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cgbrt(at)mondenet.com
Guest

Posted: Mon Nov 27, 2006 5:20 am Post subject: 701 slats again

From: "Carl Bertrand" <cgbrt(at)mondenet.com>

 To: <zenith-list(at)matronics.com>

 Subject: Re: 701 no slats again

 Hi Joe

 Have followed this thread with interest.

 I've experimented with the 701's wing design but not with vgs. I opted for

air pressure operated slats and a thinner airfoil.

 For more info on the results see my presentation at:  eaa245.dhs.org/

 I never considered flying the 701 without slat but I'm not surprised that

 it could be a hand full. My take is that the Cof G and the centre of

 pressure would move back, the Cp more so causing a nose heavy pitch moment

at all speeds and angles of attack. I would expect all stall speeds to

increase with the clean wing and top speed to probably remain the same or

decrease because of the blunt leading edge.

 Adding vgs should delay the stall but should also increase drag?

 Very interested in the results anyone gets if you try the no slat

configuration.

 Carl 701/912/amphibs

robert.eli(at)adelphia.ne
Guest

Posted: Mon Nov 27, 2006 5:52 am Post subject: 701 slats again

Carl,



I talked to Chris Heintz at Air Venture several years ago about the 701 

airfoil, and the aerodynamic design of the slats.  The airfoil is an old 

standard airfoil (it is a NACA 640-1 with  just a slot added.  In other 

words, if you simply remove the slot and leave the fixed slat in its design 

postion to define the nose of the airfoil, then you have standard NACA 

640-18 airfoil. If one wants to remove the slat from the airfoil design, the 

original airfoil can be recovered by simply covering the slots with sheet 

metal that matches the airfoil contour.



Bob Eli



---

amyvega2005(at)earthlink.
Guest

Posted: Mon Nov 27, 2006 3:23 pm Post subject: 701 slats again

All that is true however you will have moved the leading edge of the wing back 4 inches, thus needing to redo your moment and ARM. Or the CG will be off.  



Juan



--

n801bh(at)netzero.com
Guest

Posted: Mon Nov 27, 2006 5:11 pm Post subject: 701 slats again

I don't know about the 701 but,, the 801's slat leading edge profile is nothing like the wings leading edge profile. I will look very close at a 701 when I see one to see if it's like the bigger brothers. I would NEVER remove my 801's slats and fly with just the wing alone. but heck, thats just me... YMMV. 

do not archive

Ben Haas

N801BH

www.haaspowerair.com



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

--> Zenith-List message posted by: "Robert N. Eli" <robert.eli(at)adelphia.net>



Carl,



I talked to Chris Heintz at Air Venture several years ago about the 701 

airfoil, and the aerodynamic design of the slats.  The airfoil is an old 

standard airfoil (it is a NACA 640-1 with  just a slot added.  In other 

words, if you simply remove the slot and leave the fixed slat in its design 

postion to define the nose of the airfoil, then you have standard NACA 

640-18 airfoil. If one wants to remove the slat from the airfoil design, the 

original airfoil can be recovered by simply covering the slots with sheet 

metal that matches the airfoil contour.



Bob Eli



---

robert.eli(at)adelphia.ne
Guest

Posted: Mon Nov 27, 2006 6:13 pm Post subject: 701 slats again

I may have caused some misunderstanding by my use  of the word "remove".  I am not advocating removal of the 701 slat. The  point I was making is that Chris Heintz designed the 701 slat by simply starting  with the NACA 640-18 airfoil shape and then adding the opening (the gap  between the slat and the rest of the wing) through which the air flows from  the lower surface to the upper surface.  He sketched this very process for  me by drawing the original airfoil first, and then adding the air slot  afterwards, to divide the nose of the airfoil from the remaining aft portion.  You can in effect "remove" the slat by covering the openings on top and  bottom. Doing this "removes" the slat, returning the wing airfoil to its  original NACA 640-18 shape. Covering the slat openings so that the original  NACA 640-18 shape results should not cause a major change in the  center of pressure at normal flight angles of attack (and hence stability). Of  course, the lift will be significantly reduced at high angles  of attack.

