Presented by Nine Lives Racing
1 2 3 4 5 ... 9
stafford1500
stafford1500 HalfDork
3/27/19 10:59 a.m.
Keith Tanner said:
NOT A TA said:
stafford1500 said:

I ran the cambered plate you listed thru a software similar to what sleepyhead used and was going to post up the ground effect results but ran out of time this morning. It was 2D but would have shown the pressure responses and the leading edge sensitivities in pretty colors for everyone to oh-ah over. Maybe when I get home from the wind tunnel today...

Yes please!

 

Agreed, it would be really interesting and valuable information. Might be worth starting a new thread so that it doesn't get lost in the search for 30" diameter pipe.

Maybe I should do a how-to-read/decide on airfoil sections and sizing build thread, but I suck at keeping up with my own build threads...

chaparral
chaparral Dork
3/27/19 11:07 a.m.

Lower wing loading will allow you to space the ribs further apart, but fabric isn't massless. Extra area certainly hurts with carbon or fiberglass with only a few choices for thickness / # of layers.

For a freestanding rear wing mounted with center supports a lower AR will hurt efficiency because of spanwise flow and separation at the mounts. For a front wing operating in ground effect or a rear wing mounted by the endplates I'm not sure there's a L/D benefit. Check the slope of your drag curve as you go towards max CL - it's nonlinear even before you get separation. 

Operating away from CLmax can allow you to increase lift when you pitch forward under braking, but that's mostly an easier-to-drive improvement than a can-Little-Al-go-faster improvement.

mke
mke Reader
3/27/19 11:29 a.m.

In reply to Robbie :

Those graphs make much more sense.

 Again though the thing I notice instantly is how smooth the airfoil curves are and how not smooth the pipe section design curves are....it could just be the old free software as suggested, but stuff like that is usually a good indicator of problems to come.  Airfoils are not my area of expertise so maybe its fine in this case, but normally when curves are bouncing around it means you have an unstable system that will never behave very well.

Robbie
Robbie UltimaDork
3/27/19 12:46 p.m.

Here's my maniacal test plan for the wing. Hopefully you guys get a kick out of this.

stafford1500
stafford1500 HalfDork
3/27/19 12:57 p.m.
Robbie said:

Here's my maniacal test plan for the wing. Hopefully you guys get a kick out of this.

That will work. May I suggest you also make use of the early data acquisition hardware from the 1910's aircraft world: get a picture of the readings when you get to a set point on your speedometer. Tabulate/review later.

barefootskater
barefootskater Dork
3/27/19 12:57 p.m.
Robbie said:

Here's my maniacal test plan for the wing. Hopefully you guys get a kick out of this.

This is beautiful.

sleepyhead
sleepyhead Mod Squad
3/27/19 1:04 p.m.

In reply to stafford1500 :

for some reason this is tripping me up about reading a vectorized "lift" and "pitching moment" value.  would it be better to rotate around the back, and read the front?

Robbie
Robbie UltimaDork
3/27/19 1:12 p.m.
sleepyhead said:

In reply to stafford1500 :

for some reason this is tripping me up about reading a vectorized "lift" and "pitching moment" value.  would it be better to rotate around the back, and read the front?

Yeah, I have considered that I could also read drag as down force with this setup, since the wing theoretically should produce less drag at lower AoA and therefore the drag would push the rear down ward. But, 1, I really need the wing to be well controlled and I'm afraid of the front coming free and flipping over with force. And 2, if I attach the wing to the car at similar points as I use to test it, those are the forces the mounts will actually see, regardless of whether the force is caused by drag or negative lift. 

Robbie
Robbie UltimaDork
3/27/19 1:14 p.m.

I didn't draw it in the picture but I plan on the test rig to build in a limiter that prevents upward movement at the rear of the wing. 

stafford1500
stafford1500 HalfDork
3/27/19 1:25 p.m.

