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Friday, September 27th,
After a 2 hour test flight checking the performance of the 701 wing with VGs/without Slats, I got some interesting data.
First thing I checked was the takeoff run... After a few runs, I can say that the nosewheel comes off/on at 38 mph indicated. I can pull the nosewheel off as soon as the speedo gets to 38mph which is almost the same as before with the Slats. The takeoff run seems to run the same lenght but the speed seemed to build faster. I got 750 fpm at 54mph and could hold this forever.
Flying : I didn't feel a big difference except that top speed was 86mph and I could hold 70mph at 4200rpm (engine) easily. The 701 didn't seem to slowdown as fast as before when I throttled back. Turns were the same; nothing very different there.
Slow flight/ Stalls : The 701 with Slats won't stall; it will mush nose high and descend at 1000fpm under control. With the VGs You can still slow flight this thing and it will sort of stall right ahead but as soon as the nose comes down you're flying again... Lateral control stayed good at all times...My 701 is on the nose heavy side, when the speed bleeds it wants to nosedown and start flying again.
Landing: The 701 with slats has to be pointed DOWN hard to keep the speed up for a safe landing (if chopping the throttle); it is quite steep to keep the speed up. Without the Slats (with VGs), the descent is more horizontal like a C-150. You don't lose speed as fast; so if you keep some power, you can come almost flat for the landing. Once on the ground, I could keep the nosewheel up until almost stopped; something I couldn't do with the Slats.
I still have to test these VGs some more but I really like the 701 as is. My Slats won't be back for sure, I do want to add those wing fences for those high banking turns...
This is for me, my plane and with my experience. It might not be for you and I can't guarantee you will experience the same results. Check it out for youeself but one thing is sure: they work !
Fly high, Fly safe !
Friday, September 20th.
Today, we installed the wing VGs and removed the Slats. We used the spacing
noted below and it worked out perfectly. In doing so, we saved the Slats weight
and didn't seem to loose in performance.
Actually, I went for a short test flight (had to go back home) to experiment with the change.
I was solo with full fuel. It was almost a month since I last flew the 701 but the EA-81 started at the first
flip of the propeller. Gee, I just LOVE that engine! Pushed the throttle and taxied to the runup position.
Did a quick runup, everything in order. Lined up the runway and floored the juice !
First thing I remarked was the nose came up quicker than usual; it came up almost instantly. I kept the nosewheel up with ease and VERY soon the mains felt light ! Pulled gently on the stick and ...airborne !!!
Left the 701 build speed then pulled some more...Soon, I was doing 600fpm at 60mph and not even forcing it!
I usual do 550-600fpm at 52mph ...This is better ! Leveled at 1500ft and this thing is doing 85mph and keeps going!!!
I came back on the power 5300rpm, 4900rpm, 4500rpm, 4200rpm and I'm still doing 70mph !
Checked lateral control... Not much change there ! Time to come back down...Just as I was having FUN !!!
Lined up the runway on final and throttled back...Usually I keep power until touchdown, this time I had to go to IDLE and the speed wasn't even bleeding !!! That's a change !
Touched down on the mains (light as a feather!!!) and pulled the stick all the way ! I was able to keep the nosewheel up almost till the end of the rollout ! Actually, the nosewheel came down by itself around 38mph indicated.
That's a change !
I still have to test stall characteristics and do more takeoffs/landings but with these preliminary results ...The SLATS
are OFF for good ! I will add the wing fences next time I get there.
Till next time, Flight high, fly safe !
So, I dug some more on the Internet and this is what I found :
For the CH701
For the main wing, place the front tips of the VGs 140mm in front of the main rivet line
on the top of the spar. There are two rivet lines out near the tips, but use the line
that runs the length of the wing.
Starting at the wing tips, place the first 15 VGs at a spacing of 60mm with the template,
then the rest at 90mm spacing.
The VGs need to be positioned such that they have the best ‘bite’ at the airflow when
the wing is at the stall angle of attack. If they are too far aft they risk being buried
in the thickening boundary layer and the start of separation, so they lose effectiveness
at stall. If they are too far forward they are reputed to slightly increase drag at
cruise, but I have never been able to measure such - better to be farther forward than
too far aft. So, with the wing positioned at the stall angle of attack, the VGs should
be slightly forward of the highest point of the airfoil. Historically, the margin is
considered to be 8-12% of wing chord back from the leading edge to the highest point
of the VG, with most experience settling on 10% as the most appropriate.
We'll try this and let you know....
I bought the Aircraft Spruce Aluminum VG kit for EXPERIMENTAL and installed the elevator VGs with good results.
It is now time to install the WING VGs and get rid of the SLATs but the instructions on how-to install the WING VGs are not CH701 specific...
Anybody installed those specific VGs to the CH701 wing already with good results ???
I checked the StolSpeed plastic VGs and I like the Hall Brothers better (sturdier = aluminum) but the spacing for
mine and the placement on the wing baffles me ...
I would greatly appreciate any help on where in front of the spar they should be installed for greatest efficiency...