Go Back  RCU Forums > RC Airplanes > Aerodynamics
Reload this Page >

Anti-stall flow directors - anyone..??

Notices
Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

Anti-stall flow directors - anyone..??

Old 02-07-2011, 07:24 AM
  #1  
canardlover
Thread Starter
 
canardlover's Avatar
 
Join Date: Aug 2002
Location: Västervik, SWEDEN
Posts: 415
Likes: 0
Received 9 Likes on 8 Posts
Default Anti-stall flow directors - anyone..??

Hello, I have in my files an interesting article from RCM magazine April 1987 issue written by Don Sobbe (see pics). He describes an easily added gadget which is said to delay stall of the wing root and apparently used on some full size aircraft.
So simple and yet so effective also on model aircraft according to the article but I have so far never, ever seen a model aircraft use this device....have you..????
I plan to add this gadget to my current canard project on the bench in my shop but before proceeding I would invite anyone out there to share experience or viewpoints on this addition...Thanks....and Cheers/Harald

Attached Thumbnails Click image for larger version

Name:	Gd93736.jpg
Views:	41
Size:	271.2 KB
ID:	1559904   Click image for larger version

Name:	Yu63496.jpg
Views:	45
Size:	646.2 KB
ID:	1559905   Click image for larger version

Name:	Wb74311.jpg
Views:	58
Size:	714.8 KB
ID:	1559906  
Old 02-07-2011, 10:32 AM
  #2  
naval flight officer
Senior Member
 
Join Date: Sep 2005
Location: FT. Belvoir VA
Posts: 253
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??

I have never seen these on full scale before. Normally we want the root to stall first so that you have aileron control through the stall.
Old 02-09-2011, 04:07 PM
  #3  
BMatthews
 
BMatthews's Avatar
 
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,355
Likes: 0
Received 10 Likes on 8 Posts
Default RE: Anti-stall flow directors - anyone..??

It's also got far too small an area to do more than just cause turbulence.

His would not have been the first thing that was presented in magazines that had questionable theory and results associated with it.
Old 02-09-2011, 04:57 PM
  #4  
FILE IFR
 
FILE IFR 's Avatar
 
Join Date: May 2006
Location: Clinton, MA
Posts: 2,138
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??

In that application most would call it a "Strake".

To me, it seems it is an actual Vortex Generator from full sized aircraft applied to the model's fuse.
Old 02-09-2011, 05:20 PM
  #5  
cfircav8r
My Feedback: (1)
 
cfircav8r's Avatar
 
Join Date: Jul 2004
Location: Hampton, IA
Posts: 1,241
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??

It does look more like a strake and those do assist in "high alpha" maneuvers, although I have only seen them on high speed swept wing designs. I also agree you want the root to stall first.
Old 02-09-2011, 05:43 PM
  #6  
Lnewqban
 
Lnewqban's Avatar
 
Join Date: Apr 2007
Location: South Florida
Posts: 4,056
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??

I agree with the previous posts.

My opinion is that the description of the text is correct.

Although less efficiently, that device follows the principle of the LE slots, which accelerate the airflow over the top of the wing.

However, the area that the device covers is too small to generate a substantial improvement.

Besides, there is a strong circulation in the wing-fuse intersection, which generates drag, but energizes the airflow enough as to delay the stall by itself.

You can try it, but don't expect spectacular results.

Old 02-10-2011, 01:47 AM
  #7  
bogbeagle
Senior Member
 
Join Date: Apr 2003
Location: York, UNITED KINGDOM
Posts: 1,296
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??

I think that the likely purpose of those plates is to create turbulence at high alpha ... which will then be felt by the pilot, as elevator "buffet". In other words, they are there to amplify the warning of an impending stall.

Chipmunk has similar devices.

Old 02-11-2011, 03:52 PM
  #8  
Ed_Moorman
My Feedback: (1)
 
Ed_Moorman's Avatar
 
Join Date: Jan 2002
Location: Shalimar, FL
Posts: 4,059
Likes: 0
Received 1 Like on 1 Post
Default RE: Anti-stall flow directors - anyone..??

I seem to remember that issue. The idea came from a full scale plane that the author had seen and talked to the owner. I recall it made a significant difference on the full scale.
Old 02-13-2011, 06:18 AM
  #9  
gyrocptr
 
Join Date: Jul 2006
Location: Neenah, WI
Posts: 133
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Anti-stall flow directors - anyone..??

