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[QUOTE=Lazy Ace;2138554]Which book are you referring to, his original with comprehensive explanations or the newer condensed versions. I have my original copy purchased in 1990 published in 1989 and the newer versions that I gave as handouts to each new SAE Group I worked with. I am quite familiar with the contents of both books. His work is predominately identical to that of full size physics of flight with the same formulas used in full size aviation. What he does extremely well is to put it in print in language that is easily understood by us modelers. By taking the full size physics and applying it to our model sizes he has confirmed the physics apply to our models as well.

On page 74 of the old book under “Justification of High Lift Devices” he addresses exactly what I tried to explain to you. His example is a wing NACA 2412 with 15 inch cord with max lift coefficient of 1.1 and a wing loading of 36 oz per square foot will stall at 29 mph. Using  full span slotted flaps 25% of the cord deflected at 40 degrees you would double the CLmax  2.1. This would reduce the stall speed to 21 mph a whopping 27.5% reduction. At our airspeeds it works out to an 8 mph difference. In gusty or even mild weather is that 8 mph difference that discernable when you’re observing from a fixed position on the ground? Most times at the field we fly with some wind so realistically we are observing from a fixed position on the ground an 8 mph reduction in airspeed plus the illusion the reduction in ground speed due to the wind at the time. All you need is a 10 mph head wind with the 21 mph airspeed and you will observe the plane moving across the ground at 11 mph in fully controlled decent.

I have actually landed my Telemaster under full flaps backwards in a strong wind. The only reason I tried it was it was one of the claims made by Hobby Lobby in their advertisement for the kit.

Dennis

First picture is the two editions the second picture are other good books for reference.[/QUOTE]

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12-29-2014 11:44 AM

Lazy Ace

Re: Help with Vortex Generators

Quote:

Originally Posted by OLD PRAIRIE RED NECK

It's a hobby Dennis, if I have to justify every minute and dollar I spend then it would be no different than work. And I enjoy the learning experience.

Your 100% right each of us have different needs and expectations from the hobby and it will depend on how much time you allot to the hobby and your interests. If building and flying model airplanes is what you live and breath and have unlimited time to invest I envy you. I am not so lucky I have too many interests and too many hobbies. My wife says I’m worse than the kids. If I am replicating scale then the fences, vortex generators, flaps, slats and slots etc will be as close to exact scale as I can make them and I will do the research so they operate just like the full size ones. Yes time is not important when I am building a scale model I need to get it right. Now I know they may not be as effective as the full scale versions but I don’t care I need them to look right and operate in a scale like manner. The wing loading of our models will allow me to fly the subject in a scale like manner.

On the other hand like the heavy lift/STOL subjects practical is what I am interested in. So far picking the right airfoil is much more effective than anything else so spending time attempting to get vortex generators, slats or slots etc to work is not in my opinion cost or time effective.

Please notice I said “In my opinion”. It’s exactly that, for my purposes only does my opinion apply. If on the other hand your forte is exploring the world of vortex generators, slats, slots, flaps etc more power to you. If you ever come up with something that out performs what I presently use I will be the first to jump on your bandwagon. My interests are strictly what give the most bang for the buck. My first interest is Scale my non scale interests are practical applications. At present a platform with 3 independent FPV cameras. The pilot’s camera will be fixed focal length to match unaided eye sight the other two operated by separate observers are 36 times zoom auto focus with infrared capability http://www.flytron.com/camera-access...itive-ccd.html

Dennis

12-29-2014 02:50 AM

OLD PRAIRIE RED NECK

Re: Help with Vortex Generators

Quote:

Originally Posted by Lazy Ace

I have a hard time justifying the the time and effort invested for the small amount of gain.Dennis

It's a hobby Dennis, if I have to justify every minute and dollar I spend then it would be no different than work. And I enjoy the learning experience.

12-28-2014 02:47 PM

Lazy Ace

Re: Help with Vortex Generators

Quote:

Originally Posted by OLD PRAIRIE RED NECK

Dennis, go pick up a copy of Andy Lennon's book on model aircraft design and educate yourself about high lift devices for model aircraft. He did extensive testing on his own dime for the good of you and me. The only thing not mentioned is VGs, the rest are well covered. Then come back here and we will see if you still have the same views.

I am not saying they don't work. On the contrary I agree with you in that they have all been proven to work. How well they work depends on how well they are constructed and how and where they are placed on the airfoil. I have a hard time justifying the the time and effort invested for the small amount of gain.

