RSS BMAA on FaceBook BMAA on Twitter HomeLog InRegisterSearch the ForumHelp
   
BMAA Forum > Public Forums > Microlight General Chat > Turbulence compensation  Forum Quick Jump
 
New Topic Post Reply Printable Version
[ << Previous Thread | Next Thread >> | Show Newest Post First ]

Kev Armstrong
Uncultured Northern Oik



Click to send Kev Armstrong email.Personal Homepage Not AvailableSend a Private Message to Kev ArmstrongAIM Not AvailableICQ Not AvailableY! Not AvailableMSN Not Available
Date Joined Dec 2005
Total Posts : 4247
 
   Posted 21/2/2011 12:13 PM (GMT +1)    Quote This PostAlert An Admin About This Post.
(Not a demand for a cash payout for having coffee spilled on you by the stewardess in bumpy conditions)
 
Came across a discussion on Reno Racers where one design had the main spar too far backthe area in front of the main spar was big enough for the wing to be 'divergent' when flexing up and down in bumpy air. This meant the wing exaggerated bumps by flexing and 'flying' even more than it should.
 
Flex leads to shortened life on a metal skinned structure, but our fixed wings tend to be fabric over a steel or alloy tube frame; wing-warping is now regarded as old-fashioned and generally something to be dismissed as a pre first world blind alley, but you can't help wondering if the needs of even a modern microlight could make use of it?
 
The attached poor sketch tries to explain; by allowing the rear lift struts a little motion in response to bumps, the wing 'stress relieves' itself in rough air. You can engineer this pretty simply using a rocker beam at the base of the rear pair of lift struts. The problem is that the ailerons would then also 'fly' the wings in the opposite direction you want when operated, so you'd die.
 
This then led to the proposal that by the joystick actually be used to bias the rear rocker mounting, so that the wing would twist progressively along its length, rather like a propeller does. You get to dump all those fiddly cables and pulleys running around the cabin, and instead just have one ruddy great stiff tube along the middle of the cockpit floor to move the rocker beam for roll control.
 
Might be useful on aircraft such as the Skyrangercould then be feasible for the wing to fold back easily without undoing cables?
 
Sadly the flow of cranky ideas didn't stop there....
 
That centre rear pivot bearing supports half the weight of the aircraft, 225kilos for us and only half that on an SSDR. Enabling the rear centre pivot to rise and fall, against that weight, means you can vary the angle of incidence of the wing itself. This makes flaps, slow/fast flight and all sorts of other dodges possible, although losing the washout in slow flight would need expert input at the design stage.
 
So rugged, simple, easy to design and just possibly lighter than having flaps, ailerons and thier associated cables and pulley in the cabin and wing.
 
Wonder why no one has done it? Or have they?
 
Cheers
 
Kev
 
 
 
 


"The young man knows the rules but the old man knows the exceptions”...Oliver Wendell Holmes


Image Attachment :
Image Preview
Turbs Compensation.jpg
  86KB (image/pjpeg)
This image has been viewed 123 time(s).
Back to Top
 

Kirk Sutton
Someone shut this guy up!



Email Address Not AvailablePersonal Homepage Not AvailableSend a Private Message to Kirk SuttonAIM Not AvailableICQ Not AvailableY! Not AvailableMSN Not Available
Date Joined Mar 2009
Total Posts : 870
 
   Posted 21/2/2011 1:39 PM (GMT +1)    Quote This PostAlert An Admin About This Post.
Kev,

Two points

Wing free flying to relieve the structure in rough air - see Mignets (any of them) and you have an example of the light yet stiff structure of a wing floating freely through the air - no fiddly aeilerons to worry about on the free wing either (that might explain the HM1100 Courduran having them on the rear/fixed wing) The 'problem' with this form of free floating wing is that there is a solid mechanical link to the control column (except for the Courduran and one other) and this feeds the rough air back to the pilot - not a real problem because like a flex wing pilot you quickly learn to let the stick go fore/aft with the air and not restrain it.

Using differential rotation/pivot around a main spar line exists for roll control on microlights as well ... there is the French biblane with the rotating lower wings and there is a single seat flying boat from OZ that uses a single high mounted wing pivoting around the main spar.

In the case of the fleas and the OZ flying boat the wings themselves are effectively monospar wings with a minimal rear spar used to help maintain stiffness and to attach ruddy great big push/pull rods to - there is no rear lift strut on these wings.

Unless you wanted to go back to a flexible wing on a three axis machine I am not seeing the real attraction to moving to a simpler wing (ie not monospar) with a complex rear strut control system.

I can help point to you to one where it was used - the Kimberly Scout in OZ (derived from the Skycraft Scout from 1974/5) that did pull the trailing edge of each half sail down to turn (Skycraft Scout used rudder only in the MkI and II) but that was more to do with the wings being two dingy sails attached to 2 dingy masts - make do and modify rather than by design.

Cheers.
Back to Top
 

Kev Armstrong
Uncultured Northern Oik



Click to send Kev Armstrong email.Personal Homepage Not AvailableSend a Private Message to Kev ArmstrongAIM Not AvailableICQ Not AvailableY! Not AvailableMSN Not Available
Date Joined Dec 2005
Total Posts : 4247
 
   Posted 21/2/2011 2:56 PM (GMT +1)    Quote This PostAlert An Admin About This Post.
Kirk Sutton said...

Unless you wanted to go back to a flexible wing on a three axis machine I am not seeing the real attraction to moving to a simpler wing (ie not monospar) with a complex rear strut control system.

*Was hoping to tempt you to supply this info, which you hinted at when last we spoke.
The Thruster wing is two spars, just bits of tube, isn't the Skyranger similar? My point was that a fabric-covered structure is braced in torsion by the outer ends of the lift struts being spread, and mounted close together at the fuse bottom mounts; this plan view triangulation can be biased to twist the entire outer panels by a relatively small change in the base mount on the rear strut.
Must dispute only one point you make; if you look at the 'orrible sketch it is plain that a rocker beam mount is a heck of a lot simpler than the average fixed-wing aileron linkage. By utilising the lift strut itself, instead of adding light cables, you actually get two functions out of one big chunky piece of bracing tube.
A bit like a flexwing control frame; structural brace AND control bars in one elegantly simple structure.
As you say, the stick will 'kick' left to right in turbs, but in compensation for this, the fuselage will roll less; just like a trike pilot when his passenger is sitting comfortably with the trike swaying gently, and he is having to gorilla-grip the bar.
Cheers for the links
Kev


"The young man knows the rules but the old man knows the exceptions”...Oliver Wendell Holmes

Back to Top
 
New Topic Post Reply Printable Version
 
Forum Information
Currently it is Tuesday, September 02, 2014 12:30 PM (GMT +1)
There are a total of 114,665 posts in 10,051 threads.
In the last 3 days there were 8 new threads and 36 reply posts.
Who's Online
This forum has 2714 registered members. Please welcome our newest member, Redcoatduke.
28 Guest(s), 1 Registered Member(s) are currently online.  Details
Chris Bell