Answer to Statement made on Building Board

[Serge_Krauss]

Centrifugal force over head? Come on. The Centrifugal force overhead is less than gravity. Guess I never learn simple physics.

'not sure whether Robert was pulling our legs, but... Let's take a look. Of course, a model's speed is reduced in climb: so let's look at both ends.

First, flying 5-sec laps on 70' lines equates to about 88 ft/s or 60 mph. If that speed were maintained directly overhead in a wingover, the Centripetal acceleration would be...

V²/R = 88²/70 = 110.63 ft/sec²

Since the acceleration of gravity is 32.2 ft/sec², that's 110.63/32.2 = 3.4 g's.

So the CF (centrifugal force = - centripetal force) on the lines at the top of the circle would be 3.4 times the weight of the model.

Subtracting weight from line tension overhead (3.4 g's - 1.0 g's = 2.4 g's), a 60-oz model would then have a line tension of 2.4 x 60 oz = 144 oz, even without aerodynamic or thrust effects.

In order for the weight to just equal the CF, the plane's speed will have to have been reduced during climb to 37 mph, or 54% of it's level-lap value.

That's because for V²/70' to equal 32.2 Ft/sec², v = square root of (32.2 x 70) = 47.48 ft/sec.

So a successful stunter will need to be flying faster than this.

Three degrees of out-thrust would only add (sin 3^o =) 5% of the thrust to line tension, if it actually did produce 3 degrees of out-thrust, after altering the yaw angle. It would reduce CF by about 0.3%.

So CF far overshadows anything out-thrust could provide. If the plane is flying only at marginal speed, what little it adds might help one over the top. If anyone wants to quantify thrust here, be my guest.

SK

Edited to remove dumb error(s).

[Serge_Krauss]

I should add that if thrust ceases overhead, drag rapidly reduces the model's speed. It may well lose its already reduced CF tension quickly enough to fall into the circle, especially if a forward c.g. has already started to conspire with aero effects to direct the nose downward. You might ask me about any experience I have here, but two or three wrecks in my basement make me "reluctant" to comment further.

SK

[Dick Pacini]

Serge, you really shouldn't fly in your basement.

[Serge_Krauss]

'must be the butyrate fumes...

[RC Storick]

Here is a easy experiment. 2 planes on with 0 Motor off set and one with 3 degrees. Do some overhead eights and tell me which one you don't have to do squats to keep line tension both fly 5.5 lap speeds. Sure you have some line tension at warp 9 but at realistic speeds 5.4-5.5 a little less. Pie are round cornbread are square. Like Igor said to Brett where and what do those numbers mean?

[Doug Moon]

I dont use any offset and at 5.65-5.85 my 68.5oz pig pulls hard overhead. No squats here.


Of course my trim setup is quite different...

[Brett Buck]

Here is a easy experiment. 2 planes on with 0 Motor off set and one with 3 degrees. Do some overhead eights and tell me which one you don't have to do squats to keep line tension both fly 5.5 lap speeds. Sure you have some line tension at warp 9 but at realistic speeds 5.4-5.5 a little less. Pie are round cornbread are square. Like Igor said to Brett where and what do those numbers mean?

  What the heck are you talking about?  He's telling you what the centrifugal force and line tension are overhead, as you (sort of) asked. The engine offset gives you virtually nothing in terms of line tension. It's roughly the thrust times the offset in radians. The thrust is about 2 lbs, the offset in radians is (3 degrees/57.296) or about 0.052, so the added line tension from thrust offset alone (absent any yaw angle) is ~0.1 lbs. That's nothing, what you really should be getting is around 6-7 lbs depending on how much it slowed down.

   Again, this is not speculation or a matter of opinion, it's dead simple physics, and mocking it won't change the situation.

   If you don't have enough overhead tension, your airplane is out of trim or you are flying it too slowly. We can certainly help work on that, if you are willing to listen.