  

 Bob Eli

 N701K   

 [quote]   ---

secatur

Joined: 02 Nov 2006
Posts: 50
Location: New Zealand

Posted: Tue Nov 28, 2006 12:44 am Post subject: Re: 701 slats again

I find it extremely interesting that there are so many comments regarding VGs / vs Slats on the 701, and yet very few respondents seem to have read or studied much of the almost 50 years of accumulated aircraft experience regarding VGs.

If you go hunting, you will find literally hundreds of hours of actual flight comparisons, including specs of flight testing and results. The result on the 701 (with VGs INSTEAD of slats!) appears to be a slight improvement in low speed handling together with a slight improvement in top/cruise of about 5kn. One builder/pilot actually documented 140 hr of testing before finally deciding to remove the slat mountings altogether !

Why would Savannah (yeah dirty word..sorry) actually go to the trouble of offering the VG slatless (exactly same wing/airfoil) option on it's current price list if it didn't offer some value?



Is this where "Do Not Archive" goes?

secatur

Joined: 02 Nov 2006
Posts: 50
Location: New Zealand

Posted: Tue Nov 28, 2006 1:18 am Post subject: Re: 701 slats again

More interesting reading 

The vast reduction in drag allows all these aircraft to fly considerably faster for the same power, climb better, glide better, and with the benefit of Vortex Generators, lift-off and touch-down just as short as with slats, but with more control.

 

In summary for my Savannah: 



Fast cruise (at) 5200 rpm has gone from 79 kt to 85 kt.      = + 6 kts 

Top speed has gone from 94 kts to 103 kts!                      = + 9 kts. 

Fuel burn (at) 75 kts has gone from 17 L/hr to 13 L/hr.      = 23.5% less! 

Best climb rate (at) 55 kts is 100 fpm higher. 

Best glide  (at) 40-45 kts is 100 fpm better. 



Stalls (idle power, no flap): 

With slats â€“ no real stall, just a stable high-descent mush (at) less than 30 kts. 

Without slats, no VGs* â€“ a distinct stall and roll to the left (at) 34 kts. 

Without slats and with VGs â€“ no stall, just a stable mush (at) less than 30 kts. 



*VGs = Vortex Generators, more about them elsewhere. 

L/hr x 0.26  =  US Gal/hr. 

Kts x 1.15  =  mph.

 

This testing was done in a â€˜Savannahâ€™ aircraft, a kitplane from I.C.P. in Italy, www.icp.it/avio.htm or http://www.skykits.com/ .   Itâ€™s pretty much a clone of a Zenair CH701, same wing profile but a longer wing, and a different tail section.  Powered by a 100hp 912ULS, 4-blade Brolga prop pitched for climb (16Â° blocks), carrying pilot (73kg) and 30 litres fuel.  

ore interesting reading from www.stolspeed.com

rhartwig11(at)juno.com
Guest

Posted: Tue Nov 28, 2006 5:00 am Post subject: 701 slats again

This discussion contains a lot of speculation on what would happen if you

removed the slats or covered the slot between slats and wings, etc.  Some

of it is not very well thought out as to what happens to the CG range.  I

would suggest trying to learn from those who have removed the slats and

are flying their 701's in that configuration (and I suppose the

experience with modified Savannahs should also be considered.)  I would

hope that anyone making this modification would use the data from those

who have been successful and would then proceed with extreme caution.  I

understand that the CG range on the 701 is approximately 30-39 % of the

airfoil measured from the front of the slat--I have not checked that out

myself.  Unslatted wings are usually approximately 20 to 28%  (Forgive me

if these numbers are off of few % + or -.)  What is the CG range of the

701 airfoil if you measure from the leading edge of the wing instead of

the slat?  Is a slat aerodynamically part of the airfoil when calculating

CG range?  I don't know, but you can bet I am going to find out.  Also

keep in mind the effect of removing the weight of the slats even though

they are light and have a small moment arm.  Think it out.  Research it. 

Learn from others who've "dunit."  Proceed with caution.

