How to extrapolate the curve that connects airfoil coordinates for aerodynamic shape carved into foam by hand without CAD?

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
10,309
Location
CT, USA
DXF (not DFX) is a text based vector graphics format created by Autodesk to facilitate exchange of data between different CAD systems without opening up their proprietary binary DWG format (which all the other CAD vendors have reverse engineered, anyway). More advanced neutral CAD formats (IGES, STEP, SAT, x_t, etc.) are far better if supported by both the sending and receiving systems.

PDF is a hybrid text and graphics format intended to render information exactly the same regardless of what computer system or software is being used. The embedded graphics are raster, so they don't scale well, but the page size information is included so they print accurately to scale. PDF is nice because it presents a drawing, with lines, arcs, and text, exactly as drawn, whereas while most CAD translations handle geometry well nowadays, they mess up the text and dimension presentation.

JPG is a raster graphics format intended for color photos and the like, not intended for line drawings where a vector format is more appropriate. As such, it contains none of the geometric information a vector format has, it's just, in effect, a photograph of the original drawing.

CNC machinery requires vector data, but it's often nice to have a vector file for the CNC along with a pdf to see the dimensions, tolerances, and notes.
 

Tiger Tim

Well-Known Member
Joined
Apr 26, 2013
Messages
4,110
Location
Thunder Bay
My advice basically lies somewhere within here:

Further to that, I often laminate fuselage blocks for models since full-width blocks can be hard to find. The laminations have an added bonus of giving you glue lines as reference as you shape it; you want to keep those lines fair and symmetrical from side to side. If I were laminating up foam blocks I’d be tempted to dye my glue for easily sighted lines to aid shaping.

Also, no matter how your block is constructed I find the secret to carving a fair shape is to not stop until you’re satisfied with it. If you’re not satisfied it’s because you’re not done.
 
Last edited:

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
Motofaring. Just wondering if you know where to get airfoil coordinates to plot and images of what they look like. My favorite
site is "UIUC Airfoil Coordinates Database" That is the University of Illinois Urbana Campus Using NACA airfoils as a sample
look at NACA 0015, NACA 0018, NACA 16-015, NACA 16-0018, NACA 63(3)-018. These are all symetrical airfoils. They are listed
alphabetically and your criteria is the last two numbers are the percent thickness, and the third from last is a 0 for 0% camber
(the offset added to top and bottom coordinates) to make the airfoil non symetrical. You can also use the top curve of a
nonsymetrical airfoil and mirror it for your purpose. Something like a 66(2)-215, however the slope down to the tail end has to be
less than 7 degrees down from horizontal for laminer flow to keep the boundary layer attached. Anyway click the file on the right of
the line with .gif file extension to see the shape and the left side for all the data. You can also root through a bunch of cambered profiles
for the top and bottom curves. Like ones ending in -418. Having some idea of these shapes might be usefull in chassis design so that
your knees don't come out thru the top or frame tubes don't poke out everywhere. Sort of like when someone sends a firewall cross
section with a prop flange distance and some model of engine and you have to fit a cowl around it with minimum wetted area and
cooling air inlets/outlets. I figured out the landing gear/launch wheels part of this thing, really simple. Wonder why all the builds on
the site you showed seem to make a complicated mess out of them.
 

MotoFairing

Active Member
Joined
Jul 9, 2020
Messages
39
Motofaring. Just wondering if you know where to get airfoil coordinates to plot and images of what they look like. My favorite
site is "UIUC Airfoil Coordinates Database" That is the University of Illinois Urbana Campus Using NACA airfoils as a sample
That's a lot of airfoils.

For the fairing I am leaning towards an established design because I'm not skilled enough to improve upon it.

Here is the top and side view, I would omit the two wheel fairings from the plug giving me the option to raise the fairing or make it a trike.
3d3d.jpg
3.jpg


I have been welding up the frame today and when that is done I can make some cross section cut outs to discover my clearances.

It's quite a complicated shape, it would cost $16,000 to get the plug made (I sent out a bunch of quote requests) but I'll try to make the fairing complete for <$1000.

