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64 Thousand Dollar Question in Pattern Flying

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64 Thousand Dollar Question in Pattern Flying

Old 07-02-2014, 05:34 AM
  #51  
Alex Voicu
 
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Malcolm,

I use the bubble version myself but i only had some slight roll instability during transitions to vertical uplines, so i was not sure they will help you. But since the flat winglets worked so well for your plane, maybe it's worth spending some time testing the bubble version too and decide which works better.

I built mine from 1.5mm balsa, so they are hollow inside and very light. They are film covered and, as you can see from the pictures, they are attached using transparent tape so they can be removed if necessary. They are quite fragile though, so i need to be careful with them.
For the round part, i wrapped some wet balsa around a carbon tube.Once dry, it's easy to roll the balsa around the conical shape required.



Mine are rather large so they probably add some drag and battery consumption increased by 100-200 mAh. Can't remember the exact dimensions, but will measure them later this evening when i get home.

One more link: http://www.rcuniverse.com/forum/rc-p...l#post10899566
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Old 07-02-2014, 07:22 AM
  #52  
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I just measured mine, they are 104mm long and 27mm wide/tall at the trailing edge (section is 1/4 circle). As i said, they are probably a lot bigger than needed, especially if you plan to add them at the top and bottom of each wing (8 pieces for a biplane) i would make them much smaller.
Old 07-02-2014, 07:39 AM
  #53  
Malcolm H
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Thanks Alex,

The flat plate ones I have on at the moment are 120mm long and 25mm tall. I'm inclined to keep the length and reduce the height to 20mm as a starting point. Do you think even lower would work?

Malcolm
Old 07-02-2014, 09:57 AM
  #54  
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Malcolm, i'm not sure because i didn't test more versions, but mine look a little exaggerated at 27mm. The builder of the Indira biplane (Spark09) tested many versions including flat winglets, maybe it would be a good idea to PM or e-mail him if possible.
20mm looks closer to what i can see in his images:

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Old 07-02-2014, 12:28 PM
  #55  
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Malcolm I flew at a contest last week and I noticed several of the planes dancing around in the wind also. Luckily my Nuance felt locked in and extremely stable. I want to just throw a few ideas out there. Is it possible it could be your transmitter elevator pot or a bad servo? When I set up my Nuance I followed BJ Parks setup recommendations to a T. I love the feel of the plane in the air unlike any other I've ever flown. Maybe look up his setup recommendations and compare them to yours.

Evan
Old 07-02-2014, 01:46 PM
  #56  
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In the '80's and '90's a gentleman named Elmore Wasson of Sparks Nevada visually studied the same anomaly in both Formula 1 and Pattern aircraft. He convinced me that a square trailing edge on both wing (& aileron) and horizontal stab (including elevator) was the source. He built four aircraft for me, each with an abrupt square trailing edge on each surface. Although not a high level experience pilot myself, I never saw any of the aircraft "hunt". Now days I see the same sort of configuration on the trailing edge of rudders for a number of FAI aircraft, the most prominent of which is the Spark. I suspect that Elmore's conclusion was that the minor turbulence created on the trailing edge is like a mini drag chute or compensator for airflow above and below the wing surface. But that's just my take on it.
Old 07-02-2014, 09:23 PM
  #57  
Malcolm H
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Evan,

No my problem isn't radio related. In calm still air the model is very steady and only exhibits this behaviour in turbulent air. As stated previously all servos brand new, all linkages stiff and tight and the radio is used on other models with no issues.

2205,

As it happens this aircraft does have fairly thick trailing edges on all surfaces.

Malcolm
Old 07-03-2014, 08:10 AM
  #58  
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OK,

We have made our first attempt at 3D printing some parts for a pattern model.

As some of you know I run a small mechanical engineering company and I was talking to one of my colleagues about how I was going to make some permanent winglets and he jokingly suggested 3D printing. We already use 3D modelling to produce the designs of the hydraulic equipment we manufacture but as this equipment is built from steel and usually weighs several tonnes we haven't considering printing the modelled designs!

One of our young designers was keen to help and suggested we might be able to use a new facility in Glasgow, an open access digital design studio to try out 3D printing. This isn't a free service and you have to pay a membership fee and then pay for the use of the machines so the winglets in the attached pics were not cheap but they hopefully will prove a point. The first pic is the 3D model which is the input to the printing process. I wanted to try and make the undersurface of the winglet follow the wingtip profile so made a crude cardboard template which we 2D scanned into the 3D modelling software and used to generate the bottom face of the model. A better way to do this would have been to take the actual wing to the studio and use a 3D scanner to generate the profile. The next picture shows the printer in action building up the winglets layer by layer. They are completely hollow except for a horizontal rib which was both unnecessary and a mistake. I actually asked our guy to put in a vertical rib and mid length because I was worried the parts wouldn't be stiff enough but actually they are more than stiff enough for non structural parts and this could be eliminated. The material is clear ABS but the printing process leaves a texture which doesn't look unattractive. The pics of the finished parts show the curve on the underside and how these will fit on the wing. The surface finish isn't perfect using this small printer and there is some cleaning of flash to be done. Also the last pic shows the process isn't infallible as this part when wrong during the printing process. Each part weighs 5 grams as printed to 40 grams for a biplane set.

I think this is a reasonable start and will allow me to test the bubble winglet concept. I'm sure we can make these lighter and smoother once we get the hang of the process.