Rich Hartwig, 701 kit

Waunakee, WI

rhartwig11(at)juno.com

robert.eli(at)adelphia.ne
Guest

Posted: Tue Nov 28, 2006 5:34 am Post subject: 701 slats again

Rich,



I completely agree with your recommendations.  Just removing the 701 slat, 

with no modifications, produces a "snub-nosed" airfoil, that is unlike any 

standard airfoil, and would seem to create all sorts of potentially 

dangerous issues.  If the slot is covered, and the original NACA airfoil is 

recovered, then there will be CG range issues that should be carefully 

researched before risking the change.  I think the information to answer the 

latter questions are out there somewhere.  I know that extensive research 

has been conducted in the past comparing airfoils with and without slats.



Bob Eli

N701K



---

n801bh(at)netzero.com
Guest

Posted: Tue Nov 28, 2006 6:05 am Post subject: 701 slats again

Bob, I agree with you 100% on your clarification. In fact several of us 801 guys discussed doing just this to see if the speed increased. We even researched the type of tape needed to do this and came up with some helicopter stuff that was 12" wide. Maybe one day I will experiment.!!! 

do not archive

Ben Haas

N801BH

www.haaspowerair.com



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

 I may have caused some misunderstanding by my use of the word "remove".  I am not advocating removal of the 701 slat. The point I was making is that Chris Heintz designed the 701 slat by simply starting with the NACA 640-18 airfoil shape and then adding the opening (the gap between the slat and the rest of the wing) through which the air flows from the lower surface to the upper surface.  He sketched this very process for me by drawing the original airfoil first, and then adding the air slot afterwards, to divide the nose of the airfoil from the remaining aft portion. You can in effect "remove" the slat by covering the openings on top and bottom. Doing this "removes" the slat, returning the wing airfoil to its original NACA 640-18 shape. Covering the slat openings so that the original NACA 640-18 shape results should not cause a major change in the center of pressure at normal flight angles of attack (and hence stability). Of course, the lift will be significantly reduced at high angles of attack.

  

 Bob Eli

 N701K   

 [quote] ---

amyvega2005(at)earthlink.
Guest

Posted: Tue Nov 28, 2006 1:02 pm Post subject: 701 slats again

If you remove the slat or cover it it won't just reduce the speed at high angles, at any angle over 15degrees. THE PLANE WILL STALL. That is what the slat does is force the air over the wing at angles over 15 degrees.  PLane will still work great with the high cord wing if you cover the slat gap. but no extreme pull up angles any more.



Juan



--

amyvega2005(at)earthlink.
Guest

Posted: Tue Nov 28, 2006 1:05 pm Post subject: 701 slats again

you will not gain  as mouch speed if you do not elliminate the negative lift foil horizontal stab.  That is what the savana did. hence the higher speed.



--

dwieck(at)bellsouth.net
Guest

Posted: Tue Nov 28, 2006 6:05 pm Post subject: 701 slats again

He said remove the SLOT not the SLAT

 	  Quote: 	
		   Carl,

 

 I talked to Chris Heintz at Air Venture several years ago about the 701 

 airfoil, and the aerodynamic design of the slats.  The airfoil is an old 

 standard airfoil (it is a NACA 640-1 with  just a slot added.  In other 

 words, if you simply remove the slot and leave the fixed slat in its design 

 postion to define the nose of the airfoil, then you have standard NACA 

 640-18 airfoil. If one wants to remove the slat from the airfoil design, the 

 original airfoil can be recovered by simply covering the slots with sheet 

 metal that matches the airfoil contour.

 

 Bob Eli

jfosse1(at)shawneelink.ne
Guest

Posted: Tue Nov 28, 2006 7:14 pm Post subject: 701 Slats Again

For an interesting and informative  commentary on 701 and Savannah slats, or the lack thereof, go to:  www.stolspeed.com.



 Jim Fosse

   [quote][b]

secatur

Joined: 02 Nov 2006
Posts: 50
Location: New Zealand

Posted: Tue Nov 28, 2006 7:58 pm Post subject: Re: 701 slats again

From www.stolspeed.com

 

The True Story about Leading Edge Slats

 

How Zenair 701 & Savannah aircraft fly better with VGs than with Slats!!!  

