Walker's Stab Leading Edge

[frank williams]

For those who haven't seen Paul Walker's stab's leading edge, to say that its pointy is an under-statement.  Its just downright extremely sharp pointed.  I don't see his planes on a regular basis, only once a year at the Nats, but I always try to take note of the subtle design features that I think are unique.

Anyway, I wondered if there was any technical data on a pointy leading edged airfoil, and I found this.  This is data for a 0012 airfoil in both the normal (blunt end forward) and reverse (pointy end forward) orientations.  Right off I'll admit that the Reynolds number for this data is lower that what we normally have for a stunt ship stabilizer, but it better than nothing.  This data gets generated for special vertical axis wind turbine analysis that see this full range of flow.

The data shows that in the reverse configuration, the lift curve is very linear through zero alpha.  The normal configuration is not.  The normal, blunt end forward, suffers from a nonlinear loop around the zero angle of attack range.  If this was on a stuntship stab, we might see a hunting type feel in level flight.  The slope of the curve does stabilize after a few degrees, but the damage has been done.  This effect is probably due to a type of flow that is said to have laminar bubbles on the surface.  once again, this is not at exactly our Reynolds number, but ....

So maybe Paul has something here.  I think he says that it grooves better.

[Skip Chernoff]

So I'm guessing those "Green Box Noblers" and Ambroid "Ares" kits got the stab correct....

[Mike Haverly]

So I'm guessing those "Green Box Noblers" and Ambroid "Ares" kits got the stab correct....

In their day, maybe.  Things have changed, a lot!  I can tell you first hand the LE of his stabs are now "really sharp" as in pointy.

[IdRatherBeBuilding]

The problem with sharp LEs is once the AOA changes, the airflow over the surface is blacked out and stalls. This happens with any airfoil, but with a sharp LE it happens more abruptly. So it's efficient for speed, but not for maneuvers.
Kind of the same as tip stalling when the tip loses flow over one side of it's surface.

[Tim Wescott]

It'd be interesting to see a sketch of just how pointy (Mike, a picture of your hand with missing fingers would be sufficient).

The problem with sharp LEs is once the AOA changes, the airflow over the surface is blacked out and stalls. This happens with any airfoil, but with a sharp LE it happens more abruptly. So it's efficient for speed, but not for maneuvers.
Kind of the same as tip stalling when the tip loses flow over one side of it's surface.

"Efficiency" and "Stunt" do not go together.  We aren't trying to be efficient.  We are trying to carve pretty pictures in the air with a pretty airplane.

[Dave_Trible]

Well I was convinced.  May need to carry some bandaids in the flight box.

Dave

[Target]

  We are trying to carve pretty pictures in the air with a pretty airplane.

And, there is much more thrust to weight than with most prop driven full scale aircraft. This covers many sins. Our c/l planes don't need to glide efficiently like a sailplane, they just need to be controllable enough for a smooth landing.

[frank williams]

The problem with sharp LEs is once the AOA changes, the airflow over the surface is blacked out and stalls. This happens with any airfoil, but with a sharp LE it happens more abruptly. So it's efficient for speed, but not for maneuvers.
Kind of the same as tip stalling when the tip loses flow over one side of it's surface.

David ... that's not what the data shows ..... the performance is as good as or better than the forward direction.

Nobler, Ares .... yep pretty decent

[Howard Rush]

For those who haven't seen Paul Walker's stab's leading edge, to say that its pointy is an under-statement.  Its just downright extremely sharp pointed.  I don't see his planes on a regular basis, only once a year at the Nats, but I always try to take note of the subtle design features that I think are unique.

Anyway, I wondered if there was any technical data on a pointy leading edged airfoil, and I found this.  This is data for a 0012 airfoil in both the normal (blunt end forward) and reverse (pointy end forward) orientations.  Right off I'll admit that the Reynolds number for this data is lower that what we normally have for a stunt ship stabilizer, but it better than nothing.  This data gets generated for special vertical axis wind turbine analysis that see this full range of flow.

