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vgstol(at)bigpond.net.au
Guest

Posted: Thu Dec 14, 2006 7:05 pm Post subject: vg's

Sorry, forgot to delete all the previous messages -  must make a habit of that......

 [quote]   ---

vgstol(at)bigpond.net.au
Guest

Posted: Thu Dec 14, 2006 7:33 pm Post subject: vg's

Darn, just did it again....sorry.....

 JG

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[b]

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Thu Dec 14, 2006 11:14 pm Post subject: VG's

In order to spin an airplane at least one wing must be stalled. VGs tend to make a wing more stall resistant so they should also make an airplane more spin resistant.

On Dec 14, 2006, at 1:33 PM, MaxNr(at)aol.com (MaxNr(at)aol.com) wrote:

 	  Quote: 	
		  Question: Would VG's make the plane more resistant to spins?

 

 Bob D

 

	




 -- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

 



 [quote][b]

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

steveadams

Joined: 10 Jan 2006
Posts: 191

Posted: Fri Dec 15, 2006 5:36 am Post subject: Re: vg's

It is easy to make changes to an airframe to change or improve specific performance parameters. Based on your data, it seems clear that you are making the 701 a bit faster and with at least similar STOL performance. The difficult part of making these type of changes is figuring out what effects it has besides the desired improvements. I think you have shown, at least in these posts, that you have not done a thorough evaluation of these untoward effects. You have effectively changed the airfoil, changed the wing chord, decreased the wing area, changed the MAC. How does this change effect wing loading, forces on the wing attachments, VNE and flutter, center of gravity, forces on the tail and fuselage etc. The 701 is likely over designed to the point that these changes may have no overall effect, however, there could be that single weak link that is stressed a little too close to the safety margin. The wrong combination of factors could be catastrophic. You haven't shown me that you have even begun to examine these factors. So there are 10 or 20 or 50 701's flying this way without a problem. How many potential problems have shown up in certified aircraft, even after exhaustive design, research, and testing, only after many 100's or 1000's are flying? Do yourself and those considering making this change a favor and do the appropriate structural design evaluation before touting this as the greatest thing since sliced bread.

infow(at)mts.net
Guest

Posted: Fri Dec 15, 2006 3:00 pm Post subject: vg's

Noel I agree... this is for the Canadain guys wanting to remove there slats only!

  

 This is a direct quote below  from...  COPA's  -- "COPA  Guide to Amature-Built Aircraft"... in Canada Under - Reviewing The Rules – CAR STD 507 Appendix C .... The only thing is if Transport Canada's  final inspection and approval was with the Slats on then it looks like they should be informed otherwise you would be flying illegal and if something should happen... that's where insurance companies will get a little excited about!

 Design Changes

 Many builders of amateur-built aircraft incorporate changes in the aircraft they are building, whether the aircraft is being built from kits or plans. One of the great advantages of the amateur-built category is that this is allowed. It is up to builder to decide whether the changes are warranted and how they will be carried out.

 Both the CARs and the courts have been clear that when the aircraft is completed it is the builder who is responsible for the airworthiness of the aircraft, not the original designer or the manufacturer of the kit from which it was constructed. This is a good thing as it allows the builder to make changes, but it carries with it the responsibility to do a good job in making changes to a design. Ensure you know what you are doing as you will be solely and legally responsible for the outcome! 

 If you are not confident in your abilities as a designer then get professional help from the original designer or an aeronautical engineer. Otherwise don’t make the changes to the design, especially when they involve changes to the structure.

 There should be no confusion where the responsibilities are before the build and after the build after reading the above... the key word's are  "Ensure you know what you are doing" 

  

 Ron Leclerc

 Winnipeg,MBOn Tue, 12 Dec 2006 21:58:29 -0330, Noel Loveys wrote:> Mark:> I don’t' think you would have problems removing the slats to get> the plane passed the MD-RA  I've seen greater design changes made> to aircraft that passed.  Remember the paper work on W&B needs to> reflect the airplane without the slats.  The configuration is> almost considered normal in other countries with no known problems> and some of those countries have a relatively similar level of> legislation controlling aircraft authority for flight.  Now if the> 701's with the slats off were falling like flies in the Raid> factory you would no doubt have problems. > You are dead right on one point and that has to do with anyone> wanting to register their plane AULA.  No changes from the letter> of conformity are allowed.  If the plans call for a placard against> chewing gum it better be there.  I'll bet you are right on the> insurance issue of calling it a CH701 too but there wouldn't be> anything wrong with a JD701 (John Doe 701)> On the use of VGs These little devices are used on all kinds of> certified aircraft.  Their placement is usually determined by wind> tunnel testing.  Their effectiveness when properly installed is> proven.  The operative words are, "properly installed". > Considering that no one here will be hitting mach 1 I would think> that if someone installed the VGs and did the appropriate envelope> testing at altitude their use should be safe… A word of caution,> the handy man's secret weapon will probably shoot down your plane.> My question still stands:  the CH701 is noted for poor glide ratio…> does removing the slats improve the glide ratio.> Noel>>>> --

