Sailplane design question    Gallery
View related threads: (in this forum | in all forums)

Logged in as Guest



Users viewing this topic: none
    Search This Thread  
 
Printable Version

All Forums >> RC Airplanes >> Aerodynamics >> Sailplane design question
Page: [1]

Tower Hobbies Get Coupon Codes Brands  
Login
Message << Older Topic   Newer Topic >>
Sailplane design question - 12/13/2012 8:13 PM   
Beeza


 

Posts: 123
Score: 100
Joined: 1/25/2004
Last Login: 2/22/2013
From: Springfield, IL, USA
Status: offline 		I have an easy one here, I think. I built a wing for Mark's Models Bushwacker gas-powered sailplane, scaled down for 1/2A gas engine, but I built the plane for electric power. I'm using 3 channel r/cstab, ailerons and throttle no rudder control.. I built the wing without dihedral, but it's not too late to add dihedral if I need. I'd read once that the ailerons are not as effective with dihedral; that's the reason I built it without.

The wing is 48" span, area is 425 sq in and the ailerons are long, each is 1"x18". The airfoil I used is flat-bottomed.

My question isam I better off adding some dihedral, maybe like 1 1/2" at each wing tip?

I'm not much of an r/c pilot, but I can fly beginner's planes OK. I saw a pretty stable design here to work with. I love to build and have been scratch building for years.

Thanks in advance for all your help!

Beeza

Attachments
Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize


Hide Signatures
       Post #: 1

RE: Sailplane design question - 12/13/2012 11:58 PM   
soarrich



Posts: 4397
Score: 136
Joined: 2/1/2002
Last Login: 5/25/2013
From: Middletown, NJ, USA
Status: offline 		I'd try flying it first, I think it will be stable enough for you the way it is.

_____________________________

Rich Border AMA 77727
Sig Kadet Brotherhood #2

Hide Signatures

(in reply to Beeza)
       Post #: 2

RE: Sailplane design question - 12/14/2012 1:38 AM   
cfircav8r



Posts: 1156
Score: 218
Joined: 7/17/2004
Last Login: 5/25/2013
From: Hampton, IA, USA
Status: offline 		When you say "beginner planes" do you mean rudder, elevator, throttle only, or do you fly ailerons also? If you have only been flying RET then I would add dihedral, as you will go from a slower responding self righting plane to a non self righting plane with quicker responses. You can always make another wing without dihedral after you master this one. It greatly depends on your reflexes and abilities and none of us can judge that by reading posts. If you are at the point where you are way ahead of the plane and never need to think about how to move the controls to do anything then you may do well without dihedral. Anything less than that and it could go either way. You obviously scratched the wing so it should be easy enough to build both and try it out with first.

_____________________________

The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

Hide Signatures

(in reply to soarrich)
       Post #: 3

RE: Sailplane design question - 12/14/2012 1:54 AM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline 		Ask yourself what you plan to do with that sailplane?

Are you going to thermal it, hoping to spec it out as often as possible? If you want a plane that'll fly itself when near the limit of visibility, then you want some dihedral.

If you just want a sloper, where it will be close enough to see perfectly, then don't worry about the dihedral.

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to cfircav8r)
       Post #: 4

RE: Sailplane design question - 12/14/2012 2:05 AM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline 		Consider something else. There is no rule that says a glider can only have one wing built for it. Back when glider airfoils were in constant development and a new family of airfoils would pop up every so often, I used to build a wing in a week for my Killer Pickle. The suckers rubber banded on of course. They were polyhedral in the K.P.'s case and did not have ailerons. They really took less than a week to build. If you wanted to broaden that glider's envelope, it'd be easy to whip out a polyhedral wing without ailerons in a very short time.

You'd learn for yourself how the 2 different types fly compared to each other. You've got the perfect opportunity. And seem to already have an inquisitive mind that's wondering about similar questions.

BTW, if you do make a polyhedral wing for that puppy, consider keeping the present chord, but stretch the span about 1/3 greater. Polyhedral is great for gliders you want to spec out, and that'll be easier with more wing area.

Just a thought.........

