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ACRO E-mail Archive Thread: [Acro] RE: Caution on Spade Mods

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ACRO E-mail Archive Thread: [Acro] RE: Caution on Spade Mods



                


Thread: [Acro] RE: Caution on Spade Mods

Message: [Acro] RE: Caution on Spade Mods

Follow-Up To: ACRO Email list (for List Members only)

From: Doyne Keith E MECH <DoyneKE at NAVSEA.NAVY.MIL>

Date: Thu, 10 Apr 2003 17:03:54 UTC


Message:

  
	Neal:


		I think Kermit Weeks was looking at the flutter caused by
spring gear in his Week's Solution.  The result was to put a flow divider
near the spring gear.   If I remember correctly, Henry Haigh mounted the
Ratsrepus wing on a truck and measured the control stick force versus
deflection as the truck drove up and down the runway.  I guess that is how
he determined what spade size and design to start with.    At an airshow in
Connecticut, I remember asking Leo Loudenslager about his "floating" spades
on his plane.  Leo said it was his design, and didn't provide any further
details.  He actually seemed annoyed that I asked him that question.


						Fly Safe,
						Keith Doyne
						IAC Chapter 58
						IAC #10545
		     

-----Original Message-----
From: Neal Frangesh [mailto:LGAENG at compuserve.com]
Sent: Thursday, April 10, 2003 12:11 PM
To: Acro, Exploder
Subject: [Acro] Caution on Spade Mods


David:

It was a long time ago, but I seem to recall that the flutter research 
done by Kermit Weeks was done not too long after Harold Chappel was 
killed flight testing a new Laser style monoplane.  According to wittnesses,

the wing disintegrated during a high speed pass.  The probable cause of the 
accident was flutter.

Monoplanes are (probably) inherently less resistant to certain torsional
wing 
flutter modes than biplanes.  People should be very cautious when making 
changes to the size, shape, and weight of their spades.  As your e-mail so 
well points out, there is a lot more to it than just "cut and try".

Best regards,

Neal Frangesh
IAC 4431


-------------Forwarded Message-----------------

From:	INTERNET:acro at gf24.de, INTERNET:acro at gf24.de
To:	"B. Jensen", INTERNET:bjensen at integraonline.com
	"ACRO", INTERNET:acro at gf24.de
	
CC:	"LaserAeros", INTERNET:laseraeros at yahoogroups.com
	
Date:	4/10/03  8:56 AM

RE:	[Acro] Re: Laser spades

 
An article by Kermit Weeks in Sport Aerobatics of 18 July 1982 describes the
background to the introduction of spades to the Laser type monoplanes.
Kermit had arranged for "probably the world's most leading authority on
flutter", Leon Tolve,  to get involved. In those days Australia did not have
an Experimental Category and, once issued with a CofA, home-built aeroplanes
were treated very much like factory built aeroplanes. (The first-of-type
certification process was much easier however). So, any modifications
required engineering substantiation similar to an STC. Kermit's article
resulted in an Australian AD for the handful of Lasers then flying. The AD
limited the airspeed to 139 Kts pending an approved modification. Leon Tolve
recommended a particular combination of mass balances (tip plus 42" from
tip) to eliminate a potentially dangerous flutter mode. The inboard mass was
to be 8.375" forward of the aileron hinge line and weight would depend on
aileron span eg  3 lb 1 oz for 95" aileron. Tip mass was to be 1.75 lb (as
per original) 6" forward of the hinge. Leon kindly provided his flutter
analysis to assist in Australian approval of the mod. The additional inboard
mass balance added significant inertia to the aileron control system - in
hesitation rolls, for example, it was hard to stop rolling neatly on a
point.

I took Leon's data and did some flutter analysis in an attempt to optimise
the mass balance. In the end I decided that the benefits were not worth the
effort of getting Australian approval. I've heard of people deleting the tip
balance or reducing the mass of the inboard weight - neither is a good idea
without an understanding of what's in this folder I'm currently holding in
my hand. Incidentally, shaking the wingtip by hand (i.e. static on the
ground) and observing the aileron motion gives a very good idea as to
whether the correct mass balance is installed.

I next turned my hand to "optimisation" of the spade. Mass and cg required
as above (not all the experimental spades achieved that). Some scope for
different length (streamwise) of spade depending how far below the wing it
hangs. Sorta ruled out triangular shape as it'd dig a hole in the underside
of the wing with the geometry of the support tube that I had chosen. Other
variables were material, thickness and width. I started with a steel spade
(note all figures that follow are approximate) 9" wide and 7.8" long of 1/8"
thick steel. After trying one other size set of spades I had enough info to
guestimate the aerodynamic hinge moment characteristics of aileron plus
spade. Problem occurred with a large spade - length and width was quite
large so I used 0.063" thick steel (to get the mass right) which is quite
flexible (flanged sides would've helped but ...) Above 120 kts there was
sufficient flexibility in streamwise bending of the spade that spade lift
was significantly non-linear leading to aileron overbalance - progressively
worse (snatch) at higher airspeeds. The final spade tested was 13.5" wide
and an average of 8.7" long (i.e. not rectagular). 1/4" thick Aluminium gave
the required mass. The one that I ended up getting approved was 12" by
9.75". Stress analysis of the support arm and local aileron spar attachment
was done. Airspeed calibration, flight flutter and handling tests were
performed as part of the approval process. VNE 204 kts.

Regards,
Dave Pilkington
----- Original Message -----
From: "B. Jensen" <bjensen at integraonline.com>
To: "ACRO" <acro at gf24.de>
Sent: Wednesday, April 09, 2003 1:11 PM
Subject: [Acro] Laser spades


> I'm in the process of making new (more effective) spades for my Laser.
>  Can someone in acroland tell me if certain shapes and sizes work better
> than others?  Right now my spades are simply rectangular, flat pieces of
> metal. They don't have any special bends or shape to them.   I have seen
> spades made in various shapes, sizes, curved edges, etc, but what is the
> ultimate shape, and size spade for a Laser?
>
> Another thing I'm sure needs attention is keeping the weight of the new
> spade the same as the old spade, since everything is in balance right
> now.  Anything else I should know on the weight issue would be
> appreciated also.
>
> Basically, tell me all you know about spades!  (or let me know of
> someone who is a spade wizard)
>
> Thanks,
>
> Bryan
>
>





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