The data shows that in the reverse configuration, the lift curve is very linear through zero alpha.  The normal configuration is not.  The normal, blunt end forward, suffers from a nonlinear loop around the zero angle of attack range.  If this was on a stuntship stab, we might see a hunting type feel in level flight.  The slope of the curve does stabilize after a few degrees, but the damage has been done.  This effect is probably due to a type of flow that is said to have laminar bubbles on the surface.  once again, this is not at exactly our Reynolds number, but ....

So maybe Paul has something here.  I think he says that it grooves better.

I've seen data for the 0012 airfoil at perverse angles of attack that was probably at higher Reynolds numbers.  It had helicopter blades in mind.  I don't remember where I saw it.

[frank williams]

Well I was convinced.  May need to carry some bandaids in the flight box.

Dave

Dave is this a new plane? ... have you flown it? ..... what are you comments on the sharp stab?

[Dave_Trible]

Yes Frank new plane.  Actually two new ones ready to rub out and a third (take apart) under construction.  None of these have been flown yet but I'm hopeful I like the stab.  Someone pointed Paul's out to me at the last Nats and I ran a finger down the edge-SHARP!  Thought I'd try it.  I feared the angle of attack could be more critical so these stabs are removable/adjustable.  I can shim the stab incidence at the flying field if need be.

Dave

[Dave_Trible]

...

[Howard Rush]

That airplane looks good.

[Ken Culbertson]

David ... that's not what the data shows ..... the performance is as good as or better than the forward direction.

Nobler, Ares .... yep pretty decent

My first two full body planes were a Nobler and Ares (from plans).  I have put a 1/16" diameter LE on everything I have designed ever since.  Didn't know any better.    Amazing what we rediscover every 50 years or so.

Ken

[Dave_Trible]

That airplane looks good.

Thanks Howard.

Dave

[IdRatherBeBuilding]

David ... that's not what the data shows ..... the performance is as good as or better than the forward direction.

Nobler, Ares .... yep pretty decent

Thats in level flight. Once AOA changes airflow loses laminar effect on the surface earlier than that of a rounder LE. Also lose lift from the lack of turbulator effects from the flow off the LE.

Sharp LEs are great, don't get me wrong. But all airfoils have pros and cons. It'll all depends on the application. The sharp vs round LE is similar to a thin vs thick airfoil.

[Howard Rush]

Stunt stabilizer-elevator combinations are weird critters. Around zero angle of attack, pretty much any airfoil works, but the trick is to keep the laminar-turbulent transition from moving around, which causes a limit cycle.  Frank and Igor Burger wrote this up somewhere here.  Most folks use a sharp LE these days.  I have a clear vinyl lattice thing made my Mike Haverly that looks cooler (the lattice, not Mike).

At high pitch rates, such as in sharp corners, the flow is probably separated early regardless of LE radius.  The sharp LE doesn't seem to affect turning ability. Danged if I know how the stab could get much lift in this condition:

[IdRatherBeBuilding]

Here's a decent article on the subject. It explains the different applications of thin and sharp foils vs round thicker foils without getting too involved.

https://aviation.stackexchange.com/questions/58444/why-are-the-leading-edges-of-wings-not-always-made-as-sharp-as-possible

I had a really good essay from Michael Selig with reynold numbers and photos of his foils in a wind tunnel. I'll try to find my old text books and I'll post it. But they are buried deep somewhere.    It'll take time.

[Tim Wescott]

Thats in level flight. Once AOA changes airflow loses laminar effect on the surface earlier than that of a rounder LE. Also lose lift from the lack of turbulator effects from the flow off the LE.

Sharp LEs are great, don't get me wrong. But all airfoils have pros and cons. It'll all depends on the application. The sharp vs round LE is similar to a thin vs thick airfoil.

I have a personal motto in my engineering efforts: "reality trumps theory, every time".  Paul Walker and Igor Burger win contests that I'm not even good enough to qualify for.  Franks' picture shows a more linear relationship of lift vs. -- yes -- AOA for a pointy LE.  So, theory's great.

But reality is better.

[IdRatherBeBuilding]

But saying those guys flying their planes and winning because of the LEs of their models isn't reality. There's a lot more variables to consider of why the same guys win at high levels of aviation than one particular mean.