I like wizzardworks stacked templates method, I might be able to manage that.
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
The stacked templates method with 2" EXTRUDED styrofoam (not the white beer cooler expanded variety) is easy to do. I don't
understand removing the front wheel faring. For the shown height you can use it and raised up it will be a larger cutout as the exposed
wheel portion has a larger chord. With stacked foam you make a print of each slice and stick it on the foam with wall paper paste
died with dark blue rit fabric dye. Some of the smaller templates can be nested inside larger ones, or made as left and right halves
to save printing cost. That saves about 15% on the printing. You need to look up a shop that does large format ink jet printing. I prefer to
work from a flat surface and do a left side and right side that makes alignment of the foam just a matter of matching the edges to a full
size print of the centerline shape. This makes all templates half width and is the cheapest printing cost as well as most accurate and fastest
assembly. Making a left and right side plug/plugs you can hard surface the plug with some 10oz glass cloth and pop of multiple copies
to repair crash damage. Looks like you will need a tablet computer display with a camera. The camera would by logic need to be
directly above your line of sight on a "stalk or rod mount" probably 10 inches above the boundary layer. Some side glazing would
also seem a good idea. The rear wheel faring is also a tail fin for stability. Leave it on the plug and cut it off the fairing later if you can
ride this thing with reasonable stability. It also is where the landing gear would be enclosed so as not to interrupt laminar flow with
a bunch of misaligned edges and such. Take some chassis pictures from a farther than 25 feet distance. Side view, front view, and for
the top view lay the contraption on it's side and step back 25 feet. A few close ups around protruding parts would be nice. Cell phone
pictures saved as JPG are quick, cheap, and good resolution. you cm make a female mould off the top of your faring to vacuum
form the compound shape. Heat the plastic hanging VERTICALY or you get bad optics. I saw a guy on the internet press his shape into
wet concrete for the vacuum mould. He laid cotton cloth in the concrete as a cushion and some of the metal building sheet seal
compound around the flange edge. From the oven to a canopy took about 15 seconds. I suppose discussing your faring might be
insightful to designer builder homebuilts, but if the moderator wants this stopped, [email protected] .com
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
Motofaring, Might be you are going about this in the wrong order. I think you should make one side of the faring and fit the
bicycle components inside the faring. It could be based off the images you posted plus any changes you want to make. The seat
backrest and floor bulkheads would be full width. You could also do it as a top and bottom but the parts would be harder to get
off the plug. Also you would have to make a complete faring rather than one side. The test farings would then be recycled into
female moulds for the actual parts. Probably 4 layers of S2 glass, one of Kevlar 49 and an outer S2 glass for the parts, and tooling
cloth for the test shell. You would only need to furnish shoulder width and a seat bottom width. The fastest I have ever done an
all compound curve aircraft fuselage set of drawings is 3 days. That took 2 more days of printing, 2 days cutting foam templates
and 3 weeks of sanding and filling the plug. Like they say your results could vary. I don't know what the quote thing below came
from. I gave the dog the evil eye and he is looking really guilty but he probably did something I don't know about yet.







The stacked templates method with 2" EXTRUDED styrofoam (not the white beer cooler expanded variety) is easy to do. I don't
understand removing the front wheel faring. For the shown height you can use it and raised up it will be a larger cutout as the exposed
wheel portion has a larger chord. With stacked foam you make a print of each slice and stick it on the foam with wall paper paste
died with dark blue rit fabric dye. Some of the smaller templates can be nested inside larger ones, or made as left and right halves
to save printing cost. That saves about 15% on the printing. You need to look up a shop that does large format ink jet printing. I prefer to
work from a flat surface and do a left side and right side that makes alignment of the foam just a matter of matching the edges to a full
size print of the centerline shape. This makes all templates half width and is the cheapest printing cost as well as most accurate and fastest
assembly. Making a left and right side plug/plugs you can hard surface the plug with some 10oz glass cloth and pop of multiple copies
to repair crash damage. Looks like you will need a tablet computer display with a camera. The camera would by logic need to be
directly above your line of sight on a "stalk or rod mount" probably 10 inches above the boundary layer. Some side glazing would
also seem a good idea. The rear wheel faring is also a tail fin for stability. Leave it on the plug and cut it off the fairing later if you can
ride this thing with reasonable stability. It also is where the landing gear would be enclosed so as not to interrupt laminar flow with
a bunch of misaligned edges and such. Take some chassis pictures from a farther than 25 feet distance. Side view, front view, and for
the top view lay the contraption on it's side and step back 25 feet. A few close ups around protruding parts would be nice. Cell phone
pictures saved as JPG are quick, cheap, and good resolution. you cm make a female mould off the top of your faring to vacuum
form the compound shape. Heat the plastic hanging VERTICALY or you get bad optics. I saw a guy on the internet press his shape into
wet concrete for the vacuum mould. He laid cotton cloth in the concrete as a cushion and some of the metal building sheet seal
compound around the flange edge. From the oven to a canopy took about 15 seconds. I suppose discussing your faring might be
insightful to designer builder homebuilts, but if the moderator wants this stopped, [email protected] .com
 

