Posted by no spam on November 5, 2007, 4:42 pm
The son wants to comparative study of airfoil designs as a science fair
project and he (and I) need a little help.
His plan is to make blades out of balsa, put them on a small remote
controlled helo he got a few years ago, place helo on a scale (small enough
so the majority of the thrust doesn't fall on the scale) then see which
design gives the best lift.
He has found some plans for different designs but I think he could use
others. Any websites out there for this?
Also I have NO experience in working with wood models or caving and he has
even less. How would you suggest he goes about carving the foils? I was
thinking a dremal type tool would work but what kind of blade/head would be
needed?
My biggest question is how in the world do you make sure that the shape in
the wood is the shape you want?
Any and all help would be great and quickly because I'm sure he's going to
be asking me and I'd like to impress him on my vast knowledge of woodworking
and airfoil construction. ;)
Posted by Joe AutoDrill on November 5, 2007, 5:00 pm
I can't help you with the design as I'm clueless when it comes to much other
than drilling holes...
But I can tell you that asking the same question in a model airplane group
may get you better results than anywhere else. Those folks are sometimes
beyond fanatical about their knowledge of such things.
Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com
V8013-R
> The son wants to comparative study of airfoil designs as a science fair
> project and he (and I) need a little help.
> His plan is to make blades out of balsa, put them on a small remote
> controlled helo he got a few years ago, place helo on a scale (small
> enough so the majority of the thrust doesn't fall on the scale) then see
> which design gives the best lift.
> He has found some plans for different designs but I think he could use
> others. Any websites out there for this?
> Also I have NO experience in working with wood models or caving and he has
> even less. How would you suggest he goes about carving the foils? I was
> thinking a dremal type tool would work but what kind of blade/head would
> be needed?
> My biggest question is how in the world do you make sure that the shape in
> the wood is the shape you want?
> Any and all help would be great and quickly because I'm sure he's going to
> be asking me and I'd like to impress him on my vast knowledge of
> woodworking and airfoil construction. ;)
>
Posted by Chris Friesen on November 5, 2007, 5:00 pm
no spam wrote:
> The son wants to comparative study of airfoil designs as a science fair
> project and he (and I) need a little help.
I did something similar back in high school.
> His plan is to make blades out of balsa, put them on a small remote
> controlled helo he got a few years ago, place helo on a scale (small enough
> so the majority of the thrust doesn't fall on the scale) then see which
> design gives the best lift.
My technique was to build a wind tunnel using a standard house fan and
simply put the wing on a post stuck through a hole in the bottom,
resting on a digital scale. You can then graph angle of attack vs lift
for each airfoil type.
A better technique would be to hang the wing from some thread front and
back. This would allow you to graph angle of attack vs both lift and
drag for each airfoil type.
If you want to use the scale, you could flip it around so that the force
is downwards. This would solve the problem of the helicopter flying
away, and would also mean that the wind produced by the blades would be
going up, and thus not affecting the scale nearly as much.
> He has found some plans for different designs but I think he could use
> others. Any websites out there for this?
There are some at:
http://www.gliders.dk/airfoils.htm
The Kline-Fogleman airfoil is kind of interesting. It almost looks like
it has a chunk taken out of it.
> Also I have NO experience in working with wood models or caving and he has
> even less. How would you suggest he goes about carving the foils?
A knife works fine, with sandpaper to finish. If you know someone with
a tablesaw you could kerf it at intervals to give you a baseline. A
bandsaw would allow you to hog off most of the excess.
> My biggest question is how in the world do you make sure that the shape in
> the wood is the shape you want?
Kerfing as mentioned above helps. Otherwise draw the shape on the ends,
cut away everything that isn't the shape.
Chris
Posted by David Starr on November 6, 2007, 9:13 am
Chris Friesen wrote:
> no spam wrote:
>> The son wants to comparative study of airfoil designs as a science
>> fair project and he (and I) need a little help.
>
> I did something similar back in high school.
>
>> His plan is to make blades out of balsa, put them on a small remote
>> controlled helo he got a few years ago, place helo on a scale (small
>> enough so the majority of the thrust doesn't fall on the scale) then
>> see which design gives the best lift.