But if it works for you, by all means go for it.

Airfoils are not "Theoretical" they are indeed fact and proven.

This is actually a simple concept. Google stall effects of a wing. The LE plays the biggest roll in that. It's all about keeping the airflow over the wings surface. Really simple. A sharp LE causes a shadow and you lose that laminar flow, and that is a stall.

[Tim Wescott]

This is actually a simple concept. Google stall effects of a wing. The LE plays the biggest roll in that. It's all about keeping the airflow over the wings surface. Really simple. A sharp LE causes a shadow and you lose that laminar flow, and that is a stall.

OK, but how, exactly, is that detrimental to a good stunt flight?

[Jim Svitko]

The photo of Dave's plane shows a stab that has a pointed LE but then it transitions to what looks like a flat section up to the hinge line.  Frank's attachment shows an airfoil that although it has been reversed, it has an airfoil shape and not flat.   For the aerodynamics engineers, is this difference of any significance?

[Tim Wescott]

The photo of Dave's plane shows a stab that has a pointed LE but then it transitions to what looks like a flat section up to the hinge line.  Frank's attachment shows an airfoil that although it has been reversed, it has an airfoil shape and not flat.   For the aerodynamics engineers, is this difference of any significance?

Yes!

The (at least) three steps to enlightenment in this case are to run a Walker-style stab airfoil through some airfoil simulator, both with and without elevator deflection, then (if you want to be thorough) back-stop those results with wind tunnel simulations because the airfoil simulators won't have been designed to cope well with sharp leading edges, and then, finally, to sit and think about it up to -- but not over -- the point where your head explodes.

[IdRatherBeBuilding]

The photo of Dave's plane shows a stab that has a pointed LE but then it transitions to what looks like a flat section up to the hinge line.  Frank's attachment shows an airfoil that although it has been reversed, it has an airfoil shape and not flat.   For the aerodynamics engineers, is this difference of any significance?

Yes indeed it is significant.
When deciding an airfoil, the designer is going to choose a shape that follows the air shape as much as possible, Many other variables are thrown in, but that is pretty much the goal, wing shape follow airflow. Thats all your trying to do. Reversing the shape reverses the efficiency. The high point towards the rear creates more drag since that is where you're trying to merge the air back together. This is why airfoils are longer after the highest point, and thin at the end. That transition needs to have the least amount of turbulence. But it doesn't matter too much because with a sharp LE and the high point so far aft, the wing will lose laminar effect so quickly, they'll be no air to consider.
The reversed foil will have a slicing effect in the wind. When you're doing the dishes, fill the sink. Then take a knife and move it through the water. You'll notice the knife wants to take its own direction if you twist it slightly. The faster you go the more force the knife has. The knife is actually stalling through the water.
If your out driving your car, roll down the window and fly your hand like a wing. angle your hand down. It moves abruptly. Same thing as the knife. Typically we don't want that. We want a subtle transition and the flying as much as possible. In reality a wing is always in a partial stall since we do lose some laminar air flow over the surface. Different air foils dictate where those spots will be.

This isn't always so with all applications. For instance a fighter jet is very thin, and has a very sharp LE. The designers don't really care much about lift as much as drag, so they choose this style. When a jet pulls up hard and points the nose up vertical but still maintains the same path for a moment, the whole plane stalls at this time. But that doesn't matter since it has enough thrust to pull it where it needs to go.

[wwwarbird]

 Interesting, I hadn't heard of this 'til now, it's mostly Hillbilly planes in these parts. 

 I'm curious, is Howard currently flying with the pointy L/E?

[IdRatherBeBuilding]

Yes!

The (at least) three steps to enlightenment in this case are to run a Walker-style stab airfoil through some airfoil simulator, both with and without elevator deflection, then (if you want to be thorough) back-stop those results with wind tunnel simulations because the airfoil simulators won't have been designed to cope well with sharp leading edges, and then, finally, to sit and think about it up to -- but not over -- the point where your head explodes.

I Love That. 

[IdRatherBeBuilding]

It'd be interesting to see a sketch of just how pointy (Mike, a picture of your hand with missing fingers would be sufficient).

