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Anti-stall flow directors - anyone..??

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Anti-stall flow directors - anyone..??

Old 03-08-2020, 06:59 AM
  #26  
speedracerntrixie
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I think what is happening with your Hots is your deflectors are acting in the same fashion as a canalizer on a modern pattern airplane. They straighten out the prop blast so that you don't have airflow that is in a circular pattern hitting the tail. This makes the horizontal stab more efficient. You may have also noticed more rudder authority.


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Old 03-08-2020, 07:45 AM
  #27  
canardlover
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Thanks speedracerntrixie for you comment. To be honest I cannot say for sure whether my elevator/rudder got more powerful with "baffles" added. Anyway, the lowered stall speed alone makes them worth the effort. Furthermore, the "baffles" serve as a practical handle for lifting the plane and give me a firm grip while starting up.
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Old 03-10-2020, 01:48 AM
  #28  
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Default mounting the "baffles"

Hi guys, can i please "pick your brains" before deciding how to mount my newly fabricated "baffles" to achieve minimum main wing stall speed..? Which one would you go for., A, B or C...??...Thank you in advance.!




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Old 03-11-2020, 12:07 PM
  #29  
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Hi, I think it works like this with Canardlover's Hots:

A lot of turbulence is created where the wing and fuselage meet. This "dirty" air will hit a major part of the horizontal stabilizer which is less than desirable. Hots is mid-winged, its stabilizer is in the same plane as the wing and the stab is near the wing. Flow directors running up to the top of the thick wing will make the airflow more laminar. The stab will operate in "cleaner" air which will result in more elevator authority. That is the reason why Canardlover can drag his thick-winged Hots slowly through the air and still have good pitch control.

So, my belief is that the flow directors are good and the Hots became controllable at low speed with them. They are however not anti-stall flow directors so what good can they do on the rear wing of a canard? The ill-fated white/blue canard in post #11 has foreplane and wing in the same plane. The new canard with Chipmunk-wing in post #25 has the foreplane much higher. This will hopefully avoid a disturbing downsweep on the main wing.

I wouldn't go for any of the positions A, B or C.
Lars
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Old 03-12-2020, 07:12 AM
  #30  
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Hmmm......Thanks to both abachiwing and to speedracerntrixie for giving me "food for thought". What you both say is that elevator authority on the Hots should increase after adding the wing baffles. In retrospect I´m prepared to agree. Sorry speedracerntrixie I hastily answered you in the negative above...
After again "rehearsing" my flights in memory I´m prepared to confess that my Hots is now less prone to "dive out" at slow speed after addition of wing baffles and end plates. It tends to just "float around" in a "level fashion" which is just amazing. And new. WHY this difference.??:
1) Increased elevator authority.?
2) Increased main wing lift.?
3) A combination of both.?
My gut feeling - being without a wind tunnel - after these few flights is that it is a combination of both. Forced at gunpoint to say which one is the single larger effect, I would say 2).
So, sorry abachiwing but the "baffles" will be added to my canard main wing. To support my firm decision I will now quote Amelia Earhart: "I want to do it because I want to do it."
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Old 03-12-2020, 01:58 PM
  #31  
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Default deep stall

...and here is a picture from Andy Lennons article "Canards and Tandem Wing designs" in RCM magazine December 1989. This illustrates nicely what happened to me three times as described in post #11 above. Plane was just sinking vertically and the situation was like a trap. Revving my piped engines up and down to no avail - props would not "bite". To avoid that happening again I will try out the main wing "baffles" with some fresh air coming from below.


Last edited by canardlover; 03-12-2020 at 02:00 PM.
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Old 03-21-2020, 09:09 AM
  #32  
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CL, for something of this sort I would strongly suggest that you make the baffles so they can be added and removed and just as importantly moved around easily. You're going to want to do a lot of playing with them to find out if they work at all and if they do anything that is obvious to then try different mount points.

