop AOA equal. In even a shallow climb, there is a left-turn/yaw tendency with conventional props due to 'asymmetric disc loading'. The opposite is true in a descent; it becomes a right-turn/yaw. This is true in model and full-size aircraft.
Part of the problem is our models are so over-powered, and the control surfaces are so over-sized, we can correct without realizing it. Go to a pattern-flying thread and read about how they dial-in a plane against all these forces.
Many full-size planes have offset vertical fins, and right/down thrust to counteract these forces so that, at cruise speed, no left/right trim is needed. At slower or faster speeds, the pilot is expected to compensate manually.
03-24-2013, 06:46 AM
#62
Senior Member
RE: Spiral slip Stream is it real ?
Often times, when a plane is in straight and level flight, the prop will not be perpendicular to the line of flight. It would depend on the lift needed, the AOA of the wing to provide that, and the AOI designed into the plane. It would also depend on the thrust line of the engine.
Sorry if this seems like irrelevant prattle, but I needed a test message and wanted to make one that did in fact apply to the point in question.
Consider that small thrust angles are sufficient for their purpose. They often exist in designs, yet are so subtle are hard to see. Or they are like those used in the Grumman F6F.
So too are rudder/fin offsets as used on the Me109s.
Sorry if this seems like irrelevant prattle, but I needed a test message and wanted to make one that did in fact apply to the point in question.
Consider that small thrust angles are sufficient for their purpose. They often exist in designs, yet are so subtle are hard to see. Or they are like those used in the Grumman F6F.
So too are rudder/fin offsets as used on the Me109s.
03-25-2013, 07:28 AM
#65
Senior Member
RE: Spiral slip Stream is it real ?
ORIGINAL: Quikturn
I have a bucket of prop wash.
ORIGINAL: rmh
anybody want to trade a spiral prop flow for a pair of downwind turns?
I'll throw in a high lift , no drag wing -
anybody want to trade a spiral prop flow for a pair of downwind turns?
I'll throw in a high lift , no drag wing -
03-25-2013, 09:11 AM
#66
RE: Spiral slip Stream is it real ?
ORIGINAL: MTK
DaCRock, you might want to remove this one. Regardless, I'm dunn with your nonsense
ORIGINAL: Quikturn
I have a bucket of prop wash.
ORIGINAL: rmh
anybody want to trade a spiral prop flow for a pair of downwind turns?
I'll throw in a high lift , no drag wing -
anybody want to trade a spiral prop flow for a pair of downwind turns?
I'll throw in a high lift , no drag wing -
Damn dude. You sure know how to make friends. We were intertwining aviation humor with the thread topic and you start insulting people.
It's called a JOKE!
You should go out and get a sense of humor. And while you're at it, get me another roll of flight line.
03-25-2013, 09:51 AM
#67
Senior Member
RE: Spiral slip Stream is it real ?
People, this slip stream discussion has gone around in circles a few times now. That's often the case on the internet.
Please don't lose patience with the discussion you don't agree with. Nobody wins when things get personal. When you have something for just one other member, perhaps you should think about whether or not it's appropriate to the topic, is appropriate to say to someone face-to-face, and especially if it's within the RCUniverse rules.
When you discover you're writing a post TO another member, or especially ABOUT another member, think twice about what you've written before hitting that OK button. Chances are good your post is offtopic. There's also a good chance it's against RCU rules.
Please don't lose patience with the discussion you don't agree with. Nobody wins when things get personal. When you have something for just one other member, perhaps you should think about whether or not it's appropriate to the topic, is appropriate to say to someone face-to-face, and especially if it's within the RCUniverse rules.
When you discover you're writing a post TO another member, or especially ABOUT another member, think twice about what you've written before hitting that OK button. Chances are good your post is offtopic. There's also a good chance it's against RCU rules.
03-26-2013, 01:22 PM
#72
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RE: Spiral slip Stream is it real ?
More posts deleted....
I'll echo DaRock's post above to suggest that if some of you don't want to play nice then please find another thread. SOME folks want to actually discuss this stuff and do it in a reasonably serious manner. If you tend to think that it's pointless or flogging a dead horse then just move along to some other topic. For some folks this is all new and interesting.
I'll echo DaRock's post above to suggest that if some of you don't want to play nice then please find another thread. SOME folks want to actually discuss this stuff and do it in a reasonably serious manner. If you tend to think that it's pointless or flogging a dead horse then just move along to some other topic. For some folks this is all new and interesting.
03-26-2013, 02:58 PM
#73
RE: Spiral slip Stream is it real ?
ORIGINAL: Quikturn
Some more evidence. Notice more soot on the right wing?
Some more evidence. Notice more soot on the right wing?
03-26-2013, 03:24 PM
#74
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RE: Spiral slip Stream is it real ?
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?
Somewhat, but the soot in the exhaust flow diffuses such that it spreads all over.
I had a rather odd job assigned years ago in a Piper Cheyenne II twin turboprop. A local sign company wanted to test their new design of wind-resistant signs and mounts, the kind used outside gas stations. They wanted to put the signs behind the plane and video the results at different speeds. This involved lots of time at idle with the props at zero thrust during their setup, then they would stand aside and I would bring the power up in stages.
The signs performed very well and, at the end of 2 days' testing, they wanted maximum power tests. We rarely do full-power runups for many reasons, but I was surprised that the Cheyenne would hop over all 3 standard wood chocks. We called for large rubber airliner chocks and they did the trick. We generated wind speeds of just over 200 mph that day, with the signs fully failing at 150 or so.
The long periods at idle and low thrust were hard on the left sides of the nacelles and left aft fuselage. Spiral was very evident from that exercise.
As for anyone offended by the cartoon, you know the old saying about those who can't take a joke..., This is a forum about toy airplanes, not brain surgery.
This is a forum about toy airplanes, not brain surgery.
03-27-2013, 04:52 AM
#75
RE: Spiral slip Stream is it real ?
well the prop bites off chunks at an angle but the resultant flow quickly realigns with the ambient air
air does have mass -and the wannabe physic majors will say " an object in motion" etc., but real world the spiral quickly dies . a spinning mass tends to return to a straight line - unless tethered- Now if we are talking abou the moon spinning around the earth - we get into a different set of rules -involving gravity
(my next slide please)
air does have mass -and the wannabe physic majors will say " an object in motion" etc., but real world the spiral quickly dies . a spinning mass tends to return to a straight line - unless tethered- Now if we are talking abou the moon spinning around the earth - we get into a different set of rules -involving gravity
(my next slide please)