Re: Aerodynamics: Airfoil Camber, Flaps, Slots-Slats & Drag: "Smoke Lifts" c...


Gabor Halasi <kishal63@...>
 

On Fri, Jan 11, 2019 at 4:44 PM Gabor Halasi <kishal63@...> wrote:
Hi All,

I would like to suggest this video to all of you who are interested in simple aerodynamics. The presentation made by Mr. John Roncz.

Cheers from Hungary

Gabor

On Fri, Jan 11, 2019 at 3:59 PM Rob de Bie robdebie@... [Q-LIST] <Q-LIST@...> wrote:
 

Hi Gary,

I seem to remember from aerodynamics classes that
you cannot stop the tip vortex from forming, it's
an integral and inevitable part of lift
generation. I mean the horse-shoe vortex, as described here:

https://en.wikipedia.org/wiki/Horseshoe_vortex

Maybe some laborious CFD work could demonstrate what you describe.

Rob

At 13:39 11 01 2019, you wrote:
>Hi Rob,
>Very interesting link.
>Yes I mean tip vortices on one side oppose each
>other and of course the same thing also happens the other side.
>I am not of course saying the vortices on the
>same side go in opposite directions.
>They go in the same direction i.e. clockwise from seen aft on port tips..
>However, because the rear wing high pressure is
>sensed by the canard ahead (and vice versa) it
>therefore affects the strength of vortex on each
>tip effectively reducing them in so doing reducing total induced drag.
>In effect each tip vortex is prevented from
>fully forming as it would in free air were there
>not to be another similar wing ahead or behind it.
>Also imagine if the tips were only separated for
>and aft so that the centre's of rotation were in
>the same vertical plane, any vortex generation
>from either tip would then be cumulative.
>However if vertical separation is also provided
>for, and in the Q that distance is very close to
>the stagger seperation probably to optimize
>unwinding, the rotations around centres now
>oppose each other. In other words spanwise
>inflow above the canard tip vortex is opposed by
>spanwise outflow under mainwing so you can see
>there is a mechanism to reduce both tip vortices
>on the same side even though they both go clockwise!
>Hope that helps
>
>Gary
>
>
>On Thu, 10 Jan 2019, 20:38 Rob de Bie
>robdebie@...>robdebie@...
>[Q-LIST] <Q-LIST@...>Q-LIST@... wrote:

>Hello Gary,
>I have trouble understanding how the vortices
>oppose each other. Are we talking about one side
>of the aircraft? I'm pretty sure the tip vortex
>of (say) the left wings rotate in the same
>direction. Or are you talking about the vortex
>sheet behind the whole span of the canard and wing?
>I Googled on 'two vortices combining' and
>'co-rotating vortices merging' and found a paper
>by French authors showing how two co-rotating
>vortices merge sat a wingspan aft of the wing. So
>my earlier assumption that they merge was not wrong.
>It's interesting that you mention birds. I worked
>a bit on wings with a bell-shaped lift curve
>(like the Horten brothers used extensively)
>instead of the traditional lift distribtions
>(like elleptical). NASA is flying a UAV with that
>bell-shaped lift distribution:
>
><http://www.nasa.gov/centers/armstrong/features/Prandtl-D_validating_new_wing_design.html>http://www.nasa.gov/centers/armstrong/features/Prandtl-D_validating_new_wing_design.html
>It also states that bell-shaped lift distribution
>fits the bird lift distribution a lot better than
>the classic models, so the formation flying
>analysis has to be revised. Sounds like there
>still is a lot to be discovered. Nice!
>Rob
>At 17:34 08 01 2019, you wrote:
> >Hi Rob,Â
> >Yes they oppose each other but only if there is
> >sufficient stagger with close enough proximity of each tip.
> >I think the paper actually specified the Q
> >layout near as damn it, as in rear wing above
> >canard preference and chord seperation multiple
> >distance rearward required for optimum effect.
> >I think nature provides a further insight into
> >this effect with the formation of migrating
> >birds in v form. They swap positions so the
> >one on each tip not benefitting as much (only
> >half as in on one wing) gets a rest!
> >They flap in opposit directions to their
> >neighbour's but at the same timing for a reason.
> >To minimise induced drag and therefore energy spent.
> >If you picture the Q canard and wing tips from
> >aft. Left tips see inward span wise flow on
> >canard top side opposed by outward span wise flow on Mainwing underside...
> >
> >Gary
> >
> >
> >
> >On Tue, 8 Jan 2019 14:24 Rob de Bie
> >robdebie@...>robdebie@xs4all..nl>robdebie@...
> >[Q-LIST],
> <Q-LIST@...>Q-LIST@yahoogroups..com>Q-LIST@...>
> wrote:
> >Â
> >
> >Hello Gary,
> >
> >Thanks for the details! I understand the part of
> >optimum weight distribution to achieve minimum
> >induced drag. But will the tip vortices cancel
> >out? I would rather think they would combine aft
> >of the aircraft. Not that I know much about vortex behaviour, to be honest.
> >
> >I looked a bit for the paper that you mention,
> >but couldn't find it. I copied below two other titles that might be of use.
> >
> >Rob
> >
> >- - -
> >
> >Minimum Induced Drag of Canard Configurations - Ilan M.Kroo
> >
> >Calculations, and comparison with an ideal
> >minimum, of trimmed drag for conventional and
> >canard configurations having various levels of
> >static stability - Milton D. McLaughlin
> >
> >At 20:21 04 01 2019, you wrote:
> > >Hi Rob,
> > >
> > >It was initially a slow discovery process of
> > >noting increased performance with aft c of g
> > >followed by a Eureka moment -when considering
> > >what the theoretical optimum weight distribution
> > >on equivalent wing areas/aspect ratios in tandem
> > >would be to best acheive opposing cancelling tip
> > >vortices to get minimum induced drag.
> > >
> > >I later found an aerodynamics paper that
> > >suggested this would happen with optimal
> > >stagger. I think it was written by a Polish
> > >aerodynamasist whose surname began with a J
> if memory serves me correctly.
> > >
> > >Once I read that paper I wondered if it was Burt
> > >Rutan's inspiration for the original quickie
> > >design. He also built the Amsoil racer using
> > >this layout so he invested some effort in the layout.
> > >
> > >Regards
> > >Gary
> > >
> > >
> > >
> > >
> > >
> > >On Thu, 3 Jan 2019, 19:56 Rob de Bie
> > >robdebie@...>robdebie@...
> > >[Q-LIST]
> >
> <Q-LIST@...><mailto:Q-LIST@yahoogroups...com>Q-LIST@...>Q-LIST@...
>
> > wrote:
> > >Â
> > >
> > >Hello Gary,
> > >
> > >That's an amazing story, I had never heard of
> > >this aspect of canard aircraft. Did you know in
> > >advance that performance would change with a
> > >too-far-aft CG? Did you possibly pick it up from
> > >fighter design, where computers can make it
> > >stable again? Inquiring mind wants to know!
> > >
> > >Rob
> > >
> > >At 17:35 03 01 2019, you wrote:
> > > >Hi Jay,Â
> > > >Thanks for that.Â
> > > >One thing to remember though, that Mainwing
> > > >isn't represented in the canard smoke trail is it?
> > > >The Q benefits from the effective slot between
> > > >main wing and canard enormously at high angles of attack..
> > > >The biggest benefit of the tandem wing
> > > >arrangement however is the effective unwinding
> > > >of the tip vortices between canard and rear wing.
> > > >I once flew mine at ridiculous aft C OF G when overloaded.
> > > >What I discovered to my utter amazement was that
> > > >it not only flew faster, it climbed faster and by a significant amount.
> > > >The downside is loss of pitch stability meaning
> > > >it has to be flown hands on as stick release
> > > >will cause an accelerating diversion in pitch up or down..
> > > > From an induced drag minimization perspective
> > > > the ideal is 50/50 weight distribution on canard and Mainwing.Â
> > > >This is well outside the safe design envelope so
> > > >don't be tempted to repeat what I did.
> > > >With knowledge and understanding and too much
> > > >youth and curiosity I proved to myself all
> this to be the case. Â
> > > > > >So nobody else needs to. Unless you have
> > > >extremely fast reactions and/or a ballistic recovery chute.
> > > >The future of minimal aircraft parasite and
> > > >induced drag lies in the tandem wing design.
> > > >Great for minimum fuel requirement so electrification:)
> > > >
> > > >Gary
> > > >
> > > >On Thu, 3 Jan 2019 16:19
> > > >jay@...>jay@scheevel>jay@scheevel
> > .com>jay@...>jay@...>jay@...
> > > >[Q-LIST],
> > >
> >
> <Q-LIST@...>Q-LIST@yahoogroups....com>Q-LIST@...>Q-LIST@...>Q-LIST@...>
>
> >
> > > wrote:
> > > >Â
> > > >
> > > >A few years back, I ove-rposted some snaps from
> > > >that same video on my Q2 canard to get an idea
> > > >of the geometry of generalized airflow on it.
> > > >Gary, you may like this three snap sequence.
> > > >
> > > >Cheers,
> > > >Jay
> > > >
> > > >
> > > >
> > > >
> > >
> > >0
> > >
> > >
> > >
> > >
> >
> >
> >
> >
>
>
>
>

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