    Brett

[RC Storick]

I have plenty thanks. I do not like flying at warp 9 and the airplane only weighs 55 ounces not and extra 10 for added line tension.

[Howard Rush]

I'm with Robert on this one (the engine offset part).  Engine offset gives lots more side force than thrust * sin of the offset.  It turns a stream of air.  I learned this by calculating thrust * sin of the offset, then flying combat planes with different offsets.  I'm not saying that engine offset is a free lunch for getting line tension overhead in a stunt plane, though.  I doubt if it will come anywhere close to making up the airplane weight deficit in line tension overhead in a stunter.

[RC Storick]

I'm with Robert on this one (the engine offset part).  Engine offset gives lots more side force than thrust * sin of the offset. 

  Yeah Someone agreed. 

[Air Ministry .]

some people don't accede the these theories . PARTICULARLY this one " due to the swirling nature of the flow induced by the propeller "

" 2. Inflow Factors
 

A major complexity in applying this theory arises when trying to determine the magnitude of the two flow components V0 and V2. V0 is roughly equal to the aircraft's forward velocity (Vinf) but is increased by the propeller's own induced axial flow into a slipstream. V2 is roughly equal to the blade section's angular speed (Wr) but is reduced slightly due to the swirling nature of the flow induced by the propeller. To calculate V0 and V2 accurately both axial and angular momentum balances must be applied to predict the induced flow effects on a given blade element. As shown in the following diagram the induced flow components can be defined as factors increasing or decreasing the major flow components. "

http://www.southampton.ac.uk/~jps7/Aircraft%20Design%20Resources/Sydney%20aerodynamics%20for%20students/propeller/prop1.html

the thrustline and rudder configuration in relationship to the rotation drift of the slipstream aft of the propeller . Thuss a straight rudder would have effective ' inset ' .
P 51 empennage geometry & Spitfire pilots notes , in regard to inflight trim give indication to considerations in regard to this . A bit of weight ( of Air ) falling onto the
vertical Stab. will hold the nose up - knife edge ( top of wingover ) . Hence the currant popularity of left hand propellors .

[Brett Buck]

I'm with Robert on this one (the engine offset part).  Engine offset gives lots more side force than thrust * sin of the offset.  It turns a stream of air.  I learned this by calculating thrust * sin of the offset, then flying combat planes with different offsets.  I'm not saying that engine offset is a free lunch for getting line tension overhead in a stunt plane, though.  I doubt if it will come anywhere close to making up the airplane weight deficit in line tension overhead in a stunter.

   If the engine quits dead overhead, does it  instantly lose all the line tension? Because that's what Sparky said.

     Brett

p.s. note the caveats about  the yaw torque. Thrust vectoring is simple enough to figure if you know the angle. I qualified it with the proviso that the is flying tangent to the circle. As you add offset you also yaw the airplane out, which adds to the thrust angle. So instead of 10 degrees of offset, you could easily get 20, 10 from the engine relative to the airplane, and 20 more from the fact that you have a large nose-out yaw torque that adds to the yaw angle, particularly overhead.

   On a combat plane, that doesn't have much ill effect. You won't like what it does to a positively-yaw-stable stunt plane. In fact, it can easily have the effect of reducing the line tension rather than increasing it, try any method of yawing the airplane outboard like moving the leadouts aft and adding rudder offset, and see how those 4-leaf entries go. But you already know...

     The notion that you need to, or should, rely on getting more than centrifugal force, is not one with which I subscribe.

    edit - serge and I are not collaborating...

  

[Serge_Krauss]

Hey, Hey, Hey,...(He shouts into the abyss)!

