Best dead air airplane?

[Dave_Trible]

The inverse situation from the other thread.    Something very unusual for here Kansas,  for the last 8-10 days the wind has been mostly dead-call it light and VERY variable making flying pretty treacherous.   We've learned through experience on days like this it is usually better to leave the airplane in the car.  The wind streamer we use shows the wind blowing from the west.  In the center of the circle you plainly feel it coming from the south east.  Doing any maneuver twice in the same spot will probably afford you a look at the full top view of the airplane any second.  Then as it happens a 'wind event' is on the way later today which will yield unflyable winds for at least four days.   So the question:  what airplane would you choose to fly in dead or near dead air if you could predict it?   The large high powered competition stuff we normally fly churns up a storm of turbulance.   It's hard at times to back-pedal your way far enough out of it.   My thought is a smallish Classic type/sized airplane with a .35 is the best bet.   What's say you?

Dave

[Perry Rose]

I fly in dead air most of the time. Back peddling and/or moving subsequent maneuvers along the circle the only way to avoid the turbulence. I haven't been bothered in the overhead eights.

[Ken Culbertson]

The large high powered competition stuff we normally fly churns up a storm of turbulance.   It's hard at times to back-pedal your way far enough out of it.   My thought is a smallish Classic type/sized airplane with a .35 is the best bet.   What's say you?

Dave

My gut reaction is to fly one of *your* planes. 

We have had the same problem here this Spring.  It is either blowing 10-15 or dead calm. I cannot count the number of times I started a maneuver down wind and finished it up wind.  You learn to backup and sometimes that actually moves you into the wake.   Level laps can even be entertaining if it is calm enough and disaster awaits if you mistake a thermal for real wind.  The planes that don't create much of a wake are what we need.  Very light weight with no motor or flaps.

Seriously, unless you want to be picking up pieces at a contest you best learn to fly what you have in both calm and wind.  When was the last time you were at a contest with winds 5-10 and overcast?

Wake turbulence is perhaps the biggest enemy once you learn to actually trace the second maneuver.  I was shocked at how strong my 70oz twin's vortexes are.  Pray for light steady winds!

Ken

Just out of curiosity, has anybody found a way to measure how long a vortex survives and how slowly it sinks in calm air?  I have never given it much, but I have hit turbulence in the first maneuver in a series.

[EricV]

Just out of curiosity, has anybody found a way to measure how long a vortex survives and how slowly it sinks in calm air?  I have never given it much, but I have hit turbulence in the first maneuver in a series.

I don't know of any formulae but I can tell you that in hot dead air I have hit my wake after a level lap between tricks... that's pretty scary when you think about it... fly on a foggy morning and sometimes you can see the vortices rolling for a bit, but I think that is still different than mid-day dead air, its hotter and the rising heat can add to the roll. Air density altitude changes probably add to the problem, you're already searching for lift and when the wake pulls the rug out from under you like the Tower of Terror ride at Disney, you can run out of positive elevation quick, heh.

I have zero math or science to back this up, but my guess is that a lighter plane that can be flown slower and with less aggressive airfoils, will generate less turbulence than a heavy plane with thicker heavy lifting airfoils that has to be flown faster. Taking things to extremes helps me get the picture, and I envision the difference between a 36 ounce nobler flying 5.5 vs/ 80 ounce impact flying 5.0 laps.  The $64K question is, which will be affected more? The lighter nobler you would certainly think has the potential to get knocked around easier, and you would think the impact has a better chance of just plowing through, especially with modern power almost generating vectored thrust over the wings... but there is the one hope that the little nobler is flying slow enough and generating so much less wake that it's gone by the time it comes back around. Fun question, and I typed all that just to end up saying... beats me! LOL! I'm looking forward to a more informed reply.

EricV

[Brett Buck]

I have zero math or science to back this up, but my guess is that a lighter plane that can be flown slower and with less aggressive airfoils, will generate less turbulence than a heavy plane with thicker heavy lifting airfoils that has to be flown faster.

  Evidence suggests that the issue is the prop, not the wing.

    Brett

[Dennis Toth]

Dave,
When I was still down in FL we would go through those days were it was dead calm then it would pick up to 15+ very quickly, no slow increase just BAM!! The thing that helps is engine offset, now I know it is not a current day thing, but it is an old trick. Second is a flapless ship does better. Third was fly a bit faster.

Take the extreme, like a combat wing. They don't seem to care where they are they just go (maybe one of the combat guys can comment on how they are set up). But they have low profile, lots of power and most have either engine offset or reward leadouts (to get the same effect). It would be interesting to see if you took one of the combat wings and slowed it down to 55 mph how would it handle in dead calm and high wind conditions.

Charles Macky had a big flying wing job call the Monster that used ~30 ish degree of engine offset that he stated kept it out no matter were the wind. He supposedly had a few other designs that built on that concept but never got published, shame lost information.

