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Author Topic: What makes a stunt plane groove??  (Read 10188 times)

Offline Keith Renecle

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What makes a stunt plane groove??
« on: July 04, 2016, 02:10:50 AM »
Hi All,
Since the 90's and my first world champs baptism of fire in 1996, the question of what makes a stunt plane groove has been bugging me......and still does! By "groove" I mean that solid tracking and ability to lock in after a hard corner. I have asked this question of many of world's best stunt pilots and designers and I have the list of essential things, but they don't always agree. I understand that the controls have to be super smooth especially around the neutral point between up and down. I also know that good building and really good alignment is essential, but I would really like to here from the experts on this forum if there is any particular design criteria that is the trick to getting this right. I always have all of Paul Walkers incredible articles close by to study as well.

I have built quite a few models since the 90's and some of my designs like my Eze-Pro profile stunter fly really well. I have flown a few that look like they have been built well and are not heavy, but even after setting the flap/elevator for the best tracking either way they still don't groove well and tend to wander in level flight. One particular modeller down in Grahamstown here in South Africa, Peter Locke has built many of his own versions of this particular design and all of them track so well and he has used thin flat balsa stab/elevators and also thicker built-up versions and there is no noticeable difference. I have a feeling that he just builds really good and straight wings, especially the leading edge radius like Bob Hunt has written about.

I have also been told that in-line models (engine-wing-stab all in line) are not a good idea, and yet most of the Yatsenko models are all in-line. Must I mention that that the older Yatsenko Shark has just won the world champs in OZ?? It is an in-line model and has no adjustable rudder fin or an adjustable lead-out guide etc.

What about the bell-crank to flap horn ratio? Must it be geared down or 1:1 like most of Igor Burger's Max designs?

What about the actual lead-out guide holes.....does it matter if the lead-out cables float a little or what? I see that some use eye-lets and there is usually some float with them. Does it matter?

I would really appreciate hearing from the experts on this matter. Thanks in advance!

Keith R
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Offline Peter Germann

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Re: What makes a stunt plane groove??
« Reply #1 on: July 04, 2016, 03:12:50 AM »
Having built quite a number of F2B airplanes within the last years, here is, related to tracking of electrics only,  what I believe to have found:

-Sheeted wings, as opposed to film/silkspan/polyspan covered ones, seem to track better.
-Really sharp leading edge on the stabiliser seem to help.
-Near zero friction controls are essential.
-Flap/elevator deflection ratio has no influence
-In-line or not seems to be irrelevant when it comes to tracking
-In two particular cases, zig-zag turbulators did help (self adhesive tape 0.5 thick x 8 mm wide x 400 mm long. four ea. 40 mm from wing leading edge)
-C.G. position is of little influence
-Governor gain (I fly constant RPM) has no noticable effect

All in all, good old IC drive trains, in particular big bore or or 4-cycle, seem (perhaps) to do a better job when it comes to tracking. However, adding up all of the electric benefits definitely keeps me from going back.

rgds.
Peter Germann

Offline Keith Renecle

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Re: What makes a stunt plane groove??
« Reply #2 on: July 04, 2016, 05:45:18 AM »
Hi Peter,
Thanks very much for your feedback from so many years of experience. You are indeed a very good builder so I appreciate your comments.

Keith R
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Online Tim Wescott

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Re: What makes a stunt plane groove??
« Reply #3 on: July 04, 2016, 03:40:32 PM »
From reading various comments here, and from what little practical experience I have, most of Peter's comments apply to slime, as well.  "Zero friction" controls seem to be less of an issue because when you run slime you get -- absolutely for free -- a built in power vibrator that goes a long way to shaking any sticky spots in the control system loose.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Keith Renecle

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Re: What makes a stunt plane groove??
« Reply #4 on: July 05, 2016, 12:49:58 AM »
I guess that we simply unbalance the motor a little to get that effect. I use a 6 mm thick bell-crank made from polyethylene with a steel rod through it and it feels really smooth. This way I don't need to bush the centre or the ends. I can remember that the Chinese team model had bell-cranks with small ball-bearings top and bottom but maybe that's an overkill.

Peter's point about sheeted wings that seem to behave better for tracking than ribbed and covered wings I've heard before, but why would that be? I have always admired the look of I-beam wings with those steps between the ribs. So now we have this smooth sheeted surface and then we add zig-zag turbulator strips and/or vertex generators?? It gets confusing!

