Wright Stuff C

[Rossyspsce]

after reading some stuff based around tennis and tennis rackets and the addition of weight to certain spots of the racket, it led me to the thought of this years ws. With this years planes being relatively easy to build under weight, meaning that ballast will be required, does placement of the ballast matter if cg does not change between set ups. That is, does having weight at the front/nose and back/tail of the plane vs weight right in the middle(on top of the cg) vs a mix of the 2 have any significant effect to the ease of trim, performance(though more related to prop to rubber), etc.

Original: “placement of weight at opposing ends of a racket causes to be what is known as “polarized” while applying weight evenly across the racket, while still maintaining the same balance point(cg), makes the racket easier and more manageable to play with”

[lechassin]

@Brian:

More on our prop approach:

1) I'm sure an aeronautical engineer would be horrified. We used no science or math, just testing, logic (?) and deciding what looks good.
2) We settled on 3 blades because 2 spun down too fast unless we increased the pitch excessively, too increase drag (yuk). We knew that smaller rubber wouldn't give a good climb (although we're revisiting that with our offset wings plane). 4 blades was obviously turbulent (the plane flew erratically).
3) The tip of the blade is doing most of the work, so we concentrated on that first. Our first props were not helical nor did they flare. We determined that +/- 30 degrees at the tip was best for our plane/rubber/3 blade setup. Our building jig still uses the original 30 degree shim for the tip of the blades.
4) The angle of the blade is not the pitch. Pitch is the distance that the angle will theoretically travel as the prop does one full revolution. To determine that distance for the tip of our blade, we drew a 30 degree angle on a sheet of paper and projected how far the two sides of that triangle would diverge over 25cm, which is the circumference of our prop at the tip. That divergence is 5", so our tip pitch is 5".
5) This is where we trusted our gut over science: we like the tip pitch and to make the prop more efficient, we wanted 5" pitch over the full length of the blade. However, when we drew a triangle to work backwards from 5" to get the root angle, the small circumference meant that for the root to travel 5" in one revolution, the angle was way too high. It was obvious it wouldn't actually create thrust; it would either stall or have a lot of drag. So we kept the tip at 30 degrees and we cut the blades so the root is a more moderate 45 degrees.

In the end, our props are not true helices. They have 5" pitch at the tips and 4" at the root. There's some inefficiency there but if we were to go for a true helix and keep the root at 45 degrees, we would have to reduce the tip pitch to 4" to match (IDK what angle that would be). We already know from testing that at less than 5" [tip] pitch we run out of knots too soon, so that wasn't an option.

I don't know if all the best props on the market are true helices, but we went for a compromise.

[jander14indoor]

after reading some stuff based around tennis and tennis rackets and the addition of weight to certain spots of the racket, it led me to the thought of this years ws. With this years planes being relatively easy to build under weight, meaning that ballast will be required, does placement of the ballast matter if cg does not change between set ups. That is, does having weight at the front/nose and back/tail of the plane vs weight right in the middle(on top of the cg) vs a mix of the 2 have any significant effect to the ease of trim, performance(though more related to prop to rubber), etc.

Original: “placement of weight at opposing ends of a racket causes to be what is known as “polarized” while applying weight evenly across the racket, while still maintaining the same balance point(cg), makes the racket easier and more manageable to play with”

First, while it is easy to build to weight, I would be careful about building too far underweight and carrying a lot of ballast. You can better use that ballast weight to add strength to key places. I tend to target WS planes about 0.5 gm underweight at most. Some ballast to adjust cg with, but not so much that you are giving up significant strength.

As to masses vs behavior, I suspect that MOSTLY you are comparing apples to oranges when you compare planes to a racquet.
The racket is reacting to impulse forces (mostly or key, racquet hitting the ball). By moving masses around you can increase stability in the response to those forces, thus increasing the accuracy of your hit.
The plane is MOSTLY reacting to steady forces. You GENERALLY want to avoid masses in the extremes as once the plane is out of position (from for example bumping into a ceiling beam), it takes longer for the steady aerodynamic forces to reposition the plane to proper flight conditions. Now that MAY change in different conditions, lousy or active air for example, you MAY want mass more towards the extremes so the plane does not react too fast to momentary changes in the air.
So, for both, there are ideal places to put the mass, but in my experience they are not the SAME places.

But my 'experience' only goes so far. Play with differences and measure against the stop watch. But for this, you will need to introduce that noise intentionally and in controlled ways. For more on that, consider looking into Taguchi testing philosophy. Robustness to noise (where noise is not sound, but uncertainty).

Jeff Anderson
Livonia, MI

[newflight]

while struggling with bi-plane's stall issue for a while, I stopped trying it for a month. tonight is the first time since a month to fly bi-plane after fixing multiple small issues, like reducing stablizer weight, make 2 wings as parallel as possible, changes the way of creating warp when flying different directions. I only flew once tonight, but it gets 1'13" at only 13 ft high, it seems it has a lot of potential to get better time than monoplane

[bjt4888]

while struggling with bi-plane's stall issue for a while, I stopped trying it for a month. tonight is the first time since a month to fly bi-plane after fixing multiple small issues, like reducing stablizer weight, make 2 wings as parallel as possible, changes the way of creating warp when flying different directions. I only flew once tonight, but it gets 1'13" at only 13 ft high, it seems it has a lot of potential to get better time than monoplane

Newflight,

Good job! Yes, the biplane is capable of very good flight times if accurately built and carefully adjusted (and lots of practice and data gathering and analysis).

