# Is there a speed needed to achieve flight?

Is there a minimum speed needed for flight (universally)? For example, if something was going 10 miles per hour, could it achieve flight? And by flight I don’t mean throwing a paper airplane, I’m talking about the item going to that speed, then flying.

Is there a formula for calculating the speed needed for flight?

• You may want to narrow this down a bit. Helicopters, lighter than air ships, and VTOL aircraft can achieve flight with 0 forward speed. If you are strictly asking about heavier than air, fixed wing aircraft the answer is different. – Dave Mar 20 '18 at 21:35
• Definitely a legitimate question even if it appears to be a beginner question but I agree with @Dave here that it could be narrowed down a bit. – dalearn Mar 20 '18 at 21:56
• The pedal-powered Gossamer Albatross crossed the English Channel (22.2miles) in 2.81 hours meaning that it had an average speed of just under 8mph. So to your point about 10mph, absolutely you can achieve flight below 10mph, not terribly practical flight in terms of speed, carrying capacity or range but technically and demonstrably possible. – AndyW Mar 21 '18 at 10:29
• It depend how you define speed, aircraft measure their speed relative to the air since this is handy to know when computing the lift generated and stall speed. However humans tend to be more interested in groundspeed, so the distance the aircraft travels over the earth per unit of time. Airspeed vs Groundspeed in practice: youtu.be/WPyCywd4o5E?t=43s – Brilsmurfffje Mar 21 '18 at 14:53

There may be an ultimate lower bound, about where the ratio of random air motion to forward motion is near 1:1. But that is an extremely slow speed.

I've seen competitive balsa-wood gliders, weighing just a few ounces, achieve flight from a rubber band, going less than 1 mph, or a slow walking speed.

If the craft is light enough, the wings are big enough, and a little air is moving over them, lift is generated.

• Thanks, sorry if it wasn’t detailed enough. I’ll my best to detail it. Say an item was going 10 miles per hour, had wings, etc, basically an airplane (except small enough to fly) could anything with the correct wingspan, etc, fly under its circumstances? – Jackson Mar 20 '18 at 23:12
• m.youtube.com/watch?v=ZqNEoeOKH8s – Greg Taylor Mar 21 '18 at 9:42
• or this one – qq jkztd Mar 21 '18 at 10:36
• This is exactly what I was looking for, thanks! – Jackson Mar 21 '18 at 21:24
• Not even 'a few ounces': the F1D planes (like in the second video in the comments) weigh on the order of 1 gram! – Zeus Mar 22 '18 at 3:54

I suppose the most basic formula for flight is $F=ma$. Whether flying or not, your aircraft feels a force called weight (m is the mass of your aircraft and a is the acceleration felt due to gravity). In order to fly, your aircraft needs to create enough lift to equal or exceed the weight. The formula for how much lift is created is $$L = \frac{1}{2} d v^2 s C_L$$

L = Lift, which must equal the airplane's weight in pounds
d = density of the air. This will change due to altitude. These values can be found in a I.C.A.O. Standard Atmosphere Table.
v = velocity of an aircraft expressed in feet per second
s = the wing area of an aircraft in square feet
CL = Coefficient of lift, which is determined by the type of airfoil and angle of attack.

Check out this video for a more detailed explanation. Your formula is at 4:45

NASA page with more details: https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/lift_formula.html