ggower_99(at)yahoo.com
Guest

Posted: Fri Dec 15, 2006 3:56 pm Post subject: VG's

John Gilpin <vgstol(at)bigpond.net.au> wrote:[quote]       I don't know an answer to that Bob.  I see no  reason at all to get into a spin situation, or even a full stall, at least in  these ZAC machines - they're so docile and give so much warning if you practice  'tickling' the stall and learn the feeling.

  

 But I do note that CCI, a long time supplier  of vortex generators, tells of equiping a Pitts with them - the landings  improved muchly, but he couldn't do snap rolls any more!   I  don't know if that relates to spins....

  JG

 [quote]   ---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Dec 16, 2006 7:05 am Post subject: vg's

No doubt  about the fact that any change to the aerodynamics of an aircraft is reason to  have to fly off the test phase again and probably trigger another  inspection.

  

 The main  problem may well be legal, as you said the original builder is responsible for  the airworthiness of the plane......  even after it is sold.... possibly  sold several times.  

  

 Gary  Wolf, president of the RAA (Recreational Aircraft Association) asked the  question, "How would you feel if a plane you built were used for training  purposes after being sold?"?  Remember you would have no control over how  the plane is used or maintained.  You do however still have the  responsibility of the original builder.

  

  

 

Noel [quote]   

   --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

cgbrt(at)mondenet.com
Guest

Posted: Sun Dec 17, 2006 5:56 pm Post subject: vg's

I was at least partly responsible for restarting  the vg discussion with my post of 27 Nov. My sole purpose was to get empirical  data from someone that had done trials and who was not marketing something at  the same time. A second opinion is always good insurance. 

 I am part of a small group of 701 flyers,  some who showed interest in the effects of removing the slats. Before I  would advise anyone contemplating such a major change I wanted more  supporting data. I thank all who contributed points on both sides of the  question.

 In Canada major changes to the Amateur  category must be approved by Transport Canada. When I applied to have my  new wings approved, I was surprised to find the process logical and  devoid of heavy bureaucracy. I was informed that the Amateur Category  was created in part to enable persons to experiment and develop  improvements in design. At the same time Transport Canada  must take measures to protect the general public.

  

 Every owner is held responsible whether he  designs and builds from scratch or builds from a kit and makes no changes. It is  my understanding that this is also true for owners of certified a/c.  If you allow your a/c to fly then you have certified that it is airworthy  and are responsible. The onus is then on you to prove that someone  else is or shares the responsibility for any damages caused.

 Needless to say on the question of experimenting, I  fall squarely on the side of those who like to experiment but recognise that  risk is part of the game and one has to exercise due diligence for the safety of  self and others.

 Carl 701/912

  

    [quote][b]

robert.eli(at)adelphia.ne
Guest

Posted: Sun Dec 17, 2006 7:12 pm Post subject: vg's

Carl,

  

 I assume from what you are saying that you plan  to remove the slats and conduct your own flight tests. You didn't  mention whether you will add the vg's or not (but I also assume that you will,  given the reported  performance improvements).  I would  appreciate your keeping the rest of us 701 builders posted on the progress  as you take the steps toward flight testing. I for one, will be very interested  in keeping abreast of the developments as they occur.  Good  luck.

  

 Bob Eli

 N701K

 [quote]   ---

cgbrt(at)mondenet.com
Guest

Posted: Fri Dec 22, 2006 3:08 pm Post subject: vg's

Robert,

 I do not intend removing my slats as my wing  profile is different. My slats are cut from the airfoil and move forward 4  inches when they open at 10-12' A of A, When they retract they fit  perfectly to the leading edge of the wing. Removing them would leave a very sharp leading edge and a stall  with unknown caracteristics. 