 

It was way back in 1990, at the Sunâ€™nFun fly-in at Lakeland, Florida that I first heard about the possibility of flying a Zenair CH701 without the leading edge slats.  I was very interested in the CH701, so was hanging around the Zenair display, and there met a couple of CH701 fliers from Colombia.  (Usual reaction at this point is that, â€œ... it must have been for the drug tradeâ€¦â€, but thatâ€™s nonsense â€“ this was the days of 532â€™s and early 582â€™s, and the drug syndicates didnâ€™t need to fly over the jungle in two-stroke ultralights, they had the best of Bell helicopters!)  The real reason there were so many CH701â€™s flying there, is that Columbian men are real macho and always ready for adventure, so this aircraft suited them very well! 

 

Anyhow, these fellas told me that they had removed their slats and their aircraft flew better!  This was a real surprise, since those leading edge slats are one of the main distinguishing features of the Zenair CH701!  They spoke a bit of English, and I spoke a bit of Spanish, so I questioned them over and over again just to be sure, and they assured me that it flew faster without slats, and landing speed was only a little higher, â€œâ€¦Lo mismo, mas o menosâ€¦â€ (â€œâ€¦more or less the sameâ€¦)!  

 

Ever since that encounter Iâ€™ve been telling the story to Zenair CH701 and Storch fliers, suggesting that they might try flying without their slats, but no one would, so it had to wait until I had a similar aircraft myself to give it a go.  Now Iâ€™ve thoroughly tested it out on my Savannah (a clone of the CH701), and the results are astounding!  Iâ€™ll never put the slats back on.  Two Zenair CH701 fliers at our airfield have also removed the slats from their CH701s, and the results are equally impressive.  So we now have a surplus of used slats hung up in our hangarsâ€¦â€¦. 

       

  



Leading Edge Slats on a Savannah aircraft

Lots of drag and disruption to airflow.......

 

                                  



VGs instead of slats on a Savannah wing

Much cleaner - an excellent STOL wing!

 



The vast reduction in drag allows all these aircraft to fly considerably faster for the same power, climb better, glide better, and with the benefit of Vortex Generators, lift-off and touch-down just as short as with slats, but with more control.

 

In summary for my Savannah: 



Fast cruise (at) 5200 rpm has gone from 79 kt to 85 kt.      = + 6 kts 

Top speed has gone from 94 kts to 103 kts!                      = + 9 kts. 

Fuel burn (at) 75 kts has gone from 17 L/hr to 13 L/hr.      = 23.5% less! 

Best climb rate (at) 55 kts is 100 fpm higher. 

Best glide  (at) 40-45 kts is 100 fpm better. 



Stalls (idle power, no flap): 

With slats â€“ no real stall, just a stable high-descent mush (at) less than 30 kts. 

Without slats, no VGs* â€“ a distinct stall and roll to the left (at) 34 kts. 

Without slats and with VGs â€“ no stall, just a stable mush (at) less than 30 kts. 



*VGs = Vortex Generators, more about them elsewhere. 

L/hr x 0.26  =  US Gal/hr. 

Kts x 1.15  =  mph.

 

This testing was done in a â€˜Savannahâ€™ aircraft, a kitplane from I.C.P. in Italy, www.icp.it/avio.htm or http://www.skykits.com/ .   Itâ€™s pretty much a clone of a Zenair CH701, same wing profile but a longer wing, and a different tail section.  Powered by a 100hp 912ULS, 4-blade Brolga prop pitched for climb (16Â° blocks), carrying pilot (73kg) and 30 litres fuel.  

 

All tests were done in as similar conditions as possible.  It only takes minutes to remove the slats, so comparison tests with and without were conducted within one hour of each other, at the same altitude, in calm conditions, at first light before any thermal activity.  Climb and descent figures were timed with a stopwatch between 2000 and 3000 ft QNH.  Stalls and straight and level trials were conducted at 2000 ft QNH.  The with/without tests were done three times on separate days to re-confirm the figures.  The ASI was compared with the GPS by flying a 120Â° triangular course and averaging the legs, and found to be 1 kt low at 70 and 80, 1 kt high at 40 and 50, and spot on at 60; these corrections have been worked into the results.  Indicated airspeeds at 30 kts and less are truly only â€˜indicatedâ€™ â€“ inherent limitations in the ASI and the pitot at these low speeds wonâ€™t necessarily give a true airspeed, but is still adequate for â€˜before and afterâ€™ comparison purposes.