You're missing the biggest "elephant" in this room, one that has been mentioned in about all these threads. That is that the out-thrust affects the yaw angle. You must direct your thrust line (that's line of thrust - extended back) so that it passs through or inside of the c.g. of the plane. If you do not have the plane trimmed to fly tangent to the circle, you may well be balancing several forces against each other and correcting with out-thrust. You may not and quite probably do not even have three degrees of actual out-thrust, as your fuselage is aligned. I do not think that anyone is seeing this from inside or outside the circle. IOW, three degrees of shaft to the fuselage does not directly translate to three degrees of thrust offset to the circle anyway.

SO...the argument goes nowhere here, if you don't even know what direction the fuselage points with thrust, P, and precession effects operating on a plane without the "ins" and "outs" of rudders, thrustlines, and other assymetries, only some of which are actually (accidentally or not) built into the plane and power train! You have to have some neutral starting place, before you start talking about whether any given amount of engine angularity has some effect.

Talking about removing out-thrust from a plane trimmed to fly with it is not relevant to a discussion of whether out-thrust is useful in general. Of course a plane trimmed to fly with out-thrust will be out of trim without it.

SK

[RC Storick]

Brett you take everything to literal. IT WAS A EXAGGERATED  STATEMENT everyone but the smartest man on the planet gets it. You are arguing against something you said you use, If I remember right it was 2 degrees. DO you just like to argue?

[Brett Buck]

Brett you take everything to literal. IT WAS A EXAGGERATED  STATEMENT everyone but the smartest man on the planet gets it. You are arguing against something you said you use, If I remember right it was 2 degrees. DO you just like to argue?

   What in the world are you talking about now? I wasn't arguing against using offset. I even told you to use more if you have more wing asymmetry - and gave an example, and why you need it. The point is that it's got nearly nothing to do with the overall line tension.

   I couldn't tell if it was serious not. Apparently others couldn't tell, either. I have no idea what you know or don't know about model airplanes or what makes them work aside from what you are posting.

     Brett

[RC Storick]

I do use wing asymmetry , and as to what I know, hum after over 45 plus years I guess I might know something. Especially this airplane that I have built for the last 25 years in different configurations. I am not sure but somewhere someone made mention of 4 a year that's a 180 airplanes (I think its more) but that number is a start.

[Mark Scarborough]

Here is a easy experiment. 2 planes on with 0 Motor off set and one with 3 degrees. Do some overhead eights and tell me which one you don't have to do squats to keep line tension both fly 5.5 lap speeds. Sure you have some line tension at warp 9 but at realistic speeds 5.4-5.5 a little less. Pie are round cornbread are square. Like Igor said to Brett where and what do those numbers mean?

remember each airplan is a system, and there will be variences between,, to accuratly asses whether its just the offset,, you MUST control all other variables to insure they are comparable,,
to take one thing, sense a change between several airplanes,, its simply not accurate,,
but,, Robert,, do what you do,, I do what I do,, I will continue to read what everyone writes,, eat the meat leave the bone

[Mike Keville]

. . . If the engine quits dead overhead, does it  instantly lose all the line tension? . . .
     Brett

==================================================================

In one case that I recall, there's no question about it!

Many years ago, 1990 or so, I was flying Lou Crane's small, very light 'El Conquistador'/Fox .35, when the engine suddenly quit at the very top of the Overhead 8's.

It fell like a brick!  Nothing I could do to save it.  Ran back quickly, gave it 'down' then 'up'.....no response.  Model fell straight down and splattered.

Yes, I felt like a moron - but the fact is, when that Fox quit, it was like the model was shot out of the air....dropped like it was on an elevator.

Prior to that unfortunate moment, line tension was outstanding...a beautiful flight, right up until......

[Howard Rush]

That's an advantage of combat planes.  When the engine quits, the airplane still has enough kinetic energy to get out of trouble.  You don't want a stunt engine to quit on the exit of the clover.

[Igor Burger]

I'm with Robert on this one (the engine offset part).  Engine offset gives lots more side force than thrust * sin of the offset.  It turns a stream of air.  I learned this by calculating thrust * sin of the offset, then flying combat planes with different offsets.  I'm not saying that engine offset is a free lunch for getting line tension overhead in a stunt plane, though.  I doubt if it will come anywhere close to making up the airplane weight deficit in line tension overhead in a stunter.