>
> My technique was to build a wind tunnel using a standard house fan and
> simply put the wing on a post stuck through a hole in the bottom,
> resting on a digital scale. You can then graph angle of attack vs lift
> for each airfoil type.
>
> A better technique would be to hang the wing from some thread front and
> back. This would allow you to graph angle of attack vs both lift and
> drag for each airfoil type.
>
> If you want to use the scale, you could flip it around so that the force
> is downwards. This would solve the problem of the helicopter flying
> away, and would also mean that the wind produced by the blades would be
> going up, and thus not affecting the scale nearly as much.
>
>> He has found some plans for different designs but I think he could use
>> others. Any websites out there for this?
>
> There are some at:
> http://www.gliders.dk/airfoils.htm
>
> The Kline-Fogleman airfoil is kind of interesting. It almost looks like
> it has a chunk taken out of it.
>
>> Also I have NO experience in working with wood models or caving and he
>> has even less. How would you suggest he goes about carving the foils?
>
> A knife works fine, with sandpaper to finish. If you know someone with
> a tablesaw you could kerf it at intervals to give you a baseline. A
> bandsaw would allow you to hog off most of the excess.
>
>> My biggest question is how in the world do you make sure that the
>> shape in the wood is the shape you want?
>
> Kerfing as mentioned above helps. Otherwise draw the shape on the ends,
> cut away everything that isn't the shape.
>
> Chris
Go with the wind tunnel. Mounting new blades on a model helicopter
isn't a repeatable process. Changing blades will change the load on the
engine, causing it to run faster or slower, createing more or less lift.
Just changing the size or angle of attack of the rotor blades, while
keeping the airfoil the same will change the performance of the
helicopter.
Wind tunnel doesn't have to be very long. A square or rectangular
cross section works fine and is easier to make than a circular cross
section. Have the fan suck air out of the wind tunnel rather than blow
into it. The fan blades make the air turbulent which reduces lift and
adds vibration to make your instrument readings jiggle.
Make one side of the wind tunnel clear plastic so you can watch the
action. Arrange a protractor some how to let you measure (and set)
angle of attack. Angle of attack is very important, a change of a few
degrees will change the measured lift greatly.
One way of measuring lift might be to make a beam balance scale, the
airfoil under test (pointed down) goes onto one arm of the balance, and
you add weights to the other arm until the airfoil balances.
I'd go with balsa wood 'cause it's light and easy to carve to shape.
If the kid is new to carving, make sure he cuts AWAY from the
fingers holding the wood. You can get more consistant results by making
templates of the desired air foil out of file folder stock and using
them to check the shape as carving progresses. Surface finish affects
performance. Couple of coats of shellac, sand between coats, will
increase performance.
A really sophisticated tunnel would measure drag as well as lift, the
true measure of airfoil performance is the lift/drag ratio. The ideal
airfoil would create pure lift, no drag. Practical airfoils don't do
that well.
You might check with the boy and make sure that he really wants to do
a wind tunnel as opposed to flying the helicopter. He could do a
science project by measuring the performance of the helicopter, best
altitude, speed, range, payload, fuel consumption. Make the
measurements on a hot day, a cold day, a high pressure day, and a low
pressure day. See if temperature or barometric pressure makes a
measureable change in performance.
David Starr
Posted by J. Clarke on November 6, 2007, 9:58 am
David Starr wrote:
> Chris Friesen wrote:
>> no spam wrote:
>>> The son wants to comparative study of airfoil designs as a science
>>> fair project and he (and I) need a little help.
>>
>> I did something similar back in high school.
>>
>>> His plan is to make blades out of balsa, put them on a small
>>> remote
>>> controlled helo he got a few years ago, place helo on a scale
>>> (small
>>> enough so the majority of the thrust doesn't fall on the scale)
>>> then
>>> see which design gives the best lift.
>>
>> My technique was to build a wind tunnel using a standard house fan
>> and simply put the wing on a post stuck through a hole in the
>> bottom,
>> resting on a digital scale. You can then graph angle of attack vs
>> lift for each airfoil type.
