Maker Pro
Maker Pro

Help with son's science fair project (airfoil designs)

N

no spam

Jan 1, 1970
0
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. ;)
 
J

Joe AutoDrill

Jan 1, 1970
0
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
 
D

DJ Delorie

Jan 1, 1970
0
IMHO your best bet is to grind or cut a custom scraper for each
profile you want, and use that to cut the balsa to the right profile.
That way, the results are predictable and consistent - just scrape
until the scraper hits the table (holding it vertically) and you know
the profile is the same all down each blade.

Note that balsa is a porous wood; you should use a wood filler at
least, and paint perhaps, to get a smooth surface. Otherwise you have
to account for turbulence too. Hey! Something else to measure.

You could use the dremel tool to grind the scrapers.
 
A

Arnold Walker

Jan 1, 1970
0
Bob F said:
Hard foam could be a substitute for balsa. A nichrome wire cutter powered
by a transformer of some sort would cut it nicely, and a guide could be
cut from cardboard at each end for the shape. Extruded styrene from the
building materials area of the hardware store would probably work well for
this.

Bob
Amen to that ....most of us aircraft mechanics learned that way on airfoils.
You will note that since you are using a helicopter that the stall line will
be different on
a synmetrical airfoil like actually used on most helicopters and supersonic
airplanes than on a asynmetrical like used on autogyros and subsonic
airplanes.The stall line actually walking off the airfoil more at large
attack angles.
Should be able to get airfoil profiles for you to use by googling that.
I would use the blue form with one coat of fiberglass(lightest cloth like in
an model shop) over that.
with feather lite to smooth it up.For hard points to bolt blades on you can
use hardwood dowels glassed in
the form,then drilled for the bolt.
 
J

J. Clarke

Jan 1, 1970
0
no said:
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?

The Bible on wing sections is "Theory of Wing Sections" by Abbot & von
Doenhoff. 15 bucks from Amazon.
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?

Knife, maybe a cabinet scraper. I'm not going to try to describe a
sanding spline but if you google that term you should get some good
descriptions.
My biggest question is how in the world do you make sure that the
shape in the wood is the shape you want?

Make a template or set of templates out of cardboard or brass or
aluminum or thin plywood or whatever else floats your boat--when the
wing matches the templates you've got it right,.
 
A

Arnold Walker

Jan 1, 1970
0
Lew Hodgett said:
You take me back to the days of my misspent youth where a lot of time
was spent building stick balsa and tissue paper model airplanes.

The same technology works for air foils.

Use 1/8" sheet balsa to make profiles along the air foil.

Lay out and cut to size with an Xacto knife.

These profiles are glued to a spar, say 1/8 x 1/2 located in the
middle of the profile on equal spaces.

Form leading and trailing edges from balsa as required, then glue in
place.

Cover with tissue paper that has been glued in place, then stretched
by sprinkling with water and allowing to shrink while drying.

Finally, paint with model airplane dope and you have an airfoil.

Tools needed:

Xacto knife, model airplane glue, straight pins, sand paper and some
paint brushes for models.

Try to find an old time hobby shop and kibitz with some old farts, if
you can.

Have fun, both of you.

Lew
On wood blades for a helo he is close with airplane spar idea.
But it is going to have to be tougher because of blade spin.
Some like like your old Hillers were solid wood with a spar.
Other like some of your first Bells were a spar with the spacers he
mentioned and sheet of thin
plywood (balsa sheets with grain in the direction of blade length in your
case) with fiberglass or urethene coat.
Hell..... Bell in the early days built a frame on the lines of his 47 in
model format with a plugin electric motor to
test his ideas.And various blades out of wood for his prototype
helicopter......used to have some old movies of that
in his driveway testing it out.Guess he was one of the original 60/90 series
model helicopter guys.
Wood blade like wood props are fragile compared to other materials........
Have done them for a Whistler autogyro out of solid balsa (basswood is best
for beginners more stable but less reponsive)
You need a razor plane and a long sanding block.....
You also need to add reenforcing plys on the top and bottom of the root
attached with medium cyanoarcrylate.
CA is used around the mounting holes for reenforcement as well.
Mount blades and sand ...heavy blade to balance.
After you got them balanced cover with MonoKote
Then final balance ...cover... light blade tip with a different color
covering.
On these 90series blades the travel adjustment was 5" max.vertical.
AT 4 degrees negative incident .
I take it outside to check it.... holding up the rotor mast in a 5 to 7mph
wind with a quick hand spin .
It should spool on up to about 700rpms and give you a 5 pound tug for lift
on 39" disk.
This is with asymetric blades.....roughly a 8-h-12 profile
A lot of helicopters use NACA0012 profiles(If your son has that one, he has
the most popular used on helicopters)
That outer 1/3 of the blade is giving the lift.
some modelers add a 10-15 degree twist just like you see on props to extend
the lift along the leading edge.
That would have the outer half of the blade giving lift.
Since the root is moving a lot slower than the tip at a given rpm.
You would need a jig and copying dremel to carve that one......
Beyond anything I have done,so far on wood model blades.........
 
