New Products Flash Sale
Thread Tools
Old May 12, 2012, 05:39 PM
Shedofdread is offline
Find More Posts by Shedofdread
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
2,354 Posts
Discussion
Planks vs Swept tailless

Evenin' all!

I'd rather like to encourage a little debate here re the pros and cons of 'planks' vs swept wings.

I'll kick things off with a few that come to mind -

+ve plank - easy structure (no swept spars)
-ve plank - hard to set up, trim difficulties

+ve swept - science of stability is understood
-ve swept - structural issues (swept spar, torsional loads)

How do people feel the relative efficiencies stack up? Planks have the potential for more efficient planforms but sweepies can use better aerofoils....

Food for thought?

Richard
Shedofdread is offline Find More Posts by Shedofdread
Reply With Quote
Sign up now
to remove ads between posts
Old May 12, 2012, 06:06 PM
Knoll53 is offline
Find More Posts by Knoll53
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
3,135 Posts
Quote:
Originally Posted by Shedofdread View Post
Planks have the potential for more efficient planforms
Planks must use a reflexed airfoil ( and fins ). Hard to imagine that a reflexed airfoil would ever win in efficency.

Swept and twisted wings at least have the center section for un-adulterated lift. Sure the tips don't contribute, but all planes have tip losses, that is, it's not such a great loss.

Kent
Knoll53 is offline Find More Posts by Knoll53
Reply With Quote
Old May 12, 2012, 07:46 PM
RyanNX211 is offline
Find More Posts by RyanNX211
Registered User
RyanNX211's Avatar
Upper Arlington, Ohio
Joined Dec 2007
1,567 Posts
No first hand experience, yet.
But, I think visual orientation might be harder with a plank than flying something with one pointy end and a fork
RyanNX211 is offline Find More Posts by RyanNX211
Reply With Quote
Old May 12, 2012, 08:06 PM
HerkS is online now
Find More Posts by HerkS
Herk
HerkS's Avatar
Virginia USA
Joined Jun 2007
1,714 Posts
Planks can work very well for some purposes. The question that comes up first is - what is the most important function of the model. Is it to be a thermal sailplane - or a slope racer - or an acrobatic power or slope model?

The planks I've built have been sport thermal sailplanes. (well the first one was a control line model - but that was about 60 years ago). They were simple, compact and good flyers. None would be good for thermal competition because of the precision handling required for the landing task - but they soared well, were nice looking and very transportable. (That aside, I've also never flown a swept wing sailplane that I thought would be very effective in thermal soaring competition. (landing task again)

My basic design theory is that the elevator control surfaces should be near the tips (not at the center) in order to keep a favorable lift distribution. Also I would not use very much taper. Lower surface flaps can be used if they are placed at mid chord - upper surface spoilers the same. Both together really work well - but lower surface flaps are vulnerable - need protection. I have never seen or heard of a plank design that did not have a substantial fin. In fact if the model is to have elevon controls a coupled rudder function would be quite desirable.

What would really be cool is a wing-only plank - with some sort of stabilization system that compensated for no vertical surfaces. Perhaps the drag rudders on a gyro idea. Now that would be a Nurflügel.

I have flown a number of acrobatic gas powered planks and orientation is manageable. The mind and eye get used to orienting by the model's response to control inputs vice just the visual picture.
HerkS is online now Find More Posts by HerkS
Reply With Quote
Old May 13, 2012, 12:21 AM
Stupot46 is offline
Find More Posts by Stupot46
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,557 Posts
Has the swing wing ever been attempted on a tailless wing?I'm betting the answer is yes.
Stuart
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old May 13, 2012, 12:33 AM
mlbco is offline
Find More Posts by mlbco
Registered User
Palo Alto, California, United States
Joined Jan 2003
1,114 Posts
Quote:
Originally Posted by Stupot46 View Post
Has the swing wing ever been attempted on a tailless wing?I'm betting the answer is yes.
Stuart
Here's one:
Oblique Flying Wing Demonstrator (6 min 33 sec)

Steve
mlbco is offline Find More Posts by mlbco
Reply With Quote
Old May 13, 2012, 01:23 AM
Stupot46 is offline
Find More Posts by Stupot46
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,557 Posts
Thanks Steve,I've seen that elsewhere,incredible machine.I was thinking more on the lines of the blades on a pair of scissors.Ought to be do-able with the materials and electrics available today.
Stuart
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old May 13, 2012, 08:29 AM
Shedofdread is offline
Find More Posts by Shedofdread
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
2,354 Posts
The thing I was trying to get my head around is where is the balance between Planks (more efficient planform, less efficient airfoil) and Sweepies (efficient airfoil, less efficient planform and potential structural issues).