>>
>> A better technique would be to hang the wing from some thread front
>> and back. This would allow you to graph angle of attack vs both
>> lift and drag for each airfoil type.
>>
>> If you want to use the scale, you could flip it around so that the
>> force is downwards. This would solve the problem of the helicopter
>> flying away, and would also mean that the wind produced by the
>> blades would be going up, and thus not affecting the scale nearly
>> as
>> much.
>>
>>> He has found some plans for different designs but I think he could
>>> use others. Any websites out there for this?
>>
>> There are some at:
>> http://www.gliders.dk/airfoils.htm
>>
>> The Kline-Fogleman airfoil is kind of interesting. It almost looks
>> like it has a chunk taken out of it.
>>
>>> Also I have NO experience in working with wood models or caving
>>> and
>>> he has even less. How would you suggest he goes about carving the
>>> foils?
>>
>> A knife works fine, with sandpaper to finish. If you know someone
>> with a tablesaw you could kerf it at intervals to give you a
>> baseline. A bandsaw would allow you to hog off most of the excess.
>>
>>> My biggest question is how in the world do you make sure that the
>>> shape in the wood is the shape you want?
>>
>> Kerfing as mentioned above helps. Otherwise draw the shape on the
>> ends, cut away everything that isn't the shape.
>>
>> Chris
> Go with the wind tunnel. Mounting new blades on a model
> helicopter
> isn't a repeatable process. Changing blades will change the load on
> the engine, causing it to run faster or slower, createing more or
> less lift. Just changing the size or angle of attack of the rotor
> blades, while keeping the airfoil the same will change the
> performance of the helicopter.
> Wind tunnel doesn't have to be very long. A square or
> rectangular
> cross section works fine and is easier to make than a circular cross
> section. Have the fan suck air out of the wind tunnel rather than
> blow into it. The fan blades make the air turbulent which reduces
> lift and adds vibration to make your instrument readings jiggle.
> Make one side of the wind tunnel clear plastic so you can watch
> the
> action. Arrange a protractor some how to let you measure (and set)
> angle of attack. Angle of attack is very important, a change of a
> few
> degrees will change the measured lift greatly.
> One way of measuring lift might be to make a beam balance scale,
> the airfoil under test (pointed down) goes onto one arm of the
> balance, and you add weights to the other arm until the airfoil
> balances. I'd go with balsa wood 'cause it's light and easy to
> carve to shape. If the kid is new to carving, make sure he cuts
> AWAY from the
> fingers holding the wood. You can get more consistant results by
> making templates of the desired air foil out of file folder stock
> and
> using them to check the shape as carving progresses. Surface finish
> affects performance. Couple of coats of shellac, sand between
> coats,
> will increase performance.
> A really sophisticated tunnel would measure drag as well as lift,
> the
> true measure of airfoil performance is the lift/drag ratio. The
> ideal
> airfoil would create pure lift, no drag. Practical airfoils don't
> do
> that well.
> You might check with the boy and make sure that he really wants
> to
> do a wind tunnel as opposed to flying the helicopter. He could do a
> science project by measuring the performance of the helicopter, best
> altitude, speed, range, payload, fuel consumption. Make the
> measurements on a hot day, a cold day, a high pressure day, and a
> low
> pressure day. See if temperature or barometric pressure makes a
> measureable change in performance.
"Best altitude" could be an interesting project in itself depending on
how much the helicopter can lift and how high it can really fly.
--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)
XML site map
> project and he (and I) need a little help.
> His plan is to make blades out of balsa, put them on a small remote
> controlled helo he got a few years ago, place helo on a scale (small
> enough so the majority of the thrust doesn't fall on the scale) then see
> which design gives the best lift.
> He has found some plans for different designs but I think he could use
> others. Any websites out there for this?
> Also I have NO experience in working with wood models or caving and he has
> even less. How would you suggest he goes about carving the foils? I was
> thinking a dremal type tool would work but what kind of blade/head would
> be needed?
> My biggest question is how in the world do you make sure that the shape in
> the wood is the shape you want?
> Any and all help would be great and quickly because I'm sure he's going to
> be asking me and I'd like to impress him on my vast knowledge of
> woodworking and airfoil construction. ;)
>