Design

bjt4888
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Re: Design

Postby bjt4888 » December 28th, 2014, 12:43 pm

nxtxcholar,
To the best of my knowledge, test gliding an indoor rubber airplane will not provide any useful info. As the motion of the propeller has great influence in the character of the flight for these models, you need to be under power to learn anything. I would suggest constructing an airplane that is based upon a known successful design like Cezar Banks "Leading Edge" and using the Bernie Hunt design spreadsheet to calculate an appropriate starting point for center of gravity based upon the desired static stability margin. With the basic specs set for typical left propeller shaft thrustline offset, left tailboom offset, stabilizer tilt, wing offset and left wing washin and with a reasonable amount of decalage (maybe 2.5 degrees if using static stability margin of 15% to 25%) the airplane should fly fine. Probably you will encounter a gentle stalling circling flight with this setup which can be corrected by reducing the wing incidence about one degree or so. After a couple of low power flights, the real interesting science begins.

I attempted to attach the design spreadsheet to this post, but this wiki messaged that the file size is too large (it's only 351KB). Maybe someone can let me know if there is a location on this site that can accept a file of this size.

Brian T.

BGH12
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Re: Design

Postby BGH12 » January 5th, 2015, 3:50 pm

Typically how long should a motor stick and tail be? And I'm in the process of curving wing chords is here any specific way to attach/glue them to make the wing and stabilizer?

28builder
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Re: Design wing dihidral

Postby 28builder » January 8th, 2015, 6:11 pm

ok. so maximimizing wing span is best for lift. freedom flights model has the wing span very close to 50cm and then 90 degree straight up wingtip dihidal. if you have a different wing with angked dihidrals that go out to 50 cm. would that create equal lift (all other things being equal? or is the full wing withbstraight wing tip creat more lift

A Person
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Re: Design wing dihidral

Postby A Person » January 8th, 2015, 7:51 pm

ok. so maximimizing wing span is best for lift. freedom flights model has the wing span very close to 50cm and then 90 degree straight up wingtip dihidal. if you have a different wing with angked dihidrals that go out to 50 cm. would that create equal lift (all other things being equal? or is the full wing withbstraight wing tip creat more lift
From what I understand, there wouldn't be much of a difference. From what I've read about it, there will be one, but if it's like a 1% difference having the wings angled 5 degrees total, you won't notice it and it won't really matter. Thing is, however, I don't see a reason to switch to a wing with a dihedral. With how Freedom Flight has it, the wing has a single beam running down it's length, and having that bend would not only complicate building, but reduce strength at the joint that the wings meet the frame. Dihedral help stabilize the spiral mode, but it's not like you'll ever get into that.

I was really confused when I first read your post, I missed when you said wingtip dihedrals and thought you someone horribly messed up and really had the wings at a 90 degree angle.

Question, though: Do the winglets on the Freedom Flight planes help with anything other than flight stabilization? It wouldn't like help with the wing vortex because it's not fast enough, right?
"Any sufficiently advanced technology is indistinguishable from magic." - Arthur C. Clarke

jander14indoor
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Re: Design

Postby jander14indoor » January 9th, 2015, 3:21 am

Vertical wing tips like on the Freedom Flight model serve exactly the same function as angled dihedral. There are all sorts of schemes to introduce dihedral in a wing, the theoretical best is to have an elliptical shaped wing when viewed from front or rear, but that's so hard to build and has so little difference you seldom see it. Not never, just seldom.

In very competitive out door models you often see a 3 or 5 break wing approximating elliptical dihedral. Not so much indoor (except gliders, more common with them). Probably because of ease of building.

Typical indoor models have a center break, two breaks about 10 to 25 percent of span from the tips, or tip plates. Never seen DATA that proves a difference. Seen all types win tournaments.

Ease of build, I find little benefit of one over the other. Double break is probably a little faster, and can be just as strong. Wing plates give a little stronger main wing, but you HAVE to get the plates dead straight or you quickly set up a snow plow effect and add drag.

End plates and tip vortices. Turns out it requires some very precise design work to manage that, doesn't look much like what we use. May help a little but again, not much DATA.

I think in the long run, until you can fly any reasonable design consistently to near tournament winning times, you are better to pick one that suits you and spend time matching prop to rubber. Once you have that, try different designs and gather DATA. Make decisions not on opinion, but your DATA.

Did I emphasize DATA enough?

Jeff Anderson
Livonia, MI

nxtscholar
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Re: Design

Postby nxtscholar » January 18th, 2015, 11:09 am

Probably should have asked this earlier. For the Freedom Flight model users, what side are we attaching the mylar covering onto the vertical stabilizer? Looking from the front (propeller side), would the mylar be on the right or left?

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Re: Design

Postby bjt4888 » January 18th, 2015, 5:19 pm

nxtscholar,
Looking from the front, the covering should be on the right side of the rudder/vertical stabilizer. Although it is more typical to describe "sides" of an airplane as if you are sitting in it and flying it as if it were a full scale airplane. If I were sitting in the Freedom Flight kit airplane, the covering would be on the left side of the rudder. If you accidentally attached the covering to the other side, don't worry about it, the difference is extremely minimal.

Brian T.

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Re: Design

Postby DoctaDave » January 25th, 2015, 7:01 pm

I've noticed that Armor all has been frequently recommended for lubricating motors. I looked for it on amazon and found this http://www.amazon.com/Armor-All-10228-O ... =armor+all
Is this the armor all that you guys are talking about? It says its a protectant not a lubricant in the description so I just wanted to make sure.

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Re: Design

Postby Toms_42 » January 25th, 2015, 9:17 pm

I've noticed that Armor all has been frequently recommended for lubricating motors. I looked for it on amazon and found this http://www.amazon.com/Armor-All-10228-O ... =armor+all
Is this the armor all that you guys are talking about? It says its a protectant not a lubricant in the description so I just wanted to make sure.
That looks right. But we've been using the same bottle for years, so I'm not sure if it's still the same formula. A couple amazon reviews like this one:
http://www.amazon.com/review/R1J0C6UP15 ... automotive
say that they changed their formula, so I don't know if it's still the same. one said it's more viscous.
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DoctaDave
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Re: Design

Postby DoctaDave » January 25th, 2015, 9:28 pm

I've noticed that Armor all has been frequently recommended for lubricating motors. I looked for it on amazon and found this http://www.amazon.com/Armor-All-10228-O ... =armor+all
Is this the armor all that you guys are talking about? It says its a protectant not a lubricant in the description so I just wanted to make sure.
That looks right. But we've been using the same bottle for years, so I'm not sure if it's still the same formula. A couple amazon reviews like this one:
http://www.amazon.com/review/R1J0C6UP15 ... automotive
say that they changed their formula, so I don't know if it's still the same. one said it's more viscous.
Are there any other good alternatives? Or has anyone tried the new formula?


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