RE: Can anyone explain THRUST ANGLES to me?
 

I'm not trying to be hard on the man, my whole point is that this isn't an aeronautical engineering forum, it's a beginners forum. A few of us (me included--I was first) gave the man a decent answer, one that would have sufficed in the real world--with our models. I didn't realize at first that it was a life or death issue to differentiate between P factor and torque. I will defer all further thrust offset questions to those who know....

RE: Can anyone explain THRUST ANGLES to me?
 

I am in no way trying to be hard on him. I want to know what is really happening-- and when, & where, & whether or not it actually applies in practice to models. For many years I though that I understood this stuff quite intimately -- now I'm not so sure -- or maybe I am -- or [sm=spinnyeyes.gif]

RE: Can anyone explain THRUST ANGLES to me?
 

What's wrong with him doctor?

We don't know, they found him at bloody keyboard, and he keeps mumbling...."Not Tourque, P-factor!" Over and over and over.


Man look how you can read the T-Y, G-H, B-N in his forehead!

:D

RE: Can anyone explain THRUST ANGLES to me?
 

[sm=bananahead.gif] [sm=sunsmiley.gif] [sm=idea.gif] [sm=confused.gif][sm=drowning.gif]

RE: Can anyone explain THRUST ANGLES to me?
 

Ok, I apologize for my being hard statement. I'd too would like to know what is really going on. To me, if calculations can show that P-factor alone would account for the amount of right thrust our models typically carry, that pretty much puts the nail in the coffin. Maybe not as the only factor, but the most significant. Is there an easy way to run this proof? Cheers.

RE: Can anyone explain THRUST ANGLES to me?
 

Firtst, lets decide what we are actually discussing --- it started as a general query about thrust angles. That requires a generalized, but technically correct "quickie" answer, specific to model airplanes. 2Slow, Khodges & JohnW took a bite at that, but included some dubious concepts -- lets fix that before proceeding to the more esoteric aspects of the general question.

2) We can address the specific forces driving an uncommanded left turn (P-factor, torque, etc) -- but we need bounding conditions.

a. During take-off roll up to rotation

b. Climb-out & normal flight regimes

3) We can discuss/argue the validity of the spiral slipstream theory

I suggest that MajorTomski leads the discussion (that way the rest of us can keep our powder dry 'till we see the whites of his eyes).

This should be very instructive to the newbs, as well as to the rest of us.

Anyone agree?

OK, so much for that -- who dissagrees?

RE: Can anyone explain THRUST ANGLES to me?
 

Get one of these and all of your thrust angle worries boil down to 2 words:

1.) Action

2.) Reaction


It is easier to learn to fly jets that figure out all of these physics leassons!

RE: Can anyone explain THRUST ANGLES to me?
 

Agreed with 2 slow and brit brats last post and that was the point of my post that was deleted.;)

This isnt a forum to see who has the biggest p...... brain. Its a forum that should be kept simple so that the beginner RC pilot can understand what is being said. Information here is to help BEGINNERS...

And sometines comments that a person can easily demonstrate while at the controls of a plane, are not so great at putting it to type.


When someone start spouting out P factors here in rebuttal to a very basic concept conversation they are belittling the general public whether they realize it, intended or not.

K_I_S_S....

RE: Can anyone explain THRUST ANGLES to me?
 

This is useful and legitimate discussion. If this is not the appropriate forum, then move it. I see no reason to give it up because we might be "belittling the general public."

RE: Can anyone explain THRUST ANGLES to me?
 

I didnt say it wasnt useful. But there is a difference in being helpful and informative and just trying to show other people how smart you are which is precisely what the Physics professor was doing. Im not saying that is what is happening now as the thread has progressed, but the generator of the thread asked a simple question that can be answered in a practical way, simply put, so that anyone can understand, and it was done effectively, although perhaps without making a technically accurate and perfect statement. Sometimes you can get the desired outcome without laying out complicated theories and gory details that overcomplicate things and cloud the simple answer. Whats the old saying?.... "there is more than 1 way to skin a cat"

The 1st couple of posters simply tried to state the answer in simple laymans terms and they got blasted for it. I blasted him for blasting them and MY comment got deleted! lol;) I think its funny since all of this is just discussion anyway. Im sure the Major is a fine fella, I didnt do anything to him I wouldnt do to a real life Buddy that got all high and mighty and a little to big for his britches....:)

It is an interesting topic but it goes WAY beyond helping the original poster. I dunno, he may find the thread interesting though,,, not to mention its a free country with a nice 1st amendment to the Constitution.[8D]

RE: Can anyone explain THRUST ANGLES to me?
 

