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Thread: spin resistant

  1. #1
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    spin resistant

    "Spin Resistant"
    There is a Technical phrase, spin resistant, used by Airworthiness Authorities to suggest that through testing a certain type of aircraft cannot be made to spin [autorotate]. This is phrased so that they don't actually say 'non spinable'.

    Recently the American amphibian ICON A5 has released a claim statement that their aircraft is the first production type ever to be designated as 'spin resistant'.

    The Shadow & it's series were declared by UK CAA - in 1984 to be 'spin resistant' after two CAA test pilots came to CFM & tried to get a Shadow to spin. Daryl Stinton was one of these test pilots - he & I didn't get on.... but I flew him through some very unusual atitude manouvers - abuseing the aircraft for 30 mins The other test pilot tried, flying solo,to upset by pitching up vertically & when 'stopped' crossing all the controls. As Pete Davies had shown us all in 1983 the worse thing a Shadow would do was half a spiral turn. It would completely then recover on it's own. There has never been any indication that this aircraft can be made to spin - & none ever have.

    Americans have never been very good at History - it looks like they copied my wing aerodynamics.

    Cheers, David.

  2. #2

    spin resistant

    Hello David,

    please, could You write more about Shadow aerodynamics - its airfoils, wing twist, dihedral, sweep and what helps to make Shadow spin resistant ?

    Kind Regards,
    Jeri

  3. #3
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    spin resistant

    Dear Jeri Vykydal,

    Thanks for your interest in the aerodynamics of the Shadow.

    What happens in a designer's head and then in practice can be different! In my case with the shadow the purity of the aerodynamics worked just as I had imagined.

    Many times I have beem termed as controversal - I don't care -but have been glad not to have received a black eye yet... I believe in saying what I think and that is why I have my own ideas of how and why an aircraft flys. I don't hold with the Bernoulli theory but John Dickenson - a rated academic - on flight theory explains on my web site davidcookaviator.com his mention of my work. ref. date 7 12 10, &17 02 11.

    For your enquiry Jeri.......... angle of Incidence is +3 degrees

    tailplane incidence is - 1.5 shadow

    -1.0 streak

    drooped L/E 0 at root, - 2.3 degrees at tip

    zero dihedral - staight wing

    washout only on 'D' section - ie. -2.3 degrees, no wing twist

    chord thickness ratio 15% shadow

    13% streak

    If I ever asked top people certain questions, not actually 'in the book' invariably they said, 'try it & see'. So really I found my thinking was, on my own - just as good as theirs!

    Someone I admire is Ivo Boscarol of Pipistrel - Slovenia who recently invited me to his factory & congratulated the Shadow safety record. No, it won't stall or spin - the two things that endanger more than any other, the problems with flight.

    Sometimes certain individual shadows/streaks seem to 'up the game' beyond accepted normal characteristics of the series eg. 02 shadow will continue to be controllable below an airspeed of 20mph. 108 streak's performance seems to exceed others in climb & level speed - can't explain....

    I once held the control stick fully aft with an idling engine at 1500ft altitude. 02 then decended in a nose high mush decending at 200 to 300fpm and would have impacted the ground at about the same rate as a parachutist.....facinating.

    My own initial thinking was that only the first 33% of the 'D' section does the work. A bow pressure wave exists forward of the wing - just as porpoises use in front of a ship. Downward pressure is used by the wing through an angle of attack - which is revealed and shown in 'ground effect'. Downward pressure exists on the shadow wing upper surface except on the outer two panels but this can change with flaps deployed, when ballooing across the whole surface seems to happen.

    The drooped L/E is the key - something Dickenson didn't pick up. Victor V bombers had a section of drooped L/E which I noticed when serving in the RAF on 57 Sqd. - early 60's. The Vulcan eventually put their wing 'right' on the B2 series with a similar droop.

    The Icon A5 got their wing profile horribly wrong, evil it seems, to have to employ NASA's wind tunnel and the brilliant Mr. RONSZ aerodynamist to get it right. The end result now looks like... you know what ....

    Dad said that I had more ideas than a cat has fleas - some of this different type of thinking actually works.

    I had a VIP invite recently to the Typhoon Air Defence No. 3 Sqd. at RAF Coningsby. Given a two hour brief around and in this worlds top fighter it was said to be non stallable nor spinable because one of the 80 computers inside will keep the flight regime away from divergence.

    So all one has to do is spend Ģ70 million quid - or own a CFM aircraft!

    Cheers, David.

  4. #4
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    spin resistant

    David,

    I throw 2p additional to the twist/washout within the shadow wing - and sorry to teach granny to suck lemons the following exlanation is kiddy level - its my best level of operation :lol:

    There are two basic types of twist/washout being geometric and aerodynamic and I think that due to the way you have built the droop into the outer wings in the leading edge DCell only you get both so depending on how you have defined the -2.3deg it may well be effectively more.