But what about the C of G ? 

 

There was no change at all in the trim setting required for the same cruise speed, with or without the slats.  Which just confirms aerodynamic theory that the slats arenâ€™t providing any lift at cruise angles of attack â€“ they just allow the wing to operate at an angle of attack above the normal stalling angle of about 16Â°.  

 

This has solved a mystery that bothered me while building the Savannah, in that the C of G range quoted in the manual was forward limit = 30% and rear limit = 38.5%!!  Most wings need a rear limit about 30% and a forward limit about 23% so this seemed to be way too far back??  Mine weighed right in the specified range, at 31% and 37% so I flew it, and it flew really well as all Savannahs do, but it certainly didnâ€™t feel like a C of G in the 30â€™s - puzzling????  This was measuring from the leading edge of the slats, with a chord of 1435mm.  However, without the slats and now measuring from the leading edge of the actual wing itself, instead of from the leading edge of the slats, it calculates to 22% and 29% of the now 1270mm chord.   This is just the sort of range that history has shown that most wings would call for.  So, measuring from the leading edge of the slats on a slatted wing needs a different considerationâ€¦â€¦

 

I did try leaving the slats on and covering the gaps top and bottom - not recommendedâ€¦..  This now turned the slats into part of the real lifting surface, so the actual CofG was then indeed 36%, and it flew like an aft CofG â€“ much more pitch sensitive and not so quick to drop the nose on pulling power.  Cruise speed was the same as for no slats, but stall without VGs was up to 36 kts and much sharper, probably due to the smaller leading edge radius.  I didnâ€™t try VGs on that wing because I wouldnâ€™t want to experience deep stalls with such an aft CofGâ€¦â€¦

 

Fuel Consumption 



 

The large reduction in fuel consumption was the biggest surprise â€“ 23 %!  This was measured accurately and consistently on two long flights (50 hrs each) to Cape York and to Tasmania, from near Brisbane, Queensland (thatâ€™s equivalent to flying from Seattle to Anchorage, then Seattle to El Paso).  On the trip to Cape York with slats on I used 17 litres/hr.; on the trip to Tasmania without slats I used only 13 litres/hr, averaging 75 kts both trips.  On both trips I was flying in convoy with another Savannah with slats.  He used 16 litres/hr both trips which provides a good reference.  The reason I used one litre/hr more on the Cape York trip, when we both had slats, is that I run a 4-blade prop pitched for climb, while he has a 3-blade prop pitched for cruise.  I used the same 4-blade prop on both trips, and saved 4 litres/hr by leaving the slats behind â€“ a total fuel saving for the trip of $250!  I could probably get even better fuel economy with a 3-blade, but I just love the tremendous take-off â€˜gruntâ€™ of this 4-blade Brolga!  



After seeing my fuel saving on that last trip, the other Savannah owner has now removed his slatsâ€¦â€¦



STOL Performance 

 

The reason I got this Savannah aircraft was for itâ€™s STOL performance, and I certainly wasnâ€™t disappointed â€“ it was always good.  I was expecting to lose a little bit of that STOL performance after removing the slats, so it was a really pleasant surprise to find that, with the addition of the VGs, it has actually improved!!!  The VGs serve pretty much the same purpose as the slats, but do it better, with less down-side.  The Zenair CH701 owners have found the same improvements.

 

I can now haul it off the ground sooner, with better control, and accelerate quicker in ground effect, and then climb away faster.  With slats, when I hauled it back it would jump off just as short, but then wallow along, hanging on the prop, slowly accelerating behind the drag curve caused by that enormous slot exposed at that high angle of attack.  Now it just jumps up and â€˜fliesâ€™ away!  And the climb rate is much improved.

 

Slow, power-off landings are much easier and safer without the slats.  With the slats on, as the angle of attack increased, the drag increased exponentially, so that the speed slowed very quickly and the aircraft would drop suddenly and heavily.  Lots of 701's have been bent just this way!  Without the drag from the slats, my aircraft now floats on much more gradually and gently, even if flaring a bit too high - it's very forgiving!