Keith R
« Last Edit: July 05, 2016, 06:23:49 AM by Keith Renecle »
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Offline Peter Germann

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Re: What makes a stunt plane groove??
« Reply #5 on: July 05, 2016, 02:48:15 AM »
Peter's point about sheeted wings that seem to behave better for tracking than ribbed and covered wings I've heard before, but why would that be?

Could it be that vibrating coverings influence the behavior of the boundary layer?
Peter Germann

Offline Target

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Re: What makes a stunt plane groove??
« Reply #6 on: July 05, 2016, 07:47:37 AM »
Subscribing to this interesting topic.
What of the thinner elevator than stabilizer that used to be the trend? Is it still a good idea?
Regards,
Chris
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Offline Keith Renecle

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Re: What makes a stunt plane groove??
« Reply #7 on: July 06, 2016, 03:30:42 AM »
Thanks Lauri,

It was good to see you in OZ. As someone that has owned a few of the Yatsenko Sharks, would you say that the in-line configuration is an advantage or that it really makes very little or no difference. when it comes to tracking?

Murray Howell also told me that the Yatsenko models fly a lot better with the Yatsenko control handle than with any other handle setup. I seemed to remember that Orestes also used one of their handles. I flew Rob Metkemiejer's Shark with a Rob's handle which was more like the standard handle with a bit more overhang, and his model grooved very well for me.

Do you agree with Peter's comment on the bell-crank/flap/elevator ratio's having no effect on tracking?

Keith R
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Offline Andrew Tinsley

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Re: What makes a stunt plane groove??
« Reply #8 on: July 06, 2016, 10:01:17 AM »
As an heretical observation, any of my planes that do not track have been cured by introducing a small amount of slop in the elevator to pushrod joint.
I realise this is a high powered F2b theme amongst fliers that are light years ahead of me. A little slop will make an awkward %^$" of a plane into one that grooves effortlessly.
Now I realise that everyone will jump on me and point out that such a modification will affect something else in the planes performance and such a way of solving the problem is little short of treason. BUT it works, if you don't believe me, then try it and see for yourself. I would dearly love to know why this works. I was shown the trick some 60 years ago and I still do not know understand why.

Andrew.
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Offline Keith Renecle

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Re: What makes a stunt plane groove??
« Reply #9 on: July 06, 2016, 10:44:24 AM »
Thanks again Lauri. In my next life I should try harder to build better!  #^

Andrew, yes the slop in the elevator horn was offered as a cure in the 70's or even earlier, but it usually causes flats in the round loops. I say "usually" because sometimes it just does the trick and all is well. I just like to try and understand what's going on. On my previous electric stunter I added more elevator than flap and it tracks a lot better and no longer rolls out of turn #3 in the hourglass. This suggests that I have too much flap or flap area to start with. It's all pretty interesting though.

Keith R
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Offline Andrew Tinsley

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Re: What makes a stunt plane groove??
« Reply #10 on: July 07, 2016, 07:32:50 AM »
Hello Keith,
I was shown this trick about slop in the elevator around 1966, by a local "expert". I must admit that I have never seen flats on a loop with a model with the "slop" introduced, but then I am a poor flyer at best and probably would not notice such effects.
I still cannot understand why it works, I would expect that the elevator would oscillate in some way, but that it oscillates in exactly the reverse of the aircraft's instability in level flight, I find difficult to swallow.
I suppose the question that needs answering first is WHY does the aircraft oscillate in level flight in the first place? Again I have no answers. Perhaps some aerodynamicist can shed light on the problem? I have been waiting 60 years for enlightenment, so perhaps a little longer is of no consequence.
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Offline Keith Renecle

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Re: What makes a stunt plane groove??
« Reply #11 on: July 07, 2016, 11:12:23 AM »
Wow Ty......we must both be old if we know about Galloping Ghost R/C!  #^ I had a system like that when I flew single channel in the 60's. Brings back lots of memories!

Like Andrew says though, the plane should not oscillate in the first place but sometimes it's hard to figure out exactly what the problem is. I always thought that it must be the flaps fighting with the elevators for a good balance in level flight, but then I've had un-flapped stunters that also do not groove.