It is not thrust * sin, but is is STATIC thrust * sin and it gives much better numbers. I saw some research about that. If I remember well, then static out-thrust (means at zero sped) is obviously static thrust * sin, but if prop moves forward, the thrsut fall down to aproximately half of static thrust * sin at pitch speed. we fly aproximately at pitch speed so 1/2 of static thrust * sin offset is good value for estimation.

All taht means that thrust vecor os moving prop not needs to be coaxial (paralel) with prop shaft.

[Igor Burger]

....

perfect, and now try it for our indoos - lap time 5.3, weight 200g and line length 5m :- ))))))))))

[Igor Burger]

Yes, I felt like a moron - but the fact is, when that Fox quit, it was like the model was shot out of the air....dropped like it was on an elevator.

It all dpends on line length and lap time. Serge posted equations, so it is easy to check that small models with short lines will have problem with line tension overhead and the only help is offset ... and as was pointed not only motor offset, but also fuselage can make lift if angled. That is the only way how small models can ly at usefull lap times, while large models on long lines have enough line tesion from cetrifugal force.

so the statement shoud be "the line tension overhead is less gravity", not " the line tension overhead is less THAN gravity"  :-)

Edit: ok, thanks Matt, so then that then is repared 

[Air Ministry .]

so the statement shoud be "the line tension overhead is less gravity", not " the line tension overhead is less THEN gravity"  :-)

Thats Than Then . 

[RC Storick]

==================================================================

In one case that I recall, there's no question about it!

Many years ago, 1990 or so, I was flying Lou Crane's small, very light 'El Conquistador'/Fox .35, when the engine suddenly quit at the very top of the Overhead 8's.

It fell like a brick!  Nothing I could do to save it.  Ran back quickly, gave it 'down' then 'up'.....no response.  Model fell straight down and splattered.

Yes, I felt like a moron - but the fact is, when that Fox quit, it was like the model was shot out of the air....dropped like it was on an elevator.

Prior to that unfortunate moment, line tension was outstanding...a beautiful flight, right up until......

Mike according to the PISSISISTS it should have weighed twice as much to fall half as fast. Makes sense right? Not!

[Ted Fancher]

Several of us witnessed an engine quitting in the overhead, virtually directly over the head of John Simpson at a King Orange in Starke, a few years back. Seems the glow plug gave out at a critical moment and it came straight down and almost hit John. Going into the wind as well, so this played a part in the sudden stop of the plane.

Inertia is good for something.  Good old mass in motion.  

Throw a golf ball as hard as you can and then do the same with a ping pong ball.  Just guessing here but I bet the golf ball goes farther.  

They leave your hand at the same speed and have roughly the same frontal area thus the same drag yet one goes a long ways and slows gradually, the other goes hardly anywhere (relatively) and slows abruptly.  The same thing applies to John's airplane.  Add a pound of weight to it, get it going the same speed, kill the engine and it will slow less abruptly and continue to provide sufficient tension (assuming both experiments are run with zero to light winds) to remain recoverable.

Ted

[RC Storick]

Yep drop a golf ball and a ping pong ball at the same time from the same distance and let us know which one hits the ground first.

What weighs more a pound of feathers or a pound of sand? Just messing with ya TED

[Ted Fancher]

Oh, yea...a p.s.

That headwind stuff.  Inertia is a function of speed relative to a fixed point, i.e.  "groundspeed".  Going 50MPH "airspeed" into a 30MPH headwind results in a groundspeed of 20MPH and, IIRC, inertia increases/decreases as a function of velocity squared, ergo, you've lost a ton of inertia if the engine stops abruptly dead into a strong wind...no matter if in the intersection of the overhead or in level flight.  The survivability rate in level flight will be predictably larger than in the overheads!

