Heavy Elevator, maybe install a spring ????

[rogerh12]

Steve;

Not sure of what you mean about nobody using it? It's on the new Cessna Skycatcher 162.

[Slyfox]

Ok I'll bite, got pics?

I'll take some pics the next time I'm at the airport.

[szicree]

Steve;

Not sure of what you mean about nobody using it? It's on the new Cessna Skycatcher 162.

Fair enough, but do you know why they have that goofy looking fin on there? It's my understanding that they lost two different prototypes after they entered unrecoverable spins. It's important to remember that these accidents occurred during testing while the plane was being intentionally mishandled. My point was that any single change you make to the airframe is going to have effects beyond the desired one. When the plane is falling (in a spin) the vertical tail is partially blanked by the fuse and h-stab, thus reducing the effectiveness of the rudder. However, the Kitfox has huge flat fuselage sides. Adding a little ventral fin is going to add next to nothing and may produce unforeseen side effects. While I may have been a bit bold when I said nobody uses them, the fact remains that they are rare on small, slow, draggy aircraft like ours. If spins could be prevented by rivetting a little fin on the bottom of the tail, then we'd all have em by now.

[SkyPirate]

I have seen the ventral fin used on a champ that was on floats,..it was installed so the pilot did not have to continuously apply excessive rudder pressure even in cruise,..yes the plane flew straighter with less rudder pressure at cruise,..but it took more rudder at slower speeds to counter the ventral,..so ,..what happens in a cross wind landing where the plane is rated for lets say a 20 knot crosswind in stock configuration,..now add more vertical surface(ventral fin) with the same rudder area,..whats going to happen? I have a pretty good idea of what will happen even if it is a tricycle gear set up,
Roger ,..whats going to happen if you have to make a STOL take off with a ventral fin? and the fin pushed the lower longerons of the tail section up because it hit the ground? if it gets bent up..it could change the AOA of the leading edge of the horizontal stabilizer,.it doesnt take much of angle change in the horizontal stabilizer to get allot of change in flight.
Gonna stick to my guns with the "one mod at a time" until you know the characteristics of the plane in flight,..I'll add if it's a proven mod like a trim tab ,.go for it.

Chase

[rogerh12]

Steve & Chase
Yes, the little fins are small, but the key is they are in the right place, and that makes all the difference.
During a stall, for the plane to spin it has to also whip the tail around laterally. The small fin located below the horizontal tail helps to counter this initial lateral tail whip, at least that’s my understanding of it. Also, having the fin below the horizontal stabilizer allows it to avoid being blanketed by the main wing, which occurs with some high wing planes in a “deep stall”, that’s why trainers are usually built with rudders that extend below the horizontal stabilizer. Fin location in the far aft tail cone maximizes it’s effectiveness as well, from a “leverage” aspect.
Having said all that, a fin in this lower area can be damaged more easily than one above the fuse, that’s why it’s not too popular on aircraft, though on the kitfox in Tri-gear configuration, the tail skid would hit the ground first in a STOL takeoff, thus protecting it ( Please note: one can fly the kitfox in normal takeoff mode as well, STOL takeoffs are not required !!!!!!). Around here (Kansas), we have lots of ground, so I don’t’ do STOL, just regular performance take offs or short field landings at a mild angle of attack (my flight instructor would actually get mad at me if I did a STOL type landing, as he said it was hard on the plane !!!) . But in the Sky catchers case, the lower fin was a necessity as they could not sell the plane without one after the two crashes of the during testing ( though it’s primary purposed is not to get the plane out of a spin, but to keep it from entering one, even during crossed control stalls).
Roger

[SkyPirate]

I notice that in your photo Roger,..cessna also extented the rudder,.so is this your plan also?
As for STOL performance,..or wether not to do a STOL take off or landing,..sometimes it's unavoidable,..I've done a dead stick landing where the skid on the tail struck the ground,..I had no choice ,..landing in a grass patch in the woods less then 150 foot long, of course that is a worse case situation,.and protecting the plane is on the agenda but not the highest on that list ,..but I was lucky ,..didnt hurt the airframe but the piston that got burnt was a goner.

Sorry ,..but I'm still sticking to my guns about the mods

[jtpitkin06]

“Also, having the fin below the horizontal stabilizer allows it to avoid being blanketed by the main wing, which occurs with some high wing planes in a “deep stall…”,

Not true. Deep stall is an aerodynamic condition that applies to swept wing aircraft where the center of lift moves forward in the stall and the aircraft pitches up to a point where the elevator has insufficient force to lower the angle of attack.


“…that’s why trainers are usually built with rudders that extend below the horizontal stabilizer.”

Rudder location has nothing to do with “deep stall” or recovery.

[SkyPirate]

I've been trying to think of any plane that doesnt have the rudder extend below the horizontal stabilizer ,.and the only planes I can think of are the A-35's which actually dont have either a vertical or horizontal stab,..it's a "V" tail,..there might be a glider or another fixed wing plane where the rudder doesn't extend below the horizontal stab ,...but off the top of my head I cant think of one

( im thinking prop driven)

[jtpitkin06]

Well,... you can start with my Cessna Cardinal RG, then check out the Grumman American series (Tiger, Yankee). Look at the Beech Musketeer, and of course the Piper Cherokee series and the Comanche for starters.

JP

[szicree]

This is an issue on T-tail aircraft. On a kitfox there is no way that airflow across the horizontal tail would be obstructed by the main wing during a stall. In fact, the kitfox tail is lower than the wing in level flight and is more so in a stalled condition.