Keith R
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Offline Gerald Arana

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Re: What makes a stunt plane groove??
« Reply #12 on: July 07, 2016, 03:05:09 PM »
One other item on the loose elevator. I have done this on a plane that hunted when all else failed to stop it. I under stand the loose elevator oscillates just enough to dampen the hunting. Two top flyers in this area suggested it. I thought they were kidding, but it worked.
As it was explained, they said it was not unlike the old "galloping ghost"  rudder on early RC models.  Well, that made sense. H^^


Hi Ty,

I never could understand to old "kicking" duck system either. Glad I didn't have the $$$ to buy one!

Ted Fancher told me that he uses two drill sizes larger (correct me if I CRS Ted) on the elev. horn to induce a "slight" amount of slop in the control system. Works very well for him although it doesn't do much for this advanced flyer!  Guess I need to learn to fly better.............

Cheers, Jerry

Offline Matt Spencer

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Re: What makes a stunt plane groove??
« Reply #13 on: July 07, 2016, 11:51:45 PM »
The  ' floppy elevator ' trick gets Flap Deflection started BEFORE the Elevator Moves !

This effectivly alters the T.E. Hight .

This Effectivly alters the incidance !

This Effectivly Alters the LIFT .

All The While Not Altering the PITCH of the AIRFRAME .  As In the Nose is NOT deflecting UP or DOWN on initial control application .

Allowing the Ace pilot to subconciously  :-\ Keep The Plane ' In The Groove ' with subtle but telling accuracy !  LL~ %^@ ;D

Offline Igor Burger

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Re: What makes a stunt plane groove??
« Reply #14 on: July 09, 2016, 01:29:54 AM »
Well I thing the biggest problem is looking for magic solution which will do the trick. There are 100s of reasons why model make such troubles, both mechanical and also aerodynamical. So the point is well trimmed model and thus removed all sources for the problem. Essential is tip weight, hadle neutral, properly set Rabe rudder and LO guide. But also proper motor up/down offset, stab position etc.

But to the magic stuff -

I recommend to reread Davids (F.) article in stunt news some years ago. The problem was very well covered.   

To those who want to know what is probably happening on tail and causing problems, I wrote some years ago a post here ... but now I cannot find it quickly. The problem is that elevaror can cause abrupt changes in boudary layer on tail at 0 AoA and small elevator deflections, what can be (one of) answer to Davids findings. And why shaking ICs thend to cure the problem.

There is one more overlooked fact, line separation in tip can also cause and cure hunting, I wrote it several time here on SH also, the problem is that precession makes parasitic influence to controlls, which can be positive and also negative - means it can be stabilizing and also destabilizing ... the same does Rabe rudder - and that is the reason why it must be carefully adjusted (all together). My solution for that is up line back and Rabe ruder traveling only necessary amount as overdone travel will again cause hunting.

Offline Igor Burger

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Re: What makes a stunt plane groove??
« Reply #15 on: July 09, 2016, 01:38:17 AM »
In stunt, my best guess for good grooving is building precision. L

or may be imprecision, inliners are naturaly unballanced - props pushes nose up, while the rest is in neutral, so it needs permanent push down during flight - David also writes about "stab off" :- ))) ... and I would say that is just what the slope in elevator does - flaps go down in level and elevator stayis in neutral = some kind of "tail off" but slope in elevator will be my last try on PA stunter

Offline Matt Spencer

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Re: What makes a stunt plane groove??
« Reply #16 on: July 09, 2016, 04:17:18 AM »
This may be a Draftsmans Error , But it appears that theres some chap called Walker whos flown a bit of stunt , who thinks a ' Dead Zone ' Elevator is some use . The EFFECT is the SAME , Virtually .Re Flap Presidance .



Will start on Stab. Airfoil Aerodynamic Consequenes in another thread , If we're not carefull .

NO DISRESPECT INTENDED , but were each in our own part of the Universe .  ;)

The blunt ( say 5/16 rad. on 5/8 Stab. ) L E  tailplanes were said in a post on ' hunting ' to stop doing that When Sharpened , by the experts .
My view is that theres a high drag , or aerodynamic Resistance AT the L.E. there , at a reasonable ( sounds like a feminist  ???) deflection the
center or resistance , or center of pressure / The POINT ( Spanwise Line ) at which the predominant FORCE at the Tailplane SHIFTS from say
the L E to the Hinge Line ( approx ) . Although the force is Not the Same , The Value ( amount ) of force is the maximum , and thus predominant
force at the rear of the plane , Vertically . IF we look at the Std. ' hunting ' of the seperation point of the LE due to the large Rad There ,
Rather than a SHARP ' split ' at the LE where the sepearation over and under is limited in its vertical placement .