Major, are you willing to have another go at this?

RE: Can anyone explain THRUST ANGLES to me?
 

Being the original poster, I actually did feel from the first few posts that I understood the basics of trust angles as MikeEast stated below. I thank you guys for your helpful thoughts, although it did go over my head some from there on. With that said, I am still enjoying the post, not necessarily that anyone is being put down but the fact that it is a lot of food for thought, it is interesting how so many can have such different views on things but when it comes down to it, how ever each one of you guys views thrust angles and it's effects, it works for you. Please keep up the post, I am learning as this goes, thanks... [sm=lol.gif]

RE: Can anyone explain THRUST ANGLES to me?
 

I'll have another, hopefully suffciently polite, go at it in the morning.

RE: Can anyone explain THRUST ANGLES to me?
 

OK -- it's morning

I'm posting 2slow's original response to the query for an explanation of thrust angles. He is correct in global concept, but not quite right in a couple of details. Let's fix the details.

MajorTomski, you have the floor -- but keep it terms that a newb will understand.

RE: Can anyone explain THRUST ANGLES to me?
 

SaCal72's question:


the first answer from 2slow2matter:
Which is an absolutely great answer. Unlike most of us posting here on RCU he actually answered all of the points of the question. (That is a complement, not sarcasm.) Most folks on this list type a lot but never get around to answering the original question.

Then khodges went on with :

And John W expanded on this with:

OK, my short chain kicked in when I saw in all three posts a direct or inferred statement that right thrust has something to do with correcting the effects of engine torque on an airplane. As JohnW pointed out in this post:
Aircraft stability is a VERY complex issue. Many of these items cannot be studied independently of one another. Some are sequentially related. For example the way an airplane turns due to torque, and due to propeller thrust forces are completely different with respect to the sequence in which they happen. (please note I'm using the system of reference as if you are the pilot sitting in the cabin)

For torque, the engine turns the prop clockwise and the fuselage reacts by trying to roll counter clock wise. This results in a roll to the left. Now the wing is in a bank and its lift is directed to the left so the airplane begins to turn left. Note the sequence is torque, bank, turn. Bending the axis of the torque from the engine by adding right thrust has virtually no effect on this sequence.

For propeller effects. There is asymmetric airflow over the fuselage and vertical fin, causing the airplane to yaw to the left. Due to the uncoordinated yaw the left wing is now producing slightly less lift than the right wing and the airplane begins to roll to the left. And just as above it begins to turn to the left due to the banked wing. Note this sequence is; asymmetric thrust, yaw, bank, turn. Right thrust moves the asymmetric thrust from the right side of the fuselage to more closely pointing at the center of gravity of the airplane, and eliminates the forces that caused the yaw in the first place.

Take the reference to torque out of all of your answers and they are perfect with respect to the question: what do thrust lines do.


BREAK, other issues next post so my verbosity doesn't run out of room.

RE: Can anyone explain THRUST ANGLES to me?
 

I don't have any problems with that (good job 2slow & thanks MajTom).

Questions? comments?

RE: Can anyone explain THRUST ANGLES to me?
 

OK, I think I understand what you are saying, and I can academically agree with your statements--and will conceed that you definitely know more about the issue at hand than I do. So, I have a question.

I can see where torque would cause an unwanted effect along the roll axis, and not the yaw axis. So, would right thrust still not help that issue? What I mean is, with the engine 180 degrees in relationship to the logitudinal axis of the fusealage, the torque reaction would be directed along the entire length of the fusealage--running from firewall out through the tail, in a straight line. Therefore, the roll reaction to the torque would be having an effect along the entire logitudinal axis.

Whereas, with right thrust built in, the axis of torque reaction would be re-directed to go not through the centerline of the aircraft, but rather to exit the aircraft somewhere along the left side of the fusealage--again, around the CofG. Would this not reduce the rolling effect of the the torque reaction?

