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Zenith CH701 Page

 

Slats vs VGs

New Horizontal Stabilizer

Longer Wing

Cut-Away

The PegaStol Wing??

Placing VGs on the 701

Comparisons 701<>Savannah

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Hans set up for a classic STOL landing.
Short Wing with VGs
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Short take-off roll without slats
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Gene's Long Wing 701.
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Hans 701 over the Simpson Desert.
Long Wing - VGs
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On the Strzelecki Desert.
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Testimonials
 
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Joe Spencer of Mississippi has provided the most comprehensive independent flight testing of his CH701 with Feathers VGs instead of slats. 
Joe is very independent-minded and as sceptical as anyone, but is curious and adventurous, and has 20,000 hrs of flight time from wide-bodied jets to his Legal Eagle ultralight.
 
CH 701
912 ULS
3 Blade Warp Drive set at 11 degrees.
Empty Weight with slats 592, EW without slats 579, don't have the EW CofG in front of me but believe it was 12%MAC or close to that.
 
All flights were made with the same load, about 7 gallons gas, pilot, and a Wire Hair Terrier in the baggage shelf. Tried to fly as close to 60 F as possible(some variation here but minimal), and always at 1000 MSL in mostly smooth air. All speeds were taken from a GPS and 4 leg box pattern average and carefully flown. I flew first with slats installed, then with no slats or VGs and finally with the VGs in 3 different positions (ended up with the VGs at 8% MAC-permanent position). My plane at that time had round (not streamlined) lift struts installed. I found that VGg placement was important to predictable takeoff performance.
 
Cruise speed at 5000rpm, slats installed, 84.0 mph
Cruise speed at 5000rpm, no slats or vg's, 90.25 mph
Cruise speed at 5000 rpm, VGs at 8% MAC, 90.25 mph
 
Note: I flew with the clean wing for that speed, installed the VGs (2 hours) and went right back out and flew under near identical conditions and came up with an identical speed for VGs vs. clean. Real world I have found the cruise speed to be more like 88-89 mph for varying load conditions, temps etc.; still an increase of 4 to 5 mph over slats.
 
For takeoff and landing measurements: I have a 250 foot strip with markers along the sides for judging distances used. While not the best system it does work for my purposes and for real world evaluation, I think. At any rate here in Mississippi
we have to get by with what we've got so there you have it. All measurements were done no wind and same load including the terrier. All takeoffs and landings were what I call max effort.
 
Takeoff distance with slats 60 feet average (see the green one on utube video)
Takeoff distance without slats or VGs not measured
Takeoff distance with VGs at 8%MAC  60 feet average
Note: If it will make the naysayers happy I will apply a penalty of 10% to the takeoff distance just to allow for whatever tolerances...even tho I didn't come up with that in my measurements. That's a whole 6 feet. Like I said somewhere before-who cares
 
Landing distance with slats 180 feet
Landing distance without slats or vg's not measured
Landing distance with VGs 150 feet
 
Note: I never was able to match ZAC figures for landing(140 feet I think it was) even tho I often lock the brakes for rollout (skidout).
 
The big difference for me with the VGs is that the thing is so much more controllable at low speed allowing for a helluva lot more precise approach/touchdown. 
 
 I found the 701 with slats to be fairly demanding when really slowed up (Roger at ZAC says fly 50 mph-kind of like a Cessna150 I thought) and things can unravel fast close in. 
 
 The VGs cured a lot of that for me. Yes there is some flattening of the power off glide angle but once again the slip is available for obstacles so I call that a nonissue.
 
The big deal with the VG's is improved lowspeed handling, reduced buffet, and better fuel economy or higher cruise take your pick.
 
At any rate, don't take my word for it do your own testing and whatnot and make up your own mind. But don't knock it til you've tried it. 
 
Joe, Mississippi
 
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701 on Floats
Removed my Slats today and installed VG's on my 701SP on Czech 1200's with 912s warp drive prop.  First tests show 7 mph more speed at same RPM  5500 rpm 85 w/slats    92 w/vgs.  (GPS speed 2 way run done 3 times) Trim no change.... More stall tests tomorrow. But first impression was very little change in stall speeds power off .....no break.   Power on good warning with buffet...clean break...no wing fall off.  I have a set of slat's for sale!  No change to prop pitch yet and did not remove brackets....yet!  No down side that I can see on a Amphib.   More later.
I'm grinning from ear to ear!!! 
I love the 701 on amphibious floats now that it has VG's.  It's so nice to run at lower power settings!  And the handling is much improved.   I was thinking about looking for a replacement for the 701 before removing the slat's because it was so slow   at high power settings (on floats) even after I did some major airframe cleanup. Now it's a keeper!  Thanks for selling the Feather's VG's!
Tom in Florida
 