 

The Case for Slats

 

After all that, I'll now present the argument for slats!  They're really useful for power-on landing approaches.  Nose way high, hanging on the slats and the prop, 'dragging' the aircraft in below flying speed, with power controlling the descent.  Can't see where you're going with the nose so high, but easy to do a spot landing that way - just reduce the power and it'll drop down right now, no floating on.  But watch that you don't get behind the power curve too early and too high, pray that the engine doesn't stop, and hope that a stray wind shear doesn't drop a wing at such a critical moment..........  

 

Slats + VGs

 

I did try VGs along with the original slats.  In this case the VGs make no difference at all, because the slats already give good stall performance, so there's nothing more that VGs can do.  But of course this still leaves all the drag that the slats produce........ 

 

Flaps

 

Another advantage I didnâ€™t expect is that the flaps are now much more effective.  These flaperons provide lots of lift with little drag â€“ the descent rate only goes up 50 fpm from no flap to full flap (at) 40 kts.  This makes power-off landings at full flap easy and controllable at about 25 kts touch-down speed.  With the slats on, power-off landings at full flap were risky because the drag built up so quickly at low speed that, if youâ€™re not right close to the ground when it happens, you come down with impactâ€¦.  Now it just settles on gently.  And this makes sense by aerodynamic theory, in that the slats only do their stuff at a high angle of attack, while the flaps dramatically reduce the angle of attack â€“ so theyâ€™re contradicting each otherâ€¦..  To get any real benefit from the slats I had to â€˜hangâ€™ on the prop, at a very high angle of attack, and control the descent rate by power, â€˜draggingâ€™ the aircraft in â€“ I donâ€™t like that approach at all;  I prefer to â€˜flyâ€™ the aircraft in at idle power.  

 

And this Savannah with VGs instead of leading edge slats does â€˜flyâ€™ remarkably well now â€“ I just love it!!!  It now out-performs any Zenair 701 or Savannah with slats, both for STOL Ops and cruise.

 

p.s. â€“ Now youâ€™d have to wonder why the manufacturers didnâ€™t discover this long ago, eh???  Once again it may be the Columbians who provide the answer.  They said that they were told, "......Shh, don't tell anyone, itâ€™s the slats that sell these aircraftâ€¦â€¦".   Well, Iâ€™m sure glad they told me about it, and now that Iâ€™ve tried it,  Iâ€™ll tell everyone else so we can all benefit!



Now the ongoing story since NatFly 2006

 

(NatFly is our Australian equivalent of the EAA Sunâ€™nFun.)  

At NatFly 2006, I displayed my Savannah with VGs instead of slats, and with a copy of this story taped to the side of the aircraft.  The interest at NatFly was enthusiastic, because of course Aussie fliers are quick to pick up on useful ideas that are proven to work.  All over the country now Zenair 701 and Savannah owners are shedding their slats and going to VGs.

 

The visiting engineer from the Savannah manufacturing company in Italy looked at all my test data and then bought their first set of VGs from me!  Now we learn that, after seeing my display at NatFly, and doing their own testing, the Savannah factory has brought out a new model, the 'Savannah VG', with a new leading edge and vortex generators instead of leading edge slats.  So theyâ€™re still open to new ideas and quick on the uptake, and now theyâ€™re producing an even better aircraft!

 

Those of us with original Savannahs who have just removed our slats and added VGs to the original wing are getting very much the same performance figures as published for the companyâ€™s new leading edge with VGs.  So Iâ€™m eagerly awaiting the new Savannah â€˜VGâ€™  model, so I can do some comparison testing against mine with just the original wing with VGs instead of slats.  The first of the new models are due out here in August, and a friend nearby will probably be the first to finish building one.  Heâ€™s a good STOL flier so we should be able to do some really interesting comparisons.  I reckon theyâ€™re going to be very much the sameâ€¦â€¦.