Ted

[Tim Wescott]

Oh, yea...a p.s.

That headwind stuff.  Inertia is a function of speed relative to a fixed point, i.e.  "groundspeed".  Going 50MPH "airspeed" into a 30MPH headwind results in a groundspeed of 20MPH and, IIRC, inertia increases/decreases as a function of velocity squared, ergo, you've lost a ton of inertia if the engine stops abruptly dead into a strong wind...no matter if in the intersection of the overhead or in level flight.  The survivability rate in level flight will be predictably larger than in the overheads!

Your conclusions are correct, you are misremembering the meaning of inertia.  Inertia is a property of matter; it's essentially the same as mass (or it is the same as mass -- it depends on who you ask, even 300 years after Newton).

Inertial energy and centrifugal force are both functions of the inertial velocity squared, though -- that's what makes your conclusions correct.

[Dave_Trible]

I've always believed in a little engine offset.  It's more effective and less detrimental than rudder offset.  If you aren't sure then take out a decent stunt profile where adding or subtracting washers under the engine give easy adjustment.  Slow the ship down a little and go fly.  If you REALLY aren't sure,  put one washer of INSET and your good running shoes on and go fly.  I'll grant that it may be more about recovery from a light line condition than keeping them tight in the first place but it does help.

Dave

[Steve Helmick]

Long ago, I did some tests with a "Sneaker" combat model, the one Riley Wooten designed. I tried engine offset and I tried adding tipweight without the engine offset. I liked the engine offset better. Thinking back on this, the side mounted engine cylinder and baby pacifier tank mounted outboard of center would have been way more than enough 'tip weight'.

What the engine offset did was increase line tension all over, but the really good thing was that if the lines got slack, they got tight again MUCH quicker. A few years ago, I tried a bit of engine offset on the blue profile I later gave to Tim, with exactly the same result. The offset stayed. When bad things happen and the lines go slack, getting the lines tight quicker can often save your plane. Put in a little offset.  Steve

[Ted Fancher]

Yep drop a golf ball and a ping pong ball at the same time from the same distance and let us know which one hits the ground first.

What weighs more a pound of feathers or a pound of sand? Just messing with ya TED

Sparky,

Let me respond this way.  If a friend offered you the following choice:  I'm going to take a one  pound lead sinker and a pound of feathers in a pillow case up to the third story and its your choice which one pound I'll drop on your head from the window, which would you prefer?

Or, how about this one.  How do you think the terminal velocities of a fully equipped free falling 200 pound skydiver would compare to the terminal velocity of the same guy once the parachute opens?  For which state of fall would you prefer to act as a human trampoline on touchdown? 

The objects would weigh the same in either case; so why not have pick the lead weight and the free falling skydiver?

What's the difference?

Once on a short layover on the ramp at Oakland airport I picked up the Goodyear blimp that was tethered on the ramp behind our 727.  The guard said it "weighed" something like 50# at the time.  Sure enough, I could pick it up by "curling" a railing or something on the side of the cabin.  The "weight" was "liftable" but you couldn't "clean and jerk" it, for sure.  It took time because of the "mass" of the thing wouldn't allow you to accelerate it to any great degree...like pushing a big boat from a dock.  You can make it move with modest effort but accelerating the mass is another story entirely.  Some of the science whizzes like Brett, Serge, Howard or Tim can say it in a scientifically honest way that I'm not informed enough to do.

I do know this, however.  I'll stand on the pitcher's mound 60'6" away from Tiger Woods as he drives a ping pong ball at me but if you put a golf ball on the tee I'm history.  Mass times velocity squared is a powerful piece of work.

Fun topic, Sparky!

Ted

[Howard Rush]

Tiger Woods may have better things to do with his balls.