    The geometric twist is relatively easy to measure - LE to TE incidence between root and tip gives you the geometric twist ... I assume that your -2.3deg is this measure

    The aerodynamic twist is the incidence between the zero lift angle of the root and tip chords. You built all the 'twist' into the DCell leading edge and left the section behind the spar the same across the wings (Correct?) if this is so then the outer wing sections are increasingly higher lift sections and will have zero lift angles lower than the root ... adding more effective twist into the mix making the wing even more spin resistant.

    I suspect the genious of the shadow wing in practice is that the droop has added greatly to the spin characteristics without added too great a penalty in drag in cruise - same as the Jodels with the twist as a 'jump' at the wing crank. The benefit of your twist is also to move the centre of lift inboard in cruise making the wing appear smaller in span terms the air and less impacted by rougher air - lots of benefits of twist and a few obvious costs - yours seems a very happy balance.

    Cheers. Kirk

  5. #5

    spin resistant

    It has always struck me with a few hundred hours flying a variety of shadows that another couple of factors also contribute - maybe in a big way, to its stall / spin resistance. The up elevator response is quite limited, so often at forward Cg the angle of attack is limited to below the aerodynamic stall angle and even with aft ish Cg it only just tickles it. Also the rudder is quite small and limits yaw angles.

    I have carried out spin testing for the Xair, Skyranger, Swift, Nynja, and Eurofox for certification. Most of these require 'bullying in' with a good snatch of up elevator just before the stall to accelerate the alpha change and a good boot of rudder - again in advance of reaching the stall inj order to generate a larger yaw angle than woudl be possible if it were delayed. Unless full control is used most of these cant be made to spin. The Skyranger only really spins courtesy of a very big rudder - the Nynja with same wing but a smaller rudder and greater fin area is far more reluctant. many of these aircraft it appears could be made apparently 'spin resistant' by simply restricting control travel further.

    So it would be interesting to speculate which is the dominant calming force with the Shadow - elevator, wing or rudder? Or maybe a subtle combination of all? did you vere try it David in a configuration where you had greater elavtor and rudder response?

    On a side note - it always amuses me that people moan about the wing laoding restraints of SSDR, and claim you cant make a good handling machine that can be flown in any wind / turbulence at all. Of course the shadow was designed as a 10kg/M empty wing loading machine and when flown solo has a lower wing loading than a 10kg/ M empty loading SSDR would - yet has a deserved reputation for good perfromance , good handling, good turbulence rejection, and has flown to Australia twice!

    Paul

  6. #6

    spin resistant

    Dear David,

    thank You for kind and interresting explanation, info about Shadow aerodynamics. I hope I understand it right - drooped LE means twisted D-box ? Unfortunatelly we havenīt any Shadow - one was crashed by pilot years ago, so no one exist here to see it in natura.

    I always thought to have or build some plane that seems like Shadow so wanted to know more about.
    Although I heard, read that Shadow airfoil is inspirated by VJ23 or some helicopter airfoil and saw photo of Shadow wing root, I couldnīt imagine clearly its work. Please, could You share airfoil coords with wing chord at root and tip + chord and span of ailerons, flaps ? Could You share some detailed photos of wing, its parts and structure ?

    Best Regards,
    Jeri

  7. #7

    spin resistant

    Hello David,

    Could you advise on the angle difference in the front wing and tail wing in flight, in flight the nose attitude is quite steep up. would he plane achieve higher speed if the angle of attack would be flatter? and 2? if the difference between front wing back wing angles also lead to improved speed and less forward pressure on the stick?

    Thanks Andrew

  8. #8
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    spin resistant

    Dear Andrew,

    If you take the trouble to look at the technical data that I supplied to Jeri Vykydal on the same

    'spin resistant' site - your questions are mostly answered.

    Please note the D series Shadow was developed from B series, i.e. from 40hp to 65hp, thus the D series is faster. If forward stick pressure is necessary increase the trim tab 'up' range for max. level speed.

    Are you suggesting I got the design wrong?

  9. #9

    spin resistant

    Hello David ,
    Most certainly not questioning the design> Streak handles beautifully!

    I ask the question WRT to speed. The Streak flies nose up attitidude and i was thinking if it would fly faster with the fuselage section level. Would the angle of the tail have to be changed to achieve this?

    Thanks

    Andrew

  10. #10

    spin resistant

    Dear David,

    Am longer time thinking about building Streak or StarStreak, as we haven't much of them here and experienced friends would help.
    For start I have main tube, that was used in twoseater ultralight and friends experienced in composites, wood and sheetmetal aircraft repairs.

    Am I too shameless if asking for wing, fuselage drawings and info ? Yes, probably I am, but it seem that other way to Streak or StarStreak not exist.

    Best Regards,
    Jeri V.

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