Here's an example on a full size RV-8, with a more complex design to accommodate full-scale dimensions.
The accompanying text:
ā€œCheck out the VGs and the flow director at the wing root on this nice RV-8. The builder claimed that the top speed was unaffected and the stall speed was 5mph lower, IIRC. He also said that the flow director reduced the tail shake at stall. I'm not sure if that's a good thing or not if it reduces stick shake.ā€
Attached Thumbnails Click image for larger version

Name:	Ec89332.jpg
Views:	67
Size:	31.9 KB
ID:	1562741  
Old 02-13-2011, 06:50 AM
  #10  
thailazer
 
thailazer's Avatar
 
Join Date: Mar 2008
Location: Liberty Lake, WA
Posts: 1,543
Received 1 Like on 1 Post
Default RE: Anti-stall flow directors - anyone..??

Gyro... I could see how the flow director on that RV could work. At high angles of attack, there is probably a vortex coming off the fuse edge just ahead of the wing. (I.E high pressure below the A/C and low pressure above the wing with a blunt edge for vortice generation.) The flow director would tame that vortex stopping the tail plane buffet from the vortex. The Vortex Generator tabs you also see there work a bit differently, actually creating a vortex to help keep the airflow attached to the wing allowing a lower stall speed. I had VGs on my Horton STOL C-182 and the angle of attack that airplane could fly at was impressive.

That RV airflow director reminds of an F-18 problem that was resolved with a vane to break up a powerful vortex that was actually causing damage to the rudders. I was visiting the production line in St. Louis when they were retrofitting all the planes with the first generation solution: solid machined aluminum vanes. It was a serious issue. Check out:

http://www.aerospaceweb.org/question/planes/q0176.shtml
Old 02-16-2011, 02:16 AM
  #11  
canardlover
Thread Starter
 
canardlover's Avatar
 
Join Date: Aug 2002
Location: Västervik, SWEDEN
Posts: 415
Likes: 0
Received 9 Likes on 8 Posts
Default RE: Anti-stall flow directors - anyone..??

Thank you all for interesting - although a bit mixed - responses to the "flow director" idea. The reason I consider to add these on my next ship is that on my previous push/pull canard(see pic) I had three deep stall/flat spin "landings"....but fortunately with only minor damage. One of these stalls was even inverted with both fins broken in the process. Theory goes that the tractor prop slipstream prevents the canard foreplane from stalling and instead you get a deep stall...[:@]...!!
I usually go for a canard foreplane loading of 1.5 but this particular ship would not stall/mush normally....unless foreplane loading was increased to 2.00...! That was a surprise to me since none of my previous canards have behaved like that. Do not ask me why since the setup was rather "normal" with symmetrical NACA 0010 main wing at +0.5 degrees and a flat plate foreplane at +3 degrees.
Therefore my thoughts about anti-stall flow directors........Cheers/Harald
Attached Thumbnails Click image for larger version

Name:	Zx72347.jpg
Views:	60
Size:	76.4 KB
ID:	1564765  
Old 02-16-2011, 04:44 AM
  #12  
thailazer
 
thailazer's Avatar
 
Join Date: Mar 2008
Location: Liberty Lake, WA
Posts: 1,543
Received 1 Like on 1 Post
Default RE: Anti-stall flow directors - anyone..??

Harald,

Wow, that is quite the machine! It does not surprise me though coming from the home of the Vigen!

One thing I would try if I were you is to move the foreplane back a bit further. I know it sounds counter-intuitive to make that moment shorter, but doing so should increase the foreplane loading a bit more and reduce the foreplane's pitching effect (a part from simple drag) at high AOA where you are experiencing deep stall. Does that make sense?
Old 02-16-2011, 09:19 PM
  #13  
eddieC
Senior Member
My Feedback: (2)
 
eddieC's Avatar
 
Join Date: Nov 2002
Location: Jackson, MI
Posts: 2,102
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??

I think that the likely purpose of those plates is to create turbulence at high alpha ... which will then be felt by the pilot, as elevator "buffet". In other words, they are there to amplify the warning of an impending stall.

Chipmunk has similar devices.
Ding ding! We have a winner!

Strakes are used for a variety of reasons - improve handling in slow-flight, alter spin characteristics, etc. The Cessna 303 had strakes added above and below the stab/vertical fin joint to preclude icing in that area.
Old 02-20-2011, 06:34 PM
  #14  
naval flight officer
Senior Member
 
Join Date: Sep 2005
Location: FT. Belvoir VA
Posts: 253
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??

