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tuft test video - 601 HDS

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pchapman(at)ionsys.com
Guest

Posted: Wed Aug 29, 2007 11:57 am Post subject: tuft test video - 601 HDS

I finally got around to doing a little video of some tuft testing on 

the 601 HDS I fly, filmed with a 0.3 wide angle lens on the camcorder.



It is posted online at http://pcxstuff.blip.tv/file/356716/ and can 

also be downloaded as a 13MB .wmv file. It's not a particularly clear video.



It was an unprofessional test, a flight with no detailed plan, on a 

dark, turbulent day, quickly done before the weather got any worse. 

But I haven't seen anything better, so this will have to do until I 

get around to trying again.



In its nearly 2 minutes, the video basically shows slow flight, 

throttled back, with a few approaches down to incipient stalls. Audio 

was removed (including a lot of oil canning noise near the stall!), 

but some indicated speeds called out by the pilot are shown in text 

on screen. Speeds are typically low, eg 70 mph indicated before 

slowing down, then down to 50 or 40 indicated (naturally likely 

inaccurate) for the slow flight. The pitch angle against the horizon 

is an indication of the speed.



At about 37 and 49 seconds seconds there are clear stall recoveries, 

after a lot of wing rock. I don't know if there was an actual stall 

break or the pilot simply let the stick forward once the bucking was 

getting enough.



I haven't thought through it all yet myself, but a few observations 

are possible:



-- One can clearly see the region of separated airflow spread 

outboard and forward as the wing gets closer to a stall.



-- Even when in slow flight not right at a stall, a large area near 

the wing root doesn't have straight fore to aft flow. I'm not current 

on my aerodynamics, but a waving yarn might only indicate an area of 

a turbulence within a thick boundary lager, and not fully separated 

flow. One can't see the actual wing/fuselage junction, but even 

outboard of that, the flow isn't all front to back.



--  It doesn't take much to mess up airflow right down on the wing 

surface, if closer to the leading edge.

There's a yarn just behind of the aft, inboard Dzus fastener on the 

wing locker. Even when the plane dives with speed when recovering 

from a stall, that yarn doesn't like to stay straight. On the other 

hand, the yarn behind the top of the main wheel strut, also behind an 

obstacle, does stay straight. A quick guess is that the slight 

upwards bulge of the wing locker near the front of the locker is 

what's actually causing a flow problem, not the Dzus fastener. The 

slight bulge is far enough forward on the airfoil that the shape 

becomes critical, unlike for the gear strut which is further back. 

The yarn that is forward of the "behind the Dzus" one, is right on 

the locker, and it shows a tendency to lift off the surface rather 

than stay flat on the wing.



-- There is substantial inwards flow near the trailing edge of the 

wing. Some is expected near the tip as the tip vortex rotates up and 

inwards. But at low speed  there's some inwards flow component along 

the aileron pretty much all the way inboard. Some inwards flow can be 

expected from a sharply forward swept trailing edge wing, but the 

amount is much more than I expected.



-- Right when the plane is about to stall, it is impressive how many 

of those little yarns are trying to go the wrong way, to jump the 

aerodynamically sinking ship!



Peter Chapman

Toronto, ON

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Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Wed Aug 29, 2007 12:23 pm Post subject: Re: tuft test video - 601 HDS

Great video. I to looks like the air is really confused just aft of the inboard corner of the wing locker.



I wonder if this is caused by the locker?

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_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

grs-pms(at)comcast.net
Guest

Posted: Wed Aug 29, 2007 1:12 pm Post subject: tuft test video - 601 HDS

Thanks for posting the video.  The wing locker is obviously disturbing the

flow.  It would be interesting to locate an array of VGs at about 5% of the

local chord in front of the locker area.  I'd bet on an improvement.  Also I

notice that the tufts near the tip stay pretty well aligned as the angle of

attack approaches the stall point.  Credit to Chris for that.



How about tufting the canopy aft of the high point and along the top skin

behind the canopy.  I'll bet there is considerable separation there, even at

cruising speed.  I expect that Zodiacs pay a price for that great

visibility.



As for the area near the wing root, I wonder if a suitable fillet wouldn't

improve that.



George



Do not archive.



---

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Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Wed Aug 29, 2007 1:42 pm Post subject: Re: tuft test video - 601 HDS

Since you are doing tuft testing how about doing the side of they fuselage and find a good location for a static port.

