Karl Nickel's Falter 1 tailless aircraft

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

danmoser

Well-Known Member
Joined
Feb 1, 2010
Messages
642
Location
Sandy, Utah, USA
-can anybody finde short info about BKB1 stability in "Tailless aircraft" book\page circa 200-230?\
Very little mentioned about BKB in Nickel & Wohlfahrt's book .. only that tumbling (they call it "autorotating") could be started & stopped "at will" on the BKB.
This also occurs on other low-sweep wings .. like Al Backstrom's "Plank".
It does not mean it is tuck-resistant .. rule of thumb: if it tumbles easily, it will tuck easily too.
Tucking and tumbling are related to low pitch damping .. not pitch stability.
Best remedies for tucking tendencies are lower aspect ratio (longer chord), and greater sweep angle.

Tucking rotation is most often caused by strong thermals or mechanical turbulence, and made worse by most weight shift gliders being attached to the main mass (pilot's body) with a hang strap.. so the pilot mass can be decoupled from the wing briefly during negative G loads.
If the pilot falls into the glider's air-frame hard enough, it can break something.
BTW, a hang glider buddy of mine has gone into a tuck situation multiple times, flying his high aspect ratio wing in very strong thermals .. but his glider is very strong and hasn't broken (yet), so it has always recovered quickly without needing to deploy the reserve chute.
 
Last edited:

Norman

Well-Known Member
HBA Supporter
Joined
Nov 28, 2003
Messages
3,081
Location
Grand Junction, Colorado
It says that you should put turbulators on the bottom of the wing at the 65% chord point, particularly in front of a control surface. Also at 15% chord on the top of the wing. By 'turbulator', I guess they mean 'vortex generators'?
That article is from a model magazine. At the Reynolds numbers that models fly they are concerned with laminar separation. The trip mentioned is a strip is tape about 1/3 of a millimeter thick. Its purpos is simply to trip the laminar boundary layer to turbulent before it hits the adverse pressure gradient so it's less likely to separate. Vortex generators bring energetic air from farther away from the wing closer to the surface to energize the boundary layer so that it can stay attached against an adverse pressure gradient longer. Similar effect one is just bigger. I've never seen VGs on the lower surface of a flying wing but I do think it's a good idea for the same reason that you see them in front of the ailerons (but to far aft to work to delay the stall) on some high performance planes.
 

danmoser

Well-Known Member
Joined
Feb 1, 2010
Messages
642
Location
Sandy, Utah, USA
=the last phrase is very essential...\IHMO\.
referring to starting and stopping tumbling at will.

Nickel& Wohlfahrt exact wording about tumbling .. "It is also said of the Kasper-wing .. that this flight condition could be achieved, and also be stopped without difficulty"
Note that the authors were merely repeating claims that Kasper himself made about the wing, and not validating his claims independently.

I forgot to mention on the subject of tucking: it is much worse with a flexible wing hang glider, as the sail TE blowing down has a "down-elevator" effect... rigid wings do not have this problem, and can be expected to resist tucking more effectively.. the Falter 1 has a flexible TE, but it is rigidly coupled to the control cables.

Modern hang glider designs are safer now because the trailing edge is better supported with luff-lines, washout struts (AKA "sprogs"), or both ... even so, HG tucks can still occur in extreme thermal conditions, and a few reserve chutes bloom every summer. ;)
 

danmoser

Well-Known Member
Joined
Feb 1, 2010
Messages
642
Location
Sandy, Utah, USA
Dr. Nickel's partner on the Falter 1 was a fellow named "Ali Schmidt" .. but I noticed his name in another part of the book was given as "Albrecht Schmid" ..

So if any of our European friends know a guy named Albrecht Schmid, or Albrecht Schmidt, or Ali Schmid, or Ali Schmidt .. please contact him and see if you can coax him to provide some details on the Falter 1.

Thank you!
 
Top