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to da Rock)
       Post #: 5

RE: Sailplane design question - 12/14/2012 2:38 AM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline
quote:

I'd read once that the ailerons are not as effective with dihedral;


Really? Do you remember how much dihedral it took? Did the article mention how dihedral acts like ailerons when the plane is turned with the rudder? So there are times when dihedral would reduce the aileron deflection needed. Funny stuff this aerodynamics, ain't it.

Consider how effective a rudder is. You could say the vertical fin/rudder is just a wing/aileron that is 90degrees from level. In fact, rudders often induce a roll when deflected simply because they're effective.

The idea ailerons lose effectiveness probably came from confusion with the lift a wing loses due to dihedral. The theory is that wing lift is figured based on the projected area (as seen from directly above) and dihedral reduces that area. Since ailerons produce the same roll force throughout the roll, there is a strong probability they don't lose effectiveness with dihedral. If they did lose effectiveness, it isn't enough to worry about.



_____________________________

Good flying wit ya today

Hide Signatures

(in reply to Beeza)
       Post #: 6

RE: Sailplane design question - 12/14/2012 4:52 AM   
ARUP


 

Posts: 1948
Score: 134
Joined: 1/21/2007
Last Login: 5/25/2013
From: Taylorsville, KY, USA
Status: offline 		The only thing aesthetically 'wrong' with flat wings is that they look like the tips droop. Otherwise just fly it and experiment! It's fun, fun, fun until daddy takes the bird away! hahahaha

Hide Signatures

(in reply to da Rock)
       Post #: 7

RE: Sailplane design question - 12/16/2012 12:56 AM   
pimmnz


 

Posts: 1894
Score: 148
Joined: 11/9/2005
Last Login: 5/21/2013
From: Auckland, NEW ZEALAND
Status: offline 		I have been flying OD 2 metre models with just aileron/elevator for some time and there are some limitations with the idea. For a soaring model flown at height you do need some dynamic stability, a model that will not remain straight by itself becomes very difficult to fly at height and above. Ailerons only work when the model is moving along somewhat above stalling speed, rudder is more effective at slow speed, if you cannot judge airspeed then there will be a time, either up high or an approach, when applying aileron simply won't work, and if you are low and slow, then the ground will rise up...You will need to use quite a bit of differential, as you don't have a rudder to keep the model in line when turning, and if you are bunjee or winch launching, again, keep the speed up or you will tip stall it off the line, something that rudder models don't tend to do. Other than that, well it works OK, but as stated, the more dihedral used to keep the model directionally stable, the less efficient the ailerons are. Which is why most of the really effective 2 function soarers are rudder/elevator models.
Evan, WB #12.

Hide Signatures

(in reply to ARUP)
       Post #: 8

RE: Sailplane design question - 12/17/2012 5:07 AM   
Beeza


 

Posts: 123
Score: 100
Joined: 1/25/2004
Last Login: 2/22/2013
From: Springfield, IL, USA
Status: offline 		Wow! You guys gave me a lot more info to consider than I thought I'd receive. The wing will get dihedral now.

Thanks again and Merry Christmas!

Beeza

Hide Signatures

(in reply to pimmnz)
       Post #: 9

RE: Sailplane design question - 12/21/2012 1:39 AM   
BMatthews



Posts: 11656
Score: 247
Joined: 10/4/2002
Last Login: 5/23/2013
From: Chilliwack, BC, CANADA
Status: offline 		Personally I'd just fly it as it is for now and see how it goes.

Although some dihedral would make it self leveling that simply does not mean that it's going to be a terror to fly with flat wings. You might well like it as it is.

Da Rock makes valid points about wanting a little more self stabilizing effect if flown out at distances where you're flying by instinct. But if you are not comfortable flying with the model that far away at this point you may well find that you don't need that self leveling effect.

When folks mention that dihedral reduces the effect of ailerons they are talking about rather large amounts. Such as putting ailerons onto a high angle polyhedral style wing or similar. Ailerons on your model with an inch or two of dihedral is NOT an issue.

_____________________________

Witty saying to be plagarized shortly.....

Hide Signatures

(in reply to Beeza)
       Post #: 10

Page:   [1]
All Forums >> RC Airplanes >> Aerodynamics >> Sailplane design question
Page: [1]





Jump to:


 
Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

RC Universe is a service of Internet Brands, Inc. Copyright © 2001-2013.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America


0.547RCU1