Hey

Anyone knows some freeware program, for calculating stallspeed, by input data as airfoil, span, corde and weight?

Or - can anyone calculate expected minimum stallspeed for me?

Known data:
Airfoil Clark Y 13%
Span 276cm / 108"
wingcord 43cm / 17"
total area of stab 10dm2 / 155 inch2
expeted weight 2kg / 70 OZ


the project is a 1/4 Cub in depron. Pictures can be seen here ( sorry, all written in danish)
[link]http://www.modelflyvning.dk/forum/showthread.php?t=59991[/link]

http://adamone.rchomepage.com/cg_calc.htm

You need to determine what is the minimum air velocity that will sustain the weight of the model in horizontal flight, solving V from the lift formula.

Since that flight condition will be possible only at the maximum practical angle of attack (just before stall starts), the max CL needs to be found and used.

Vstall = Square root [ 2 * weight / (wing area * air density * CL max)]

For exact results, you need to know the maximum coefficient of lift for that wing at the speeds it will fly.

Then, you need a more exact weight than the estimated one.

http://en.wikipedia.org/wiki/Lift_(force)

As lneqban says, but for model airfoils, Cl max can be taken as 1. It don't seem to matter what shape the foil is, at our sizes there is little to choose between them so far a Cl max is concerned. Most of the airfoil data available is for full size sections and does not relate well to model sizes, for example. Cl max for this sort of wing occurs around 14 to 16 degrees AOA, but the model foil will stall around 8 to 9 deg. AOA so will never reach the published Cl. The other question I would raise is; what use is the information going to be? Unless you have very accurate telemetry from the model to you, you will have no idea how fast the model is flying. Knowing the stalling speed will not be much use otherwise.
Evan, WB #12.

According to the calculator my 150 sq inch, 14 oz planes have a stall speed of 18 mph as they glide home.

great calculator!!
This I gotta see

I've got a whole fleet of these planes in the same ballpark for size and weight with .049-.061 engines and I've never come close [as far as I can tell] to stalling any of them.
I must be a lousy judge of what 18 mph looks like, but these planes just plop down in the grass at what looks like jogging speed.

Thanks for replys.
I just wanted to know how slow it will proberbly fly. So I could get an idea about, is it possible to fly in our gym
I didnt need to know it very precisly.

Anything above 10 mph is simply too fast
try running as fast as you can alongside the model -in the gym
We have a group which fly indoor types in small medium and large gyms
anything above one ounce per sq ft loading -is simply too fast for compfortable flying
Dial up an indoor aerobatic contest - watch the speed of these models . The newest types are very slow - now imagine running along side one - how fast can you run.

I'm a little slower than Usain Bolt, who has clocked nearly 28 mph during the 100 M dash.

One oz/sq ft seems a bit on the light side. Two oz/sq ft is slow enough for gyms.

Well - speed isn´t necessarily a big problem for indoor. We use to have fun flying speedflying with wings that flyes much faster than this one will do.
With a speed of ~5m/s it will take 24sek to fly a round - thats no problem.

And if a 12ft Cub can fly indoor, a 9ft can too

[link]http://www.youtube.com/watch?v=AQMjG05HqJw&feature=related[/link]

Apparantly we all have our own ideas as to what a desireable speed indoors looks like
For a referrence point - a stock VAPOR on a good battery -That is "about right "

Nice Cub Polle!


While I agree with this in general terms for smaller models (in fact Clmax can be as low as 0.6-0.7 due to low Reynolds numbers) bear in mind that with a span of 43cm at 5m/s the Reynolds number is almost 150k.

I have experimental data from Selig which shows Clark Y acheives a Clmax of 1.3 at Re 100k.
Using Clmax of 1 won't be far off as a conservative starting point, but CL1.2ish may be possible - ie slower still.

I have a feeling that the airfoil on Polle's Cub is not proper Clark Y though? Maybe flat bottomed 13% instead...

Maybe Yak, but then this OP wants to fly indoors in a hall, and knowing the stall speed ain't gunna be any help at all, for one, as stated, without really accurate telemetry from model to pilot, he isn't gunna know what speed it's flying, and two, if he wants to turn around at the end of the hall he will have to be travelling somewhat is excess of minimum, otherwise the thing will just flop on the floor. Your Reynolds might be good at 5 m/s, but I bet he wants to go a bit slower than that...If the object is to fly this thing indoors, then perhaps the questions he needs to be asking is how to build the thing really light, with adequate strength.
Evan, WB #12.

