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Author Topic: SO Wright Stuff 2020  (Read 2009 times)
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Olbill
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« Reply #75 on: September 25, 2019, 11:56:54 AM »

I've heard the reason for short motor sticks on one of the commercial kits has to do with manufacturing or shipping. I can't remember which.
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Little-Acorn
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« Reply #76 on: October 07, 2019, 03:46:59 PM »

Lighter wingset, no dihedral, wingtip plates on upper wing, 3/16" x 3/8" x 24", 5 pounds/cf balsa motor stick. All for the goal of saving weight and simplifying assembly and aligning. Now 24" hook to hook, skinniest and lightest fuselage I could come up with that doesn't bow under motor tension and torque. Plane weighs in at 6.1 grams without ballast or rubber motor.

Tried .072" and .065" rubber so far. Longest flight 1 min 5 sec with the .072" motor, 0 min 59 sec with the .065" motor. 2,400 winds each, can probably go higher with the .065" motor. Plane was "sort of" well trimmed, meaning it can probably do better when we fine-tune it, at least with the .065" motor. See https://youtu.be/LlEOMuBIVps for video of 1 min 5 sec flight.
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Little-Acorn
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« Reply #77 on: October 07, 2019, 08:01:20 PM »

Here are the plans for the tractor straight-wing biplane with tip plates, as shown above. Feel free to use them in whatever way. If anyone builds one, let me know how it goes!  Grin

Print them out on an 11x17 sheet with 1/4-inch margins, it will come out exactly to scale.

Plan is sort of busy, I know. Maybe I should write up a list of building instructions, and get the written instructions off the plan itself.

Maybe later.  Smiley
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« Last Edit: October 07, 2019, 09:08:49 PM by Little-Acorn » Logged
klastyioer
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« Reply #78 on: October 07, 2019, 08:58:35 PM »

Here are the plans for the tractor straight-wing biplane with tip plates, as shown above. Feel free to use them in whatever way. If anyone builds one, let me know how it goes!  Grin

Plan is sort of busy, I know. Maybe I should write up a list of building instructions, and get them off the plan itself.

Maybe later.  Smiley

what torque are you launching at? still trying to figure out why you need such a thick piece of wood for the motor stick. also why is the prop further out from the stick with an extension piece?
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Little-Acorn
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« Reply #79 on: October 07, 2019, 09:16:45 PM »

Here are the plans for the tractor straight-wing biplane with tip plates, as shown above. Feel free to use them in whatever way. If anyone builds one, let me know how it goes!  Grin

Plan is sort of busy, I know. Maybe I should write up a list of building instructions, and get them off the plan itself.

Maybe later.  Smiley
what torque are you launching at? still trying to figure out why you need such a thick piece of wood for the motor stick. also why is the prop further out from the stick with an extension piece?
Haven't measured the torque. For the 1 min 5 sec flight, I wound up the .072" motor to 2,400 winds. I could feel it getting tight for the last few hundred winds, so I knew I was getting close. Plane climbed quickly to the ceiling, where the down-blowing fans in Miramar College gym hammered it downward a number of times during the flight. For a later flight, did it again, and the motor broke just as I was reaching 2,400 winds, so I guess that's about the max for a 24" motor of .072" thickness. The .065" motor should wind up a little more, and I figure it will probably climb OK if I can get free of those damned fans. Only one way to find out.

I had a longer motor stick, 28" hook to hook, 6 pounds/CF balsa, 3/16x3/8. It was trying to bend like a bow with the .072" motor, so I shortened it to 24" hook to hook, now it seems less inclined to bend. I might try a 1/8" thick x 3/8", but it might get bendy again even at 24".

The "extension" is a 2mm aluminum tube from the local hobby shop. Lets me add right thrust, downthrust or whatever, quickly and easily, but is strong enough not to bend when I want it to stay where I put it. I didn't mind the weight too much since it was extremely forward in the nose, and I needed nearly 2 grams of ballast to bring the plane up to 8 grams (That all goes in the nose, of course).
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klastyioer
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« Reply #80 on: October 07, 2019, 09:19:21 PM »

Here are the plans for the tractor straight-wing biplane with tip plates, as shown above. Feel free to use them in whatever way. If anyone builds one, let me know how it goes!  Grin

Plan is sort of busy, I know. Maybe I should write up a list of building instructions, and get them off the plan itself.

Maybe later.  Smiley
what torque are you launching at? still trying to figure out why you need such a thick piece of wood for the motor stick. also why is the prop further out from the stick with an extension piece?
Haven't measured the torque. For the 1 min 5 sec flight, I wound up the .072" motor to 2,400 winds I could feel it getting tight for the last few hundred winds, so I knew I was getting close. For a later flight, did it again, and the motor broke just as I was reaching 2,400 winds, so I guess that's about the max for a 24" motor of .072" thickness.