As I said at the beginning this is an expensive way to make these parts so I doubt it will be commercially viable for a while at least. I would be happy to share the 3 D model STEP file.

Malcolm
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Old 07-03-2014, 08:18 AM
  #59  
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Sorry in my haste to post I left off the image of the printer at work and have added an image of the 3D Model file instead of a pdf.

Malcolm
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Old 07-03-2014, 11:04 AM
  #60  
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Malcom, it would be quite easy to take your 3D printed parts and make molds from them. A nice light fiberglass part can be made from there. Great work though. I am going to try a few different shapes myself over the weekend on my 40% extra. I'm going to start super simple and take some 9mm CF tubing and split it lengthwise about 200mm long and simply slip it onto the trailing edge of the aileron at the tip. Some clear tape will hold in place. We have been doing this for years on the rudder to improve tracking, I can't see why it would not work on the ailerons too.
Old 07-09-2014, 11:16 PM
  #61  
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Hi Malcolm,

Great work on the 3D printed bubble winglets.
Have you tested them yet? Please let us know about your results, i am curious to hear how they felt compared to the flat version.
Old 07-10-2014, 12:55 AM
  #62  
Malcolm H
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Hi Alex,

i got got to fly the model last Saturday with the winglets in place. Went with 100mm long x 20mm high in the absence of any better information. The site we flew at was very very bumpy with a nasty crosswind too so I'm really not too sure whether this design was better than the flat plate ones. My gut feeling was that they were slightly worse but I really need to fly again. As I write this I am on holiday in Cyprus so will need to wait for a couple of weeks to get that done. I will report back later.

Malcolm
Old 07-10-2014, 06:52 AM
  #63  
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Secret weapons seen at Arvin yesterday. I'm told we'll see lots of them at the Nationals.
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Old 07-10-2014, 09:53 AM
  #64  
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Are vortex generators band aids?

http://www.avweb.com/news/reviews/18...l?redirected=1

Sounds like what we need for slow flight.

Jim O
Old 07-10-2014, 11:18 AM
  #65  
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Hi Jim,
The C/L Stunt guys, at least the ones without killer light airframes, are loving the effect of the vortex generators.
It's 2012 all over again, just on another forum!
Regards,
Dean Pappas
Old 07-10-2014, 11:06 PM
  #66  
Malcolm H
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As Dean says, invigorating the boundary layer isn't new, the C/L guys have been doing it for a while and the free flight guys forever with many different designs of turbulators and trips. A couple of years ago I tried zigzag turbulator tape on my Asyuler again to try and get the elusive "locked" sit in the air. I think it did make a slight difference but these things tend to be subjective, the only thing I know for sure was that the throws had to be turned up to keep a decent snap.

As Jim's article on full size highlighted the difficulty with all these devices is the correct placement without either a lot of trial and error experimentation or wind tunnel work. Have the C/L guys come up with some rules for the design and placement of these devices?

Malcolm
Old 07-11-2014, 11:11 AM
  #67  
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Hi Malcolm,
The turbulator positions usually range from the airfoil high-point to maybe 10% of the chord forward of that.
Lengths are typically around 3/8" long and 3/32" to 1/8" tall.
They are usually positioned at a 45 degree angle to the chordline and spaced 4" to 6" apart.
Do remember, the Stunt guys use these to try and eliminate any and all stalling in maneuvers.
Snap rolls and spins may suffer!

take care,
Dean Pappas
Old 07-11-2014, 11:29 AM
  #68  
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Stunt's wing airfoils are considerably thicker (about 1.5X ?) than used in Pattern wings and the LE radii they use are huge in comparison. I suspect these factors change the transition region of the boundary layer compared to Pattern wings.

Here's one approach.....have the extended surfaces radio operated.....and tuck then away when not needed.
Old 07-11-2014, 11:57 AM
  #69  
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' Do remember, the Stunt guys use these to try and eliminate any and all stalling in maneuvers.
Snap rolls and spins may suffer! '

A good point !
Would suggest that to invigorate the inner 50 to 60% of span and to leave the tips be would be the way to go with a pattern model.
With the correct ratio it may help with stability, not take from snaps etc and even help with stall recovery - a magic bullet !!

Brian
Old 07-11-2014, 10:56 PM
  #70  
Malcolm H
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Brian,

That approach is actually the opposite to what I was thinking of trying. Bearing in mind my experiments are all about trying to keep the wings from rocking about, I was going to try the vortex generators out near the tips which kinda looks like the full size approach.

Malcolm
Old 07-12-2014, 12:21 AM
  #71  
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Malcolm,
Yes ! The question is ; where do you want to squeeze that balloon ?
This way allows for the useful addition of tip fences.

Btw, I'd have thought they go full span in most full size 'normal' speed applications. Also it seems ,to me anyway, that VG's used like the ones pictured have the effect of establishing an air fence/curtain rather than exciting the boundary layer.
There are applications ,in the 'real world', where these same devices are used in sufficient numbers and spacings to excite the boundary over full or specific partial spans.

Brian
Old 07-12-2014, 02:08 AM
  #72  
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Originally Posted by Malcolm H View Post
Brian,

That approach is actually the opposite to what I was thinking of trying. Bearing in mind my experiments are all about trying to keep the wings from rocking about, I was going to try the vortex generators out near the tips which kinda looks like the full size approach.

Malcolm
Malcolm,
Does the tail wag the dog ??
Get the dog to sit still !!

Brian

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