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A month or so ago I started a discussion thread about the effectiveness (or lack thereof) of the pre-war trim tabs. I learned that just about everyone else had the same experiences as I had. Perhaps the little popsicle stick tabs worked OK with 40 horsepower at 75 mph.
Because the trim tabs are held on with three screws, and because it is not messing with a primary control, and because I am frankly tired of not being able to trim my airplane at 90 miles an hour or more... I have been working on an improved set of trim tabs.
No Taylorcrafts were damaged in the making of this fictional film.
I decided to do it in steps, i. e. one side at a time for safety and sanity. So far, I have made one new tab, which has been slightly modified. The initial results are promising, but far from definitive.
I used a popular model airplane flying wing airfoil ("Zagi wing"), because it is 'reflexed' to eliminate the pitching moment, but still able to provide lift. This was in hopes that the needed "nose down-tail up" trim force would occur with the tab as close to neutral as possible. The new tabs had to be sharply tapered, to put some more area forward of the pivot point for aerodynamic balance, yet not interfere with the lower tail brace wire. The tabs are about 1/3 larger in total area.
Only the port side tab was replaced for initial flight testing. The original starboard tab was left in place for safety. No cutting, welding, drilling, or modifications were made to the original airframe. The tab was made using established R/C model wing technology that has been flown at well over 100 mph. Cores were hot-wired from blue foam, a solid Birch spar/pivot was machined and inset into the core. (Birch harder than AC Spruce for fastener crush loads) A Balsa wood leading edge was sanded to match the airfoil ocntour. 1/64" three-ply Birch aircraft plywood skins were epoxy laminated to the core and Birch spar. Balsa root and tip ribs were expoxied in place. The assembly was sanded smooth and covered with an iron-on fuel-proof fabric to match the aircraft's color. AN and MS hardware was used to attach the tab to the aircraft's pivot arm.
First flights showed that I had over-estimated the need for aerodynamic balance. The tab would "over-center" either to the full nose up or nose down position at cruise speed. It was also evident that there was too much reflex in the airfoil, because the tab wanted to go nose up (airplane nose down) more than the other way. The trim lever had to be held in position by hand to keep the airplane level, but the good news is that the airplane could be held level in 100 mph cruise...the tab was making enough force to trim the airplane.
An aluminum strip extension was attached to the trailing edge of the tab adding "damping" area aft of the pivot point, as well as reducing the effective reflex. This change was in the right direction... the trim tab was far less prone to flop one way or the other. But it still wasn't showing positive stability. Lying on my back at the secret flight test facility, I bent the extension to give it a little positive camber (tab nose down, airplane nose up), and the test flight back home showed that I was very close to having it right. I have to remove just a little bit of that adjustment and it should have the right combination of neutral stability (the tab not wanting to move off of the desired setting) and more trim authority.
Even with one of the new tabs and one of the old tabs, the airplane will now hold a trim speed of 63 mph power off (was 70+ before), and hold level high speed cruise at 95+. When the other tab is finished and adjusted, I am GUESSING it will have enough trim authority to hold 55 mph on approach and probably a 110 mph descent power on. The benefit that I have seen already is that with the lifting aurface of even one tab the trim force is achieved with less drag than a 30 degree deflection of the original tab. I saw an unofficial, un-verified, non-proven 3 mph increase at the same RPM.
Of course, this was an experiment which can be reversed with three screws. All flight testing was done by Air Force and/or CIA test pilots in Class H airspace, quite a distance above FL500 and short distance north-west of Las Vegas, Nevada where a 25,000 foot runway and a fully equipped flight test airbase facility does not actually exist. Rocket deployed ballistic recovery systems were available, as well as spiin chutes. Polished aluminum and neon orange colored F-104 chase aircraft were on station, as well as the latest in telemetry and hi-res ground based optical observaation. The flight was also monitored by XXXXCLASSIFIEDXXX satellite imagery. If and when this upgrade has been proven safe and effective, the CIA will transmit this information to the government of the People's Bureaucratic Republic of Oklahoma City for discussion.