"Efficiency" and "Stunt" do not go together.  We aren't trying to be efficient.  We are trying to carve pretty pictures in the air with a pretty airplane.

All airfoils are based on an efficiency coefficient. Not necessarily a glide ratio, but drag vs lift vs speed vs AOA.

[Brett Buck]

OK, but how, exactly, is that detrimental to a good stunt flight?

   It's not correct in the first place (or at best, moot), so, don't worry about it, you don't need to concern yourself with stalls on the stab, the issue us more how to keep spot where the flow separates and/or goes turbulent as stable as possible. If it stalls, you have already lost.

   There's no such thing as a "shadow", there is the normal force/pressure, and there is where it separates (if at all). Keeping the normal pressure as far aft as you can and as stable as you can is the goal. Howard's comment earlier is probably most on point, and the blunt airfoils tend to separate near the LE, the ultimate in blunt being a flat stab with a round LE, which loses all the normal pressure right where the radius ends, slight changes at very low AoA tends to make it separate on the top, then the bottom, then the top again, causing Howard's limit cycle and inconsistency right around zero. You can do it that way and have success, but in many cases you end up with turbulators to get the flow to stay attached.

   The relatively pointy (it doesn't have to be as pointy as shown) airfoil just needs to have a positive gradient over a sufficient fraction of the chord to avoid really sharp pressure gradients until you can't avoid it (the hinge line) and even then that needs to be smooth and benign as possible.

   This is a previous discussion on the same topic:

    http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=69453&mesg_id=69453&listing_type=search#69459



    Brett

   

[IdRatherBeBuilding]

Actually the term "shadow" is used widely in aeronautical engineering. It's where the surface of an object is blocked from the airflow by itself.
Stalling is an import degree on all surfaces of a plane especially over the emennage. Stalling the stab will result in loss of control of the elevator, since stalling is a loss of airflow.

The airflow over round LE are not all over the place as the planes transitions in AOA. On the contrary. It is actually the reason for a round or blunt LE.

The shape of a LE is to keep the air flowing over as much of the surface behind it as possible. That's all it really does.

[Target]

I'm surprised that nobody has even mentioned the big thing that disturbs the air before the LE of the stab even gets a crack at it. Especially in a square corner.

[Brett Buck]

Actually the term "shadow" is used widely in aeronautical engineering. It's where the surface of an object is blocked from the airflow by itself.
Stalling is an import degree on all surfaces of a plane especially over the emennage. Stalling the stab will result in loss of control of the elevator, since stalling is a loss of airflow.

The airflow over round LE are not all over the place as the planes transitions in AOA. On the contrary. It is actually the reason for a round or blunt LE.

The shape of a LE is to keep the air flowing over as much of the surface behind it as possible. That's all it really does.

   There you go Paul, better get out the wood rasp!

    Brett

  P.S. look at Frank's CFD, figure B. See that big bubble? Now, move that to 1/4" from the LE and make it bigger and rounder - that's what happens with a flat stab with a round LE (i.e. the ultimate in "blunt") . Change the AoA even a little to the other side, the bubble on top goes away, and a different one forms the other side. That's what causes the limit cycle Howard was discussing and *just about everyone who has ever done it that way has found in practice*. That's why most of these airplanes end up with turbulators right near the LE.

   Of course, you can build it any way you want,  but you might at least consider *how a 12-time national champion and world champion (not to mentioned a retired Senior Fellow from Boeing) thinks it ought to be done*, instead of dismissing it out of hand. Same with Frank and Howard, both engineers with relevant experience at the highest professional levels.

[Howard Rush]

There you go Paul, better get out the wood rasp!

It better be a carbide rasp.  Paul went to extreme measures to make a sharp stab. 

[Howard Rush]

The photo of Dave's plane shows a stab that has a pointed LE but then it transitions to what looks like a flat section up to the hinge line.  Frank's attachment shows an airfoil that although it has been reversed, it has an airfoil shape and not flat.   For the aerodynamics engineers, is this difference of any significance?

I don't think so, but I'm outvoted two to one so far.

[Howard Rush]

All airfoils are based on an efficiency coefficient. Not necessarily a glide ratio, but drag vs lift vs speed vs AOA.