 

The Savannah manufacturing company is offering an upgrade kit, with a replacement leading edge and VGs.  I sure wouldnâ€™t be ordering that upgrade kit for $1000 until I see some really noticeable improvement in performance.  To take the wings off, drill out all those important rivets in the spar (and end up with oblong and oversize holes), and then fight get that new skin (with an even sharper radius) installed so that the holes line up again, then paint it all again, Iâ€™d have to be sure there was a really significant gain to be hadâ€¦â€¦  Thereâ€™s certainly nothing at all wrong with my wing as it is â€“ I just love it!  Best to wait and see I reckon â€“ weâ€™ll probably know well before Christmas and will publish the results in this website.  

 

In the meantime, join the rest of us whoâ€™ve done it, and pull those mongrel slats off and add some VGs, and fly better!

 

You can hedge your bets by leaving the slat brackets on the wing, but a couple of us seemed to notice an improvement without them.   Hans detected a big difference for his 701, but the comparison tests couldnâ€™t be done in exactly the same conditions, and of course he canâ€™t go back and do another â€˜beforeâ€™ test once theyâ€™ve been cut offâ€¦..  So Iâ€™m making â€˜pretendâ€™ brackets that we can tape back onto our wings to do all the comparisons again.  As you can see, I certainly believe in thorough flight testing to get valid results.  Update Oct 06:  Results just in from a retired CASA engineer who has done considerable testing.  He flew his Savannah for quite awhile with the brackets before removing them, and has now noticed a considerable improvement in lateral stability and benign stall charcteristics.  So better remove the brackets for best results.

 

Iâ€™m often asked just how to cut those brackets off with least hassles.  I used one of those very thin cut-off discs in a small angle grinder.  Just hold it at a 45Âº angle and carefully cut a groove on each side as close in as possible.  Donâ€™t try to cut right through â€“ once there is a suitable groove on each side, you can flex the bracket a couple of times and break it off.  Then just grind out any portions that sit proud of the wing.  There are five rivets alongside the bracket which look really crude once the slat is off.  I drilled them out and put countersunk rivets instead.  I used polyester autobody filler to heal the scar, but epoxy filler would probably be better. 

 

I have a fetish for STOL Ops, and this Savannah with VGs is just ideal.  Itâ€™s performing STOL so well now that I just canâ€™t help showing off all the time, even on long runways!  

240hours in the first year, and itâ€™s all been a blast!

 

For NatFly I had imported some VGs from the USA, and they sold to Zenair 701, Savannah, Bingo, Lightwing, Skyfox and Jabiru owners.  Since then Iâ€™ve been doing lots more testing and comparison, and have come up with the new design of Feathers VGs that are described elsewhere in this website. 



  

Fair skies and tail winds.

 

JG 

Aug 06 



Do Not Archive

lo2u

Joined: 11 Apr 2006
Posts: 46
Location: Upstate New York

Posted: Tue Nov 28, 2006 9:26 pm Post subject: 701 slats again

Pictures please ..also from what I have read in these posts of late just 

removing the slats would seriously alter the profile of the wing and that it 

was designed from a wing with no slat but shaped as if they were not a 

seperate item and then Chris Heintz move the "slat" part forward thus giving 

a slot. So are the 701 owners at your field using  just the present wing 

less the slots without altering the wing itself??? Did they have to alter CG 

etc??? More explanation and a few pics would certainly help clear this up..

Thanks,

701 Scratch Builder ... not to the wings yet!

---

secatur

Joined: 02 Nov 2006
Posts: 50
Location: New Zealand

Posted: Tue Nov 28, 2006 10:43 pm Post subject: Re: 701 slats again

READ previous post, or go to www.stolspeed.com

harina(at)bigpond.net.au
Guest

Posted: Tue Nov 28, 2006 11:21 pm Post subject: 701 slats again

I've been flying my 701 for 475 hrs total,175 hrs  without slats, so I think maybe I should comment on this thread. I was the first  701 flyer in Australia to remove the slats ,after seeing the results that the  savannahs got. See www.stolspeed.com. I  must say that I like it much better without the slats and will never change  back!!

 Since then two other 701's at our airfield have  removed their slats,and I have flown their aircraft-same result.