[Ted Fancher]

Your conclusions are correct, you are misremembering the meaning of inertia.  Inertia is a property of matter; it's essentially the same as mass (or it is the same as mass -- it depends on who you ask, even 300 years after Newton).

Inertial energy and centrifugal force are both functions of the inertial velocity squared, though -- that's what makes your conclusions correct.

Tim,

I'm sure you're right.  That's why I referenced guys like you, Brett, Howard, Serge, etc. in my note to Sparky on golf balls, feathers, lead weights, etc.  I'm full of opinions but can only use lay terms to pontificate because, from the perspective of a true student of science, math, etc. I cast a pretty small shadow.  Pretty much my entire grasp of mass/inertia is summed up in the old saw about objects in motion tending to stay in motion and objects at rest to remain at rest unless acted on by an outside source...such as thrust or drag in the case of a stunt ship with or without the engine running.  

I sort of used such lay person similes with Sparky when I tried to illustrate the difference between weight and mass using the pick up the blimp and throw it story.  I think the "concept" is accurate although the testimony is, no doubt, fractured.

fun subject.

Ted

[Tim Wescott]

Yep drop a golf ball and a ping pong ball at the same time from the same distance and let us know which one hits the ground first.

It depends on where you're standing, Robert:

[Ted Fancher]

I've cut and pasted the following as a follow up to the feather versus hammer race cleverly posted by Tim.  It's from Wikipedia although the resource doesn't matter as the science is well founded and consistent regardless of the source.

The terminal velocity of a falling object is the velocity of the object when the sum of the drag force (Fd) and buoyancy equals the downward force of gravity (FG) acting on the object. Since the net force on the object is zero, the object has zero acceleration.[1]

"In fluid dynamics, an object is moving at its terminal velocity if its speed is constant due to the restraining force exerted by the fluid through which it is moving. (The term "terminal velocity" is used rather than "terminal speed" even though we are not concerned with a vector, but just a scalar value.) 

As the speed of an object increases, the drag force acting on the object, resultant of the substance (e.g., air or water) it is passing through, increases. At some speed, the drag or force of resistance will equal the gravitational pull on the object (buoyancy is considered below). At this point the object ceases to accelerate and continues falling at a constant speed called terminal velocity (also called settling velocity). An object moving downward with greater than terminal velocity (for example because it was thrown downwards or it fell from a thinner part of the atmosphere or it changed shape) will slow down until it reaches terminal velocity. Drag depends on the projected area, and this is why objects with a large projected area relative to mass, such as parachutes, have a lower terminal velocity than objects with a small projected area relative to mass, such as bullets.


Based on wind resistance, for example, the terminal velocity of a skydiver in a belly-to-earth (i.e., face down) free-fall position is about 195 km/h (122 mph or 54 m/s).[2] This velocity is the asymptotic limiting value of the acceleration process, because the effective forces on the body balance each other more and more closely as the terminal velocity is approached. In this example, a speed of 50% of terminal velocity is reached after only about 3 seconds, while it takes 8 seconds to reach 90%, 15 seconds to reach 99% and so on.

Higher speeds can be attained if the skydiver pulls in his or her limbs (see also freeflying). In this case, the terminal velocity increases to about 320 km/h (200 mph or 90 m/s),[2] which is almost the terminal velocity of the Peregrine Falcon diving down on its prey.[3] The same terminal velocity is reached for a typical .30-06 bullet dropping downwards—when it is returning to earth having been fired upwards, or dropped from a tower—according to a 1920 U.S. Army Ordnance study.[4]

Competition speed skydivers fly in the head down position and reach even higher speeds. The current world record is 1,357.6km/h (843.6mph/Mach 1.25) by Felix Baumgartner who skydived from 38,969.4m (127,852.4ft) above earth on 14 October 2012. The record was set due to the high altitude where the lesser density of the atmosphere decreased drag."[5]