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701
I got my "feathers" from John Gilpin with Stolspeed.  With his directions they are very easy to install.  Less than one day.  My czech 701 has electric flaps and I land with them in 30 degree and 15 degree take off.  Still to windy for more accurate numbers, but take off distance and landing distance  is as good as before vg's.  At 4900 actual rpm my indicated airspeed before was 83 mph with an actual gs of 85 mph (gps triangle test).  Now it is a solid 86 mph indicated at 4900 rpm. At 45mph with 1/2 flaps my rate and angle of climb is better.  I am using actual distance and clearance at this point of testing as I have only had time for 4 T/O's.  My prop is set so I can turn actual 5800 static RPM as I fly out of a 600 ft. field. The factory set prop gave me at least 8 mph IAS more then I get now, but I bought the AC for it's stol performance. I plan to remove the attachments for the slats after complete testing.  
 As you can see, I'm very pleased with the results.      
Joe from FL
 
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701
I now have over three hours flying time and several landings on my 701 with the slats removed and VG's on. I have over 75 hours in/on this plane. At this time I see no reason to ever put the slats back on. I will leave the mounting tabs on, as some day when I sell the new owner may want to try the slats. I have lots of them, (56 VG's) on each wing They are placed in the CCI pattern, which is, 2 close together then about a 5" inch gap and so on. The leading edge of the VG's is ten percent back from the leading edge of the wing chord, which includes the flaperons, but not the slats. My plane is
ever so much easier to land. It sure feels like it climbs better. No stall just the mush as before. Trims are identical as with the slats on. If I didn't look out the window in flight I would never know the slats were missing. I think I have more VG's on then I would need though, as a result I may be getting some drag as I only gained 4-5 miles per hour at the same RPM.
Ron, Arizona
  
More from Ron, Re: Tail Feathers on his 701
I put VGs on my 701 elevator as per your instructions. 
 Before, I didn't have enough up trim to keep the airspeed at landing speed with power off, and no back pressure on the stick. I now only need 1/2 of the nose up trim to keep it at landing speed without any back stick pressure, amazing. I should be able to reduce the size of my trim tab to 1/2 its present size and still do the job it couldn't do before the VGs..
What a dramatic example of the effectiveness of VG.
Ron, Arizona 
 
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701
I removed my slats on Saturday and have seen an incredible improvement in flight characteristics.
I did about three hours of flight testing stalls, climb, glide at various weights up to 1200# with fully loaded baggage area. With just me (175lbs) and light fuel the 701 stalled normally with no nose drop.   
As you indicated on your website, the cruise speed increased significantly . Max speed is now somewhere close to 110 mph. and used to be ~95 mph. Now cruises 85 at 4500 rpm. The acceleration and climb improvement alone is enough reason to not put the slats back on. I was really used to it slowing down much quicker when I pulled power, but that is something I can get used to along with the smooth landings.
Ken, Oregon, USA
 
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701
I had another fly around yesterday with the VG's under the elevator. I put them on at 30 mm spacing as you suggested. Boy, does that make a difference! Previously with the slats on, I couldn't get the nose up enough to induce a stall at 40 knots. Now I can actually get it to stall clean at about 33 knots with the C of G at around 17 percent of chord. I need to get the C of G back a bit to stall it properly with flaps down. The stall seemed to be pretty benign with no tendency to drop a wing, just a bit of a waffle up and down.
Coming in to land, I approached at 50 knots with half flap, pulled the power as I crossed the fence and flared just a bit high and just kept the stick back while it settled fairly quickly with just a slight bounce, pretty much the same as it used to do with the slats, except that with the VG's under the tail, I was able to get the nose a bit higher in the flare.
David, Victoria, Australia
 
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701
Just a quick one to say thanks for supplying and making me aware of your vg's.
All test's have been done to the extent, last week I cut off the slat brackets, no need for them anymore. My personal results are, take off and landings the same, the big bonus is 8 kts improvement in cruise. Now I can either keep the extra 8 kts for the same rpm, or reduce the rpm and save fuel. An extremely good investment, I thank you once again.
Mike, Perth, Western Australia
 
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701
I am really impressed with the increased climb rate and cruise speed the VGs have given my 701.
My landings are definitely smoother then they used to be but will take some work to get shorter. I tend to float down the runway more.
I have noticed a real change in my level flight attitude. Nose has dropped quite a bit. Had to fly with the trim to keep her level until I figured out where the nose should be relative to the horizon.
Yes the tail feathers are definitely the ticket. Installed them on the elevator and have about 20 landings. It is sure nice to have the elevator control right up to and even after touch down.
Cam, Alberta, Canada
 

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701

JG,
Installed the VGs on my 701 today.  WoW!  What a difference.  At flair, I can now chop the throttle and hold AOA to touchdown.  Don't need the power to land. 

 My CFI is also very impressed.  Thanks for the good work you have spent in development.  The installation was very easy and straightforward.

Ken, North Carolina.

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701 with 750 wing

JG,
I have the scratch built 750 “style” wing installed on my 701 with your VG’s on wing and elevator and it performs great. 
Stall (that's if you can call it a stall) with just me is so low it's difficult to measure, but seems to be around 30mph with 200lb copilot!  

Ken, Oregon 

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Tail Feathers

Longer Wing

701 Door Warning

Placing VGs on the 701 

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