According to some source or other (I forget which now) it is theoretically impossible for bumblebees to fly by virtue of their size/bulk/aerodynamic properties. Is this old adage apocraphyal or true? And if its true, how come they do fly?
This story may have originated with August Magnan and André Sainte-Laguë. In the forward to his book Le vol des insectes, August Magnan wrote
Tout d'abord poussé par ce qui se fait en aviation, j'ai appliqué aux insectes les lois de la résistance de l'air, et je suis arrivé avec M. Sainte-Laguë a cette conclusion que leur vol est impossible.
First, prompted by what is done in aviation, I applied the laws of air resistance to insects, and with M. Sainte-Laguë came to the conclusion that their flight is impossible.
(my translation ... please correct if it's wrong).
He is talking about insects, and not specifically bumblebees.
No it's an urban myth. It's impossible for them to fly using a very simple and inappropriate model of wing behaviour - possibly closer to say that bumble bees can't glide like albatrosses
Insect flight is different than bird flight. With insects, the rapidly moving wings, which do a figure 8 sort of motion, generates a vortex tube over the wings. This vortex by Bernoulli principle has less pressure, which permits the larger air pressure underneath to lift the animal up. If one is trying to understand insect flight according to the mechanics of bird or aircraft flight you are then pounding a square peg into a round hole, which makes you conclude bees can’t fly.
I would just like to add something here.
These answers are great but I might have another answer. At first it was indeed a mystery how these insects were capable of flying, but thanks to high speed recordings they found something which investigators didn't concider. The wing motion has a sort of dubble lift feature. By twisting her wings over at the end of each downstroke, the upward momentum is never lost. basically, this means that even when the wings are going upwards, the wings provide upward lift.
(this also explains why bumblebees are so massive, they need a lot of muscle to get at the needed (Ca.) 300 flaps a minute)
I hope this was a complete answer! Cheers.
The key is to correctly take scale into account. At insects scale, the Reynolds number is low, meaning that flow around an insect wing is mostly laminar, not turbulent. Moreover, kinematic viscosity of air is higher than water : at their scale, insects do not fly like birds, they litteraly swim in air.
protected by Qmechanic♦ Feb 4 '14 at 12:46
Thank you for your interest in this question.
Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
Would you like to answer one of these unanswered questions instead?