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_________________
W.R. "Gig" Giacona
601XL Under Construction
See my progress at www.peoamerica.net/N601WR

pchapman(at)ionsys.com
Guest

Posted: Wed Aug 29, 2007 2:40 pm Post subject: tuft test video - 601 HDS

George wrote:



 	  Quote: 	
		  How about tufting the canopy aft of the high point and along the top skin

behind the canopy.  I'll bet there is considerable separation there,


	


Good idea.

There's a single canopy tuft test picture that I took years ago, 3/4 

the way down the page:

  http://web.ionsys.com/~pchapman/zdc/zdc_photos_construction.htm

(I haven't updated the 601 part of my website in years.)



 	  Quote: 	
		  As for the area near the wing root, I wonder if a suitable fillet wouldn't

improve that.


	


.. Like Dave Austin put on his plane. While the video showed an area 

of disturbed airflow much larger than a fillet, the video was all at 

low speed and not cruise.  (A small photo of Dave's fillet is on the 

same web page mentioned above.)



Gig wrote:



 	  Quote: 	
		  Since you are doing tuft testing how about doing the side of they 

fuselage and find a good location for a static port.


	


I'm NOT planning to duct tape the camera to the wingtip to look back inboard.

Peter Chapman

Toronto, ON

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grs-pms(at)comcast.net
Guest

Posted: Wed Aug 29, 2007 3:50 pm Post subject: tuft test video - 601 HDS

Peter:



Nice set of pictures.  I wonder if VGs mounted on the aft canopy bow would

be too far aft to improve the situation.  It should be relatively easy to

attach them to the screws that tie the bow to the plexiglass and experiment

a bit.  Ideally the VGs should be forward of the crown of the canopy, but,

at least in your photo, the flow appears to remain attached aft of that

point.



George



Do not archive

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Terry Phillips

Joined: 11 Jan 2006
Posts: 346
Location: Corvallis, MT

Posted: Thu Aug 30, 2007 6:43 am Post subject: tuft test video - 601 HDS

Peter, thank you for posting the video. Very interesting results there. It 

is really great when someone takes the time and effort to produce real 

data, rather than just speculating--like I am doing 



Your study reminds me of the work that Klaus Truemper did on his HDS--see:



http://www.utdallas.edu/~klaus/Airplane/airplane.html



and follow the link to the wing root fairing. Klaus used a manometer to 

look at the pressure at various points on his HDS and demonstrated that the 

curvature of the fuselage over the wing creates a low pressure region at 

the wing root aft of the widest part of the fuselage. Klaus built wing root 

fairings that reduced the effect of the low pressure zone and improved the 

performance and stall behavior of his aircraft. Is it possible that the 

inward flow at the aileron is caused by the low pressure region all the way 

in at the wing root? I plan to put fairings on my 601XL, but I'm hoping 

that someone will start selling them before I get to that point so that I 

don't have to make them myself.



The turbulence around the wing locker is troubling. I am putting in the 

wing lockers, and I am planning to use flexible tape to cover the hinge. 

Soaring pilots commonly use tape to seal gaps, see, e.g.,



http://www.wingsandwheels.com/page29.htm



My goal was primarily to seal the rain out. However, there might be a 

fringe benefit of reducing boundary layer separation caused by the locker 

door hinge. The separation along the inboard side of the wing locker door 

could be caused by air leakage from the inside of the wing. The bottom of 

the wing is a high pressure area. I'm guessing that the inside of the wing 

is pressurized through any small opening on the bottom of the wing. There 

appears to be a gap along the inside edge of the locker door. Leakage 

through that gap could induce separation, and your video suggests that is a 

problem area on that wing. It would be interesting to know if taping that 

gap would affect the separation in that zone. If leakage is causing the 

problem, possible fixes might be to use more Dzus fasteners along the door 

edge, putting a thin gasket to improve the seal, or stiffening the door by 

gluing or riveting on longitudinal doubler strips to the inside of the door.



Thanks again for posting the video. Nice work.



Terry

At 03:54 PM 8/29/2007 -0400, you wrote:

 	  Quote: 	
		  

I finally got around to doing a little video of some tuft testing on the 

601 HDS I fly, filmed with a 0.3 wide angle lens on the camcorder.



It is posted online at http://pcxstuff.blip.tv/file/356716/ and can also 

be downloaded as a 13MB .wmv file. It's not a particularly clear video.