The Rearward Force at the LE of a blunt entry tailplane can osscilate say 1/4 vertically - Preimarilly a Rearward Resistance , it is over the
Airframes center of resistance . In the case of the inline set up , Its Still Over the Wing Wash - which would be to a degree turbulant ,
thus varying in % therefore the resistance of the tailplane ( in level flight ) is not entirely constant . Thus a Blunt LE Tailplane is perhaps
not suited to a reaward C of G , unless countermeasures are employed -

thus a simlar % variation in lift to maintain ' Tracking ' .

while a ' Dead Zone ' elevator , and a ' free deflection ' ( maybe it should have a softish bush ?? ) elevator are not identical ,
they havre as many similarities as differances - in regard to airflow & force input . So can be considered related .

FURTHER , Al's Airfoil tests in bumpy air were said to consider a sharper LE was ' More Constant ' ( less variation ) in its lift characteristics
than the more commonly accepted ' blunter ' entry type .
Again the ' seperation point ' ( in airflow under & over ) is more sharply ( excuse the pun ) defined .

I would think a reliable / stable center of lift & its proximity to the center of gravity , combined with a similarly stable center of resistance
( longitudinal Airflow fore to aft ) provide the ' locked in ' hot knife through butter ' traction ' for non erratic vertical stability .

Assuming No Control System Deflection ( i.e. a Fully Ridgid input / output Atmospheric Wind Flow )


Id say over 15 Kts Wind a wing loading around 15 Oz Sq Ft alows the inertia and control inputs to stand a beter chance of ' flying straight ( On Course )
Than a wing loading below say 12 Oz Sq Ft . And Less Liklyhood of spontaeneous disintegration of the ship in winds over 20 knots , particular gusting / turbulant .

AND with a Fully Ridgid Airframe AND Control Syastem , A loading of 20 Oz Sq Ft WILL Track Superbly through 25 Kt Winds , with suficant Control Authority .
Thoughitll take a day or two to calm ( the pilot ) down after . But that wouldnt be unexpected in other forms of ' motorsport . S?P   H^^
« Last Edit: July 09, 2016, 12:18:08 PM by Matt Spencer »

Offline Howard Rush

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Re: What makes a stunt plane groove??
« Reply #17 on: July 09, 2016, 02:27:57 PM »
To those who want to know what is probably happening on tail and causing problems, I wrote some years ago a post here ... but now I cannot find it quickly.

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=133980&mesg_id=133980&listing_type=&page=6

Frank Williams also posted something about laminar separation bubbles.
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Offline Howard Rush

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Re: What makes a stunt plane groove??
« Reply #18 on: July 09, 2016, 02:31:39 PM »
This may be a Draftsmans Error , But it appears that theres some chap called Walker whos flown a bit of stunt , who thinks a ' Dead Zone ' Elevator is some use .

Draughtsmans?  Mr. Walker's elevator is rigged about 4 degrees down with zero flaps, so I doubt if the deadzone, if there is one (and my crude XFoil runs say there isn't) manifests itself in level flight, particularly upside-down level flight.
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Offline rustler

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Re: What makes a stunt plane groove??
« Reply #19 on: July 09, 2016, 05:41:38 PM »
http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=133980&mesg_id=133980&listing_type=&page=6

Frank Williams also posted something about laminar separation bubbles.

I haven't the faintest idea if this is relevant, or even the same subject, but.....
Mike Gaster, the 1954(?) world F/F power champion (now Professor in Experimental Aerodynamics and FRS) appeared at our F/F Nats a couple of years ago. Intrigued I googled him and discovered he has a most distinguished history. One of the things mentioned was that he has produced significant research into bubbles in the boundary layer. At this point I opted out, but what a magnificent career. Still working well into his 80's.
Ian Russell.
[I can remember the schedule o.k., the problem is remembering what was the last manoeuvre I just flew!].

