WIG Airfoil

[durabol]

I am planning on building a plane that is towed behind a boat. Because
of the low speed (25mph stall) I am planning on using a high lift
airfoil. Some airfoils with high coefficients of lift are: FX72150B
(2.0), FX73CL3(2.25), GOE225(1.9), GOE226(1.9), GOE234(2.0), GOE243
(2.0), GOE244(2.0), S1210(2.25), S1221(2.2), S1223(2.3), S1223RTL
(2.5). This is a link to the airfoils and polars: http://www.kaiyipboxing.com/WIG/INDEX.HTM
I know some of these airfoils are for model airplanes and might not be
suitable. Some also have very thin trailing edges which may be hard to
build. I don't know very much about aerodynamics so I was wondering if
anyone has any opinions.

Brock

[Bob Kuykendall]

On Jun 20, 5:05*pm, durabol > wrote:
> I am planning on building a plane that is towed behind a boat...

Were it I, I'd go with an NACA 23000-series (23012 for 12% t/c or
whatever) and be done with it. Good enough for the 1-26 and 1-23
sailplanes, good enough for the Bonanza and the early Citation
business jet, probably fine for a boat-towed glider toy.

[Brian Whatcott]

durabol wrote:
> I am planning on building a plane that is towed behind a boat. Because
> of the low speed (25mph stall) I am planning on using a high lift
> airfoil. Some airfoils with high coefficients of lift are: FX72150B
> (2.0), FX73CL3(2.25), GOE225(1.9), GOE226(1.9), GOE234(2.0), GOE243
> (2.0), GOE244(2.0), S1210(2.25), S1221(2.2), S1223(2.3), S1223RTL
> (2.5). This is a link to the airfoils and polars: http://www.kaiyipboxing.com/WIG/INDEX.HTM
> I know some of these airfoils are for model airplanes and might not be
> suitable. Some also have very thin trailing edges which may be hard to
> build. I don't know very much about aerodynamics so I was wondering if
> anyone has any opinions.
>
> Brock

The old saying goes, "You don't get nothin' for nothin'",
and I guess this applies to hi lift airfoils too.
Need to take care of surface and profile etc.

Low speed application means less sensitive to (speed related) drag
effects, but more wing area required. If it needs to be compact, you
could even consider a biplane approach - they are helluva strong, but a
little draggy - and here that's not too worrying.


Brian W

[Bob]

On Jun 20, 5:05*pm, durabol > wrote:
> I don't know very much about aerodynamics so I was wondering if
> anyone has any opinions.
> ----------------------------------------------------------------------------

Dear Brock,

The best answer depends on the speed of the boat; if the airfoil is
subject to spray, how long the wing can be and so forth.

-R.S.Hoover

[Oliver Arend]

> S1210(2.25), S1223(2.3), S1223RTL (2.5).
> This is a link to the airfoils and polars:http://www.kaiyipboxing.com/WIG/INDEX.HTM

Yes. But those polars were calculated for a Reynolds number of 2.5
10^6, which is way too high for your application. I did a run with
XFOIL on the S1210 and the S1223RTL with Re=1 10^6, which is closer to
your application. With a 1 m chord, you will get Re=7.5 10^5 at 25 mph
(around 11 m/s). The max c_L is still close, but from comparing XFOIL
results to wind tunnel tests on other profiles I know that XFOIL is
too optimistic. Usually even flapped airfoils don't go beyond a c_L of
about 2. But a normal flap on any of the airfoils you mentioned won't
give you more lift as you would have immediate flow separation on the
flaps upper surface at high angles of attack.

I would look for wind tunnel test data on flapped or other high-lift
airfoils and go from there. If the weight of your airplane and the
intended wing surface don't allow for a normal airfoil, try:

Investigation into high-lift systems such as fixed slats (such as used
on the Fieseler Fi 156 "Storch"), slotted flaps, or, maybe the best
option as a compromise between efficacy and simplicity is a Junkers
flap, which is just another small "wing" installed at a small distance
behind the main wing (Wikipedia and Google should give you some
insight on how this system is laid out and on which airplanes it was
used).

HTH,
Oliver

[Capt. Geoffrey Thorpe]

"durabol" > wrote in message
...
>I am planning on building a plane that is towed behind a boat. Because
> of the low speed (25mph stall) I am planning on using a high lift
> airfoil. Some airfoils with high coefficients of lift are: FX72150B
> (2.0), FX73CL3(2.25), GOE225(1.9), GOE226(1.9), GOE234(2.0), GOE243
> (2.0), GOE244(2.0), S1210(2.25), S1221(2.2), S1223(2.3), S1223RTL
> (2.5). This is a link to the airfoils and polars:
> http://www.kaiyipboxing.com/WIG/INDEX.HTM
> I know some of these airfoils are for model airplanes and might not be
> suitable. Some also have very thin trailing edges which may be hard to
> build. I don't know very much about aerodynamics so I was wondering if
> anyone has any opinions.

Popular Mechanics had plans for a tow behind biplane in the early 70's late
60's - fwiw...

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[cavelamb[_2_]]

durabol wrote:
> I am planning on building a plane that is towed behind a boat. Because
> of the low speed (25mph stall) I am planning on using a high lift
> airfoil. Some airfoils with high coefficients of lift are: FX72150B
> (2.0), FX73CL3(2.25), GOE225(1.9), GOE226(1.9), GOE234(2.0), GOE243
> (2.0), GOE244(2.0), S1210(2.25), S1221(2.2), S1223(2.3), S1223RTL
> (2.5). This is a link to the airfoils and polars: http://www.kaiyipboxing.com/WIG/INDEX.HTM
> I know some of these airfoils are for model airplanes and might not be
> suitable. Some also have very thin trailing edges which may be hard to
> build. I don't know very much about aerodynamics so I was wondering if
> anyone has any opinions.
>
> Brock

Before I'd consider any particular airfoil, what's your Reynolds Number
range?