I may be all wrong, and can accept any correction in my assumptions.

Also, since we have officially turned this thread into the perverbial "can of worms" :D, could you please post some mathmatical concepts explaing the P factor and what it means, and what it does to aircraft? I am now interested in this conversation. I believe we have gotten this thread back to a civilized coversation, so let's continue the lecture, shall we?

RE: Can anyone explain THRUST ANGLES to me?
 

THIS next bit has nothing to do with answering SaCCaL72's original question

Now, where I started to muddy the waters is when I went off on my own personal crusade against the slipstream spiral theory that has been a SIGNIFICANT part of aviation, both full scale and model since the publication of the book Stick and Rudder

The author of this book first penned the theory that the wind off the propeller is spiraling around the fuselage, striking the vertical fin from the left side, causing a higher angle of attack on the right side, which results in a yaw to the left. In full-scale flight a pilot is required to demonstrate slow flight and a power on stall. In both cases the airplane is at a very high (relative to normal flight) angle of attack and at a very high power setting. Just before the airplane stalls, you have the right rudder peddle stomped as far down as it will go with all the force your leg can put behind it, deflecting full right rudder to overcome the strength of this supposed spiraling air around the fuselage.

Here is where my own crusade against this theory kicks in. This spiral is always illustrated in a side view of the fuselage and the vertical fin. No one ever stops to think of what it is doing to the rest of the plane. If it is taking all my right foot force to hold a heading with the rudder due to a higher angle of attack on the fin. Why am I NOT holding a bunch of aileron to counter the now differential angle of attack over the wings and horizontal stabilizers? Because if the spiral is creating all this force on the fin and rudder should it not also be creating that much more force on both sides of the stab and wing? Which should be a very strong roll to the RIGHT, not left, as the airplane always wants to go.

I came to the conclusion that spiraling slipstream is a myth because it is the only aircraft stability function that is not quantified. Designing the aerodynamics of an airplane is a cookbook plug and crank set of mathematical operations. Take a set of interactive equations. Plug in a bunch of numbers, and it cranks out the answers of area and angle of attack for all of the flight controls. The one thing missing in all those equations is the mathematical definition of the slipstream and how much the fin should be offset to fix it.

And as shown in the photo in post #20 above, when you can see these spirals off the prop, they are going the wrong way to support the myth.

So what’s the answer? My personal theory, and I haven’t fully cooked it up yet, is that the airflow doesn’t spiral around the fuselage. But rather at high angles of attack and high power settings, due to the differential thrust called P factor, it is simply moving faster down the right side of the fuselage. This too creates a higher AOA on the fin and rudder and causes left yaw. But it also causes locally higher lift on the right wing and horizontal stab, which causes left roll, what the airplane actually does.

Again I most humbly apologize if I have offended any of you. Offending any of you was never my intent. I simply get a little too carried away in my outlook on aeronautical definitions.

By the way 2slow2matter, when I teach folks to fly RC it is the KISS principle. I only teach the mechanical aspects of how to do what with the controls to get the airplane to do what you want it to do. Never, ever, do I get into a discussion of aerodynamics or why, to avoid getting into this kind round-and-round discussions.

Thank you all for a chance to share.

SaCCal72, did you get an answer?

T

RE: Can anyone explain THRUST ANGLES to me?
 

Aha -- Bernoulli strikes again!! Interesting theory, & plausible as well.

However, this is where we part company. Go back to the torque rings and think about what you are seeing. You are looking at the "track" that the prop tips are following as the prop advances through the air (it doesn't matter if the plane is stationary, the props are still advancing through the air). Keep in mind that they are driving the slipstream, rather than being driven by it. What you are seeing is an interconnected series of loci showing where the prop tip was a few moments previously. You see exactly what you should see in a prop turning clockwise. The slipstream is indeed swirling from left to right, as the prop tip is moving from left to right.

In the case of the (relatively) absent roll in the high AOA approach to a power on stall, you are now faced with the contention surrounding fluid dynamics vs Newtonian physics in explaining the effects of the swirling slipstream on the wings of the aircraft.