For high angle of attack response to delay the rear wing stall you might also want to try long tapered LEX's on the rear wing similar to those used on jet fighters like the F18. The function of those strakes is to cause a strong mid section rolling around of the airflow spilling over the edges and "fill in" the center section. In this way they work much like a delta wing with a strong sweep angle that produces a strong upper surface vortex to resist stalling in the classic sense.

Keep in mind too that small things on our models can often be hidden by the turbulence around what they are mounted onto. So if I'm looking at your pictures correctly these diverters you show don't look to be all that wide for span. You might need to increase the span of these addons. Another good reason to make them attach with a bit of tape so they can be played with. And along those lines I think I'd say to bend some of the flanges up and some down so you can seat the tape such that it'll resist air loads from both directions.

I've also read early on that you really don't want the front wing to stall second. One way to avoid front wing stall is to give it more camber. And if you're using the front wing as your elevator surface with "flaps" on the trailing edge part of their function is to increase the camber at the same time the flaps increase the angle of incidence. So by holding up elevator you might be causing the stall on the canard to delay to a point beyond where the rear wing stalls first and causes the issue of the tail dropping away.
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Old 03-24-2020, 03:46 AM
  #33  
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Default good points BM..!

Thanks a lot for chipping in BM, here are my responses to your post #32 above:
1)..do a lot of playing with them. Well, there is no problem to move "the baffles" around a bit on the profile fuselage but rather to evaluate the difference objectively without a wind tunnel. I can certainly force a stall trying to discern differences but that is a bit risky since we have a rather large pond/swamp just under our normal flying area.
2)..LEX's on the rear wing similar to those used on jet fighters like the F18. BM, could you please elaborate a bit on that item.Thanks.!
3) these diverters you show don't look to be all that wide for span. Correct, but I was astonished over their pronounced effect on my Hots. In addition I do contemplate to add wing tip end plates on the main wing and strakes similar to the ones added to my small Delta - picture attached.
4) ..to avoid front wing stall is to give it more camber. Good point so my essentialy "flat foreplane" has a modified "droop nose" to that effect.
That´s it for now BM, and to all of you out there - please keep ideas coming..THANK YOU.! The covid19 has forced me, at 75 years of age, to stay at home and spend more time in my shop..!


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Old 03-25-2020, 12:01 PM
  #34  
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Howdy, I´m a bit disappointed no one gave me response on baffle positions in post #28....! Well, now it is too late for you all to contribute since baffles are just mounted according to the TLAR principle (That Looks About Right). Very scientific and it came close to alternative B in post #28.
I add two pics to show off all 6 separately movable surfaces (ailerons are on dual servos). This will certainly stretch both my Futaba 7 Tx and my poor brain to the limits when programming later on.....! I will aim for what I believe you americans call a "crow" for slowing down at landing.
PS...I feel a bit stupid for not being able to upload thumbnails...PLEASE HELP..!..DS


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Old 03-26-2020, 10:55 AM
  #35  
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BM, could you please elaborate a bit on that item.Thanks.!
Like the triangle shaped side strakes along the root of the fuselage on the F18 and F16. The point of those is that at high angles of attack they form a strong rolling vortex that flows over the upper center section to aid with reducing a high degree of separation and thus lower drag. Your side strakes are doing the same thing but they are acting a bit more like the forecanards on some of the modern jet fighters. Some of those canards are actually movable and are used for flight control. But some of the smaller foreplanes are fixed. They are there to do the same function of causing air to flow up and over the center section at high angles of attack and delay the stall or reduce the drag of a large separation bubble at the stall point.
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Old 03-27-2020, 09:04 AM
  #36  
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OK, so what you describe now is the vane as referenced by thailazer in post #10 above. In my mind the LEX acronym is a bit misleading here..?!
Aerospaceweb.org | Ask Us - F-18 Leading Edge Extension Fences
Think I got it now but it sure looks tiny on the F18. Problaby quite effective at high speed though..Thank You..!

