Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by lear999wa, Mar 31, 2013.
Any info on the Ski-gull from Oshkosh this year? Wonder if it made it.
Didn't quite make it but Burt will be unveiling the configuration today.
Here is the AOPA article
I hate those struts.
Plastic rod ends,44% fowler flaps...interesting.
I am waiting for Jarno to comment on this. He makes a very good case for a strutless high AR wing. I am wondering if the struts double as some kind of a guide for the wing fold onder:
Struts will save weight with a small drag penalty. Some new concept airliner designs have been shown sporting struts in Aviation Week over the last couple years and that's at Mach .8 where the drag penalty is much higher.
Looks like a pylon wing. I would say the struts are there to lighten the pylon structure and not the spar.
I've been seeing that as well. I think the main thrust behind the use of struts on those airliner concepts is to help allow much larger aspect ratios for cruise drag reduction with heavily-loaded wings, less than any potential weight reduction. Autoreply has been arguing that there is no significant weight reduction with struts, when you consider the weight of the strut itself, all the mounting hardware at both ends, fuselage strengthening to accommodate the wing bending loads transferred into it, etc.
I'm not at all convinced that his assertion applies unambiguously to all cases (sorry, Autoreply), but I think there's some merit to his arguments in some particular use-cases. At least enough to look at the consequences of using struts or cantilever wings in a particular application in-depth, when laying out the wing structural choices. I like Berridos' thought that, with a pylon-mount wing, struts might lighten the pylon structure enough for a reasonable weight-savings overall.
One presumes Rutan has done that with the Ski-Gull, or has some other justification that justifies the existence of struts on the design. Then again, even Rutan sometimes susceptible to "it just looks right to me" engineering, from time to time.
For folding. Only strutted wing he has ever done.
Don't think so on this one. It's a narrow pylon with and engine and wing on top that has to take wet and dry landing, ski landings, flight forces, folding wing mechanism, engine vibration. It would have to be a massive and draggy pylon shape to hold onto all that plus a high AR wing and any speed. The I am surprised it isn't triangulated or double struts. Rutan is not known for a lack of thinking things through and compromising properly. He probably did the speed/weight/drag analysis and figured out the struts were right on the cross-hairs of optimized.
Seriously Jay? <sigh>
The struts are all-carbon, airfoil shaped, and taper in span. I did the FEA for the buckling analysis because hand calcs weren't accurate enough- they're optimized.
That's what I said. "NOT known for a lack of thinking things through"... Meaning he thinks everything through and compromises properly every time. I'm agreeing... Sorry if the double negative wasn't clear.
Curious how the loads are reacted around the vertical axis? For instance if a tip is grounded or hits the water? There is a pretty long tail moment and fuselage weight and the span is pretty big so ther is a lot of leverage to scissor the wing and fuse junction. I guess there is no clear view of the pylon but it looks quite short an narrow in the pic. Is there a tubular steel superstructure in the middle?
Can't wait to see the rest of the details of this thing.
Could the struts be there because he is getting old and needed something to hold on to while entering/exiting the airplane? My grandma was always looking for a handhold while getting out of any vehicle...
Is it possible the strut could be transferring load either from or to the wing during hard water landing?
I apologize, should have read it more carefully.
The pylon is actually better than a steel tube in the center- it's a boxed carbon structure with really efficient use of carbon tow. I can only say this because he covered it in his talk, but what he showed was an integrated bulkhead that combined numerous hardpoints and spar attachments into one piece so that loads are evenly distributed (wings, engine, fuselage, struts, sponsons, pneumatic ski retract system, etc). Hard to describe without a picture [maybe someone took one of his slide from the talk?] but trust me, it's very innovative and efficient. In his talk he mentioned that he designed the pylons for a 10g wave hit so the craft is designed for high loads.
<sitting in Chicago airport going through withdrawals from having to leave OSH to go to a family reunion>
Is it still legal as a motorized glider or has the FAA seen through that ruse and shot him a disapproving look? The AOPA article does not mention motorglider. The one and only one area in which Rutan has more or less missed the mark is in soaring.
Does that include his Solitaire? I don't know much of it's history, but it won a homebuilt sailplane design contest in the 80's...
I had the... pleasure... of flying alongside the Solitaire 30+ years ago when it was new. Granted I was in a very high performance sailplane, but on that day I understood the Solitaire was being flown by one of the greatest living test pilot / soaring pilots around, Mr. Einar Enevoldson. There is no question about poor pilot technique at that moment. The soaring performance of that aircraft was dismal, because (IMHO) the canard was in its high drag pre-stall condition during the time when the glider was attempting to climb in a thermal.
When thermaling a sailplane, you are flying around a few knots above stall... that is normal and expected. A stall-resistant canard (formulee' Rutan... sorry Matthew ) is designed for the canard to stall before the main wing... just about exactly during this "climb" condition.
So, despite my aero engineering ability being .00001 of Burt's ability, I can say that a canard set up for stall resistance is absolutely the wrong configuration for any soaring aircraft. Now if I can understand this, I have to believe that Burt knew this.
So, IMHO Burt failed to deliver an airplane that succeeded at its target mission.
I believe it "won" a sailplane design competition the same way Stalin "won" re-election in Russia.....
The FAA is ten times more relaxed than any other government agency Ive ever seen. I was reading some complaints about ultralights and the people were going BERSERK... but the FAA basically answered "Thats nice sweetheart, now go outside and play with your friends". Because outside of hang gliders, injuries are pretty low. And hang gliders only have the injury rate of football.
I cant wait for football licenses!
But really, what hes designing is not much more advanced than anything coming from Pipistrel. Pipistrel Aircraft Sinus | Pipistrel
And yes, I had to look up that name. Good lord.
here another view!
funny i uploaded this concept to the vehicle sketch pad hangar TWO years ago!
link to my vsp model
VSP Hangar | MH6
Its ok i wont charge Burt a licensing fee. ps i charge a fraction of what burt does for conceptual design ! :lick:
Struts are heavier on light airframes. Airliners are apples to pears. Light aircraft structures are ruled by buckling, ie, min skin thickness. Airliners are ruled by strength and hardpoints add way less weight.
As such, the complete strut on a light aircraft might easily be 5-10 times the weight fraction it'd on an airliner.
Folding is one of the USP's of struts with some configurations.
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