Canard lover,
I think you might want to consider reducing the size of your canards. Having a smaller area might cause the canard to stall before your main wing which is one of the main reasons for using them in the first place. If you can get the canard to stall first your main wing won't get the chance and this should prevent the deep stall/flat spin you experienced before. Either way keep you speed up.

Scott
Old 02-20-2011, 07:33 PM
  #15  
rmh
Senior Member
 
rmh's Avatar
 
Join Date: Dec 2001
Location: , UT
Posts: 12,630
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??

The canard fuselage -side area fwd the CG is the Flat Spin problem Once a rotation is started -it's gooood by
Old 09-06-2011, 08:29 AM
  #16  
jquid
Senior Member
 
jquid's Avatar
 
Join Date: Jul 2002
Location: st. charles, IL
Posts: 185
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anti-stall flow directors - anyone..??


ORIGINAL: Lnewqban

I agree with the previous posts.

My opinion is that the description of the text is correct.

Although less efficiently, that device follows the principle of the LE slots, which accelerate the airflow over the top of the wing.

However, the area that the device covers is too small to generate a substantial improvement.

Besides, there is a strong circulation in the wing-fuse intersection, which generates drag, but energizes the airflow enough as to delay the stall by itself.

You can try it, but don't expect spectacular results.

You can try it but don't expect spectacular results......
I put these on a Sig Kobra many years ago. It flew so much better with them on!!! The results were more than I expected. They made the plane so much more stable, and smooth.
Old 09-10-2011, 07:07 PM
  #17  
invertmast
My Feedback: (23)
 
invertmast's Avatar
 
Join Date: Dec 2003
Location: North Port, Fl
Posts: 7,854
Received 5 Likes on 5 Posts
Default RE: Anti-stall flow directors - anyone..??

We've got one of those installed on the outer surfaces of the nacelles' on one of our King-Air 90's. It is used in conjunction with Vortex generators that are mounted on the outer wing panels, bottom of the stab leading edge, and the hinge-line of the rudder.

$4,000 modification that did nadda for slow flight or stall performance
Old 09-13-2011, 10:24 AM
  #18  
BMatthews
 
BMatthews's Avatar
 
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,355
Likes: 0
Received 10 Likes on 8 Posts
Default RE: Anti-stall flow directors - anyone..??


ORIGINAL: thailazer
....That RV airflow director reminds of an F-18 problem that was resolved with a vane to break up a powerful vortex that was actually causing damage to the rudders. I was visiting the production line in St. Louis when they were retrofitting all the planes with the first generation solution: solid machined aluminum vanes. It was a serious issue. Check out:

http://www.aerospaceweb.org/question/planes/q0176.shtml

I always wondered why the F18's had that stuck on vane. At one point I thought it may be a special antenna for something fitted to the plane later and hence why the odd looking mount. I hadn't realized that the kludgey looking thing was a fix for an aerodyncamic issue.
Old 03-02-2020, 01:34 PM
  #19  
canardlover
Thread Starter
 
canardlover's Avatar
 
Join Date: Aug 2002
Location: Västervik, SWEDEN
Posts: 415
Likes: 0
Received 9 Likes on 8 Posts
Default anti-stall flow diverters added to Hots

Howdy, some 8 years later I finally added a pair of "flow diverters" to my Hots and I can tell you they sure make a BIG difference..!! This ship - now with added end plates on wing tips - is virtually impossible to stall. I can slow it down close to walking speed before it drops one wing.
So my next project will be to add such a "flow diverter" to the main wing of my next canard project..! Anyone interested..??



Last edited by canardlover; 03-02-2020 at 01:46 PM.
Old 03-03-2020, 04:52 PM
  #20  
ahicks
My Feedback: (2)
 
Join Date: Aug 2008
Location: Waterford, Mi/Citrus Springs, Fl
Posts: 3,758
Received 6 Likes on 6 Posts
Default

Just another opinion, OK?
It's no surprise here that a plane like this will slow to a walking speed prior to stalling a wing (if it drops a wing at all, some will drop nearly straight down, without ever dropping a wing completely). A straight leading edge, lots of wing area, likely light weight, oversize control surfaces to help maintain control, and my guess is, a CG that's neutral to maybe a hair tail heavy. All those are going to add up when it comes to low speed handling for this plane, just like those exact same features add up to do about the same thing on a well built Edge 540. The Edge (and other very similar air frames) will actually warn you of that stall by rocking their wings from side to side prior to stalling nearly straight ahead....