Never heard of efficiency coefficient.  What's the definition?

[Howard Rush]

Actually the term "shadow" is used widely in aeronautical engineering.

I've used it myself.  I built a 1/10th-scale 777 wing to investigate whether the ground maneuvering camera that Dave Fitzgerald doesn't like could see the landing gear when the sun was reflecting off the wing and the gear was on the other side of the wing from the sun: a phenomenon we called "shadow". 

[Doug Moon]

This is all very good stuff.

I have been using a 1/2" flat stab with a molded round LE and TE for years, basically since I started building built up models, and it works really well.  I have thought about trying the sharp LE but at my building rate the super pointy will probably be out of style by the time I finish one.  I tend to shy away from it as I worry I wont be able to make the Stab perfectly the same across the LE like I can with a molded LE.  Also 1/2" think built up is super strong.  I fear a thinner stab at my building skill level will flex and that would be a lot worse than a flat stab that is rigid.

I don't have the issues people say I should have, except inverted flight tends to be a little iffy at times but not too bad.  Many others have used this same stab with good results as well.  Then again maybe I am having these issues and I just fly around it and don't notice....hmmmmm. Why don't I have the issues? 

I have an RC friend who says certain areas of CL stunt is purely "VooDoo aerodynamics" sometimes I have to agree. 

Is Paul's Stab pointed then flat like Dave's or is pointed at the LE and airfoiled back to the TE?  Are Elevators airfoiled back to a point as well?  I would really like to see a cross section of the Stab and Elevator on his design.  Anyone got one?  Paul?

[Doug Moon]

I've used it myself.  I built a 1/10th-scale 777 wing to investigate whether the ground maneuvering camera that Dave Fitzgerald doesn't like could see the landing gear when the sun was reflecting off the wing and the gear was on the other side of the wing from the sun: a phenomenon we called "shadow".

 

[Randy Cuberly]

I distinctly remember this topic coming up at a VSC that got rained out about 18 or so years ago.  the rain (only time that has happened at VSC) caused everyone to retreat to the Motel meeting room for a general bull session which then became a series of discussion groups, each headed by a genuine EXPERT to discuss various do's and don'ts within each group.  I was in process of building my first Trivial Pursuit and the question of level flight stability came up.  The group leader, none other than Mr Ted Fancher discussed some experimentation done by some fairly young guy named David Fitzgerald concerning level flight stability.  Using different stabilizers (because of course his airplane was a take apart) with different configurations of leading edges on the stabilizer.  Ted said the conclusion of the experiments was that a "sharp" leading with no other changes solved the instability problem.   Then there was an article in Stunt News by none other than David Fitzgerald some months later showing and discussing the changes and their findings. 

Me! I just took Ted at his word, went home and sharpened the leading edge on my Trivial Pursuit and never looked back.  No level flight instability ever reared it's head.
Just a great flying and extremely well flying and easy to trim airplane.

The assumption at the time (I think) was that a nice rounded leading edge on the wing was a very good thing because it stalled at a higher angle of attack, but on the stab was less stable because it stalled at a lower angle of attack.  Yes I know that isn't really true in aerodynamic terms but in layman terms the stabilizer has very different requirements  (like stabilizing a big massive blunt air foiled  wing that is inherently willing to turn quickly in response to forces on a long lever) like the fuselage.

AT any rate I just wanted to mention that the idea of sharp leading edges on a stabilizer is not a new trick and the first place I heard about it was from Ted Fancher, and David Fitzgerald Many years ago (I think around 1997 or 1998).

It definitely works...Just ask Ted!

Randy Cuberly

[Tim Wescott]

... I have thought about trying the sharp LE but at my building rate ...

My Atlantis has some really ugly balsa leading edge shoes and scotch tape in its (near) future.  I figure I can scotch-tape a pointy LE onto the thing, try, then rip it off and try again.  I fear that I'm not good enough of a pilot to tell the difference, but -- I'll find out!  All of a sudden, a hand-me-down aircraft with NO attached appearance points seems like an advantage!