You are working on first approximations here. In a perfect world your pivot would be live on the balance (scale) and you would record moments as well. Early wind tunnel measurement were made with what are effectively balance beams (weigh beams for the proper name, like scientific mass scales). Add weight at a know distance to ge the wing/plane/model back into equilibrium and you know how much force and moment you are applying thru the pivot. It is just statics at that point. Drag is going to be part of your measurement, unless you determine the neutral pitching moment location (or close to neutral). I mentioned that up thread when I spoke about the CM 1/4 plots from the airfoil data. The general neutral moment point is going to be near the 33% chord location.

Your rig will produce results that are comparable as long as you keep the pivot to loading rod pick-up distance the same (within reason, AOA change will affect it some).

Appleseed
Appleseed MegaDork
3/27/19 2:32 p.m.

Any big box construction store will have the blue foam.  Pink foam is less manly, but works just as well. Google hot wire cutter. That will allow you cut any profile you want. 

sleepyhead
sleepyhead Mod Squad
3/27/19 3:13 p.m.

In reply to stafford1500 :

ok... I figured there was a "this is close enough" argument.  But, I thought there might be some worth in being semi-pedantic questioning... for when someone else comes along and decides to build a similar rig

I agree with limiting it from "taking off"

and, I can't find a picture... but supposedly Burt Rutan did similar back in the '06's to develop his canard setups.

TurnerX19
TurnerX19 HalfDork
3/27/19 3:48 p.m.

In reply to AngryCorvair :

Warning if you use foam core, you must use epoxy resin which is not challenge friendlysad

Appleseed
Appleseed MegaDork
3/27/19 4:06 p.m.

Cover the entire wing in overlapped, cheap masking tape. Then you can use the cheap resin. I wouldn't trust it on an airplane, but would have no qualms about a home made car wing. I've had personal success doing exactly this on a complex shape of a cafe racer seat.

SVreX
SVreX MegaDork
3/27/19 4:18 p.m.
Appleseed said:

Any big box construction store will have the blue foam.  Pink foam is less manly, but works just as well. Google hot wire cutter. That will allow you cut any profile you want. 

This isn’t correct if you are planning to use anything like fiberglass resin over it. 

The box store sell products by Dow (blue), and Corning (pink). These are extruded polystyrene foam. You can’t apply polyester or epoxy directly to polystyrene foam. It will melt. 

You need to use polyurethane foam, or if you are going to use polystyrene, you have to coat it with an epoxy activator like Styrocoat, or a polyester MEK-P product like Styro-Shield. Either of these will create a hard protective shell which can then be resined over. 

alfadriver
alfadriver MegaDork
3/27/19 4:32 p.m.

So can the models used do a multi element wing?  Which should allow the wing to be aggressive and keep the boundary layer still attached ( like what is seen in many Motorsports). 

sleepyhead
sleepyhead Mod Squad
3/27/19 5:07 p.m.

In reply to alfadriver :

xfoil doesn't do multi-elements

I've read some about people pulling single element data out of xfoil for each element and using it to create their own multi-element predictions... but I haven't tripped that far down the rabbit hole yet.  Drela, who wrote XFOIL, apparently wrote a multi-element code... but the license was 5? figures?  Although, that was back at the turn of the century.

but, if stafford knows of some codes that aren't as exclusive... I'm all ears

sleepyhead
sleepyhead Mod Squad
3/27/19 5:52 p.m.

so, a couple of notes on the "Cambered Plate" coordinates...

- these look like they're "rotated nose down ~1deg from the classical definition"... which is not a "big deal", but something to keep in mind.  but it could throw things off as you start to mess with them in xfoil

- It also looks like they've skimped some on the coordinates come out of the leading edge... which might be causing some issues with calculation.