Anyway I like the idea of a smaller ship with lots of power, more engine offset (say 3 - 4 deg) and not flaps maybe something like Larry S's Grey Ghost or Bob Baron's Humbug (file:///C:/Users/DAT%20Interests%20Inc/Downloads/Humbug_CL_oz11311_article.pdf) and like Brett said small diameter prop (maybe a three blade).

Best,   DennisT

[EricV]

  Evidence suggests that the issue is the prop, not the wing.

    Brett

That's interesting, because the stuff I saw on the foggy mornings was rolling off the wingtips, just like jets at high speed, and then at the bottom of the tricks, you would see a roll the width of the wing, not just some spiral wake from the prop... not that I doubt you, I'm sure your sources are way better than my seat of the pants instincts. I just always thought it was more about the combined disturbed air from lifting surfaces, flap and elevator deployment combined with propwash, and the heavier the plane, the worse the effect. I have some high-speed pic's I took somewhere of the puff puff puff smoke from the piped planes, and it's pretty cool, and the individual puffs are coming straight back, only gently swirled by the prop wash, but that could be a blanketed area down below the fuse. We need a smokey pattern sized wind tunnel and a bunch of yarn, heh heh. I know I've stood down wind of a lot of planes doing the tricks, and some planes about knock your hat off, and others you hardly feel a thing...

Thanks for the insight, Brett, this stuff is fun to contemplate.
EricV

[Ken Culbertson]

  Evidence suggests that the issue is the prop, not the wing.

    Brett

My own experience confirms what Brett has concluded.  Although flaps and weight do add some in the way of tip vortices, it is the prop, or in my case props, that make the "leaping sharks".  I thought that counter rotating might make them more manageable, but it just made them wider!

I don't know if this is a comment on my flying ability, but I cannot recall ever hitting one on an overhead 8.

Ken

[Reptoid]

"Take the extreme, like a combat wing. They don't seem to care where they are they just go (maybe one of the combat guys can comment on how they are set up). But they have low profile, lots of power and most have either engine offset or reward leadouts (to get the same effect). It would be interesting to see if you took one of the combat wings and slowed it down to 55 mph how would it handle in dead calm and high wind conditions."

    If you slow them down to 55 MPH they fly horrible. Even slowing them down to 75-80 MPH for the speed limit events requires substantial retrimming; i.e. tip weight, nose weight, engine offset. etc. and they still don't perform like they do at 100 MPH +. Because they have almost no side area, have very short moments, and are very light, they are very sensitive to changes in CG. A fully competitive F2D airplane at 100 MPH is still effected by wake turbulence and wind while test flying if you do consecutive tight maneuvers, and if dead calm you can get the occasional "top view" if not careful. In spite of what some think, the good competitive flyers spend considerable time trimming their combat models for optimum performance and feel. De-warping the wing using a heat gun until upright and inverted are identical, adjusting tip weight until upright and inverted are perfectly level, and adjusting the CG and control throw until maneuvers and stability around neutral are ideal.

[Dave_Trible]

My own experience confirms what Brett has concluded.  Although flaps and weight do add some in the way of tip vortices, it is the prop, or in my case props, that make the "leaping sharks".  I thought that counter rotating might make them more manageable, but it just made them wider!

I don't know if this is a comment on my flying ability, but I cannot recall ever hitting one on an overhead 8.

Ken

I have-twice a couple days ago.......No comment about flying ability .....

[EricV]

I have-twice a couple days ago.......No comment about flying ability .....

In dead air, my favorite place (NOT!) to hit my wake seemed to be the intersections and tops of the V8, and just past the intersection on the down leg of the HG as strange as that sounds but for some reason those were fairly common, that and the top outside corner turn at the intersection of the SQ8... Am I alone on those? It can be pretty scary when you don't expect it!

EricV

[Ken Culbertson]

I think we are all different.  Mine seem to always be on the down sides.  I guess it all depends on how accurate we are.  I know when I was learning and avoiding wake turbulence was mentioned, my reaction was "what's that?" 

Ken

[Dan McEntee]

  Evidence suggests that the issue is the prop, not the wing.

    Brett

    From the crashes I have had and witnessed over the years, I think flaps add the most to the cocktail. I have flown big and small models, big and small engines. Bigger models disturb the most air. Big 13-6 props churning away creates its rotational effects but flap deflection is something akin to running your hand through still water at an angle and see how it creates the disturbance in the water. If you could turn it horizontal, you could see how it could drive an airplane right into the ground. I have flown unflapped models , from Ringmasters to the Primary Force and the Sakitumi and just have not experience anywhere near the degree of turbulence that even a Nobler can stir up. While the Ringmaster and P-Force are smallish airplanes, the Sakitumi is fairly large but still does not disturb much air.  I don't think I have ever hit my own wake flying a Ringmaster. One of these days it would be interesting to set up a smoke barrier to try and fly through and see what actually happens. You would need a smoke generating machine I think that would let you put it where you want it and semi control it, and a still air to keep it in one spot.
  Type at you later,
  Dan McEntee

[Dave_Trible]

Might be interesting to put a smoke generating device on an airplane and fly it in dead air.    Might learn a lot.   

Dave