 A friend that has the original ZAC wings is  seriously considering removing the slats. If he does, I am sure he will share  the results with the list. My interest was only in getting a second opinion to  confirm the Australian findings. At least two members of the list from N.A have  encouraging results.I tip my hat to the gent(s) that first tried removing  the slats as I would have expected some serious negative results.

  

 Most of my experience with the 701 is on floats.  Slats are of little use on a float plane until you get airborn because you  cannot attain sufficient A of A while on the water for the slats to generate  lift. The heel of the floats dig-in and reduce or stop acceleration if I rotate  above 10-12' A off A. The exception in when in the plow before getting on  the step where they probably generate some lift and help get on the step.  The best lift devices during T.O. from water are the flaps. I just about always  use 30'. The exception is strong variable winds.

 Where I find the slats improve handling is in  tight turns when going into or out off small lakes surrounded by high hills. I  reduce flaps to 20' as soon as it is safe to do so after T.O., and increase A of  A to 20'. With 1000# gross I can safely turn at 40 kts inside a 300 foot circle.  I practice these turns at altitude on many of my flights, they improve  handling and are real confidence builder for getting out of tight  spots.

 For normal flying, I lift-off at 35 kts  and I immediately start to retract flaps and accelerate to 50 kts in  surface effect. I then raise the nose to maintain 50 kts in the climb and  reduce power to 5200-5300. At 1000-1100 gross the slats are at least half in  and the A of A is 8-10'. That is one area when I would like to have a  manual override to lock the slats in as they are not required for lift and are  producing a bit of drag. Another area that an override would be nice  is when flying at reduced speed in rough air. In the auto mode they cycle  needlessly. It's an easy mod but I just never gave it the priority to get it  done.

 Now for the question: Slats or no slats  with VGs. Clearly, if you can get the same slow speed handling without  the slats and get increased cruise speed to boot, I would choose the no slats  with VGs. You save weight and complexity, and get increased cruise speed or  reduced fuel consumption. If you don't care about slow speed handling then the  decision is even easier.

  

 For those who are not interested in experimenting  the decision is easy also.

 Those are the recommendations I will make to my  friends.

  

 Hibernating for the winter,

 Carl

 701/912

 Do not  archive      

    [quote][b]

nyterminat(at)aol.com
Guest

Posted: Fri Dec 22, 2006 5:39 pm Post subject: vg's

Carl are you using the Peg a Stol wing? If you are, what kind of performance are you seeing with this wing?

  

 Bob Spudis

 N701ZX/95hrs

 do not archive

  

  

  

 In a message dated 12/22/06 18:09:58 Eastern Standard Time, cgbrt(at)mondenet.com writes:

  	  Quote: 	
		    Robert,

 I do not intend removing my slats as my wing profile is different. My slats are cut from the airfoil and move forward 4 inches when they open at 10-12' A of A, When they retract they fit perfectly to the leading edge of the wing. Removing them would leave a very sharp leading edge and a stall with unknown caracteristics. 

 A friend that has the original ZAC wings is seriously considering removing the slats. If he does, I am sure he will share the results with the list. My interest was only in getting a second opinion to confirm the Australian findings. At least two members of the list from N.A have encouraging results.I tip my hat to the gent(s) that first tried removing the slats as I would have expected some serious negative results.

  

 Now for the question: Slats or no slats with VGs. Clearly, if you can get the same slow speed handling without the slats and get increased cruise speed to boot, I would choose the no slats with VGs. You save weight and complexity, and get increased cruise speed or reduced fuel consumption. If you don't care about slow speed handling then the decision is even easier.

  

 For those who are not interested in experimenting the decision is easy also.

 Those are the recommendations I will make to my friends.

  

 Hibernating for the winter,

 Carl

 701/912

 Do not archive      

 	  Quote: 	
		  

	


	
  

  [quote][b]

robert.eli(at)adelphia.ne
Guest

Posted: Sat Dec 23, 2006 7:00 am Post subject: vg's

Carl,

  

 Thanks for the clarification and all of the great  info with regard to the flying qualities of a slat-equipped 701.  I had  restricted my thinking to take offs and landings, where it seemed that the slats  had little to offer over the no-slat with vg's (based on what our friends  down-under had to say), especially since you save significantly with the  increased cruise fuel efficiency.  What I had not been aware of is  what the slats can do for you in tight low speed turns.  This latter  feature would seem to be a benefit to seriously consider, since I live in  mountainous terrain.  I will be starting on the wing construction soon, and  have been having second thoughts about building the slats.  It has been a  tough decision for me that is still not final. I will probably go ahead and  build as per plans, but I have no problem in giving the no-slats approach a shot  since I have no problem with being an experimentalist (part of my lengthy  past was a stint as an aerospace engineer).