Because the trim tabs are held on with three screws, and because it is not messing with a primary control, and because I am frankly tired of not being able to trim my airplane at 90 miles an hour or more... I have been working on an improved set of trim tabs.
No Taylorcrafts were damaged in the making of this fictional film.
I decided to do it in steps, i. e. one side at a time for safety and sanity. So far, I have made one new tab, which has been slightly modified. The initial results are promising, but far from definitive.
I used a popular model airplane flying wing airfoil ("Zagi wing"), because it is 'reflexed' to eliminate the pitching moment, but still able to provide lift. This was in hopes that the needed "nose down-tail up" trim force would occur with the tab as close to neutral as possible. The new tabs had to be sharply tapered, to put some more area forward of the pivot point for aerodynamic balance, yet not interfere with the lower tail brace wire. The tabs are about 1/3 larger in total area.
Only the port side tab was replaced for initial flight testing. The original starboard tab was left in place for safety. No cutting, welding, drilling, or modifications were made to the original airframe. The tab was made using established R/C model wing technology that has been flown at well over 100 mph. Cores were hot-wired from blue foam, a solid Birch spar/pivot was machined and inset into the core. (Birch harder than AC Spruce for fastener crush loads) A Balsa wood leading edge was sanded to match the airfoil ocntour. 1/64" three-ply Birch aircraft plywood skins were epoxy laminated to the core and Birch spar. Balsa root and tip ribs were expoxied in place. The assembly was sanded smooth and covered with an iron-on fuel-proof fabric to match the aircraft's color. AN and MS hardware was used to attach the tab to the aircraft's pivot arm.
First flights showed that I had over-estimated the need for aerodynamic balance. The tab would "over-center" either to the full nose up or nose down position at cruise speed. It was also evident that there was too much reflex in the airfoil, because the tab wanted to go nose up (airplane nose down) more than the other way. The trim lever had to be held in position by hand to keep the airplane level, but the good news is that the airplane could be held level in 100 mph cruise...the tab was making enough force to trim the airplane.
An aluminum strip extension was attached to the trailing edge of the tab adding "damping" area aft of the pivot point, as well as reducing the effective reflex. This change was in the right direction... the trim tab was far less prone to flop one way or the other. But it still wasn't showing positive stability. Lying on my back at the secret flight test facility, I bent the extension to give it a little positive camber (tab nose down, airplane nose up), and the test flight back home showed that I was very close to having it right. I have to remove just a little bit of that adjustment and it should have the right combination of neutral stability (the tab not wanting to move off of the desired setting) and more trim authority.
Even with one of the new tabs and one of the old tabs, the airplane will now hold a trim speed of 63 mph power off (was 70+ before), and hold level high speed cruise at 95+. When the other tab is finished and adjusted, I am GUESSING it will have enough trim authority to hold 55 mph on approach and probably a 110 mph descent power on. The benefit that I have seen already is that with the lifting aurface of even one tab the trim force is achieved with less drag than a 30 degree deflection of the original tab. I saw an unofficial, un-verified, non-proven 3 mph increase at the same RPM.
Of course, this was an experiment which can be reversed with three screws. All flight testing was done by Air Force and/or CIA test pilots in Class H airspace, quite a distance above FL500 and short distance north-west of Las Vegas, Nevada where a 25,000 foot runway and a fully equipped flight test airbase facility does not actually exist. Rocket deployed ballistic recovery systems were available, as well as spiin chutes. Polished aluminum and neon orange colored F-104 chase aircraft were on station, as well as the latest in telemetry and hi-res ground based optical observaation. The flight was also monitored by XXXXCLASSIFIEDXXX satellite imagery. If and when this upgrade has been proven safe and effective, the CIA will transmit this information to the government of the People's Bureaucratic Republic of Oklahoma City for discussion.
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