[Bob]

> Before I'd consider any particular airfoil, what's your Reynolds Number
> range?
--------------------------------------------------------------------------------------------

"Towed by a boat" and "..stall speed of 25mph" pretty well defines
the lower end of the envelop.

Since the thing is a water craft, apparently meant for recreational
purposes we can assume two-place, side-by-side for the load and a
stepped hull, probably with a T-tail. As with most water craft it
probably needs to be designed to allow it to be taken to where the
water is. The need for portability tends to suggest a wide-chord, low-
aspect wing, probably strut-braced to improve it's portability and
ease of set-up, which points us toward one of the low-speed airfoils
developed at Gottingen University during the 1920's... or an RAF-
series airfoil from the same era... or something from the fat end of
the 23000 series...23021 or whatever... but that would probably want a
full-span, all-flying Junkers 'aileron' for control, as mentioned by
Oliver. Brian's mention of biplane wings is a hands-down winner for
strength but becomes a mare's nest when it comes to portability and
ease of erection.

As for getting off of the water and into the air I think the real
problem is getting free of the water without the characteristic 'pop-
up.' In any case, the fact you want it to take-off and land on
water,, plus the fact it is a flying boat rather than an airplane on
floats, means it's going to have to be hell for stout if you want it
to last more than one season.

----------------------------------------------------------------------------------

As always, this Group can over-engineer the thing for you :-) Or you
could just jump right in, whip something out and play with it until it
breaks.

-R.S.Hoover

[Jim Logajan]

Bob > wrote:
> As always, this Group can over-engineer the thing for you :-) Or you
> could just jump right in, whip something out and play with it until it
> breaks.

An old contrarian saying comes to mind: "A month in the lab can save you an
hour in the library."

In this case I say it never hurts to try to sit down and try to make some
estimates, however rough. Otherwise yes, one can always start building
something and after enough trial and error construction and testing
eventually come up with something.

[Capt. Geoffrey Thorpe]

"Capt. Geoffrey Thorpe" <The Sea Hawk @See My Sig.com> wrote in message
...
> "durabol" > wrote in message
> ...
>>I am planning on building a plane that is towed behind a boat. Because
>> of the low speed (25mph stall) I am planning on using a high lift
>> airfoil. Some airfoils with high coefficients of lift are: FX72150B
>> (2.0), FX73CL3(2.25), GOE225(1.9), GOE226(1.9), GOE234(2.0), GOE243
>> (2.0), GOE244(2.0), S1210(2.25), S1221(2.2), S1223(2.3), S1223RTL
>> (2.5). This is a link to the airfoils and polars:
>> http://www.kaiyipboxing.com/WIG/INDEX.HTM
>> I know some of these airfoils are for model airplanes and might not be
>> suitable. Some also have very thin trailing edges which may be hard to
>> build. I don't know very much about aerodynamics so I was wondering if
>> anyone has any opinions.
>
> Popular Mechanics had plans for a tow behind biplane in the early 70's
> late 60's - fwiw...

Close, but not quite right.

August 1967 Popular Science:
"Aqua Glider: A great new sportscraft you can build"

NACA 4412 airfoil

Stall speed 35 mph

Weighs 180 pounds

Designer Bill Skliar

N6498D

Currently in the EAA museum:
http://www.airventuremuseum.org/collection/aircraft/Skliar%20Aqua%20Glider.asp


--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[cavelamb[_2_]]

Jim Logajan wrote:

> An old contrarian saying comes to mind: "A month in the lab can save you an
> hour in the library."
>

Every time!

[[email protected][_2_]]

On Jun 22, 5:32*pm, cavelamb > wrote:

> > An old contrarian saying comes to mind: "A month in the lab can save you an
> > hour in the library."
>
> Every time!

Not every time! You never did the book research and then tried to
apply it ............... only to find out the author didn't have any
real world experience?

Bought an EconoTIG years ago. Wasted money on published (not direct
advertising) "expert" advice.
=================
Leon McAtee
Always on the look out for contrary points of view.

[Peter Dohm]

> wrote in message
...
> On Jun 22, 5:32 pm, cavelamb > wrote:
>
>> > An old contrarian saying comes to mind: "A month in the lab can save
>> > you an
>> > hour in the library."
>>
>> Every time!
>
> Not every time! You never did the book research and then tried to
> apply it ............... only to find out the author didn't have any
> real world experience?
>
> Bought an EconoTIG years ago. Wasted money on published (not direct
> advertising) "expert" advice.
> =================
> Leon McAtee >Always on the look out for contrary points of view.
>

However, he did say an hour in the library, not an hour with a random book.

I have been tricked as well, although in my case, it was a class in
mechanical drafting--in which the Prof prattled on, asserting that he
understood common processes, but clearly had no clue at all how a sheet
metal brake actually stretches metal.

Peter

[durabol[_2_]]

Thanks for the information. I'll choose a conventional airfoil such as
a 4418 and maybe go with a biplane configuration. I wanted to keep the
design fairly simple so I didn't plan on using flaps. The Junker style
flaps seem great for good lift but they also increase the required
angle of attack (the problem with slats as well).

I have some information on a glider pulled behind a boat called the
"Aqua Glider", although I planned on using foam core fibreglass
construction. I want to build a fairly solid structure as I may want
to put and engine on it in the future.

Brock