Your theory is dependent upon conventional fluid dynamics, as represented by Bernoulli's equation. If you view it through Newtonian physics, a different picture could emerge, at least in certain circumstances. Think of the slipstream swirling from left to right (it can't go in any other direction) & visualize it impacting the flat underside of the inboard left wing -- action & reaction. At the same time, visualize it impacting the curved upper surface of the inboard right wing -- again action & reaction -- but less reaction force as the air spills more easily off the curved surface.

This represents a moderate right-roll force that counters the left roll torque reaction force, which combines with the roll resistant normal lifting forces in the outer wing pannels -- ergo no roll untill stall, wherein the total loss of conventional lift permits the torque forces to overcome the weaker spiral slipstream effects.

RE: Can anyone explain THRUST ANGLES to me?
 

Britbrat wrote: This is off subject but I feel I must make a statement:
Conventional fluid mechanics IS Newtonian physics! Nothing less nothing more.
All the equations usually associated with fluid mechanics and aerodynamics are derived from basic Newtonian principles even though some engineers seem to believe otherwise.

/Red B.

RE: Can anyone explain THRUST ANGLES to me?
 

Well if you don't like that one, here is another much simpler explanation for lack of left roll until stall -- the (normally) proverse rudder-roll couple is offsetting the torque reaction, thus preventing, or reducing the left roll. In aircraft that exhibit adverse rudder-roll, they will indeed roll left prior to stall.

I have more.

RE: Can anyone explain THRUST ANGLES to me?
 

Yes that's true -- lots of them.

RE: Can anyone explain THRUST ANGLES to me?
 

If I may interject for a moment, I have been reading this post and I am utterly amazed at how much you guys know, how much knowledge you all have, AND THAT ISN'T SARCASM, I REALLY MEAN IT. It makes common folk like me realize how much we take for granite for some of the conveniences we have, we just buy a ticket on USAirways or whatever and expect to get to where we are going, NOT UNDERSTANDING that there are people out there who have to know how all this works. There are people out there who actually thought this stuff up and figured it all out. It's amazing, just a big eye opener. I don't claim to be dumb or anything, but it is just cool to see. A LITTLE OFF THE SUBJECT of thrust angles; I am a Biomedical Technician for the VA and I repair and maintain medical equipment and life support equipment and many people think my job is important, and it is, but it is people like you guys who invent the stuff I repair, and that to me is far more important. Although I do have to say that sometimes engineers who design some of the equipment don't have the end user or technician in mind as it can be a nightmare at times to repair. Thanks for listening to my 2 cents...

RE: Can anyone explain THRUST ANGLES to me?
 

MajorTomski wrote: The spiraling slipstream is not a myth although when graphically represented in pictures, the twist angle is often very exaggerated.
NACA has investigated the magnitude of the twist in the propeller slipstream experimentally. If you look up p. 9 and 10 in the [link=http://naca.larc.nasa.gov/digidoc/report/tr/12/NACA-TR-712.PDF]NACA-TR-712[/link] technical report you will find the result of an experimental measurement of the twist of the propeller slipstream. Twist does exist!

In this [link=http://pdf.aiaa.org/jaPreview/JA/1987/PVJAPRE45440.pdf]article[/link] from NASA Ames the effect of the spiraling slip stream on the stalling behaviour of light aircraft is experimentally investigated.

/Red B.

RE: Can anyone explain THRUST ANGLES to me?
 

Ahh but... The swirl theory is based on the assumption that the propeller imparts energy to the air particles that causes them to move in the same direction as the propeller. This is the source of the clockwise rotation. The problem with this is that it violates airfoil theory. Air particles moving over an airfoil are forced down and AFT. To make the slipstream work they'd have to go down and FORWARD! (neat trick if you can do it) I have access to a book written before Stick and Rudder that points to a mathematical solution showing that the airflow from the propeller is a winding sheet bounded by the propeller root, or the fuselage, and that vortex we see in the picture. Again that sheet has the air flow running around the fuselage in a counter clockwise path. Or at best straight back from the prop. Again no swirl in the slipstream. Then again try to find a shot of an aerobatic airpane with smoke on in just a straight high G pull up. This is where the slipstream says stuff should be wrapping around the fuselage. Yet I've been unable to find anything like that.