[Doug Moon]

My Atlantis has some really ugly balsa leading edge shoes and scotch tape in its (near) future.  I figure I can scotch-tape a pointy LE onto the thing, try, then rip it off and try again.  I fear that I'm not good enough of a pilot to tell the difference, but -- I'll find out!  All of a sudden, a hand-me-down aircraft with NO attached appearance points seems like an advantage!

Back in 2000 or 2001 I taped 1/4" triangle stock onto the LE of my Saturn stab.  It was thick flat and round LE. The plane locked in on rails in level flight.  But when I turned it for a square corner it almost crashed.  At about 70 degrees into the turn it would stall violently and shudder.  I nearly smashed it bad on the first turn.  Scared me real bad.  I tried it a few more times that day with the same result.  Take off the 1/4 triangle piece and it went back to its normal self.  Don't know what was happening....

[Howard Rush]

Thats in level flight. Once AOA changes airflow loses laminar effect on the surface earlier than that of a rounder LE.

That's the point of the pointy LE.  Transition stays put.

When deciding an airfoil, the designer is going to choose a shape that follows the air shape as much as possible...

Not me.  I choose a shape that determines the air shape (as much as possible).

When you're doing the dishes, fill the sink. Then take a knife and move it through the water. You'll notice the knife wants to take its own direction if you twist it slightly. The faster you go the more force the knife has. The knife is actually stalling through the water.
If your out driving your car, roll down the window and fly your hand like a wing. angle your hand down. It moves abruptly. Same thing as the knife. Typically we don't want that. We want a subtle transition and the flying as much as possible.

Your examples suggest the flow is not stalled. The rate of change of lift with angle of attack is higher with attached flow than it is with the wing or knife or hand stalled. 

This isn't always so with all applications. For instance a fighter jet is very thin, and has a very sharp LE. The designers don't really care much about lift as much as drag, so they choose this style.

They care about both, but fighter jets go fast, and they need to worry about squishing the air.  The F-104 has a really sharp LE, but not as sharp as Walker's new stab.

But that doesn't matter since it has enough thrust to pull it where it needs to go.

Those were almost the exact words my boss said when we added some draggy external armor to the F-4.  It brought a tear to the aero guy's eye, though.

Stalling the stab will result in loss of control of the elevator, since stalling is a loss of airflow.

Curiously, it doesn't seem to, maybe because of what Target mentions above.

[IdRatherBeBuilding]

Never heard of efficiency coefficient.  What's the definition?

Finding the best compromise of given requirements. Like the lift, drag, etc.. to conclude the best overall decision. That would be efficient.

[Howard Rush]

I have been using a 1/2" flat stab with a molded round LE and TE for years, basically since I started building built up models, and it works really well.  I have thought about trying the sharp LE but at my building rate the super pointy will probably be out of style by the time I finish one.  I tend to shy away from it as I worry I wont be able to make the Stab perfectly the same across the LE like I can with a molded LE.  Also 1/2" think built up is super strong.  I fear a thinner stab at my building skill level will flex and that would be a lot worse than a flat stab that is rigid.

Mine's the same, but with a sanded solid LE, which accounts for some of the ballast in the nose.  Between the trip strips on the LE and the elevator downrig that maybe gives some stab angle of attack in level flight, I get away with it.  The next one may be pointy.  I know what you mean about slow building and fashion.  The world went electric before I could make a plane for my four-stroke engines. 

[Paul Walker]

I typed a lengthy response, but has disappeared into SH ether. Will have to re-do.

Ugh....

[IdRatherBeBuilding]

hmm. Did you read the article I posted earlier with a link.

[Howard Rush]

Finding the best compromise of given requirements. Like the lift, drag, etc.. to conclude the best overall decision. That would be efficient.

You've made a personal definition for a standard technical term.  You'll fit right in with the stunt community.

[Howard Rush]

I typed a lengthy response, but has disappeared into SH ether.

Speaking of not being up-to-date, this guy hasn't heard the Michaelson-Morley news.