Offline Keith Renecle

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Re: What makes a stunt plane groove??
« Reply #20 on: July 10, 2016, 09:18:55 AM »
Thanks Igor (as always!), I understand that there is no quick fix because of so many things that can cause this problem, but I am trying to figure out if there is something basic that I am repeating that is inherently wrong. I take your point about in-line model theory, and if I do build another big stunt model I will not use it again. Having said that, it seems to work well on the Shark, especially the older version. Maybe it has built-in down-thrust??

Thanks to Howard for the link to the older article on Stuka Stunt. I'll take some time to read that in detail.

Keith R
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Offline jim gilmore

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Re: What makes a stunt plane groove??
« Reply #21 on: July 10, 2016, 12:37:37 PM »
I though coming in inverted at about 10-15 degrees up elevator  at full speed made a nice groove in the ground. n~ S?P

Offline Andrew Tinsley

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Re: What makes a stunt plane groove??
« Reply #22 on: July 10, 2016, 02:58:31 PM »
Just to be clear, I think using elevator play is a "last resort" when trying to stop hunting in a stunt model. The best model that I ever built was aligned to perfection, I took hours and hours getting everything straight in terms of wing stab and engine alignment etc. It turned out to have the worst hunting problem that I ever encountered. So I probably am not so good a builder as I thought I was! A small amount of slop in the elevator cured the problem.
I would certainly like to track down Ted Fancher's Stunt News article. Ted has a knack of explaining things in terms that I understand!

Andrew.
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Offline Chris Wilson

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Re: What makes a stunt plane groove??
« Reply #23 on: July 10, 2016, 08:49:37 PM »
I am firmly in the down thrust camp with counter clockwise engines.

And I am sure that the all inline Sharks have a slightly raised thrust line to ensure that the thrust wants to pull the upper half of the model around the centre of pressure to counter the natural opposite.

Even if its setup at 0-0-0- the act of raising any one of those datum lines in parrallel will have an effect.
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Offline Matt Spencer

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Re: What makes a stunt plane groove??
« Reply #24 on: July 11, 2016, 02:45:26 AM »

I think rephasing the QUESTION , to ' What Makes a Stunt Plane NOT Groove ' might be a better propisition !

Quote
Nevil Shute Norway (17 January 1899 12 January 1960) was an English novelist and aeronautical engineer

Some of his books give a good insight into flight stability issues - The 1930s era - where minimal airspeeds could lead to erratic  flow patterns .
The other extreme is the ' Laminar Flow ' where a dead fleas dropping can cause seperation .

Quote
I though coming in inverted at about 10-15 degrees up elevator  at full speed made a nice groove in the ground. Stir the pot

Indeed . The Spifire / g 51 ! , with a bulky nose , 3 in spinner , and tapered fuse from the mainspar to 1/4 in. at the tailpost , chuffing along at say 6 sec a lap is semi stalled , or at least ' nose up , tail down , waffling along.
Decidedly ' UN - Locked in ' .
However at about 65.5 the flow suddenly attaches / suffers a ' pressure switch ' , or assumes akin to laminar flow and it ' locks in ' positive control responce and ' neutral ' steering .   HOWEVER .
Levering on the Elevator one Night , there was a bizzare GRAUNCHING Noise . %^@

Later Flying it with the G-51 It Had a Strange noise in the Engine , so was parked for a bit .

Id tried it on a 10 x 4 three blade earlier , for a more locked in control in rough air - the engine sounded a bit odd . Wondering if a colder plug wouldve stopped it sound like it was going to blow the top of the motor .
Got a g 40 Now for 4 in pitch & high Revs / output . For that sort of thing .
ANYWAY ;
Put in a new IRVINE 40 FiRe , zorst up'n out the tubes up there , and went flying .
V Good & ' locked in ' but a bit quick , and The Engine made a funny ( graunching ) noise , :-\
third flight & it'd loosened of and leaned a bit. And Still Had a Funny Graunching Noise in the / engine ? untill the wingover , where ( for those who are practised at reading Tach's & Guages in corners ) On The Pullout at level
the nose started drifting DOWN , First Responce was Flaps Down ( LIFT ) ( or they were UP , but as we're inverted ) elevator Neutal . 90 Degree Free Play . :-X which got it back in the GROOVE , the nose drifted Down ( or Up
which when inverted is Down ) This Time a weight down on the handle Got Flaps Toward the Ground , also . . . The Elevators . . .
So From a Straight Fast wingover & hard turn out at about 4.5 a lap on the 10 x 6 Black tree blade ( my Last ) there was a trench from 50 ft from the corner to 60 ft. Along with the outboard wing ( Diheadraled .Now Disjuinted )