My point here is that if you enjoy flying like this, you might want to see what you can do with a late model, state of the art Edge 540 air frame. They've become pretty well known for similar low speed handling and you may be in for a pleasant surprise. That said, I get it if you prefer to strike out on your own with something like what you are talking about. Just tossing out an option. -Al
Old 03-04-2020, 03:05 AM
  #21  
canardlover
Thread Starter
 
canardlover's Avatar
 
Join Date: Aug 2002
Location: Västervik, SWEDEN
Posts: 415
Likes: 0
Received 9 Likes on 8 Posts
Default

Originally Posted by ahicks View Post
Just another opinion, OK?
It's no surprise here that a plane like this will slow to a walking speed prior to stalling a wing (if it drops a wing at all, some will drop nearly straight down, without ever dropping a wing completely).............. -Al
Well, my club buddies were just gaping in awe when I "walked by" with my Hots and they are certainly no beginners. Most of us are 70+ by now and "have seen it all". Why not try adding this gadget to to your Edge 540 and report back..?!
Old 03-04-2020, 04:54 AM
  #22  
ahicks
My Feedback: (2)
 
Join Date: Aug 2008
Location: Waterford, Mi/Citrus Springs, Fl
Posts: 3,758
Received 6 Likes on 6 Posts
Default

The "why not" would be that an Edge already flies just fine at low speed (most accepting it as one of the best air frames available when talking good low speed manners), without the added weight and complexity of the baffles you enjoy.

Similar effect on my flying buddies who mostly refuse to see just how slow their planes really can fly, or fly anything but the "suggested" CG. Many confessed to holding their breath just prior to one of my planes touching down.

Myself, just a young 'un at 68, that's been flying RC since the late 60's. Been focused on teaching myself 3D for the last 7 or 8 years now. Still suck, but having a lot of fun pushing my abilities nearly every time out.

No intent to offend, just sharing my experience with planes like your Hots (which have always been lot of fun) vs. the newer designs. Flying big horizontal figure 8's at 3' or less out in front of me, as well as on KE (at much higher altitudes, but still very close in). The newer designs can really enable some spectacular flying. Sharing that concept is the reason I wrote. I get it if you aren't interested, but thought maybe you might be. -Al

Old 03-04-2020, 10:02 AM
  #23  
canardlover
Thread Starter
 
canardlover's Avatar
 
Join Date: Aug 2002
Location: Västervik, SWEDEN
Posts: 415
Likes: 0
Received 9 Likes on 8 Posts
Default

I think thailazer described the function of these "baffles" very well in post #10 above:..."creating a vortex to help keep the airflow attached to the wing allowing a lower stall speed." Sure thing, the effect of these "baffles" on the Hots exceeded my wildest expectations so I will certainly keep them despite the "added weight and complexity". My Hots is currently a "test bed" for evaluating these "baffles" intended to be used later on the main wing of my next canard project.
If you look at post #7 in below thread you will see my efforts to avoid the dreaded main wing "superstall" frequently experienced on canards:
canard foreplane loading..??
Congratulations ahicks for being 68 years young, I recently passed 75 and started CL flying in 1957 with a Webra 1.5 ccm diesel...those were the days..!
Old 03-05-2020, 05:10 AM
  #24  
ahicks
My Feedback: (2)
 
Join Date: Aug 2008
Location: Waterford, Mi/Citrus Springs, Fl
Posts: 3,758
Received 6 Likes on 6 Posts
Default

Got it. Guilty of not reading the entire string as you probably suspected.

Was flying CL back then too, but for me it was trying to get a Wen Mac running using a 1.5 volt dry cell......
Old 03-05-2020, 09:15 AM
  #25  
canardlover
Thread Starter
 
canardlover's Avatar
 
Join Date: Aug 2002
Location: Västervik, SWEDEN
Posts: 415
Likes: 0
Received 9 Likes on 8 Posts
Default

No hard feelings ahicks.....! Supply a pic of my latest canard creation hanging "in the balance". It is a composite of some "left-overs" from earlier crashed or decommissioned planes. Wing is from a Chipmunk and foreplane from my now crashed FSW canard....! **** happens..!
Profile fuse is new and also my use of push-pull 4 stroke engines(Saito.50/56) So what remains is to add the "baffles" in front of main wing and some more paint

. Wish me luck...THANKS..!

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.