  

 Best wishes to one and all for the  holidays

  

 Bob Eli

 [quote]   ---

lrm(at)skyhawg.com
Guest

Posted: Sat Dec 23, 2006 8:15 am Post subject: vg's

Here are some thoughts or  interesting  questions.  If slats really don't serve much purpose as some of you have  claimed, then why do all airliners have retractable leading edge  slats?   Why do many fighters such as an F16 or even WWII fighters  such as the ME-109 have leading edge slats?  How about the a Storch or  Helio Courier?

 So I guess all of these manufacturers could  have save millions/billions of dollars of R&D and manufacturing costs and  just stuck a few cheap VGs on top of the wings and gotten better  performance.  Someone needs to inform the airline manufacturers of the  errors of their ways.

  

 The 701 is normally an ugly airplane, the Savanna  isn't as bad.  But why would one want to ugly up their plane more than it  already is by removing the slats and sticking a few VGs on the wings for  such "little" performance gain, if it's true?  If it were 20%, I'd say "go  for it", but 2 or 3%?   Could it be that most of the alleged  performance gain is because 14 lbs is being removed from the wings?

  

 All of us like to experiment, especially me, but  all in all I think this one is without much merit.

  

 Another of my fine 2 cents worth, Larry, N1345L, www.skyhawg.com

 [quote]   ---

p.mulwitz(at)worldnet.att
Guest

Posted: Sat Dec 23, 2006 9:07 am Post subject: vg's

Hi Larry,



 I have noticed many airliners (probably from Boeing) with both retractable slats and dozens (hundreds) of fixed VGs on each wing.  Also, every heavy plane I have ever seen has fully retractable flaps.  I am not an aeronautical engineer, but I must assume the airline designers go to great lengths to improve the landing and takeoff performance of their aluminum clouds to allow them to operate on shorter runways and improve airplane sales.



 I tend to agree with you that these issues are not so apparent with a 701 that barely needs a runway to start with.  However, anyone who wants to spend their lives second guessing Chris Heintz on the best way to design a small airplane for inexperienced pilots and first time home builders can have my share of that activity.  I'll just stick with his judgement and proven track record.



 Paul

 XL fuselage

 do not archive



 At 08:14 AM 12/23/2006, you wrote:

 [quote]Here are some thoughts or  interesting questions.  If slats really don't serve much purpose as some of you have claimed, then why do all airliners have retractable leading edge slats?   Why do many fighters such as an F16 or even WWII fighters such as the ME-109 have leading edge slats?  How about the a Storch or Helio Courier?[b]

robert.eli(at)adelphia.ne
Guest

Posted: Sat Dec 23, 2006 9:40 am Post subject: vg's

Larry,

  

 The following is not intended as a "lecture"  (although as a college prof., I have a tendency to head in that direction);  but it is serving as a vehicle to get my own thoughts straight about these  matters.

  

 It's been awhile since I studied my airfoil theory,  but as I recall, the airfoils on all of the high speed aircraft are optimized  for the higher speeds, and are characterized by a much longer chord length as  compared to their thickness (thin airfoils).  Also, they are often more  symmetrical (the stagnation point (zero velocity point) is designed to be at the  nose of the airfoil in the cruise configuration).  All of these features  result in an airfoil that tends to stall abruptly at higher angles of  attack.  The movable slat, when activated, allows high pressure air to  escape from the lower side of the nose of the airfoil to the upper side when the  stagnation point moves to the underside of the airfoil nose at higher angles of  attack. Ideally, the stagnation point moves into the lower slat opening  when airfoil is at the higher angle of attack in the takeoff and landing  configuration. The stagnation point is the highest pressure location on the  entire airfoil, and the slat opening converts this energy into a high velocity  jet.  The slat is shaped to direct this high velocity air into  the upper airfoil boundary layer (the air moving against the airfoil skin) to  introduce more energy into the boundary layer as it moves rearward  along the upper airfoil surface. The extra energy keeps the boundary layer  from separating (preventing stall) at higher angles of attack, which is by the  way, the same purpose of the vortex generators.