I had a longer motor stick, 6 pounds/CF balsa, 3/16x3/8. It was trying to bend like a bow with the .072" motor, so I shortened it to 24" hook to hook, now it seems less inclined to bend. I might try a 1/8" thick x 3/8", but it might get bendy again even at 24".

The "extension" is a 2mm aluminum tube from the local hobby shop. Lets me add right thrust, downthrust or whatever, quickly and easily, but is strong enough not to bend when I want it to stay where I put it. I didn't mind the weight too much since it was extremely forward in the nose, and I needed nearly 2 grams of ballast to bring the plane up to 8 grams.

okay cool makes sense
you should probs start to measure torque soon though
it seems as if its quite high for your motors so far
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calgoddard
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« Reply #81 on: October 08, 2019, 11:19:59 AM »

Little-Acorn -

You did a nice job drawing up the plan for your WS 2020 model.

It is absolutely essential for success in flying indoor stick duration models to wind to max torque, and then back off to a predetermined launch torque that will get you a no-touch flight close to the lowest ceiling obstruction.   The turns count on your rubber motor is only a very rough estimate of max torque and launch torque, and varies from motor to motor and from flight to flight.  The turns count also varies from batch to batch of rubber.  Laser-Cut Planes sells a very inexpensive torque meter.

The width of the rubber motor, i.e. .065 inches, is only a very rough measure of the size of the rubber motor.  Experts go by length and weight of a rubber motor.   It is not possible to accurately strip rubber to a uniform width over a given length, whether the stripping is done by a supplier, or by an expert with a Harlan rubber stripper.  Also, commercial rubber varies in thickness and density along its length.
  
It looks like the ribs on your wings do not have sufficient camber.  By my calculation, drawing the ribs with a circular radius (R) of 5.75 inches would give you about a 7% camber for a wing with a 3.15-inch chord (8 cm).  I like a wing camber of between 5 and 7 percent on indoor stick duration models.  An air foil shape rib is not necessary on very slow flying indoor models.

You can overcome your motor stick bending problem by using a Kevlar thread brace.  Glue vertical posts about 1 inch tall a couple of inches from each end of your motor stick.  Use CA to glue the thread taut from the forward end of the motor stick, over the upper end of each post, and then to the rear end of the motor stick.   On heavy models like a WS 2020 model I would use segments of round toothpicks for the posts. Saw a small groove in the upper end of each post for retaining the thread. Put a drop of CA on the upper end of each post after you have the Kevlar thread glued to each end of the motor stick and taut. Kevlar thread does not stretch.  You can saw angled slits that are centered in the ends of the motor stick for receiving and holding the ends of the Kevlar thread.  A little CA will lock the ends of the Kevlar thread in place in these slits.
 
« Last Edit: October 08, 2019, 12:17:07 PM by calgoddard » Logged
cglynn
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« Reply #82 on: October 08, 2019, 11:23:05 AM »

In addition to what Cal said, I have found it really difficult to get meaningful torque data when flying in sites that have "down air", whether it be from HVAC systems or natural conditions due to the design of the building.  The problem I have run into is that the down air requires a lot of power to punch through.  You may need to wind a motor to near max torque just to approach the ceiling in a turbulent site, then find when you get to a site with still air that the same torque value sends the model through the roof.

Still air is really needed in order to get good data.
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Little-Acorn
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« Reply #83 on: October 09, 2019, 02:33:49 PM »

Little-Acorn -

You did a nice job drawing up the plan for your WS 2020 model.
Thank you! Used Visio 2007, and oldie but goodie.

Quote
It looks like the ribs on your wings do not have sufficient camber.  By my calculation, drawing the ribs with a circular radius (R) of 5.75 inches would give you about a 7% camber for a wing with a 3.15-inch chord (8 cm).  I like a wing camber of between 5 and 7 percent on indoor stick duration models.  An air foil shape rib is not necessary on very slow flying indoor models.
There's a little history to my choice. When I started coaching Wright Stuff (back when it was a DivB event), I designed a plane with roughly 10% camber. Looked very pretty, flew pretty well. Did a lot of trimming to try to lengthen the flight time, with varying success. A friend designed another plane, similar to mine, but with far less camber, ribs were nearly flat. I told him there was no way that would fly well, too much turbulence along the leading edge etc., and recommend my airfoil.

His plane consistently flew better then mine, and with skinnier motors. Finally I took my wing off my plane, borrowed his, and put his wing on my fuselage. The two wing designs were similar, except for the curve of the airfoil. Immediately my plane (with his wing) flew noticeably better, and did far better than my original plane had. I was able to go with skinnier motors and still climb slowly to the ceiling, getting much longer run times.

I was convinced, then and there. And have used that almost-flat airfoil ever since, including on this plane. With very encouraging results.

