Stolspeed VG installed on Zenith 701

As we have three 701s and three Savannahs at our airfield, we’re in a good position to compare the two aircraft. We fly them intensively, especially practicing STOL operations and out-field landings, as well as considerable cross-country cruising in company, so we can compare performance directly. For that reason, I have included some additional information for the 701 and a comparison with the Savannah.

• Read instructions for Placing the Stolspeed VGs on the 701
• Comparison of the 701 and the Savannah
• Origin of the 701 and Savannah designs

Joe of Mississippi has provided the most comprehensive independent flight testing of his CH701 with Stolspeed VG's 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 B52 jets to his Legal Eagle ultralight.

CH701 Configuration

• Engine: 912 ULS

• Prop: 3 Blade Warp Drive set at 11 degrees

• Empty Weight with slats: 592 lbs

• Empty Weight without slats: 579 lbs

• EW CG: Not on hand, but believed to be 12% MAC or close

Testing Conditions

All flights were made with the same load:

• ~7 gallons of gas

• Pilot

• Wire Hair Terrier in the baggage shelf

Flights were done:

• As close to 60°F as possible (some variation, but minimal)

• Always at 1000 MSL

• In mostly smooth air

All speeds were taken from GPS, using a 4-leg box pattern average and carefully flown.

Flight sequence:

1. With slats installed

2. With no slats or VG's

3. With VG's in 3 different positions (final position at 8% MAC, permanent)

Note: Plane had round (not streamlined) lift struts. VG placement was found important for predictable takeoff performance.

Cruise Speed at 5000 RPM

• With slats: 84.0 mph

• No slats or VG's: 90.25 mph

• VG's at 8% MAC: 90.25 mph

Note: I flew with the clean wing for that speed, installed the VG's (2 hours), and went right back out and flew under near-identical conditions. Result: identical speed for VG's vs. clean wing.

Real world, I have found the cruise speed to be more like 88–89 mph depending on load, temps, etc. Still an increase of 4 to 5 mph over slats.

Takeoff & Landing Distances

Testing done on a 250 ft strip with markers along the side for estimating distances.
Same load each time (including the terrier), no wind, and max effort on all runs.

Takeoff Distance

• With slats: 60 ft average (see the green one on YouTube video)

• Without slats or VG's: Not measured

• With VG's at 8% MAC: 60 ft average

Note: If it will make the naysayers happy, I’ll apply a 10% penalty to the takeoff distance just to allow for whatever tolerances. Even though 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 ft

• Without slats or VG's: Not measured

• With VG's: 150 ft

Note: I never was able to match ZAC figures for landing (140 ft I think it was), even though I often lock the brakes for rollout (skid-out).

Handling Notes

The big difference for me with the VG's is that the thing is so much more controllable at low speed, allowing for a lot more precise approach and 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 Cessna 150 I thought), and things can unravel fast close in.

The VG's cured a lot of that for me. Yes, there is some flattening of the power-off glide angle, but the slip is available for obstacles, so I call that a non-issue.

The big deal with the VG's is:

• Improved low-speed handling

• Reduced buffet

• 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

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 slats for sale!
No change to prop pitch yet and did not remove brackets... yet!
No downside that I can see on an 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 slats 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 Stolspeed VG's!
Tom in Florida

I got my Stolspeed VG's from John Gilpin. 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 takeoff.

Still too windy for more accurate numbers, but takeoff 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 45 mph 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 than I get now, but I bought the AC for its 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

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 someday 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 10% 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 than I would need though, as a result I may be getting some drag, as I only gained 4–5 mph at the same RPM.
Ron, Arizona

More from Ron 

I put VG's 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 VG's.

What a dramatic example of the effectiveness of VG.
Ron, Arizona

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 (175 lbs) 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, 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

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% 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

Just a quick one to say thanks for supplying and making me aware of your VG's.

All tests have been done to the extent, last week I cut off the slat brackets, no need for them anymore.

My personal results are: takeoff and landings the same. The big bonus is 8 knots improvement in cruise.

Now I can either keep the extra 8 knots for the same rpm, or reduce the rpm and save fuel.
An extremely good investment, I thank you once again.
Mike, Perth, Western Australia

I am really impressed with the increased climb rate and cruise speed the VG's have given my 701.

My landings are definitely smoother than 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 touchdown.
Cam, Alberta, Canada

JG,
Installed the VG's on my 701 today.

Wow! What a difference. At flare, 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

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 30 mph with 200 lb co-pilot!
Ken, Oregon

Finally had time to install VG on my CH701 and do test flights — they work really well, thank you so much.

The difference in control during landing and takeoff is significant.

Adam, Czech Republic

Hans 701 over the Simpson desert                                                      On the Strzelecki Desert