As Herk so rightly writes (!), it depends on the intended application but if we look at the pros and cons within individual flight regimes (fast slope, cross-country, thermal duration) we can compare 'apples with apples'.

I can see for slope racing, planks would have the edge (flutter resistance, low moment of inertia in pitch axis). What would others' thoughts be for other regimes? For thermal flight, it could be argued that a plank would need less structural material - would this offset (to a degree) the lower potential Clmax of the +ve CMo section?

Richard

PS Herk - love the idea of a synthetic yaw stability plank! Hmmmm.... Is that a gyro I see before me?
Shedofdread is offline Find More Posts by Shedofdread
Reply With Quote
Old May 13, 2012, 09:19 AM
Jim Thomerson is offline
Find More Posts by Jim Thomerson
Registered User
Joined Jan 2008
1,208 Posts
In his 1951-52 Model Aeronautic Year Book Frank Zaic discusses his Sailwing 50 glider design. It has 30 degree sweepback; 165 sq in wing and 50 square inches of tip elevators set at -8 degrees to the wing.
Jim Thomerson is offline Find More Posts by Jim Thomerson
Reply With Quote
Old May 13, 2012, 08:05 PM
mlbco is offline
Find More Posts by mlbco
Registered User
Palo Alto, California, United States
Joined Jan 2003
1,114 Posts
Here's a paper (very poor copy in .pdf format) that attempts to answer the questions of what planform is optimal for performance versus handling qualities:

http://spyplanes.com/wp-content/uplo.../05/gnc_92.pdf

This analysis did not consider reflex airfoils because they compromise performance too much for the design problem considered. The analysis also focuses on the impact of artificial stability on tailless aircraft design.

Steve
mlbco is offline Find More Posts by mlbco
Reply With Quote
Old May 14, 2012, 12:04 AM
Knoll53 is offline
Find More Posts by Knoll53
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
3,135 Posts
Quote:
Originally Posted by mlbco View Post
Here's a paper (very poor copy in .pdf format) that attempts to answer the questions of what planform is optimal for performance versus handling qualities:
Not to mention a little history of the development of the SWIFT.
Kent
Knoll53 is offline Find More Posts by Knoll53
Last edited by Knoll53; May 14, 2012 at 12:33 AM.
Reply With Quote
Old May 14, 2012, 05:32 AM
Il Pampa is offline
Find More Posts by Il Pampa
Registered User
Il Pampa's Avatar
Italy, Umbria, Assisi
Joined Aug 2008
24 Posts
Can we consider the Genesis II Sailplane a plank?
In effect its wing is slightly swept forward (mainly for balancing reasons) and the "tailplane" is more a trim tab than a tailplane.
The efficiency is not so bad to be a sailplane equipped with a reflexed airfoil.

Il Pampa is offline Find More Posts by Il Pampa
Last edited by Il Pampa; May 15, 2012 at 04:32 AM.
Reply With Quote
Old May 16, 2012, 10:13 PM
Robbie d is offline
Find More Posts by Robbie d
Crazy Cessna Owner
Robbie d's Avatar
Australia, SA, Windsor Gardens
Joined May 2001
1,936 Posts
not to mention the geat shape
Robbie d is offline Find More Posts by Robbie d
Reply With Quote
Old May 16, 2012, 10:36 PM
nmasters is offline
Find More Posts by nmasters
internet gadfly
nmasters's Avatar
Colorado
Joined Aug 2006
2,228 Posts
There's a Genesis in this video starting at 3:40
Vuelo a vela pre Mundial Gonzalez Chaves 2012 (7 min 3 sec)
nmasters is offline Find More Posts by nmasters
Reply With Quote
Old May 17, 2012, 12:35 AM
nmasters is offline
Find More Posts by nmasters
internet gadfly
nmasters's Avatar
Colorado
Joined Aug 2006
2,228 Posts
BTW Mr Marske started designing the Pioneer III before the Genesis. Some folks may be interested to know that the P III finally became a real aircraft a few months ago.
PIII Takeoff low res.m4v (2 min 15 sec)

Jim Marske Flying Wings 10 (7 min 31 sec)
nmasters is offline Find More Posts by nmasters
Reply With Quote


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Delta VS Plank JerseyDevil Foamies (Scratchbuilt) 31 Dec 07, 2011 11:48 AM
Question EPP plank or swept wing for thermal sky_surfer_fra Foamies (Scratchbuilt) 1 Nov 10, 2011 02:05 PM
Discussion CG With Swept wings Vs. High AR Flying Wings?? flyingwing12 Flying Wings 2 Nov 17, 2009 06:36 PM
Discussion Straight vs. swept wing Mikey C. Flying Wings 4 Aug 13, 2009 12:15 PM
Help! Mini wings_Delta vs. swept wing design flight characteristics Mchone, Jake Flying Wings 0 Dec 26, 2007 11:52 PM