When I was in college at Embry-Riddle Aeronautical University, Piper Aircraft came to us to test a Suer Cub Tail with and without Gap Seals in the wind tunnel. What we learned was that Elevator Gap Seals decreased Drag (Higher Top Speed) but increased the stall speed of the tail. In other words the tail stalled at a higher speed with Gap Seal. Think about Fowler Flaps . The separation of the flaps allows energized airflow to cross from the bottom of the flap to the top of the flap. This energized airflow helps keep the flow attached to the surface. The same thing is happening on the tail only the tail is producing lift in the opposite direction. Your best combination to reduce the horizontal stabilizer stall speed would be VG’s with NO Gap Seal.
I am not a pilot, or an engineer. I am a gearhead, and love flying. I was drawn to your channel exactly because of this content. Your testing regimen is outstanding, and you deserve every MPH you gain (or lose) based on the effort you have put in both building this airplane and wringing it out. Thanks for sharing this. Enjoyed it a bunch.
I'll offer up a theory on the tail, which might explain why the mods didn't help. I wonder if at high angle of attack, airflow underneath the tail is being pushed up through the elevator hinge gap and flowing over the top of the elevator (much like the slot in a frise aileron), which in turn might be helping all the airflow over the top of the horizontal stabilizer / elevator maintain an attached flow with reduced turbulence. I suspect you're right about the non aerofoiled tail surfaces reaching their AoA limitations.
Would be interesting to fit a larger horizontal stabilizer and elevator off a Superstol or something similar to see how it works. Not an easy project I'm sure.
Brian I found the same results with the tail vgs, nothing. It is interesting how much the slats helped slow you down. I wonder how the factory came up with the 33 mph advertised stall speeds on the sti wing. I have found no one below 39-40ish on them yet. The tail is definitely the first thing to drop out on my plane for sure. Thanks for the time you put in on this testing. Harlan
Would love to see tail modifications, try a larger elevator surface area, larger control surface area. I see comments below about having air going thru the gap with out gap seals, would increasing gap or a mini slat on the tail help, upside down slat? Some kind of built in secondary surface that deploys under the tail surface similar to a trim tab or spoiler to change the shape. On cable system like flaps.
What's with the apparent sharp lip on the underside of the slat leading edge? Seems like a radius here would be more appropriate. A camera and some tufts in the slot to check airflow would be interesting.
Here in Europe we use Yuma, Zenair/Zenith CH701, and especially ICP Savannah for low speed. Savannah still fly quite normaly at 45km/h (28 mph) with a little bit of gaz in absolute clam weather (full flaps with vortex generator..no slats) . A friend of mine did a vertical landing in front of me with a Savannah (55 km/h of wind axed with a big grass runway). And he told me that he event did flight in reverse due to front wind!
Instead of trying to make a horizontal stabilizer/elevator with an inverted airfoil, you could try increasing the elevator’s span (area), maybe with temporary extensions like Steve Henry’s wing extensions. I would cover the whole wing with yarn before doing that though, because to me it looks like whether or not it’s the tail or wing that is stalling is still inconclusive. If the tail is the limiting factor, it looks like the airflow is separating from the top of the HS first, not separating from the bottom of the elevator as it would if it was stalling normally. If that’s the case, the front of the HS needs to move down more, or you could try making it fatter and rounder (like the leading edge of a 701 stabilizer) so the air can flow around it without separating from the leading edge at high angles of attack. But increasing the span of the elevator beyond the ends of the stabilizer could work.
The terminology I'm familiar with is that slots are fixed, but slats are movable. Wikipedia uses this same terminology. Nevertheless, great project and flight testing!
Technically these are not fixed, since the back opens and closes with speed. Typically Slots are built into the leading edge of the wing and are not removable.
Nice…. A $250 total outside retail part for $500 just because this cat wants to live in the middle of nowhere….. ? Alaska and Hawaii are just plan shipping nightmares in either direction and will be for ever ! Excellent vid though….
The flapperons start to get a little mushy at 33 mph but you still have roll control, however at these speeds you should be using your rudder for control correction to avoid stalling a wing.
So the cord line is dependent on shock position or is there a way to adjust to match the wing cord? Feel like if someone had these off they could be a flap. I kinda wanna order these and see if I can make them float.
What about making the slats fully adjustable and retractable in flight? And what difference will they make on a hot and heavy day, see you are wearing a jacket during testing?
TELL ME BOWEN IS IT BETTER TO PUT BIGGER WINGS ON AIRCRAFT LIKE THIS TO MAKE BETTER STALLS? LIKE THE DAKOTA HAWK WOODEN AIRPLANE I LIKE THE QUICK LANDINGS IN THE STALL WINGS.
Nice testing, my elevator stalls first on my Zenith 750 even with the inverted airfoil. At the National STol event at Gainesville we made the mistake of removing the doors to save weight right before the event, and it jumped the Stall speed from 35 to 39. So with the Slat Sections only 4 ft long would you consider taking them off and storing in the baggage area for a long cross country flight?
@@BowenAero One thing you could try it, this worked on the Zenith, put VG's on the inboard flaperon, It cleaned up the air to the elevator and made it more effective at 4-5 mph slower. But it may not work as well on the KitFox as the horizontal is not in line with the wing as it is on the Zenith.
Couldn't you change the angle of incidence on the horizontal stabilizer to reduce the effect of having a negatively cambered airfoil at cruise. AKA... do the upside Zenith upside down airfoil style horizontal but give it a few degrees angle of incidence to get the results you want in cruise and stall.
Because they charge $36k for an engine that can be built up for around $10k. I have a turbo engine built and I’m working out the components now, the end result will be much more tunable than the edge engine.
Those TAS vs Indicated numbers don’t really add up.. do you not have a static port installed? Your TAS should be 2%per1000 feet faster, so at 8,000 feet, you should see TAS 16% higher than indicated.
@@thomasaltruda 2 degrees per thousand feet is the standard lapse rate for temperature, but doesn’t account for pressure changes during non standard atmospheric pressure. If it was 15 degrees C or 59 F and the pressure is 29.92 at sea level, a Aviation standard day, the standard lapse rate would be 2 degrees C per thousand feet and the True airspeed vs indicated would be predictable.