  

 I am pretty sure that the slat is more effective in  preventing stall at high angles of attack, as compared to VG's.  Therefore,  for serious low speed, high angle of attack flying, slats are the gold  standard.  I think that the reason the VG's have been found to work well  for the 701 airfoil (without the slat) is that it is already a big FAT airfoil  that is naturally a good performer for relatively high angles of  attack.  The 701 airfoil (without the slat) is highly asymmetric, with  the noise of the airfoil in a low position, therefore, at higher angles of  attack the stagnation point remains near the noise of the airfoil, which is the  optimal place to be to help prevent stall.  Since the slat is gone, the  airfoil will stall fairly abruptly when the airfoil reaches a high enough angle  of attack (as reported here by some of the Aussie guys - as I recall).  The  VG's, when added to slatless airfoil, introduce some additional energy to the  upper boundary layer that delays the stall a little more, and then when stall  occurs, they make it occur in a less abrupt manner (a lot more friendly than  would be the case without them).

  

 The bottom line, in my mind, is that the fixed  slats in the 701 (Chris's original design) is about as good as it gets when it  comes to low speed high angle attack flying on the cheap. However, in the cruise  configuration, the stagnation point moves to the nose of the slat, and (ideally)  very little air goes through the slat opening.  The downside is that the  slat adds significant drag during cruise due to most of the air trying to bypass  the slat opening, which results in wasteful turbulence in the slat openings (as  opposed to useful turbulence as produced by the VG's).  If you have a  movable slat that can close the gap during cruise, then you have the best of all  worlds. I may be wrong, but I suspect that a careful wind tunnel study  would verify that the original design, with the fixed slat, performs more  effectively at low speeds and high angle of attack than compared to no slat, but  with VG's.

  

 Bob Eli

 [quote]   ---

pacificpainting(at)comcas
Guest

Posted: Sat Dec 23, 2006 9:43 am Post subject: vg's

Larry, 

  

 I disagree. I believe that your post is worth at  least 2 1/2 cents. Possibly as much as .03.

  

  

 MERRY YOU KNOW WHAT TO EVERYONE.

  

 DAVE IN SALEM

  

  

 [quote]   ---

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Sat Dec 23, 2006 9:56 am Post subject: vg's

Fixed slats and VGs perform a similar function on an aircraft wing, they help keep the airflow attached to the wing at higher angles of attack to delay the stall and allow the plane to fly at a slower speed. Slats have been around for decades and are a well known quantity while VGs are a relatively new device. VGs were probably not a very well known quantity when the 701 and many other aircraft were first designed but slats were, which may help explain why the 701 was designed with slats and not VGs. If Chris were designing it today, would he do it differently? The 701 was also designed around an engine with significantly less power than the ones typically used on it today. At high angles of attack, the engine thrust provides a fair amount of lift all by itself. And how many people really push the airplane to its performance limits on landing? Probably, the only way to get a definitive, objective measurement of the difference between slats and VGs on the 701 is to put both versions in a wind tunnel.

Apparently, on the 701, the performance difference between the two devices at the low end are small (at least in the somewhat subjective flight tests that have been done). But you have to remember, the 701 already uses a high lift airfoil designed for low speed flight. Many of the aircraft mentioned below used an airfoil designed for high speed flight. I doubt that VGs alone would give them the kind of low speed performance they require. The retractible slats used on these aircraft provide an additional effect not produced by fixed slats. As they are extended, they not only extend outward from the wing, they extend downward from the leading edge, effectively increasing the camber of the wing. This along with the slotted flaps also used by these aircraft change the wing shape from a thin, high speed airfoil to a much thicker, higher camber, low speed airfoil.



VGs are appearing more and more on modern airliners, which shows that even with all of the high lift devices in use on them, it's possible to squeeze out some additional benefit.



On Dec 23, 2006, at 11:14 AM, LRM wrote:

 	  Quote: 	
		  Here are some thoughts or  interesting questions.  If slats really don't serve much purpose as some of you have claimed, then why do all airliners have retractable leading edge slats?   Why do many fighters such as an F16 or even WWII fighters such as the ME-109 have leading edge slats?  How about the a Storch or Helio Courier?

So I guess all of these manufacturers could have save millions/billions of dollars of R&D and manufacturing costs and just stuck a few cheap VGs on top of the wings and gotten better performance.  Someone needs to inform the airline manufacturers of the errors of their ways.

 

The 701 is normally an ugly airplane, the Savanna isn't as bad.  But why would one want to ugly up their plane more than it already is by removing the slats and sticking a few VGs on the wings for such "little" performance gain, if it's true?  If it were 20%, I'd say "go for it", but 2 or 3%?   Could it be that most of the alleged performance gain is because 14 lbs is being removed from the wings?