It was an unprofessional test, a flight with no detailed plan, on a dark, 

turbulent day, quickly done before the weather got any worse. But I 

haven't seen anything better, so this will have to do until I get around 

to trying again.



In its nearly 2 minutes, the video basically shows slow flight, throttled 

back, with a few approaches down to incipient stalls. Audio was removed 

(including a lot of oil canning noise near the stall!), but some indicated 

speeds called out by the pilot are shown in text on screen. Speeds are 

typically low, eg 70 mph indicated before slowing down, then down to 50 or 

40 indicated (naturally likely inaccurate) for the slow flight. The pitch 

angle against the horizon is an indication of the speed.



At about 37 and 49 seconds seconds there are clear stall recoveries, after 

a lot of wing rock. I don't know if there was an actual stall break or the 

pilot simply let the stick forward once the bucking was getting enough.



I haven't thought through it all yet myself, but a few observations are 

possible:



-- One can clearly see the region of separated airflow spread outboard and 

forward as the wing gets closer to a stall.



-- Even when in slow flight not right at a stall, a large area near the 

wing root doesn't have straight fore to aft flow. I'm not current on my 

aerodynamics, but a waving yarn might only indicate an area of a 

turbulence within a thick boundary lager, and not fully separated flow. 

One can't see the actual wing/fuselage junction, but even outboard of 

that, the flow isn't all front to back.



--  It doesn't take much to mess up airflow right down on the wing 

surface, if closer to the leading edge.

There's a yarn just behind of the aft, inboard Dzus fastener on the wing 

locker. Even when the plane dives with speed when recovering from a stall, 

that yarn doesn't like to stay straight. On the other hand, the yarn 

behind the top of the main wheel strut, also behind an obstacle, does stay 

straight. A quick guess is that the slight upwards bulge of the wing 

locker near the front of the locker is what's actually causing a flow 

problem, not the Dzus fastener. The slight bulge is far enough forward on 

the airfoil that the shape becomes critical, unlike for the gear strut 

which is further back. The yarn that is forward of the "behind the Dzus" 

one, is right on the locker, and it shows a tendency to lift off the 

surface rather than stay flat on the wing.



-- There is substantial inwards flow near the trailing edge of the wing. 

Some is expected near the tip as the tip vortex rotates up and inwards. 

But at low speed  there's some inwards flow component along the aileron 

pretty much all the way inboard. Some inwards flow can be expected from a 

sharply forward swept trailing edge wing, but the amount is much more than 

I expected.



-- Right when the plane is about to stall, it is impressive how many of 

those little yarns are trying to go the wrong way, to jump the 

aerodynamically sinking ship!



Peter Chapman

Toronto, ON




	




Terry Phillips

ttp44~at~rkymtn.net

Corvallis MT

601XL/Jab 3300 slow build kit - Rudder done--finally; working on the stab

http://www.mykitlog.com/N47TP/

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_________________
Terry Phillips
Corvallis, MT
ttp44<at>rkymtn.net
Zenith 601XL/Jab 3300 slow build kit - Tail feathers done; working on the wings.

pchapman(at)ionsys.com
Guest

Posted: Thu Aug 30, 2007 8:14 am Post subject: tuft test video - 601 HDS

At 10:37 30-08-07, you wrote:

 	  Quote: 	
		  


	


 	  Quote: 	
		    Is it possible that the inward flow at the aileron is caused by 

 the low pressure region all the way in at the wing root?


	


For all I know, sure, it could be encouraging some of that inwards flow.



 	  Quote: 	
		  There appears to be a gap along the inside edge of the locker door.


	


Yes that particular locker door is a little bulged in spots -- I 

think a snugly fitted door would do better. Just didn't come out 

perfectly when built. Next time I should put yarn right next to those 

gaps to see if I can detect outflow -- or tape up the gap for one 

flight. I personally wouldn't worry about gap taping the hinges given 

all the other drag sources, and because water can also leak in from 

the sides. But no objections if one can get it to fit snugly over the 

hinge. (I did use some sort of gap seal like tape on the top wing 

skin where the locker doors press on them when closed, to try to 

reduce any metal on metal (or metal on paint) rubbing.)



I sometimes thought of doing water manometer tests of pressures in 

the rad ducting in my engine compartment... and now that I've looked 

again at Klaus' page, I see he has done exactly that.

Peter Chapman

Toronto, ON

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