[Paul Walker]

In my working days, there used to be a saying we used, and the Air Force used on us: Emperical data trumps analytical data. This is why there are so many full scale aircraft tests for structure, aero, etc. Even at these levels, analytical data has to be proven. Many times it was found that the analytical data/analysis was not "correct". Tests verify! I try to structure tests that minimize variables as much as possible to get a "good" test, in real aircraft and models as well.

I became interested in the sharp HT LE's in the mid '90's. I built a new stab with a sharp LE on a take apart Impact in '97. This test replaced a removable stab with one the same size and weight. I tested it and found no significant improvement. It was dropped at that point.

Years later after I had switched to electric power, I became unhappy with the variation I found in HT effectivness in colder to warmer conditions. Either could be adjusted to quality, but the change was unacceptable. Once again I pulled out that same stab from '97, and installed it on 2 Impacts, and the second Predator. The change in each plane was remarkable. Tracking improved, turn and stop improved, the control feel was more linear. The second Predator was interesting as it had non linear flap mechanisms in it, and still felt more linear.

Since that test, I have built nothing but sharp LE HT's. I have flown a lot of other quality pilots planes, Nat's winners, and World Champ's planes, and as far as I am concerned, the 3rd Predator is the best plane I have ever flown. The control response is very linear, and corners can be executed at what ever radius you are wanting and willing to do. It still does nice rounds, and the turn and stop is perfect. Yeah, it took me years to get it there, but it is there now. There are several factors that have made it this way, but the sharp HT LE is a significant part of it.

As far as the wing goes, the wing LE is fairly blunt, but not as blunt as Brett's Infinity. My Impacts and Predators have a blunt enough radius as they are, and work just fine. Sharp wing LE's are clearly a bad thing. No argument there.

Bottom line for me is the sharp HT LE clearly works, and are on all my planes now.

[L0U CRANE]

Just curious...

Has anyone considered the ACTUAL PATH the model flies in executing a 'square corner' (at any elevation)?

Seem to recall a photo of a stunter oriented vertically (reference to the ground below the model) at LESS THAN  the model's fuselage length above the last 'level flight' posture before the turn. (Brett's model, 4, 5 or more years ago?)

Thoughts of standard aerodynamics, presuming smooth, steady flow conditions, cannot apply! The model had to be 'dirt-tracking' like an "outlaw" stocker! I could only conclude that the model rotated - in pitch - to vertical, but did not FLY there. If you've ever stood near the edge of the flight circle where good squares are being done, you've felt a strong smack of wind - like someone dropping a door flat next to you, right? That ain't smooth, streamlined flying...

The momentum of level flight at usual speed apparently is absorbed by this non-aerodynamic event. We do have sufficient power to reduce any apparent velocity loss, but remember, this is a time interval so brief that I suspect we humans cannot actually control it. Instead we develop models that can dirt track around to the desired rotation, then are positioned and powered to resume (apparently) what we wish.
 
IM(amateur)(not so)HO...

Just another candy bar in Caddyshack's swimming pool?
\LOU

[Howard Rush]

Has anyone considered the ACTUAL PATH the model flies in executing a 'square corner' (at any elevation)?

Seem to recall a photo of a stunter oriented vertically (reference to the ground below the model) at LESS THAN  the model's fuselage length above the last 'level flight' posture before the turn. (Brett's model, 4, 5 or more years ago?)

Thoughts of standard aerodynamics, presuming smooth, steady flow conditions, cannot apply! The model had to be 'dirt-tracking' like an "outlaw" stocker! I could only conclude that the model rotated - in pitch - to vertical, but did not FLY there. If you've ever stood near the edge of the flight circle where good squares are being done, you've felt a strong smack of wind - like someone dropping a door flat next to you, right? That ain't smooth, streamlined flying...

The momentum of level flight at usual speed apparently is absorbed by this non-aerodynamic event. We do have sufficient power to reduce any apparent velocity loss, but remember, this is a time interval so brief that I suspect we humans cannot actually control it. Instead we develop models that can dirt track around to the desired rotation, then are positioned and powered to resume (apparently) what we wish.

Mine's so bad you can hear it.

I'd like to know the pitch rate in these corners so I can get more of a clue as to what's happening at the tail.  That's why I'm excited to get a data TUT, but you can hardly get a regular TUT anymore.