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Old Jan 09, 2013, 02:05 AM
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Malaysia, Selangor, Kajang
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Originally Posted by Stupot46 View Post
Neat.Just put one inside the other and mark over.Locating plastic cups without any "ribbing" could be a problem,I'll have to see what I can find,something I could tinker with in a quiet moment.
Stuart
One alternative I've started playing with is tracing paper. It's actually lighter than the plastic cup. And with the camber is fairly stiff. But it needs some balsa spars to prevent it from bending under load.
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Old Jan 09, 2013, 07:18 AM
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I decided to rebuild the prop and tail block. I realized that the rather loose fit of the prop shaft would make trimming up or down thrust impossible. I'm taking this opportunity to document how the prop is built.
Cool.

A similar approach with a different blade shape ... the Clem prop:



There is an error on that image, the angle of the centerline of the blade should be 23 degrees and not 32 degrees.
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Old Jan 09, 2013, 08:36 AM
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Originally Posted by Cap_n_Dave View Post
Cool.

A similar approach with a different blade shape ... the Clem prop:



There is an error on that image, the angle of the centerline of the blade should be 23 degrees and not 32 degrees.
That's interesting because my props are oriented the opposite way: the root at the bottom of the cup and the tip at the top. The bottom of the cup has more camber and most electric slowfly props I've seen have more camber towards the root and are almost flat at the tips.

Mine has a 20 degree tilt so that's similar.
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Old Jan 10, 2013, 06:19 AM
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I made a fairly large one for a Baxter XE-5 and a smaller one for a Baxter P-Cat ... I thought they were pretty darned good.

Why don't you give one a try?
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Old Jan 12, 2013, 12:40 AM
SlingWinger
San Bernardino, California, United States
Joined Oct 2004
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Perhaps you're familiar with the Swift hang glider design. The name stands for "Swept Wing with Inboard Flap for trim".

If your planform has enough sweep, you can lower the trailing edge in the inboard, or root area of the wing to get a nose-up pitching moment. In many cases this is better than increasing reflex in the outboard, or tip area of the wing. I use this to get better sink rates from my Sling Wings.
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Old Jan 12, 2013, 01:02 AM
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USA, ID, Coeur D'Alene
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Originally Posted by dayhead View Post
Perhaps you're familiar with the Swift hang glider design. The name stands for "Swept Wing with Inboard Flap for trim".

If your planform has enough sweep, you can lower the trailing edge in the inboard, or root area of the wing to get a nose-up pitching moment. In many cases this is better than increasing reflex in the outboard, or tip area of the wing. I use this to get better sink rates from my Sling Wings.
i built a small free flight balsa glider that had inboard flap trim. it made for a very nice flight envelope, on launch it would fly fast and a mild pitch up and then transition to a slow stable glide. the only explanation i could come up with was that during high speed flight, the flaps' upper airflow separated until it slowed down enough to reattach. wore out my arm throwing that little thing many times
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Old Jan 12, 2013, 02:39 PM
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Originally Posted by dayhead View Post
Perhaps you're familiar with the Swift hang glider design. The name stands for "Swept Wing with Inboard Flap for trim".

If your planform has enough sweep, you can lower the trailing edge in the inboard, or root area of the wing to get a nose-up pitching moment. In many cases this is better than increasing reflex in the outboard, or tip area of the wing. I use this to get better sink rates from my Sling Wings.
Isn't increasing twist better still? Increasing up elevator and deploying flaps both deform the airfoil. Increasing twist increases the difference of incidence between the root and the tips. Which is exactly the same as deploying flaps without making things draggy.

Flaps do have another effect that matters though. They can increase the camber of the root airfoil (or decrease if you deploy them "up"). This is what most RC glider pilots use flaps for - to control the behavior of the airfoil. This is neither better nor worse than increasing up elevator (indeed, deploying flaps often upsets trim and has to be accompanied by changes to the elevator). It's just a different thing to control.

For free flight stuff the same effect can be had by choosing different airfoils for root and wing tips.
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Old Jan 20, 2013, 03:27 AM
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She flies! Very well behaved too. But she needs a fairly large space to fly in. The turning circle is quite large. Could just about fly in our indoor venue but kept hitting the walls. Finally gave up when a crash into a wall cracked a longeron.

Today I fixed her up and decided to try flying outdoors. Was trying to trim her for a tighter turning circle but it was too windy to tell if it worked. But she flew beautifully.

Here's a video of a 30 second flight:

Rubber powered wing (0 min 22 sec)
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Old Jan 20, 2013, 06:30 AM
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Wow,that thing really moves well!Did you recover it ok/in one piece?
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Old Jan 20, 2013, 08:25 AM
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Cool. Does she usually fly that fast, or was that an artifact of the wind?
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Old Jan 20, 2013, 08:34 AM
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Wow,that thing really moves well!Did you recover it ok/in one piece?
Yeah. The camera angle is a bit deceptive. It didn't fly off field. In the last few seconds of the footage you can just about see a goal at the end of the field. It landed about 5 meters in front of it.
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Old Jan 20, 2013, 08:45 AM
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Cool. Does she usually fly that fast, or was that an artifact of the wind?
That's most probably due to the thickness of the rubber. She flies at roughly the same speed indoors.

I used .085 on that flight. I tried 1/16 (.0625) but it didn't provide enough thrust. I think .070 or .075 would be better. But I don't have rubber at those sizes and I don't (yet) have a rubber stripper.

I've ordered some .075 and I've also bought a rubber stripper. Both are on their way. So later I'll be trying it with lighter rubber and see if it flies any better.
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Old Jan 26, 2013, 01:55 PM
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Finally managed to trim it for indoor flight. Used thinner rubber - .075 vs the previous .085. Now it's flying much slower but still with enough power to climb.

Trimmed it to fly left circles. Since this is a reverse prop it's the same as trimming a regular plane to fly right circles - meaning that it's circling the opposite of the torque.

Part of my problem earlier was that the plane started flying straignt as the rubber wound down. Which is bad for indoor because it kept flying into the walls towards the end of the flight. Trimming it to fly the opposite of the torque eliminates this problem. As a bonus, the torque prevents the plane from banking too far into a spiral.

To trim it for left circles I added a lot of left thrust and some up elevon trim tab on the left wing and a couple of drag rudders on the left wing.

Here's a video of a flight from tonight's session:

Flying wing trimmed for indoor (0 min 50 sec)
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Old Jan 26, 2013, 02:51 PM
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Here are some pictures of the trim tabs I added.
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Old Jan 26, 2013, 03:14 PM
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Here's another rubber powered flying wing project I've posted in the Free Flight forum:

http://www.rcgroups.com/forums/showthread.php?t=1818182
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