Zenith Aircraft Builders and Flyers
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Increasing elevator span
Install .016 elevator tips outside the elevator hinges, increasing span by 180mm. Will add end plates to both horizontal stabilizer ends.
Replies to This Discussion
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Permalink Reply by Chumphol Sirinavin on
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A custom mod. for my CH701.
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That is correct.
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This is a customized add-on elevator tip. It is like building the rudder end rib with 108mm flanges and 76mm wide nose skin.
I made the first pair from .025"6061T6. Then I scrouged through my aluminum scrap box and built another pair with .016", for my other CH701. The .016" tips are quite strong for the job, but the .025" ones can last more mirror polishes. Polished control surfaces help to be seen in the sun. At first I wanted to double-use the clear pastic window for pre-flight/post-flight inspection, as well as access to work on the cotter pin and lube the elevator hinge during big/annual inspection, but I didn't like installing the plastic window outside the aluminum frame. So, the window riveted as shown while 6 screws (and Loctite) under the nose skin of the tip are for quick access to the elevator hinge. A 20mm strip of .025" riveted inside the inboard of the nose skin keeps it in shape against the strong head wind. I need to check that these tips are not obstructing elevator travel before riveting them in place.
Hoping to add more positive pitch control on no-engine flare, I could have built the tips wider but they are limited by my left-over aluminum and my knowledge/ignorance. Wider elevator span can cause additional problem when towing airplane wing-folded on trailer via highway to and from airport.
Champ
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Permalink Reply by John Austin on
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On my composite elevator tips/HT fence mod, I found you really didn't need a window. The gap or offset (inboard on the front of the tip for fence clearance) let's you see the elevator pivot and cotter pin during pre-flight when the elevator is fully down.
Since the lip or flange of my tip that faces the tip fence is 3 layers of BID cloth, it's very strong and did not need further reinforcement. However, to be conservative and avoid the tip scraping the fence, I left a several mm gap. I'm thinking about bonding a rubber seal or wiper along the inside of the flange so as to almost completely close the gap. The main thing would be keeping it thin enough that there is no possibility of jamming the elevator if it came loose but yet strong enough that it won't deflect significantly in the slipstream.
The elevator authority has been quite an improvement! I fly without slats, however, so I look forward to a report on how well this works in a plane with slats. Nice work, Champ ... your ideas helped stimulate me to do this project and I appreciate your participation in the forums!
John
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John,
The problem is I don't leave several mm gap between the horizontal stabilizer end plates/fences and the add-on elevator tips. So the window is needed for inspection. If I could bond nut plates behind the clear plastic window and screw it tight inside the aluminum window frame of the tip, I could do without the 6 sheet metal screws under the nose skin for service access. I could replace them with 6 rivets and double use the window to lube the elevator hinge every now and then. A member suggested to me Click Bond nut plate that will stick in place with glue. I need to check that some time soon.
By the way, a .016" add-on tip weighs 186 grams or or 6.56 ounces ready to be installed. A tip takes no more than an evening to complete.
Champ
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However, if you add the HT fences, you'll have to have at least a few mm cut-back or "gap" on the inboard side of the tip so it will clear the fence! This has to extend slightly aft of the fence so it won't bind as the elevator moves up and down. When the elevator is fully deflected up or down, this will leave the aft portion of the gap open for a few centimeters since it is not occluded by the fence. You can look through this gap to see elevator pivot and cotter pin. I made my tips removable rather than riveting them on so as to have access to the pivot for maintenance, so I guess you'll need the window or access plate for that, anyway.
John
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That's correct.
The window on the elevator tip can be that Punk Factor you mentioned. I might have picture of Snoopy inside waving to people who look through the window!
Champ
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Permalink Reply by Samuel McNair on
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Champ;
This appears to be the only way I can reply to your post. Not optimal, but hope it works.
I spoke to SUPERCUB people starting a few weeks ago and just got the latest response.
Their slats with VG's and with slotted Fowler Flaps reduce the SUPERCUB stall speed by 50% to in the range of 18 to 20 mph. It also cuts the cruise from 100 mph to 95 mph. Their slats simply attaché to the leading edge skins with just self threading sheet metal screws, a concept that I am not comfortable with. They explained that even when closed there is a small gap at the top of the slat to leading edge interface, which along with the open gap at the bottom probably accounts for the extra drag.
The JustAircraft SuoerSTOL slats go to extreme lengths to seal the top of the slats and to bridge the gap at the bottom when the slats are closed. And the bottom of the slat is slightly above the bottom edge of the wing when closed. Along with the sharper leading edge profile it makes and the tight seal, that is probably explains why adding slats to the JustAircraft wing increased their cruise speed some.
Also the people at SuperCub noted that having the slats mounted such that the bottom of its nose is 1/2" to 1" below the bottom surface of the wing radically improves the STOL performance. Drag also radically increases. This is consistent with all of the other info sources & data I have researched. Their trips extend a little below the bottom surface of the wing when deployed, but he was not able to tell me how much so, but from the pictures it was not much. But then in my experiment it didn't take much to make a big change in stall speed, drag, and stability.
I am going to make plywood full scale cross sectional mock ups of my leading edge and my slats and the mounting tabs, then play around with various pivots and hinges to see what works and is simplest. to install. I may have to change the slat profile somewhat to make it work out. I will keep you posted.'
I do not live that far from the Mexico City Zenith site. If you are ever in the US, please consider being my guest,.
'Sam McNair.
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