The GRAUNCH had been a diagonal split along the wire half thru for 1/2 an inch . We THOUGHT it was the MOTOR . Both Times . There was No Coincedance . It was NOT the Motor making the odd graunching sound in resonance.
It was the rear of the pushrod . :P

O.K. so , Some things that can cause orrible tracking "

The Old Fokker D VIII Trick . Torsional Ridgidity ALONG the Wing . = Non Stable Incedance . IN the Fokkers case it was a ridgid REAR Mainspar & a bowable front spar, So At Speed ( Snoopy on the Tail ) Turning ( nose down, full tit )
The Front of the Wing would Try to Wrap around the Rear of the Wing . aka , Control Reversal , or the Ailerons acting as Trim Tabs. BUT bot in this case , INCREASED Loading on the WING caused the Front Spar to Bow - like most do
at some point .
But the Ridgid rear spar would not. The Increased Incedance ( twist ) remember at speed ( Tho Thats Irellevant - Its The CONCEPT of torsional imbalance ) increased to load which increaed the incidace . Which tore the wing apart.
Pretty Much in an iota .of time . Count of Two .

The Genisis Ive just Got has Soft Horn Arms / ( Theyre Springy ) Twisting Them Approximating Paerhaps HALF the Flight Loads Has Them Deflected say 5 degree . Flight Load perhaps twice that , but more springy . OBVIOUSLY
if the Control Surfaces are SPRINGING About, somethings going to happen . As Theyre Aerodynamic . The Control Surfaces .

Secondly , The 1/4 Sheet Flaps arnt covered in any paper / Fabric / Cloth . Theyre Horrbly Soft and soggy . In the Thubs Theyll Coil about 20 degrees . Or More - at about this or that with the tumbs . You Hesitate at twiting em 30 .

Thirdly ( Being a Good Chap and knowing Bob ( the designer ) hates elevator slack . I Bushed it OUT . Zero Slack .

SO NOW , where before it was just the wind rolls & gusts that had it deviating , Now Its inclined to ' go its own way ' if you pay any attention to it . i.e. tryb steer it in a groove , rather than following it with the handle .
Zero Slack gets SPRING everwhere .

Obviously the swine needs New horn Arms , and the flaps need looking at sternly . But at 55 Oz for the size , Worth the bother . When I find the time . And Likely the 4055 abc K&B 40 .

The Spitfire ( Cribbed From Tony E$fflanders  device that won the British Nats TWICE , and Compostellas thing that won the Euro & Italin Chaps Half a Dozeb Times , But Built like a Sopwith Camel . Only Better .

Remember SOPWITH ran in the Americas Cup when they had Real Boats, not Plastic Ones , and 90 man crews . Also A Pioneer of Aviation and Director of HAWKERs Aviation.

Thus This Overly Glued Spruce And Silk Monstrosity ( 72 Oz , 63 in ) Could be Got Over Your KNEE and the Tips pushed up and down a few inches . AT say 20 Lb Load @ Ea Tip/ OR MORE .

The Early Aircraft Companys Calculted Their Strengths Via Sandbag Loadin the Inverted Aircraft . Used to wonder What'd happen to your average Stut Ship with 20 ' G's ' worth of weights strewn about it .
A worthwhile pursuit if you have one thats not going to see the air Again , I should Think .
« Last Edit: July 11, 2016, 03:55:21 AM by Matt Spencer »

Offline Matt Spencer

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Re: What makes a stunt plane groove??
« Reply #25 on: July 11, 2016, 03:56:37 AM »
Better to make use of whats available rather than nothing at all .



Next Thing is WIRES . .016 solids strech a bit more than 7 strand .018 steel . Ive Found .

.015 stainlesss 7 strand in the calm on a 57 Oz Plane were fine , at lunchtime. At Sundown in the rolling gusty coastal air were on the verge of uncontolable and breaking , with the stretch . Brand New . ST 40 / 46 & a 11x5 or 4 .

