Trimming

[jander14indoor]

Both rules of thumb are out there. Let the stopwatch decide.

Jeff Anderson
Livonia, MI

[Less_Incidence]

Personally, with WS planes, I've had much more success using very thin rubber and landing with lots of turns left. Flying on .081 rubber, I wind to 2000 turns and the plane usually has 200-300 left on a good flight. When I went from .094 to .087 rubber, it was an instant 30 second improvement, and then another instant 30 seconds when I went from .087 to .081. It seemed like the more turns I ended up landing with, the higher my time was - but this probably also had something to do with my relatively low-pitch prop.

I also once heard from Bill Gowen, a world-class indoor flyer, that he has a rule of thumb for low ceilings of using a very long, heavy, thin motor and landing with lots of turns left - now of course we're all using 2 gram loops, so the "heavy" aspect doesn't apply, but one can see his point. In theory, the more turns on the motor, the more turns the propeller will perform in flight; and the more turns are left at flight's end, the slower the descent is near the floor. There's probably more to it, but that's my two cents. (Pennyplane pun definitely intended)

P.S. If my team were going to nationals I would get a rubber stripper and make some .076. Again, it's different for everyone, but for the 18-24' ceilings I've been flying in, thinner seems better.

[DoctaDave]

My plane can currently launch with a max torque of about .7 in. oz. (my torque meter is not calibrated, but on a half motor, this is about 1200 winds with 25-30 winds backoff on .081 rubber.) The plane begins to roll from the high torque, but when I increase the wing wash in to compensate, the plane no longer cruises with the wing level as the difference in lift causes the inside wingtip to be higher than the outside wingtip. When the wing doesn't fly level, the circle tends to drift and the plane drops altitude randomly a lot. Any suggestions to increase my max launch torque without causing the plane to fly with an unleveled wing?

Edit: I realize this should be in the trimming forum, but I hope its okay here. oops

[Chris_L]

have you tried to make your motor stick stronger? A bend in the motorstick could contribute to the overall downward torque at the beginning of the flight. This could be fixed with carbon fiber...

[DoctaDave]

I know it isnt the motor stick thats bending. THe motor stick is very stiff and has cf on the top and bottom, and the issue of rolling and then diving is fixed when I increase the washin, but introduces the issues I posted before. You can also visibly see the plane banking after it is released.

[bjt4888]

DoctaDave,
Please describe the rest of your setup and typical low-ceiling flight specs and characteristics, including: airplane design, propeller type (freedom flight kit or custom (describe in detail)), prop pitch, wing incidence, stab incidence, wing mount description (freedom flight kit w/ rubber bands; of not) center of gravity location, stabilizer tilt, rudder offset, thrustline offset, rubber motor thickness (or density) and length, max winds and max torque and backoff and launch torque and turns remaining for full motor low ceiling launch (ceiling height and altitude achieved) and flight time, max winds and max torque and backoff and launch torque and turns remaining and flight time for 1/2 motor flight.

Describe your current 1/2 motor flights at .7 in oz, at .65 in oz (ex. launch at shoulder height, banks hard left for 1 full circle losing 3 ft. of altitude then climbs normally to about 25 ft.; or, launch at shoulder height, banks hard (10 degrees, 20 degrees?) left and hits floor in 1/2 circle).

Are you preparing for Nationals?

Supply any other information you think might be pertinent. If you can supply yet tonight, I can probably give you some ideas to work on right away.

Brian T.

[bjt4888]

DoctaDave,
One more thing. How big is your flight circle during the cruise phase of the plane's flight before introducing more left wing washin? How big after you increase the washin? Without the rest of the data I requested above, I am thinking that the simplest solution is to increase stab tilt about 1/4" or a little more. If the tailboom is soft and light enough, you can just twist it way past the desired setting and hold it for about 60 seconds (maybe also breath on it to heat it up as you twist). Hold the fuselage tailboom joint together by squeezing it as you twist the tailboom so that you don't twist this joint apart. Stab tilt increase shouldn't make the roll during the early portion of the flight any worse and should tighten the cruise circle and reduce the drift and roll to the right during cruise. The drifting roll is basically a kind of stall as the additional wing washin has effectively increased decalage. A small shift forward of the CG (maybe 1/8", which is a 4% change in the SSM) may also be required to handle the increased decalage angle.
If this is the Freedom Flight kit you are flying, I actually believe that the left wing offset (left wing is longer than the right) is a little bit excessive. This spec doesn't make much difference at low torque and for low ceilings, but is more of an issue for high ceilings and high torque (this is an extremely minor critique and I love the Freedom Flight kit, this is a personal preference type of thing).

Brian T.

[DoctaDave]

Here's my set up:
For the most part, its a the FFM kit with a few modifications.
Prop: 28 degrees of pitch at 3", normal ikara prop, harlan bearing (with a small block of wood inside to keep the front of the bearing from bending under high torque.)
Wing: 8cm chord, 50cm span, about 1 degree of positive incidence, wing attachment posts are glued to the plane, so they are not twisting during flight. Washin of about 1/8"
Stab: 6 cm chord, 30 cm span, about a quarter inch of stab tilt, -1 degrees of incidence, rudder is tilted a few degrees according to the FF kit, and tail boom droops about 2.5 inches, and is tilted to the same amount according the to FF kit.
Thrustline is offset about 3 degrees, and 0 degrees of downthrust.
CG is about 1.5 inches behind the TE of the wing.
The motorstick is a rolled balsa tube, made with high density balsa, so it's very stiff.
The plane cruises with the nose about .5-1 inch higher than the rear of the motor stick, which is 16 inches in length.
Plane circles with a diameter of about 30 feet.
Mass: 8.01 g

Rubber density is about 1.00-1.03 g/21"
I wind to 1200 with a half motor reaching a torque of 1.3 in oz, then dewind 20 to get to a launch torque of .8 in oz. The plane almost always climbs a little at first, then starts banking and loses about 2.5 ft of altitude and hits the floor within 2/3 - 1/2 of the circle. Can't say how many turns remain as it never completes a flight.

For a launch torque of .7 in oz, I wind to 1200 reaching a torque of 1.3 in oz, and dewind about 25 (2.5 winder turns). The first circle it loses some altitude, maybe a foot, but then it slowly climbs to about 20 feet.

For a launch torque of .65 in oz, I wind to 1200 reaching a torque of 1.3 in oz, and then dewind about 30. It immediately begins to climb when launched from a low crouched position, and climbs over 20 feet. I would estimate that it can climb to at least 25 ft with a half motor, as even after it hits AC units, and falls 10 few feet, it can still climb about 3 more feet.

For a launch torque of about .6 in oz, the plane goes right below the AC units (20 ft) and gets a time of around 2:10-2:15 and has about 150 turns remaining.

[DoctaDave]

And when I increase the wing washin, the plane can climb after launch with about .75-.8 in oz of torque, and it usually hits the ceiling. So with a launch torque of .6 and the same settings, during cruise the plane banks away from the inside of the circle and drifts (sometimes, losing a little bit of altitude), before correcting itself and resuming a normal circle diameter, and then during the descent especially, the wing remains banked away from the inside of the circle, and the plane loses altitude very quickly.

Thanks so much for the help by the way, Brian.

[bjt4888]

DoctaDave,
Good data! How long is your nose moment arm (nose to the wing LE)?

Brian T.