J

J. Clarke

Jan 1, 1970
0
Kerry said:
Styrofoam (house insulation) and a hot knife might work well. For
the
hot knife, you can use a couple of feet of steel wire (guitar
string;
can't remember which one, but just a single wire) and an auto
battery
charger. If he makes a couple of templates (cardboard works fine) in
the shape of the airfoil he wants, then sticks them to each end of a
block of Styrofoam, then hold the wire against both templates at the
same time as he moves it around the templates, he can make smooth,
light weight airfoil sections.

Careful with the selection of foam though--the beaded stuff won't cut
smoothly that way and polyurethane gives off toxic vapors when
hot-wired. If you're got non-beade polystyrene though the technique
works a treat--that's basically the procedure that Burt Rutan
specified for cutting the wing cores for the VariEze and LongEze.
 
J

J. Clarke

Jan 1, 1970
0
David said:
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.
 
J

J. Clarke

Jan 1, 1970
0
Kerry said:
John,
Yep, that's why I suggested Styrofoam (house insulation).

Styrofoam is a brand name for a variety of products, some of which can
be hot-wired safely and others that can't. The blue Styrofoam at the
local Home Depot is polyurethane, not styrene.

Read the label, know what it's made out of, don't just assume because
it's "house insulation" that it's safe to hot-wire.
 
E

Edwin Pawlowski

Jan 1, 1970
0
J. Clarke said:
Styrofoam is a brand name for a variety of products, some of which can
be hot-wired safely and others that can't. The blue Styrofoam at the
local Home Depot is polyurethane, not styrene.

Read the label, know what it's made out of, don't just assume because
it's "house insulation" that it's safe to hot-wire.

All the rigid board is extruded polystyrene.
http://www.dow.com/styrofoam/na/res-us/products/
 
J

J. Clarke

Jan 1, 1970
0
Kerry said:
John,
I agree that reading the label is very important - polyurethane does
give off toxic fumes. But, from Dow's website, when they refer to
Styrofoam they say "Styrofoam rigid foam insulation" or "Styrofoam
extruded polystyrene insulation". And the sheet of blue Styrofoam
I'm
looking at is marked "Extruded polystyrene insulation" as have been
all other sheets of blue rigid Styrofoam I've ever seen, including
at
Home Depot. Can't remember if this particular sheet came from Home
Depot. There might be blue rigid foam insulation at Home Depot that
is polyurethane, but I doubt that it's also Styrofoam.

Dow Corning TUFF-R.

I don't understand why you're so resistant to the notion of specifying
the foam by chemistry, which is on the label on any foam sold
commercially, instead of by the intended use "house insulation" or the
brand "Styrofoam".
 
E

Edwin Pawlowski

Jan 1, 1970
0
Kerry Montgomery said:
Edwin,
Actually, Bayer makes rigid board polyurethane insulation:
http://tinyurl.com/2rytbj
but it's not going to be marked Styrofoam.
Kerry


Correct, I was referring to the Dow products. Thee are plenty of other
materials available.
 
A

Arnold Walker

Jan 1, 1970
0
Edwin Pawlowski said:
Correct, I was referring to the Dow products. Thee are plenty of other
materials available.

And the toxic from polyurethane is cyanide......like you used to see used in
the spy movies.
I was refering to Dow blue polystyrene because of the extra density needed
for the blades
and the ability to hot wire.
Pvc and nylon does pretty well on the hardpoints if he doesn't like
hardwood.For the added compression strength
needed for bolts to attach the blades.Full size helicopters.... you also
have different metals used for hardpoints.


At the same time, I have used polyurethane,nylon , wood, and pvc in building
composite structures.
On models I have even used cotton/linen rags instead of fiberglass.
As well as honeycombs made out cardboard,tinfoil, fiberglass,and kelvar.
Each have advantages and disadvantages.
Both models and full size aircraft.....though most of my experience is
limited to rotorcraft and hovercraft.
 
J

J. Clarke

Jan 1, 1970
0
Kerry said:
John,
Not resistant at all to specifying foam by chemistry, but the brand
Styrofoam is a perfectly adequate way to specify Dow brand rigid
Styrofoam, which is what I suggested to the OP as a material to
investigate.
The only TUFF-R that I know of is insulation clad on both sides;
don't
remember what color the core is, but it's not labeled Styrofoam. And
wanted to correct any misconception that you may have caused by
saying that there was "...blue Styrofoam at the local Home Depot is
polyurethane, not styrene.", as there isn't any such thing.

If you had said "Styrofoam _brand_ blue insulating foam but make sure
that it's really Styrofoam brand and that it's really polystyrene" I
wouldn't have had any problem with what you said, but walking into a
store and asking for "styrofoam house insulation" is just too likely
to get the wrong stuff.
 
Top