The Wirlwind on its first flight in steady rural air ( Steadilly And Firmly Moving , somwhat ) porpised . Contry to the first urge I OPENEd the Line Spacing . the Sepearation got the stretch Less % of Movement , and it tracked. Good.
Thats 60 Oz  , two 19s nitro & 60 Ft 016 solids moving ( Stretching - on a small plane ( a Twin Injuned 60 Oz Oriental in fact ) giving ' the weave ' / porposing .

I cant see how Any Plane can groove , let alone fly accurately on 7 strand .015s in and good wind . Particularly if they havnt been run down with a rag & allowed to revolve to get rid of half of it . Tho I can remember people
using SWIVLES in the Line Connectors back in the 70s. a few anyway. In Comps .

SO I Belive stretchy Wires have Dictated Stunt Design . A Windys Tape has a Eight Winged thing doing a respectable schedule . Has This Made the Conventional ship Obsolete , as ( with )a few decades development it should
surpass it easilly !  >:D ??? n1

Offline Matt Spencer

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Re: What makes a stunt plane groove??
« Reply #26 on: July 11, 2016, 04:26:17 AM »
When you realise how atrocious many aircraft were over the years , you can understand that not all preconcieved the pitfalls inherant in aeronautics , or the unknown .



the aerodynamics of a C/L stunt ship , due to Speed Range , would be More Akin to THIS order of Aircraft than most . Believe it or not . Look through the paraphanalia for its Essence , Area - Longitudinal Stability - & Manouvreability .
its got to get a torpoedo in , Straight & True . Drop in on a wing - Hit a ' Groove ' to stabilise Aim . The ( Hopefully ) Skip The Target . One way or another . Double the chord and loose a wing ( Forget the struts & wires ).
of couse you could leave it as it is , use symetrical airfoils , and get Two Foot ' Square ' corners .  S?P S?P
« Last Edit: July 11, 2016, 04:47:30 AM by Matt Spencer »

Offline Steve Helmick

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Re: What makes a stunt plane groove??
« Reply #27 on: July 17, 2016, 12:11:24 AM »
After Matt's contribution, I feel so inadequate!

But I recall one Canadian fella (Bruce Perry) saying that he hadn't been able to get his new (#1) "Jester" (IC powered) to groove on Saturday's practice, but he went home and read Paul's "Impact" article from Flying Models (yet again), went down in the shop and moved the LO's aft 3/16" (~4.7mm) and no more problem. Was it moving the LO's, or was it just from reading Paul's article?  ;) Steve
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Offline Matt Spencer

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Re: What makes a stunt plane groove??
« Reply #28 on: July 18, 2016, 06:50:51 PM »
 %^@

rather rthan resurect the New Hack - Genisis post , HERE we Go . :P

" If you dont breath to heavily , it flys o.k. , but if someone over the fence waves a hand, it goes into convulsions "  ;)

A bit of a breeze , and the SPONGE in the controls has it veering about elswhere , other than where you intended. AND it only weighs 55 ounce . >:(

SO , ' WE've Hacked in , sawed thru the horn arms ( A blade wedged in to hit , rather than saw thru the wing , when the wires gone ) De Solder ,

Bend and twist , the Wires removed from the wing ( he hadnt sanded the wire & used Aryldite - Just As Well !  :P)

Was already semi butchered , patches inside the fuse. there from a crack up , maybe from ' vibes ' . Who Knows ?
So will need a CUT down from the TOP , to slide in a NEW 1/8 in. dia. Flap Horn set up . Then a few doulbers and a bit ( more ) of Patching ,
flatting off / sanding in .  :o

Flaps'r still soft . Should Tissue . obviously fitted before paint.

A flap will twist 10 - 15 degrees .
The Horn twisted 15 Easy . Twisting ONE flap Set the rest of the controls of - somewhere . Elevators 5 Deg from moving ONE Flap ! .

Elev Horns a bit soft too , but less critical as shorter wire length / torsion arm . So Stays. FOR NOW . on a .40 ship USE ONE EIGTH Dia. WIRE .

 H^^

Offline Bruce Perry

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Re: What makes a stunt plane groove??
« Reply #29 on: July 27, 2016, 05:32:46 PM »
Psychedelic paint makes it groovy Baby! 

...although that may not be what you were after......

B

Offline Keith Renecle

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Re: What makes a stunt plane groove??
« Reply #30 on: July 28, 2016, 12:14:50 AM »
Hi Bruce,

Good one!  #^ I still love your Jester......that is groovy for sure!