MotoFairing

Active Member
Joined
Jul 9, 2020
Messages
39
20211206_222103[1].jpg
Stacked foam is logical choice as I have a hot wire cutting table.

I will have to test clearances and decide on fairing then I will go ahead with the foam.

Yes I'll have a wing to mount front and rear lights for visability.

I have no plans for camera operation, I'll need to make a windscreen.

Yes landing gear will be needed, I'm unskilled. I will build and test single and trouble telescopic landing gear. Also test suspension landing gear.

Thanks for your input.
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
Motofaring, The height above the seat is also a needed dimension. Is this for a land speed record streamliner or city streets/ road
race track use. The former runs straight and vertical, the latter needs to lean into turns and have a lot of visibility. Something that
steers needs a constant velocity joint connection to a steerable front wheel or be rear drive. Any objection to making the seat back a
little more vertical to look over the faring? I was toying with the idea of the computer tablet display for forward vision, and NACA ducts
shaped side windows that are also air intakes. These ducts trip the boundary layer into the duct so imperfections in the fit could be better tolerated. Personally I don't like suspension on the balance/landing gear wheels. Any give in support increases lean angle and you are
limited in weight shift to get back in balance. I had a business building custom motorcycles and chassis for them. Do you know how
bicycles and motorcycles maintain balance? The short version. The steering head points to a position on the ground ahead of the tire
contact point. Turning the fork aligns the tire contact patch to travel at an angle, while at the same time being back about 3-1/2" behind
the steering head axis (trail) the contact patch swings left or right making vehicle weight pull the motorcycle over into a coordinated
lean angle. For increased stability on motorcycles we increase the trail dimension by increasing the fork angle. 27 degrees (rake angle)
for road racing. Also to get faster corner entry a smaller front tire diameter (17") is used. If you are thinking looking down through
your bike, a smaller front wheel and lower crank position would help visability. I just couldn't say at what point in seat back angle you
loose power or compromise speed or endurance. Unfared recumbant bicycles have likely zeroed in on the best ergonomics over the
last 30 years or so. a Random thought....Recess a large boundary layer tripping duct over the upper nose leaving the rear end of the duct
open for air intake and visibility. That couldn't fog up from being in close proximity to a swetty gasping human.
 

MotoFairing

Active Member
Joined
Jul 9, 2020
Messages
39
Motofaring, The height above the seat is also a needed dimension. Is this for a land speed record streamliner or city streets/ road
race track use. The former runs straight and vertical, the latter needs to lean into turns and have a lot of visibility. Something that
steers needs a constant velocity joint connection to a steerable front wheel or be rear drive. Any objection to making the seat back a
little more vertical to look over the faring? I was toying with the idea of the computer tablet display for forward vision, and NACA ducts
shaped side windows that are also air intakes. These ducts trip the boundary layer into the duct so imperfections in the fit could be better tolerated. Personally I don't like suspension on the balance/landing gear wheels. Any give in support increases lean angle and you are
limited in weight shift to get back in balance. I had a business building custom motorcycles and chassis for them. Do you know how
bicycles and motorcycles maintain balance? The short version. The steering head points to a position on the ground ahead of the tire
contact point. Turning the fork aligns the tire contact patch to travel at an angle, while at the same time being back about 3-1/2" behind
the steering head axis (trail) the contact patch swings left or right making vehicle weight pull the motorcycle over into a coordinated
lean angle. For increased stability on motorcycles we increase the trail dimension by increasing the fork angle. 27 degrees (rake angle)
for road racing. Also to get faster corner entry a smaller front tire diameter (17") is used. If you are thinking looking down through
your bike, a smaller front wheel and lower crank position would help visability. I just couldn't say at what point in seat back angle you
loose power or compromise speed or endurance. Unfared recumbant bicycles have likely zeroed in on the best ergonomics over the
last 30 years or so. a Random thought....Recess a large boundary layer tripping duct over the upper nose leaving the rear end of the duct
open for air intake and visibility. That couldn't fog up from being in close proximity to a swetty gasping human.
Road use, something cool and exciting to ride.
Front wheel drive can be a hassle but everything is a compromise, no constant velocity joint in the drive train
With head out design the seat inclination is set that the eye line is just above the knee top so you can see the road.
Head bubbles have been used effectively. I have heard the optics are good. Fairing can be top bottom symmetrical and only make one half plug.
head bubble.png
Left: Head in fairing adapted to head out, compromised. Right: Fairing designed to be head out, optimized.