Well according to the figures provided, the stall speed is going to be about 4.8m/s so he's not going to be able to go much slower! I'm with you on reducing weight... for indoors anyway.

Trying to resolve the "indoor" problem with airfoil studies is pretty much a waste of time
The setups which actually work, are first off, minimum weight (wing loading)
next they must be capable of flying at EXTREME angles of attack with no floundering.
The VAPOR is still the best commercial example of what can be done and with some time spent flying one at all speeds - the parameters needed become obvious-unless one chooses to believe the same effeciency requirements for large aircraft apply.
They don't-
If you are serious about this - watch some of the video coverage of indoor precision aerobatics . There are plenty of examples on UTube etc..

The calculated stuff is simply wrong. A case of GIGO
The VAPOR will fly easily at less than ONE meter per second- held at a high angle of attack.
That's at 4350 ft elevation .
we probably have 50 hours flying time on this simple model design. Our group meets during the week for social indoor flying - usually a half dozen VAPORS cruising lazily or looping etc..
Trying to duplicate the same speeds with conventional looking stuff simply has not worked - the weight (wing loading) simply gets out of hand.
IF- you make the model larger, the loading can increase.
An example : the VAPOR is about 60 sqin and weighs 17grams
A GOOD, competitive indoor aerobatic setup is 300 sq in and weighs under 5 ounces

The wing loading of 1-2 ounces per sq ft is where you need to be .
Airfoil? just a plate is fine.

The speed of 4.8m/s refers to this Cub model. NOT your Vapor.

Sorry for my bad english, but what is an OP?

Yak> the airfoil is not flat bottomed.

About weight, I offcorse agree, the lighter the better. The "Shocks" we flies today is about 130-140g, and thats fine. But - when we started on those planes, the weight was about double-up, and they where still flyable and easy to make lots of aerobatic in a small area.
And about learn to build light, this plane was NOT intended for indoor - trying fly it indoor is just a result of provocation from my flying-"friends"

Years ago i build this "Cub" in depron. It was 63 inch, and with a .50 Irvine the weight was 77 Oz. There was no problem flying in the area of handball court.
An indoor handball court is huge

It means 'Original Poster' - in other words you! [8D]

The Cub is looking cool!

Oh . thanks

And - thanks for your compliment!

A few more explanations on this aircraft and its construction / weight:
It is built with the aim to fly outdoors with a 800w setup. For the casual flight, but also for 3D.
If I only was going to fly indoors, it was obviously built differently

And I just wanted an indication - will the speed be 10 or 20mph.

easily 20 mph and less if you have power enough to hold a higher angle of attack
Slow flight is not all about stall speed - the plane will still fly in a stalled attitude IF you have thrust loading high enough to keep it up
yesterday when we were doing indoor flight (Friday meeting is in a very large gym). We eyeball measured forward speeds -Our group includes Physics prof, Structural engineer Professional model designer etc., and we all agreed that the little VAPOR could fly , slightly vectored at aprox 1 meter per second.
level flight brought the speed up to closer to 4-5 m per second. ( lift /drag change makes big difference).
My own, old Seniorita which weighed 3.5 lbs -800 sq in., would fly outdoors in the under 20 mph speed range
Just some comparitive info-
Your own results may vary

This evening the Cub was in the gym. We got access to 2 gyms, and this was the small of them, so I was just going to try out the groundhandling, or should it be floorhandling in this case? Perhaps let it rotate and lift a wheel.
At very slow speed the tail lifted, and I almost P in my pants when it short after was airborn - that wasn´t intended. Here showed up a problem: the long offrun when it touchdowned again.
I did a few of these short take-offs and touchdowns, and that should have been that.
The other guys had other opinions, and it went out with some half and full cirkels.
It was all with shaking knees and fingers, and true chicken flying, but it flew.
I´m sure that when I get the nerves down, and use a little time to learn to know it, it will be a cool indoor model.
Videos are incomming - guess they are in the air tomorrow.
Great evening - the arms are still up

Video is up.
All handling on this video I used 770mah, from 2200mah pack.
Its the raw video, so 13min´s.
[link]http://www.youtube.com/watch?v=_oex-_ZzWVM[/link]