Zenith Aircraft Builders and Flyers
Online Community of Zenith Builders and Flyers
Half Slats
Has anyone tried removing only half the slats and installing VG's?
It may be a useless half measure but I am curious if maintaining some of the ability to land over obstacles would be maintained while still seeing some net gains in cruise speed and fuel efficiency.
One of the characteristics of the 701/750 I don't like is the tendency of the plane to stop flying just off the ground. The number of nosegear damage incidents on low time pilots in the plane is clear evidence of this tendency. Mine lands best by keeping just a touch of power in and flying it to the ground. I wonder if a partial slat removal cleaning up half the wing might improve this.
Like to hear from anyone who might have tinkered with this.
Thanks
Replies to This Discussion
-
Permalink Reply by Walt Snyder on
-
Agreed, typically you want the inboard to stall first, so it will be interesting to see what's going on with this mod, obviously a multimillion million dollar company has access to a 'few" good engineers.
-
Permalink Reply by Samuel McNair on
-
Do we know that this is a factory mod, or is this someone exercising their right to experiment without necessarily having all the information to do so with adequate margins of safety?
I would want to put on a chute and do some stalls (and possibly unintended spins) at a range of load and CG AT ALTITUDE before I played with that one close to the ground.
I hope it works out well for him.
Having the inboard portion of the wing stall first is a very proven design safety feature. Possible exception might be AC that use spoilers with no ailerons.
The 801 achieves this with a straight, no twist wing by having the outboard half of the flaperons at a different AOA than the inboard, Cessna does it with twist or washout, Stinson did it with integral outboard slats, and some others do it with stall strips on the inboard. But generally they all do it one way or another. If this guy's inboard does stall before the outboard, them he should ditch the slats because the outboad configuration is outperforming the inboard. He would do better with airbrakes.
-
-
Stinson does have washout in their wing, like most GA. I wouldn't consider the CC mod until it's clarified what being achieved and why.
-
Permalink Reply by Lonny M. Kirk on
-
This is a factory testbed plane. I spoke to Cubcrafters and they are testing the idea now and waiting for pilot feedback. They may be looking to slow the plane down on approach and possibly get steeper approaches over obstacles than the current wing.
I notice the shape of this slat is much different than a Zenith slat being lower profile and much more open on the lower leading edge.
If more info becomes available I will pass that along.
-
-
Great. Thanks for the info. So it is a controlled experiment.
Walt, some of the Stinsons had plenty if washout and no embedded slats. From a few owneRS I know I am told that washout is minimal on those with the embedded slats (like the station wagon midel). One of those owners was my uncle, an aeronauticsl engineer. But, if I have passed on erroneous information, I stand corrected. I felt that I had info on good authority.
But I do think we all generally agree that as long as the roll control comes from the outer part of the wing, sound design is for the inner part to stall first.
Having those draggy old slats out there do allow you to hang it on the prop without such rediculous deck angles.
In my reading, one person tried blanking off the gaps between the slat and the wing, but that effectively made the cord line of the wing about 8" longer and he reported that it acted like a plane loaded dangerously close to aft CG.
Even though zenith does CG based on a %of MAC that includes the slat, the slat does not rrally change the MAC that much as long as the gaps are open.
My problem is that both 801s tend to always be near aft CG limit with any real load in them.
-
-
I appreciate all the feedback here and my original thought about half slats seems less ridiculous than I thought it might be. I intend to investigate this further and am encouraged by the Cub research going on.
Your statements about the root of the wing being the area that should stall initially for control reasons seems logical and indicates some level of knowledge of aerodynamics so I will ask a couple questions.
Intuitively I had originally thought to do just what has been done on the Cub thinking of VG's on the wingtips just because I thought the cleaner airflow would be at the tips so eliminating the slat drag there would produce the most effect. Again purely intuition. I was also thinking that in a very slow landing, some power on final would produce prop induced airflow on the slat inboard and give me an ability to control the stall with power vs. relying solely on airspeed.
It raises the question of why they opted to put it at the base of the wing, since obviously lowered stall speed is a primary effect of a slat, which makes it fly in the face (no pun intended) of what you are saying about the stall happening at the wing root being necessary for safe handling.
I know that everything I read about slats vs. VG's shows a one to two mph increase in stall speed of the wing with VG's instead of slats which would lead me to believe this configuration would cause the wing to stall outboard first. I read the Stolspeed article where he closed the slat gap and it sounded like it scared him because of the aft CG effect. This makes me very hesitant to experiment. I know what 1/8" of frost can do, much less radical changes like this and I am no test pilot.
Can you shed some light on why putting it at the base of the wing is not creating a dangerous handling situation?
-
-
Good call on waiting for more info on the slat configuration, a lot of us are. I'd look into the slats vs VGs debate more, now that pilots are pushing the STOL to extreme and there is more info available on the real world performance of slats. You may want to keep the full length slats and not deal with the headache of modifications.
It's interesting, years ago VGs were the hot ticket for STOL, they perform very well in what they were designed to do, and quite a few of the backcountry flyers put them on. Now, it's becoming unusual to see a slatless hardcore STOL performer, which says quite a bit in the slats vs VGs performance debate.
