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