Last edited by canardlover; 03-27-2020 at 09:06 AM.
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Old 03-27-2020, 09:25 AM
  #37  
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Originally Posted by canardlover View Post
OK, so what you describe now is the vane as referenced by thailazer in post #10 above. In my mind the LEX acronym is a bit misleading here..?!
Aerospaceweb.org | Ask Us - F-18 Leading Edge Extension Fences
Think I got it now but it sure looks tiny on the F18. Problaby quite effective at high speed though..Thank You..!
Yeah, I don't know where the article got the name. It was called a vortice disrupter vane at the time. The thing is about 30 inches long and the first ones were hogged out of a solid aluminum billet. The energy contained in a vortice is quite impressive apprarently.
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Old 03-27-2020, 10:03 AM
  #38  
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Thanks thailazer, good to see that you are still around..! Now you guys - BM and thailazer - got me scratching my head how to add this vertical "vortice disrupter vane". Any suggestion much appreciated..!!..Cheers/
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Old 04-01-2020, 09:45 AM
  #39  
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They added that as a patch to massage the air flowing up and around the LEX. Without a wind tunnel to test for if you need it or if it is needed there's no point in trying to put something like that onto your plane. Also it's to adapt the air flowing around the LEX. No LEX then no need or anything gained from using the vertical add on.
Old 04-01-2020, 09:48 AM
  #40  
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...

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Old 04-02-2020, 06:29 AM
  #41  
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Originally Posted by BMatthews View Post
They added that as a patch to massage the air flowing up and around the LEX. Without a wind tunnel to test for if you need it or if it is needed there's no point in trying to put something like that onto your plane. Also it's to adapt the air flowing around the LEX. No LEX then no need or anything gained from using the vertical add on.
OK, I agree..!
Old 04-08-2020, 11:38 AM
  #42  
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Default now with four "baffles" in place..!

Hi again.! I hereby admit that I simply could not resist the temptation to add the newly fabricated canard "baffles" to the wing tips of my Hots. Just 8 screws - that´s it. Flight report will follow in due course as soon as whether permits. I plan to make a comparison after having flewn the Hots as pictured below and then immediately remove all four "baffles" and evaluate the difference. Will keep you posted....Cheers/


Old 04-08-2020, 03:16 PM
  #43  
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I'm very interested in the results. I predict not much different in stall but maybe stronger aileron authority. Looking forward to what you find.
Old 04-08-2020, 11:17 PM
  #44  
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Looks like those wing tip baffles will really catch the air trying to escape around the wing tips.
Looking forward to read the flight report.

Lars
Old 04-23-2020, 02:06 PM
  #45  
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Any recent news?
Old 04-24-2020, 03:44 AM
  #46  
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Originally Posted by speedracerntrixie View Post
Any recent news?
Yes, I flew it the day before yesterday and was a bit disappointed about the latest addition of the outer baffles. Not much difference - it seems the inner baffles are the ones making THE real difference..! Will continue evaluation and get back soon.Very windy today....!.Cheers/
Old 04-24-2020, 06:09 AM
  #47  
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Did you notice any difference in aileron authority?
Old 04-24-2020, 06:50 AM
  #48  
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Originally Posted by speedracerntrixie View Post
Did you notice any difference in aileron authority?
No, I did not - but to be honest I did not really pay attention to aileron authority. Sorry, will keep that in mind for next flights. I plan to pick a good calm day and consider a flying programme like this:
1) Fly around with all 4 baffles and do all the different tricks and figures for a while.
2) Remove outer baffles and fly again as above.
3) Remove also inner baffles and fly again as above.
I will try to retain the c.of g. in the same spot throughout with some lead taped to the fuselage.
Please have your viewpoint on the above...Thank You....Cheers/
Old 04-24-2020, 07:11 AM
  #49  
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Sounds like a solid plan. I commend your efforts, this is how we learn things. All too often guys will dismiss something based on full scale philosophy. Our models operate at much different parameters.
Old 04-25-2020, 01:05 AM
  #50  
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Originally Posted by speedracerntrixie View Post
Did you notice any difference in aileron authority?
I see your rationale for this question: increased airflow over the outer portions of ailerons. Will keep an eye on this when going from 1) into 2) in my plan..!

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