Yes I have actually just welded up the head tube a couple days ago, 64 degrees, 75mm trail, 215mm radius wheel (16" 40mm tyre).
Seat inclination is a complicated problem to solve, my understanding is that power production in linear, like rolling resistance where as aerodynamic drag is cubic so frontal area minimization should be prioritized over seat inclination.

However drag coefficient is of highest importance because you can improve it by 100 times but you can only improve frontal area by about 2 times.

There are various options for ventilation, I am considering fan forced ventilation at the nose and exhaust on the trailing edge. In velomobile racing, some teams were gaining a 10% increase in speed due to using RC plane propellers on the nose for ventilation. They were subsequently banned but that does not have to stop me using them.

With the wheel openings and door sealed a lot of air could be forced through the fairing cooling me and propelling me forward. I would use ear plugs.

Ok time to weld.
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
MotoFaring, Actually..... Making a symetrical plug does not have to be a compromise. Looking at the ETA sketches you posted, if the
parting line of the tub and lid started from the leading edge stagnation point and passed thru the mid height of the faring at the
shoulder station that would work. The wheel farings would be a bolt on addition when making a tub and left of making the lid. A canopy
would go over a cutout in the lid. Make the plug a little long and trim the tail for the optomized "cool" factor. I have an idea on
ventelatiuon with insignificant drag penalty. The RC motor idea is making non human powered thrust so if you have tech inspection
that is a non starter. Question does the pedal connection have to be chain and sprockets. A cyclonic linkage applies force to more
than 180 degrees of crank rotation while the pedal sprocket is more like 120degrees power transmission. Without a CV joint you
would have to not pedal anytime you are in a curve so as not to derail the drive chain. A monofork with a CV joint off a car steering
wheel you could pedal anytime. Does either road wheel have suspension planned?
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
MotoFaring, Just a quick loft to see if we are on the same planet. This is the top half of Eta mirrored. The front wheel is not a 16" here. The cross section is an elippse. The tail is larger, and I left off the front wheel faring because it is easier to just make it out of foam. There are inconsistancies in the loft around the nose which require adjusting some control points. Motofaring5.jpgMotofaring4.jpgMotoFaring3.jpgMotoFaring2.jpgMotoFaring1.jpg
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
MotoFarang, The whole thing can be scaled up or down, well probably not down, or scaled longer, wider, or higher in any combination
up until it gets sliced and diced. Minimizing surface wetted area is your goal. The tail of the shape may have suction in the air holding
you back. If so get out the speedbore bit and bore some holes. Are you familiar with tuft testing (bits of yarn taped on to check
streamlining) that can be done with the thing up above a trailer towed by a pickup truck. And a clear plastic tube held just clear of the
surface (manometer) to check for pressure or suction at questionable points. The rear wheel faring can also be sliced foam.
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
MotoFarang, Just to show all ideas are not good ideas. The dog snarled at this one. The idea was to put a NACA duct cutout on the nose
for cooling air and as a view outside. It would have been cut out of the faring and the back end tilted down leaving a viewport. Looks
alright from top or head on but butt ugly in profile.MotoFarang6.jpgMotofarang9.jpgMotoFarang7.jpg
 

MotoFairing

Active Member
Joined
Jul 9, 2020
Messages
39
I was thinking of a symmetrical body with zero angle of attack, the windscreen could be a blown head bubble, a flat wrap plastic or no windscreen. I would want a windscreen.
cuda-w-iowa2006-4_360.jpg0433F815-EF47-449E-A3C2-2E2431BA1BF6-3241-000005466C34FB09.jpgwhpsc2002-sprints-kyleedge.jpg
Cuda-W, Sean Costin's ?, Kyle Edge

With your example I can see how the symmetrical body construction would work. It does look very striking.