Dennis

12-28-2014 02:00 PM

Lazy Ace

Re: Help with Vortex Generators

I have applied some of the knowledge from reading these publications. The challenge was to design and build a model with 1000 square inch's of wing area including the tail. Power was to be an unmodified OS .61. Lift as much as possible from a 400 ft grass runway. I did not want to use ailerons as the deflection of the ailerons would change the shape of the airfoil and reduce the overall lift. Instead I used spoilerons coupled with an oversized rudder. I was still able to keep the dihedral down to 1 degree. The small horizontal stab (so I could max the main wing area) required an absolutely neutral center of gravity and center of pressure in the design. The total area of the horizontal stab and elevator combined is only 144 square inches. Most 40 size trainers have more than this. Because its so well balanced at all times it fly’s like its on rails.

The video is of the two finalists the weight to see me carrying is solid lead plates over 22 lbs.

[YOUTUBE]www.youtube.com/watch?v=vBgWUceKmR0[/YOUTUBE]

12-28-2014 01:24 PM

Lazy Ace

Re: Help with Vortex Generators

Quote:

Originally Posted by OLD PRAIRIE RED NECK

Which book are you referring to, his original with comprehensive explanations or the newer condensed versions. I have my original copy purchased in 1990 published in 1989 and the newer versions that I gave as handouts to each new SAE Group I worked with. I am quite familiar with the contents of both books. His work is predominately identical to that of full size physics of flight with the same formulas used in full size aviation. What he does extremely well is to put it in print in language that is easily understood by us modelers. By taking the full size physics and applying it to our model sizes he has confirmed the physics apply to our models as well.

On page 74 of the old book under “Justification of High Lift Devices” he addresses exactly what I tried to explain to you. His example is a wing NACA 2412 with 15 inch cord with max lift coefficient of 1.1 and a wing loading of 36 oz per square foot will stall at 29 mph. Using full span slotted flaps 25% of the cord deflected at 40 degrees you would double the CLmax 2.1. This would reduce the stall speed to 21 mph a whopping 27.5% reduction. At our airspeeds it works out to an 8 mph difference. In gusty or even mild weather is that 8 mph difference that discernable when you’re observing from a fixed position on the ground? Most times at the field we fly with some wind so realistically we are observing from a fixed position on the ground an 8 mph reduction in airspeed plus the illusion the reduction in ground speed due to the wind at the time. All you need is a 10 mph head wind with the 21 mph airspeed and you will observe the plane moving across the ground at 11 mph in fully controlled decent.

I have actually landed my Telemaster under full flaps backwards in a strong wind. The only reason I tried it was it was one of the claims made by Hobby Lobby in their advertisement for the kit.

Dennis

First picture is the two editions the second picture are other good books for reference.

12-28-2014 06:54 AM

OLD PRAIRIE RED NECK

Re: Help with Vortex Generators

Quote:

Originally Posted by Lazy Ace

There have been many experienced builders who have debated the value of any of these devices on our models. Lots of data for full size but very little testing has been done for our model sizes. There is no return value for the time and money involved in testing model airframes. If you feel its working for you then by all means it’s probably going to make your experience better and that’s what this hobby is all about.

When I read the percentage of improvement one would expect on the full size I tend to think we would be extremely lucky to achieve the same percentage of improvement for our models. If a full size realizes a 20% reduction in landing speed with the proper use of flaps and the reduction goes from 100 knots to 80 knots that is outstanding. On the other hand our model landing at 30 mph if it could achieve the same advantage would only land 6 mph slower. In calm conditions it might be noticeable but with a few gusts thrown in I doubt most would be able to discern the difference.

Realistically lets hear what you think the percentage improvement is with your device? Estimated landing speed without vs with?

Dennis

12-28-2014 12:16 AM

bcsaltchucker

Re: Help with Vortex Generators

real improvement of course is best gained by higher end ultralightweight construction, not VGs. Just amazing what a high end superlight 3D plane can do, how slow they can land just because they are so light and gobs of power. I wish someone would make model STOL type (and scale) planes built with ultralight CF fibrefusion like the high end 3D planes have

12-27-2014 10:09 PM

Lazy Ace

Re: Help with Vortex Generators

12-27-2014 04:14 PM

Flypaper

Re: Help with Vortex Generators

Here's leading edge slots I put on a scratchbuilt plane to keep from tipstalling at slow landing speeds. Keeps the airflow smooth at higher angles of attack.

12-27-2014 02:39 PM

bcsaltchucker

Re: Help with Vortex Generators

another item to try if you want STOL imporvments is leading edge slats. Some are fixed and stay in the normal airflow on cruise, but at high AoA they become very effective by re-charging the boundary layer when a normal airfoil would stall.

The Zenith 701 was a great example of light plane using these to achieve 60 ft TO and Land roll (if my my wife lets me I'd lke to build one some day - fullsize). I see Hobbyking was selling a Fiesler Storch with leading edge slats. http://www.hobbyking.com/hobbyking/s...54mm_PNF_.html

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