If you fly it and land it like a Cessna, you will not notice much difference. If you want the ability to fly it and land it like Deane is below winning the 2015 New Zealand STOL contest, you should contact him re. how slats perform.
Walt Snyder
And, slats or VGs are not just for extreme STOL, they also allow Deane and others to enjoy doing this……. and that's what it's really about…...
-
-
To be honest here this started as me concerned about the landing characteristics of the plane and it branched out from there. I have installed VG's on the underside of my elevator and by all accounts that is a no compromise enhancement.
I went from there considering what else might be done to improve the flight characteristics of the plane which has lead to a great deal of research into the "Beanie Mod" and the induced drag/lift loss at the critical moment of landing. Quite a few 701''s have had nosegear damage trying to land this like a Cessna, and it doesn't translate.
I still intend to do the Beanie Mod and have corresponded with Ari Hulkonnen on his version. I may take it a bit further and modify the windshield to try to eliminate the wing cap at the cabin roof entirely. It appears this gap was originally done to keep prop wash for rudder authority but I think the effectiveness of that has been disproven. It appears the sharp angle and flat cabin roof at steep angles of attack disrupt airflow negating this effect and that a smoother airfoil shape may actually provide better airflow past the rudder and eliminate the loss of 30 or so square feet of lift surface at the critical moment.
I have learned to hold power on final to maintain control but in a power out landing this aircraft needs some speed coming in, which the slats want to dump. A step approach until the last moment is an absolute requirement in a power out situation and this ups the ante on required skill. Just sayin'.
The last thing on my list was the slats vs. VG discussion and I am having that now. The experimenter in me appreciates all the good input. Fly safe.
-
-
Gotcha, my bad, I thought you were building, that's why the don't cut the slats brackets off yet approach. Yep, any high drag aircraft is going to have a different approach to power off landings, but, that low speed, low kinetic energy, greatly improves your chances and areas to land. There's a group of about 5 of us that take our plane out every few months and do power out practices in a dry lake, well worth it, and an eye opener for those that haven't and do not know how to manage that energy.
-
-
Walt,
Where do you fly out of for your dry lake practice? I have yet to work up the nerve to try it. These planes are too easy to total from a hard landing so this is one maneuver I am going to approach cautiously.
I hold significant power on landing and this would be a much different approach.
Thanks
-
Permalink Reply by John Austin on
-
I've got a STOL 750 Ed.1/Ed.2 with the "flat" cabin roof window. Rudder control at the slowest of speeds has never been a problem, but I felt the elevator was marginal, even with the Zenith VG's on the underside.
I thought long and hard about the Beanie Mod or something similar but it seemed to me that it would be easier (in a completed and finished flying aircraft) to directly attack problems in the HT and elevator as they would be easy retrofits.
So, I fabricated 4" fiberglass elevator tip extensions and tip fences for the HT similar to a Pilatus Porter and faired-in the huge gap under the tail that is very disruptive to airflow:
The net effect of these mods is the elevator has a much more linear and positive response to control inputs - felt like I suddenly had "power steering!" Not only can I gently lower the nose on roll out, I can even pick it back up if I want! Like I said, for a retrofit situation, seems a lot easier than modifying the cabin roof or the wing, but if I was still building, I definitely would have done either a "Beanie Mod" or something similar. I do wonder, however, if the positive effects of the Beanie Mod on the tail would be anything near the results I got with modifying the tail directly?
John
N750A
-
-
I made similar fairings for my 801 looking to pick up some speed (+1.5 knots) and to close that gap off. They look almost identical to yours except that your paint is MUCH prettier. I also saw improved response. The VGs on my tail also helped quite a bit but they are very non linear, when they are exposed and get the right bite, the tail goes down quickly. You have to be a bit careful but it does help keep the nose up
Anyone out there have any structural concerns with adding more span to the elevator?
I have a spare set of tips to play with.
Did the end plates add anything to the stability of the AC? My 801 has the old style 30 gallons in a single tank long range tanks instead of the newer 2 x 15 gallon per side tanks. As a result fuel slosh makes it want to wag its tail side to side in flight at the right speed range. Thinking of adding tank baffles but that would involve opening the wing and cutting open the tanks.
Any ideas out there?
- ‹ Previous
- 1
- 2
- 3
- 4
- Next ›
New from Zenith:
Classified listing for buying or selling your Zenith building or flying related stuff...
Custom Instrument Panels
for your Zenith:
Custom instrument panels are now available directly from Zenith Aircraft Company exclusively for Zenith builders and owners. Pre-cut panel, Dynon and Garmin avionics, and more.
Zenith Homecoming Tee:
Flying On Your Own Wings:
A Complete Guide to Understanding Light Airplane Design, by Chris Heintz
Builder & Pilot Supplies:
Pro Builder Assistance:
Transition training:
Aircraft Spruce & Specialty for all your building and pilot supplies!
How to videos from HomebuiltHELP.com
Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit HomebuiltHelp.com for the latest DVD titles.
© 2024 Created by Zenith.Aero.
Powered by