With a symmetrical airfoil in ground effect there can be problems. The Orion, mitigated this by raising the body high off the ground, the Cyclops lowered the angle of attack and had to fill in the void at the back to stop separation. The Orion also had separation at the back and used vortex generators to keep the flow attached. If the shape is good, no need for vortex generators.
Orion.png001_sm.jpg078_sm.jpg
Orion, cyclops.

Ventilation, I am aware that favored places for ventilation ducts are in high pressure areas such as the stagnation point on the nose and the area just before a head bubble. I would not want to break the silhouette with a vent. It gets hot here in Australia and ventilation would be needed for some comfort, there is no precedent or established thrust testing for ventilation fans on bicycles, its a grey area.

U-joint, I saw a student project that used a u-joint in the way you describe to keep the chain straight while turning. In the current iteration I am using standard FWD recumbent drive train. There are some fancy drive trains used but that will be for the next iteration. I have a lot to comprehend as it is so one step at a time.

Suspension, suspension will likely be needed as speeds increase. Future iterations of the frame will likely include this.

That's a pretty cool looking loft you have there, if the void at the back could be filled it could be really fast.
external-content.duckduckgo.jpg
White Hawk

I am a bit worried about the windscreen.
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
Motofarang, I hope to do an attachment rendering of the cyclonic drive I was thinking about. As far as lifting bodies with airfoil shape
they really don't make lift. The airfoil shape mainly provides laminar flow in 3 dimensions. The Eta bike published CFD analysis of their
faring which looks really clean, and they did go 86 MPH plus. The negative angle of attack if it has any effect at all it would be downforce.
The rear wheel faring has a 3" radius fillet and that causes a strange render. Actually as long as the faring would clear a sprocket cluster
it can be a lot flatter. Let me do a zero AOA version in a day or two also with the same top and bottom plug. I take it you want to do
away with the tail?Motofarang 13.jpgMotorarang 12.jpg
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
I did different left and right sides one has the eta shape and the other is more rounded. wetted area is increasing. This one
wouldn't be so ugly if we could lower it a couple inches, Any idea what lean angle you want?
 

MotoFairing

Active Member
Joined
Jul 9, 2020
Messages
39
I did different left and right sides one has the eta shape and the other is more rounded. wetted area is increasing. This one
wouldn't be so ugly if we could lower it a couple inches, Any idea what lean angle you want?
45 degree lean angle. Not that I will lean that far but touching the road means crashing.

Here is an example, I think the fastest symmetrical streamliner Kyle Edge.
IMG_1308.jpg
IMG_1295.jpg
Kyle Edge

Add a head bubble and you get Cuda-W

A cambered shape looks better but Kyle Edge was faster than Vertual Rush/Vertual Edge.

263721308_318372850133248_55379723803727439_n.jpg
Vertual Rush/Vertual Edge

I am using cut down 140mm crank bicycle cranks, pedal box should be pretty small.

The more the main body prevents separation at the rear the easier/smaller the rear wheel fairing is to make.

Do you think the rear wheel fairing could prevent separation in your design?

A horizontal cross section would have to be similar to the airfoil shape without sharp transitions.
 
Last edited:

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
Motofarang, Separation comes from exceeding 7 degrees from free stream airflow. Separation starts at the trailing edge and progresses
forward having unattached/turbulent flow. None of these shapes just looking at them should have significant separation. Aircraft wings
change their angle of attack to change lift and at some angle typically above 13 degrees separration goes into stall conditions. Your angle of
attack is constant with the most disruption to the boundary airflow being roughness of the surfaces. Things like dead bugs and roadrash scratches. Not using CFD analysis I would go for what we call "ramp appeal" and make a nice looking shape that you like and looks
fast just sitting parked. Something someone would like buying a copy of.MotoFarang19.jpgMotofarang18.jpgMotofarang17.jpgMotoFarang16.jpg
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
Motofarang, Instead of thinking out of the box we can reshape the box into a sphere or dodecahedron. Going from complete sanding to minimum sanding and retaining top the same as the bottom with whetted area maximized. The dog gave a tail wagging, tail slapping on the last one, this one he carried off my beer.MotoFarang21.jpgMotofarang20.jpg
 
Top