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Old Sep 03, 2008, 04:43 PM
Geaux Saints
Hopalong X's Avatar
Grafton, Il
Joined Nov 2007
1,913 Posts
Quote:
Originally Posted by jhtitan
and I will PM you Hopalong later tonight. let me check with the wife and make sure she wont mind the date I have in mind

thanks again guys
Jon
Any Sunday you and Greadapult get together I'll try to make it. Just let me know by the Friday before.
The coming weekend is out. My parents are in town from New Orleans. They made like geese and got out of H. Gustav's way.

Mike
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Old Sep 03, 2008, 05:17 PM
Slipping the Surly Bonds
dz1sfb's Avatar
Attica, MI
Joined Dec 2006
10,698 Posts
Kfm2 on a 33" BB question

This question is open to all.

I am upfitting a previous BB (the flourescent 33"er) to a Kfm2 wing for the neighbor kid. He has adequate experience to fly the BB on his own. The question is; How much dihedral should I put in this wing? This is a RET ship, so no ailerons. Also how will flight characteristics be affected by this wing? Just starting to get into the Kfm wing thing.

Thanks for your input,
Ken
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Old Sep 03, 2008, 05:24 PM
In Rc for a LONG TIME FFAA#1
laserman's Avatar
Canada, ON, Ottawa
Joined Jun 2004
1,377 Posts
Quote:
Originally Posted by dz1sfb
This question is open to all.

I am upfitting a previous BB (the flourescent 33"er) to a Kfm2 wing for the neighbor kid. He has adequate experience to fly the BB on his own. The question is; How much dihedral should I put in this wing? This is a RET ship, so no ailerons. Also how will flight characteristics be affected by this wing? Just starting to get into the Kfm wing thing.

Thanks for your input,
Ken

on mine i have about 3/4 " go for about 1 to 1.25 if you want to have more stability for the young guy

laser
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Old Sep 03, 2008, 08:05 PM
treefinder
springer's Avatar
SE MI
Joined Oct 2004
9,861 Posts
I think i'd stay with no more than 1"/side. When I first did the Pete variants, I did kfm2 with no more than 2"/side, and RET low wingers need more dihedral than high wingers, or so they say.
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Old Sep 03, 2008, 08:21 PM
Registered User
SergeyK's Avatar
United States, NY, Kings
Joined Feb 2006
892 Posts
kfm3 for bb24 sizes

Here is a cutting diagram with the sizes I used for the 24" kfm3 wing.
The photos of the wing internals are at
http://www.rcgroups.com/forums/showp...postcount=7522
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Old Sep 03, 2008, 10:11 PM
Tinkerer
jfhspike's Avatar
RI
Joined May 2005
184 Posts
Quote:
Originally Posted by chewytm
To understand pitch speed, just imagine the prop as a screw (an airscrew). Eg take a prop with a 7" pitch rotating at 8000 rpm.

For every revolution of the prop, it would theoretically (in a perfect world) go forward 7". If you ignor slippage etc etc blah blah

So, at 8000rpm, it would go forward 8000 x7" /12" = 4,666.7 ft/min

This is about 4,666.7 ft/min x 60 min/hr /[ (3 ft/yd) * (1760 yd/mile)] = 53mph.

Hope that makes it clearer.

chewy
Nice explanation, Chewy.

One nice thing about the computation above is that almost everything is a constant. The only varying things are (1) prop pitch and (2) RPM. Because we usually measure RPM in thousands (i.e., 4000 RPM or 6000 RPM, but no one ever says 3186.25 RPM), you can rewrite Chewy's computation like this:

7" x 8 x 1000 RPM * 60 min/hr /(5280*12 inches/mile) -> 53.03 MPH

If you're willing to fudge a little, you could call that "56 MPH". Here's why that's a good idea: you get the rule of thumb that

PITCH SPEED (in MPH) is [just a little less than] pitch (in inches) * RPM (in thousands).

Example: a 4025 prop at 5000 RPM:

pitch in inches: 2.5
RPM in thousands: 5
Pitch speed in MPH: about 2.5 * 5 = 12.5. [The correct answer is closer to 11.8 MPH, but so what?]

--John

PS: Thanks, Chewy, for making me think about this. I'd always done it out longhand like you, but your explanation helped me see that it was really very simple and that the approximation works pretty well.
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Old Sep 03, 2008, 11:19 PM
Registered User
Ipoh, Perak Malaysia
Joined Jul 2006
4,011 Posts
Or you can just do the simple multiplication:

pitch speed = pitch (inches) x rpm (thousands) x 0.947

eg 7" x 8 (krpm) x 0.947 = 53.03 mph

chewy
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Old Sep 04, 2008, 01:30 AM
Registered User
SergeyK's Avatar
United States, NY, Kings
Joined Feb 2006
892 Posts
finished 24" kfm3 wing

The Kfm3 wing for my 24" BlueBaby is done.
The wing weight is 42.1g (the original UC wing is 27.7g), which gives the total airframe weight of 122.3g or the AUW with 460mAh 2s LiPo of 149.9g

Now need to fly it.
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Old Sep 04, 2008, 06:36 AM
Slipping the Surly Bonds
dz1sfb's Avatar
Attica, MI
Joined Dec 2006
10,698 Posts
Sergey,

Very nice workmanship! and very light. I would like to build another one of these wings without any wood (foam spar and tip plates) to see what I can get the weight down to.

What motor are you using? Sorry, I am sure you posted this info already.

Yours should fly beautifully!

Ken
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Old Sep 04, 2008, 08:05 AM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by ginodouglas
Tony

A KFm2 would be great! Sorry for the trouble.

Gino
No trouble Gino, the plans for the BB24 KFm2 wing are now posted on page one, post one. Enjoy!

Tony
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Old Sep 04, 2008, 08:10 AM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by springer
I think i'd stay with no more than 1"/side. When I first did the Pete variants, I did kfm2 with no more than 2"/side, and RET low wingers need more dihedral than high wingers, or so they say.
Concur. 1" per side.

Tony
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Old Sep 04, 2008, 08:11 AM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by SergeyK
Here is a cutting diagram with the sizes I used for the 24" kfm3 wing.
The photos of the wing internals are at
http://www.rcgroups.com/forums/showp...postcount=7522
Very nice Sergey. Thank you.

Tony
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Old Sep 04, 2008, 08:14 AM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by SergeyK
The Kfm3 wing for my 24" BlueBaby is done.
The wing weight is 42.1g (the original UC wing is 27.7g), which gives the total airframe weight of 122.3g or the AUW with 460mAh 2s LiPo of 149.9g

Now need to fly it.
Beautiful BB Sergey. You did a terrific build at a very impressive weight. Congrats, I sure it will fly as good as it looks.

Tony
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Old Sep 04, 2008, 08:47 AM
Slipping the Surly Bonds
dz1sfb's Avatar
Attica, MI
Joined Dec 2006
10,698 Posts
Quote:
Originally Posted by Tony65x55
No trouble Gino, the plans for the BB24 KFm2 wing are now posted on page one, post one. Enjoy!

Tony
Tony,

I will give this one a try also.

Thanks,
Ken
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Old Sep 04, 2008, 08:49 AM
Slipping the Surly Bonds
dz1sfb's Avatar
Attica, MI
Joined Dec 2006
10,698 Posts
Tony,

I have a question though. You are calling for a 1/4" spar in the wing. The foam is only 3/16" thick. I will have to sand down or modify for 3/16" sq. spar.

Ken
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