- there's probably room to say that using the 16% camber section would give you more downforce

- if we're assuming a 16" chord length... with 3/4" plywood... then you "section thickness" would end up being closer to 4.7%... while these sections are 5.1% thick.  Which is relatively negligible from the prediction of these sections performance compared to your wing.  However, doubling the plywood, would give us a section thickness of 9.4%.

and, when we combine a double layer section, and 16% camber, and "non-tapered" trailing edge...

which means your downforce has gone from 1.8 to 2.3, and seems to be more gentle in how it changes with AOA.

important caveat: I had to completely redo the bottom curvature of the nose after blowing it up from 5.5% to 8.8% thickness in xfoil... since it became very "droopy" and "out of circle"... 

paying attention to that area when making the wing will pay dividends... and might warrant putting a front "cap strip" of hardwood so the leading edge is easier to shape

Robbie
Robbie UltimaDork
3/27/19 6:05 p.m.

In reply to sleepyhead :

Wow! So did the 2.3 graph come from the red profile nose or the "droopy" one?

sleepyhead
sleepyhead Mod Squad
3/27/19 6:17 p.m.

the red one... although getting to 2.3 has more to do with the thickness change, iirc

the other two plots are the "stock" cambered plate 5.5% thickness 16% and 14% camber sections with non-pointed trailing edges

by making the leading edge more rounded the flow gets accelerated around the front and onto the top "softer"... so it can 'hang on' up to higher angles... but also it won't generate a "spike"... which the others are doing.  it's important to keep in mind that the "stagnation point" on the wing will move backwards along the "lower surface" the higher you pitch up, so the flow has to make it around the leading edge.

1.8 to 2.3 is worth ~50#s on the 8ftx16" wing, at 60mph (~225lb vs ~175lb)... subject to verification

DHBomber
DHBomber New Reader
3/27/19 11:23 p.m.
SVreX said:
Appleseed said:

Any big box construction store will have the blue foam.  Pink foam is less manly, but works just as well. Google hot wire cutter. That will allow you cut any profile you want. 

This isn’t correct if you are planning to use anything like fiberglass resin over it. 

The box store sell products by Dow (blue), and Corning (pink). These are extruded polystyrene foam. You can’t apply polyester or epoxy directly to polystyrene foam. It will melt. 

You need to use polyurethane foam, or if you are going to use polystyrene, you have to coat it with an epoxy activator like Styrocoat, or a polyester MEK-P product like Styro-Shield. Either of these will create a hard protective shell which can then be resined over. 

I've used the insulation foam for a lost core plug to build an airbox. I haven't tried poly or vinyl ester, but West 105 epoxy didn't harm it even while vaccuum bagged. 

 

Appleseed
Appleseed MegaDork
3/28/19 12:01 a.m.

I left the foam intact that way it would support the fibreglass skin. Taped the whole thing in the cheap, sticky original tan masking tape, and then the fibreglass resin and woven mat right over the tape. Did not melt it at all.

GTXVette
GTXVette UltraDork
3/28/19 7:05 a.m.


The Easy to Shape Nose is A Stair Step Leading edge called a Bull nose and are in a few shapes and width's.

alfadriver
alfadriver MegaDork
3/28/19 7:31 a.m.
sleepyhead said:

In reply to alfadriver :

xfoil doesn't do multi-elements

I've read some about people pulling single element data out of xfoil for each element and using it to create their own multi-element predictions... but I haven't tripped that far down the rabbit hole yet.  Drela, who wrote XFOIL, apparently wrote a multi-element code... but the license was 5? figures?  Although, that was back at the turn of the century.

but, if stafford knows of some codes that aren't as exclusive... I'm all ears

So I totally understand the rabbit hole, so this is shallow. Does the model predict where the flow would separate on the back?  If I get my very basic aero understanding right, that would be the area of the split, right?

Matt
Matt New Reader
3/28/19 7:53 a.m.

In reply to stafford1500 :

this would be cool, then i could build a new wing that works and replace the one i built last year!  this is the profile i tried to build, but through the magic of garage fabrication, i can not confirm i have succeeded 100%, but probably 95% true to form...im still not sure on if the end plates are good

1 2 3 4 5 ... 9
Birthdays
Our Preferred Partners
Ik5RySEf1zBraVhGzevq0nZH9bvMUjjvoW8w2OnsPmPHYNDOY500H2YbKOsrxYrx