 To answer some of those specific dire  predictions:

  

 >my take is that the C of G and the  centre of pressure would move back,the Cp more so causing a nose heavy pitch  moment at all speeds and angles of attack<

  

 Not so in real life..... before I took the slats  off I did a test flight and set the trim to neutral cruise. About one hour later  I did another test flight with the slats off, same conditions,same load. no  change at all in cruise trim! Take-off,climb,decent,and landing,all felt  balanced and correct...

  

 >I would expect all stall speeds to increase  with the clean wing<

  

 With the clean wing,yes of course the stall speed  increased and became more abrupt,but with the VG's it came back very much like  with slats,and angle of attack much the same as with slats.

  

 >and top speed to probably remain the same or  decrease because of the blunt leading edge<

  

 Not so- top speed and cruise speed definitely  increased without the slats and fuel consumption really decreased for the same  cruise speed.15%.The blunt leading edge doesn't seem to effect the speed in this  speed range.You would think so,but the Savannah with that same blunt profile as  the 701 goes pretty much the same speed as the new "finer" leading edge that the  Savannah put on their new "VG" model .

  

 >adding VG"s should delay the stall but should  also increase drag?<

  

 No they do not increase drag-see the Updates  page in www.stolspeed.com.   

  

 >if one wants to remove the slats from the  airfoil design, the original airfoil can be recovered by simply covering the  slots with sheet metal that matches the airfoil contour

  

 Be careful about that one! See the slats vs. VG's  page, C of G section, in www.stolspeed.com. When original built with  slats, 95 litre wing tanks,and 912 S,my loaded Cof G calculated at 477 mm  aft of the slat leading edge,1433 mm cord = 33% m.a.c This number would seem  quite far aft by conventional practice,but it sure didn't fly as if it had a aft  C of G .removing the slats moved the leading edge aft 160 mm , so the same C  of G position was now located 317 mm from the new leading edge, with the  cord now 1270 mm = 25% m.a.c. , which is right in the range recommended for any  conventional wing. I recently did a new weight and balance on very good  scales-

 without slats =26%m.a.c, loaded up for travel-  full fuel ( wing tanks),20 kg baggage , 40 litres of fuel in pax seat - 503  kg ( 1107 lbs).It flies just perfect like this.

  

 Well I have tried no slats and I wouldn't go back,  no way! And it's not as if I am easily influenced by other people's claims- I'm  a sceptical, independent-minded Dutchman,ex-Royal Dutch Air Force. I fly my  plane hard,and practice STOL landings all the time,so I have a really good feel  for it at all speeds. Always doing glide approach and idle power landings-That  is the real test of a well balanced aircraft.

  

 Hans van Santen

  

   

  

    [quote][b]

ggower_99(at)yahoo.com
Guest

Posted: Wed Nov 29, 2006 4:43 pm Post subject: 701 slats again

I am part of your team Ben...   To many years to enjoy flying yet 



Saludos

Gary Gower

701 912S

Flying from Chapala, Mexico.

Do not archive



"n801bh(at)netzero.com" <n801bh(at)netzero.com> wrote:[quote] I don't know about the 701 but,, the 801's slat leading edge profile is nothing like the wings leading edge profile. I will look very close at a 701 when I see one to see if it's like the bigger brothers. I would NEVER remove my 801's slats and fly with just the wing alone. but heck, thats just me... YMMV.

 do not  archive

Ben Haas

N801BH

www.haaspowerair.com



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

--> Zenith-List message posted by: "Robert N. Eli" <robert.eli(at)adelphia.net>



Carl,



I talked to Chris Heintz at Air Venture several years ago about the 701 

airfoil, and the aerodynamic design of the slats.  The airfoil is an old 

standard airfoil (it is a NACA 640-1 with  just a slot added.  In other 

words, if you simply remove the slot and leave the fixed slat in its design 

postion to define the nose of the airfoi l, then you have standard NACA 

640-18 airfoil. If one wants to remove the slat from the airfoil design, the 

original airfoil can be recovered by simply covering the slots with sheet 

metal that matches the airfoil contour.



Bob Eli



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pacificpainting(at)comcas
Guest

Posted: Thu Nov 30, 2006 8:37 am Post subject: 701 slats again

Me too.

  

  

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