 

All of us like to experiment, especially me, but all in all I think this one is without much merit.

 

Another of my fine 2 cents worth, Larry, N1345L, www.skyhawg.com

 	  Quote: 	
		  	
	






 -- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

 



 [quote][b]

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

cgbrt(at)mondenet.com
Guest

Posted: Sat Dec 23, 2006 12:08 pm Post subject: vg's

Hi Bob 

 I am not using pegastol. It is similar but  with modified GA airfoil. I made a presentation to my eaa chapter, if you  need further check their web site at eaa245.dhs.org/

 Carl/701/912

 Do not archive

    [quote][b]

n801bh(at)netzero.com
Guest

Posted: Sat Dec 23, 2006 5:23 pm Post subject: vg's

This is the BEST explanation of slats I have read yet.   Thanks Mr Eli... You all have to keep in mind the  main guy who is claiming VG's are better then slats is the same guy selling them.....  

happy holidays and do not archive...

Ben Haas

N801BH

www.haaspowerair.com



-- "Robert N. Eli" <robert.eli(at)adelphia.net> wrote:

 Larry,

  

 The following is not intended as a "lecture" (although as a college prof., I have a tendency to head in that direction); but it is serving as a vehicle to get my own thoughts straight about these matters.

  

 It's been awhile since I studied my airfoil theory, but as I recall, the airfoils on all of the high speed aircraft are optimized for the higher speeds, and are characterized by a much longer chord length as compared to their thickness (thin airfoils).  Also, they are often more symmetrical (the stagnation point (zero velocity point) is designed to be at the nose of the airfoil in the cruise configuration).  All of these features result in an airfoil that tends to stall abruptly at higher angles of attack.  The movable slat, when activated, allows high pressure air to escape from the lower side of the nose of the airfoil to the upper side when the stagnation point moves to the underside of the airfoil nose at higher angles of attack. Ideally, the stagnation point moves into the lower slat opening when airfoil is at the higher angle of attack in the takeoff and landing configuration. The stagnation point is the highest pressure location on the entire airfoil, and the slat opening converts this energy into a high velocity jet.  The slat is shaped to direct this high velocity air into the upper airfoil boundary layer (the air moving against the airfoil skin) to introduce more energy into the boundary layer as it moves rearward along the upper airfoil surface. The extra energy keeps the boundary layer from separating (preventing stall) at higher angles of attack, which is by the way, the same purpose of the vortex generators.

  

 I am pretty sure that the slat is more effective in preventing stall at high angles of attack, as compared to VG's.  Therefore, for serious low speed, high angle of attack flying, slats are the gold standard.  I think that the reason the VG's have been found to work well for the 701 airfoil (without the slat) is that it is already a big FAT airfoil that is naturally a good performer for relatively high angles of attack.  The 701 airfoil (without the slat) is highly asymmetric, with the noise of the airfoil in a low position, therefore, at higher angles of attack the stagnation point remains near the noise of the airfoil, which is the optimal place to be to help prevent stall.  Since the slat is gone, the airfoil will stall fairly abruptly when the airfoil reaches a high enough angle of attack (as reported here by some of the Aussie guys - as I recall).  The VG's, when added to slatless airfoil, introduce some additional energy to the upper boundary layer that delays the stall a little more, and then when stall occurs, they make it occur in a less abrupt manner (a lot more friendly than would be the case without them).

  

 The bottom line, in my mind, is that the fixed slats in the 701 (Chris's original design) is about as good as it gets when it comes to low speed high angle attack flying on the cheap. However, in the cruise configuration, the stagnation point moves to the nose of the slat, and (ideally) very little air goes through the slat opening.  The downside is that the slat adds significant drag during cruise due to most of the air trying to bypass the slat opening, which results in wasteful turbulence in the slat openings (as opposed to useful turbulence as produced by the VG's).  If you have a movable slat that can close the gap during cruise, then you have the best of all worlds. I may be wrong, but I suspect that a careful wind tunnel study would verify that the original design, with the fixed slat, performs more effectively at low speeds and high angle of attack than compared to no slat, but with VG's.

  

 Bob Eli

 [quote] ---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Mon Dec 25, 2006 3:25 pm Post subject: vg's

If you are going to put  hundreds or thousands of tons of weight into the air you will need to use every  trick in the book.... Slats, Slots, VGs, Fowler flaps and let's not forget about  lots of raw power!

  

  

 

Noel [quote]   

   --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

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