Thermal turns & landings: X vs V

[F3X]

I field a lot of questions about the differences between models in my work. I would like to throw this out for discussion to the F3X guys.

Thermal turn: I like my models with the differential set to allow a roll with little or no yaw. On a big F3J model this is somewhat more difficult than on a short fast F3F ship. You may need a bit of A>R mix or a little left thumb (mode 2)

Once the bank is started, I (depending on the model) roll in a little camber for the size of circle I am flying and usually neutralize the aileron input and keep in the rudder. Its a mix between Ail-Rud-Elev the whole time. I add or reduce camber as needed for the circle diameter. I find small tight thermal turns need a bit more camber to hold bank + airspeed and larger radius circles require less. I am a slider guy, I add a little and take a little out. In real tight high bank thermals I have thrown in launch mode a time or two until I get that one hooked and can open up the turn.

On landing. With V tail models I like the final approach w/o A>R mix. I find the tail tracks much better without throwing in a little yaw with aileron input due to having them mixed. More so for V tail than X tails. I think a lot of guys flying V's should try this (if you don't already)

With a few small adjustments, I find v tails are as easy as X tails for F3J tasks.

In the USA if it's not a x tail it ain't :censored:

I think that statement is pure :censored:

What do you think?
Fire away!

[dephela]

In the USA if it's not a x tail it ain't

I think that statement is pure


The spot is very easy to line up and hit in azimuth with a V tail.
If I were flying the AMA landing task, I might not hit as often.
I don't fly with the pressure of an F3J landing, none of my comments are probably valid.

I like to have enough diferential in the rudders that the nose doesn't point up or down with rudder applied. I guess everyone looks for that. Pure thermalling, I'll fly rudder/elevator till I make a mistake or spiral instability brings the inboard wing low and use ailerons to correct. In a tighter turn, I'll be horsing the plane using ailerons and elevator. Right, ailerons are nice to roll it nto the air at times.

I still haven't found that camber does anything to improve my flying and seldom use it.

Maybe I should fly thermal duration more.

Nah!

[roydor]

I used to fly V and X tail Superiors at the same time period (WC 2006) so I can compare between the two and since they were the same weight the comparison is very relevant:

X tail is a little more stable and its easier to float the model around in light air and at slower speeds getting lower sink rates.
You can get nice results out of V-tails but they're a bit less stable. This has to do with the fact that most calculate the tail volume of V-tails wrong and they end too small. This has been discussed in the past and given an excellent explanation by Joe Wurts and Mark Drela.
As for landings, I don't see much difference probably due to my flying style which gets me to the spot at a speed slightly higher than the speed for best L/D. this lets me slow down if I come early and gives better handling. Also better resistance to ground turbulence. In full Crow I also reduce diff down to 30% and have 60% of ai->rud for better handling.

In normal flight I Have a very small amount of ai->rud mix (10%-15%) and a large amount of dif (60%-70%) in order to give the model a "clean" roll at slow to medium speeds. When circling I set the turn radius with the rudder and compensate with the ailerons as necessary. High diff helps me to avoid tip stall due to high aileron deflections with camber even if theoretical performance might suffer.

Its not a question of performance but rather low work load in far away thermals and rough air. As a principle I prefer to give away some "theoretical performance" to handling and reduced work loads for better results over the long run. This from 10 years of experience in F3J. BTW, X-tail is a bit less work load and fits better with my style of flying.

I use camber a lot. It sometimes requires a bit of elevator compensation to work well. I usually fly with 1 mm of camber in between thermals (0 in strong winds). 2 mm in thermals (0-1 mm when in rough air) 0-reflex(-2) in bad air to get out of it fast.

V-tail is usually a bit more "slippery" and penetrates slightly better in wind but X tail is better for me as an all round.

Since I don't have weight issues with my models, I prefer the X tail over the V tail for F3J and if I do have weight issues I just build a lighter elevator and stick with the X tail...

[tomcat5109]

Roydor,

I currently fly a Superior x and also use the somewhat higher diff for smooth turning. In thermal turning do you couple Ail->Flap as well as Ail->Rud? Seems like coupling Ail->Flap and using less TE movement would help keep airflow attached in thermal turns. Does the Superior like this?

Tommy

[roydor]

I tried it a few times, used to fly my Eraser that way but the Superior felt too "jumpy" and the speed was not as smooth and constant during the turn. I think that once you learn to input the flap to the conditions at hand you don't need mixes that might give you too much flaps in tight, full elevator thermals, in those I prefer no flaps or very little in order to fly at a higher speed so not to tip stall. When the thermal "opens up" and gets wider, a larger amount of flap is nice for large stable turns, in those I usually fly with very little elevator so very little flaps. Again a matter of handling and personal flying style, for the Eraser it worked well since it was slightly dragier and tended to keep the airspeed a bit more stable, The Pike is a bit more slippery.

Just a clarification, the ail->rud mix I use does not push the nose of the plane into the turn. It only keeps it from being pushed out due to aileron drag and gives a clean roll around the fuse axis. pushing the nose into the thermal is done with the rudder. That's why we have two sticks on the transmitter.

[tomcat5109]

My meaning was about using flaps as ailerons mixed with the ailerons on the aileron stick for thermal turns. Not sure if that is the way you answered.

I'm just addressing the question whether or not it's beneficial to use the entire trailing edge of the wing as ailerons if there is already some thermal camber set into the flaps while turning in thermal circles.

[Wing-span]

I know where this is going :D

[roydor]

I don't have the ability to mix the flaps as ailerons so can't answer from my own experience but can give a "theoretical" answer which like I implied before might not be the way to go but is a good start.

When the wing is rolling the center panel serves as a damper to the roll because one side has a grater angle of attack due to the roll than the other. this creates a roll moment which is opposite to the wing roll direction.This requires more aileron movement to counter the center negative roll moment and to create the desired roll rate. This results in the drag going up in both the center and the tips.

If one would add a bit of aileron like movement in the flaps, the center panels damping affect would be reduced and you'll need less ailerons even without the flaps them selves creating roll!

This would be achieved by just a few mm of movement.
I wish I could try it and know that I would like to try two modes:
1) 4-5 mm of movement at max ail->flap mix for cruise on both the raised flap and the lowered one (0 diff on the flaps)
2) 4-5 mm for only the flap going up for thermal flight with full camber (0 diff)

try it and tell me how it goes, I would imagine you would need about 20% less aileron movement for the same roll rate. This would be beneficial on models with long flaps such as Sharons and Perfects the most

[roydor]

An example of set up using ail->flap mixing in the Perfect:
http://www.f3j.com/perfect/settings_060306.pdf

[tomcat5109]

Thanks, your answer is the kind of information I'm looking for. Sorry for the sidetrack in this thread.