Brian T

[lechassin]

This discussion about biplanes has me wondering: are we are the only ones using three-bladed props? It seems like 3 blades gives an advantage similar to using a biplane, i.e.: more thrust at lower pitch, analogous to more lift at lower incidence. At these low speeds, the reduced drag from less pitch/incidence seems to trump the increased drag of additional lifting/thrusting surfaces.

As for gym time: after getting the run-around for three months, I pulled Luke off the team unless the school's bureaucracy sorted things out. They may have cringed at the thought of losing their best performing event because within a week, we got gym access every Sunday morning for 3 hours. It's sad to have resorted to playground tactics, but in any event, we hope to post videos again starting tomorrow.

As of today, we're at 1'45"+ with authoritative climbs to 25' and with 25' circles, both ways with centered wings. The goal now is to trim the plane with adjustable offset wings. It hits the ceiling multiple times unless we back off to under 0.2 in-oz torque. That isn't much more than the 1.5 in.oz we need to cruise and even then it hits once. We got some thinner 0.060" rubber to see what that does tomorrow.

[xiangyu]

This discussion about biplanes has me wondering: are we are the only ones using three-bladed props? It seems like 3 blades gives an advantage similar to using a biplane, i.e.: more thrust at lower pitch, analogous to more lift at lower incidence. At these low speeds, the reduced drag from less pitch/incidence seems to trump the increased drag of additional lifting/thrusting surfaces.

As for gym time: after getting the run-around for three months, I pulled Luke off the team unless the school's bureaucracy sorted things out. They may have cringed at the thought of losing their best performing event because within a week, we got gym access every Sunday morning for 3 hours. It's sad to have resorted to playground tactics, but in any event, we hope to post videos again starting tomorrow.

As of today, we're at 1'45"+ with authoritative climbs to 25' and with 25' circles, both ways with centered wings. The goal now is to trim the plane with adjustable offset wings. It hits the ceiling multiple times unless we back off to under 0.2 in-oz torque. That isn't much more than the 1.5 in.oz we need to cruise and even then it hits once. We got some thinner 0.060" rubber to see what that does tomorrow.

Awesome, I'm glad you worked out the gym issues with your school. In regards to the 3-bladed prop, I made a couple more and plan to try them next Monday when I'll have gym access. Hopefully they won't fail. I'll let you know how it goes. I'm also going to look at bi planes again now that I have no more time pressure to get a decent plane in the air and flying consistently,

Thinking back, perhaps one of the reasons why my biplane was stalling so much is because I'm using too thick rubber which gave it too much power. I'm going to try a thinner rubber and also try to straigten the wings - it's just so hard to do XD.

Does anyone build a jig to help position their wings correctly? I'm thinking about doing that, I'm just so bad and placing things and making sure nothing is warped.

EDIT: I'm looking at my wings again and I've noticed that some are warped not due to the placement, but due to curvatures in the carbon fiber rods. Does anyone have suggestions on how to straighten carbon fiber rods?

Xiangyu

[coachchuckaahs]

EDIT: I'm looking at my wings again and I've noticed that some are warped not due to the placement, but due to curvatures in the carbon fiber rods. Does anyone have suggestions on how to straighten carbon fiber rods?

Xiangyu

We use carbon from CST, and have not had issue with curvature. I understand that other sources may have some curvature. Best thing to do would be to determine the curvature when building, and put it front to back rather then vertical. Then you could have a curved/swept wing, or if the LE curves to the front and the TE to the back, the ribs would take out the curvature.

Coach Chuck

[xiangyu]

EDIT: I'm looking at my wings again and I've noticed that some are warped not due to the placement, but due to curvatures in the carbon fiber rods. Does anyone have suggestions on how to straighten carbon fiber rods?

Xiangyu

We use carbon from CST, and have not had issue with curvature. I understand that other sources may have some curvature. Best thing to do would be to determine the curvature when building, and put it front to back rather then vertical. Then you could have a curved/swept wing, or if the LE curves to the front and the TE to the back, the ribs would take out the curvature.

Coach Chuck

Good idea! Thanks. That does mean I have to redo a couple of my wings but it should fix the problem. Also just curious, how much do these warps affect flight time? By a lot or a little?

[bjt4888]

EDIT: I'm looking at my wings again and I've noticed that some are warped not due to the placement, but due to curvatures in the carbon fiber rods. Does anyone have suggestions on how to straighten carbon fiber rods?

Xiangyu

We use carbon from CST, and have not had issue with curvature. I understand that other sources may have some curvature. Best thing to do would be to determine the curvature when building, and put it front to back rather then vertical. Then you could have a curved/swept wing, or if the LE curves to the front and the TE to the back, the ribs would take out the curvature.

Coach Chuck

Good idea! Thanks. That does mean I have to redo a couple of my wings but it should fix the problem. Also just curious, how much do these warps affect flight time? By a lot or a little?

Xiangyu,

Small wing warps can be problems if the warp is not in the direction needed. For instance, (as I’m sure you already know) if circling left you really don’t want left wing washout. If this is the direction of your warp, I would break the wing to wing strut joint, correct and reglue the strut (or place a new strut). However, if circling left and you have 1 or 2 mm too much left wing washin, you can live with this and probably get to fly ok by adding a little more left rudder.

It’s difficult to evaluate effect on duration but we are getting identical good flight times from several airplanes even though they have 1 or 2 mm differences in washin and in rudder setting.

Brian T