Quote
You can overcome your motor stick bending problem by using a Kevlar thread brace.  Glue vertical posts about 1 inch tall a couple of inches from each end of your motor stick.  Use CA to glue the thread taut from the forward end of the motor stick, over the upper end of each post, and then to the rear end of the motor stick.   On heavy models like a WS 2020 model I would use segments of round toothpicks for the posts. Saw a small groove in the upper end of each post for retaining the thread. Put a drop of CA on the upper end of each post after you have the Kevlar thread glued to each end of the motor stick and taut. Kevlar thread does not stretch.  You can saw angled slits that are centered in the ends of the motor stick for receiving and holding the ends of the Kevlar thread.  A little CA will lock the ends of the Kevlar thread in place in these slits.

Sounds interesting, and worth a try. I try to avoid having things sticking perpendicularly into the air stream, especially with round cross-sections like toothpicks. A round cross-section is THE worst thing to stick into the airstream, it produces more drag than anything else. The Wright brothers found that out way back when. I used round-cross-section carbon fiber rods to mount the wings on this current model, with my knees knocking. They are stiff, straight, and simple, which the 1/32" plywood pylons I used to use often aren't. No obvious bad effects yet (fingers crossed).
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Little-Acorn
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« Reply #84 on: October 12, 2019, 12:20:30 AM »

Went to Mesa Verde Middle School tonight in San Diego, where the gym has virtually no wind currents, nearly ideal. With 2,550 winds on the .065" motor (24" hook to hook), the plane flew for 1 min 13 sec. Not too bad, considering it's still not ideally trimmed. This is the biplane with tip plates but no dihedral, that I posted pictures of earlier.

See https://youtu.be/02mqJoTwAAE for video of flight.
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AC01010
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« Reply #85 on: October 16, 2019, 09:01:22 PM »

When does the Finny usually come out?
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cxflyer
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« Reply #86 on: October 16, 2019, 09:24:49 PM »

Went to Mesa Verde Middle School tonight in San Diego, where the gym has virtually no wind currents, nearly ideal. With 2,550 winds on the .065" motor (24" hook to hook), the plane flew for 1 min 13 sec. Not too bad, considering it's still not ideally trimmed. This is the biplane with tip plates but no dihedral, that I posted pictures of earlier.

See https://youtu.be/02mqJoTwAAE for video of flight.


Nice flight!
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ceandra
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« Reply #87 on: October 16, 2019, 09:53:19 PM »

When does the Finny usually come out?

When Bill is Finny-ished with it?
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Olbill
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« Reply #88 on: October 17, 2019, 06:44:53 AM »

When does the Finny usually come out?

Maybe never. I haven't decided if I want to buck the horrible rules.

Besides that I just got out of the hospital after 11 days so I'm not quite up to speed yet.
« Last Edit: October 17, 2019, 06:56:12 AM by Olbill » Logged
Olbill
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« Reply #89 on: October 17, 2019, 06:52:53 AM »


Sounds interesting, and worth a try. I try to avoid having things sticking perpendicularly into the air stream, especially with round cross-sections like toothpicks. A round cross-section is THE worst thing to stick into the airstream.

You've been given the way to solve your problem that is used on virtually every indoor model where it is allowed. If you want to resist this method then I think you should expect continuing problems.

FYI I use 4% arcs for wings and 2% arcs for stabs. It works for me.
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OZPAF
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« Reply #90 on: October 18, 2019, 06:44:08 PM »

Hope you recover quickly Bill.

Quote
A round cross-section is THE worst thing to stick into the airstream, it produces more drag than anything else.
Although this is true as far as the drag coefficient is concerned - sufficient strength and stiffness at these light weights is far more important.
The wing loading will have far more impact on the duration and sufficient stiffness and strength is necessary to ensure a consistent trim.
The actual drag from the posts , incurred in any case is very low due to the low flying speed.

John
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flydean1
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« Reply #91 on: October 18, 2019, 08:49:22 PM »

Light weight was the secret of the Gossamer Condor's success.  It was basically a scaled up indoor model.  It got into the air well ahead of more streamlined, but heavier pedal planes.  MacReady had little access to super space age materials.  His later pedal aircraft did benefit from them, especially the Channel Crosser.

If it is light enough, you can fly so slowly the parasite drag is irrelevant.
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AC01010
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« Reply #92 on: October 21, 2019, 06:06:22 PM »

What modifications should I make to the Finny designs to make it work for 2020? I'm planning to keep the same wing "design" overall, but obviously changing specs for the parts. No idea how I can get the 8cm prop and really long motorstick to work though. Implementing both wings as well is going to take a lot of experimentation.

Any ideas on where I should start?
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cxflyer
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« Reply #93 on: October 21, 2019, 06:55:40 PM »

What modifications should I make to the Finny designs to make it work for 2020? I'm planning to keep the same wing "design" overall, but obviously changing specs for the parts. No idea how I can get the 8cm prop and really long motorstick to work though. Implementing both wings as well is going to take a lot of experimentation.

Any ideas on where I should start?


Replacing the flight surfaces and implementing 6cm wide posts to accommodate the new flight surfaces. Also, get rid of the tailboom offset, as the plane will have to be ambidextrous.
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