I've highlighted the last paragraphs as particularly germane to my skydiver reference.  Yes, on the moon both the free faller and the guy who popped his chute would impact the ground at the same time as there is no "resistance" to motion in the fluid through which they are falling "(there ain't no air up there!).  Of interest, the parachute wouldn't have filled for the same reason...nothing with which to fill it.  On a heavenly body with an "atmosphere" the rate of descent of the chutist (or the lighter ping pong ball, for that matter) will be reduced based on their terminal velocity through whatever the density of that atmosphere is...I think...help me out here science guys.  That resistance is what we love to call drag in our toy airplane discussions.  It is also why the same airplane a pound heavier (and of greater mass and inertial as a result) will slow less rapidly and to a higher terminal velocity when thrust is removed.  It is also why extended glides for landing are much easier to achieve with a higher wing loading given identical trim conditions...primarily CG location.

Ted

[Tim Wescott]

On a heavenly body with an "atmosphere" the rate of descent of the chutist (or the lighter ping pong ball, for that matter) will be reduced based on their terminal velocity through whatever the density of that atmosphere is...I think...help me out here science guys.

Yes.  At the speeds we care about, and in a gas*, lift and body drag are proportional to fluid density times velocity squared.  In fact, that relationship is so handy that fluid dynamicists give it a name: the dynamic pressure of a moving fluid is (1/2)(density)(velocity²).  When you're piloting and you look at your airspeed gauge, you're seeing a measure of the difference in pressure between the static fluid (at the tip of the pitot tube) and the moving fluid (at those holes in the side of the pitot tube).  In other words, your airspeed indicator is directly measuring dynamic pressure, then converting the results into a speed in units that you're happy with (stadia per day, cubits per tithi -- you know, whatever the airline wanted).

* I wanted to say "fluid", but what of molasses?  I'm pretty sure that if the viscosity is dominating the behavior then the flow is laminar, and if the flow is laminar then you need to throw the whole "dynamic pressure" thing out the window.  I would have said "and laminar flow", but I'm not that much of a fluid dynamicist.  So rather than opening myself up to elliptical comments by a future world F2B champion, I decided to qualify it with what I do know.  I can't say much about the fluid dynamics of molasses, other than to mention that if you get caught up in another Great Molasses Flood like happened in Boston a while back, just take a deep breath and try to keep your face above water the fluid.

[Howard Rush]

It is also why extended glides for landing are much easier to achieve with a higher wing loading given identical trim conditions...primarily CG location.

I think that's a bit too much extrapolation.  They may be, but maybe because a heavier plane whips better. 

[Ted Fancher]

I think that's a bit too much extrapolation.  They may be, but maybe because a heavier plane whips better. 

I suppose.  I expect that's why combat ships glide so far without streamers.

Ted

[Jim Thomerson]

When I flew the four leaf clover, I was whipping all the way.  I've had the engine die coming up to exit, without a problem, because I was probably putting more energy into the airplane by whipping than the engine was.

[RC Storick]

I have always used the TLAR method and it has worked pretty well so far.

[phil c]

Steve got it exactly right.  The "right" amount of engine offset will help keep the plane out everywhere around the circle.  It has to be balanced against the leadout angle.  With more offset the leadout guide has to move forward to keep the plane square on the lines.  With the correct balance between the two the plane self-corrects as the line tension changes.  It reduces the plane  turning in at you.  But it doesn't help if the motor quits.  The only thing that can help then is a heavy plane and a strong arm.  As Jim said, whipping can muscle enough horsepower into a plane to keep it going into the wind.  Judging from how much you can change the airspeed in level flight by holding back or whipping I guestimate it can add about 1/4-1/2 a horsepower when you need it most.

I saw Jim Silhavy at the NATS do this with his Gypsy.  Coming into the wind you could see the nose start to turn in near the top and then turn out as he whipped it through.  Outthrust works the same way.  If the line pull goes down it pulls the nose out, keeping the plane straight.  Saves you having to run to places you'll never get to to save a plane.