Keith R
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Offline Matt Spencer

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Re: What makes a stunt plane groove??
« Reply #31 on: July 29, 2016, 11:24:09 AM »
Quote
Psychedelic paint makes it groovy Baby! 

Clear , Concise , & to the Point . Youve Hit the Nail on the Head .  :) H^^

Offline FLOYD CARTER

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Re: What makes a stunt plane groove??
« Reply #32 on: August 12, 2016, 10:42:04 AM »
I printed Paul's trimming articles, and taped them to my plane's wing for 2 weeks.  At the end of that time, I found all my trim problems had gone away.

Anyone else tried that?
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Offline Chris Wilson

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Re: What makes a stunt plane groove??
« Reply #33 on: August 16, 2016, 07:50:18 PM »
I printed Paul's trimming articles, and taped them to my plane's wing for 2 weeks.  At the end of that time, I found all my trim problems had gone away.

Anyone else tried that?
Increased drag, outboard wing - something like that?
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Offline phil c

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Re: What makes a stunt plane groove??
« Reply #34 on: August 29, 2016, 11:52:44 AM »
Keith, I think it's ruts in the air that make a model groove.  So many practice flights just beats the air into submission.

Phil C
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Offline Keith Renecle

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Re: What makes a stunt plane groove??
« Reply #35 on: August 31, 2016, 11:39:23 PM »
The first time I actually saw this groove thing was when Percy Attfield brought back a video from the world champs in Radec Kralove in the early 90's and this was when Paul Walker won with his tuned pipe Impact. I can remember thinking that there must be some kind of transparent "rail" in the sky at 5 foot because the Impact seemed to lock into that groove all the time. Maybe it is a "rut" like you say!  #^

Keith R
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Offline Peter Germann

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Re: What makes a stunt plane groove??
« Reply #36 on: September 22, 2016, 09:37:58 AM »
Sept. 22 2016, Crossfire

Attempting to improve level and inverted flight tracking by reducing elevator efiiciency around neutral, while maintaining ability to corner, 4 ea. 254 mm (10 in.) long and 4 mm (0.16 in) thick triangular turbulator strips have been temporarily added at the hinge line:
 
Result
A (before):    Stab TE and Elev. LE equally thick. Normal Sensitivity, a bit touchy
B (after):    Very insensitive, tight corner no longer possible. Speed 0.3 sec/lap slower
Peter Germann

Offline Chris Wilson

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Re: What makes a stunt plane groove??
« Reply #37 on: September 22, 2016, 02:47:45 PM »
It 's about here that I want to hear Brett say the word "Phugoid" again!
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Offline Dennis Toth

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Re: What makes a stunt plane groove??
« Reply #38 on: September 22, 2016, 06:37:46 PM »
Peter,
Interesting approach it a step-up from the thick stab, thin elevator approach. Another approach may be using a "Gurney Flap" on the stab top and bottom at the hinge line (I'm thinking a piece of 1/64" ply that extends a 1/16 above and below the edge at the hinge line).

Best,   DennisT

Online Brett Buck

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Re: What makes a stunt plane groove??
« Reply #39 on: September 22, 2016, 07:45:54 PM »
It 's about here that I want to hear Brett say the word "Phugoid" again!
   

     Usually, the phrase "limit cycle" is more applicable.

     Brett

Offline Peter Germann

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Re: What makes a stunt plane groove??
« Reply #40 on: September 23, 2016, 08:36:24 AM »
Peter,
Interesting approach it a step-up from the thick stab, thin elevator approach. Another approach may be using a "Gurney Flap" on the stab top and bottom at the hinge line (I'm thinking a piece of 1/64" ply that extends a 1/16 above and below the edge at the hinge line).

Best,   DennisT

I was, on purpose, exaggerating the thickness of the turbolator to get an idea of the efficiency of the thick stab - thin elevator approach. From the massive influence on sensitivity I found, it seems to have a very noticable effect. Next I will try a 0.8 x 6 mm (1/32 x 1/4) strip.
Peter Germann

Offline Howard Rush

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Re: What makes a stunt plane groove??
« Reply #41 on: September 23, 2016, 05:39:13 PM »
I think you caused (or encouraged) the flow to separate at the stabilizer trailing edge.  A thicker stabilizer might have a different effect.  

It was a nice experiment.  Thanks for doing it.
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