How Much Lift Do Houseflies Get from Air Displacement?

[pervect]

What would the appropximate mass and volume of a housefly be? For context, I'm wondering about how much lift they get from buoyant forces - it's fairly obvious that they are heavier than air, but do they get any significant "lift' from the air they displace, or is it negligible in comparison to their mass?

 

[Moonbear]

Maybe you should ask these kids:

Head of Science, Dr Angus MacEwan explained, "We are delighted that the Science Department is being recognised for the good work that is being done in our school. For example, in the last few years A level Physics students, working with the support of Dr Dunn (Head of Physics) have competed in the National Physical Laboratory's National Measurement Awards and created a simple balance to measure the mass of a housefly.

http://science.rolls-royce.com/media/release.php?id=12


Okay...I don't know if this is right since it's something off of someone's powerpoint slides that are online (linking to the html version I hope).

Typical housefly:

Adult size: 5-7 mm = 0.005-0.007 m

Adult mass: 12 mg = 0.000 012 kg

Lifespan: 7 days = 604 800 s

http://72.14.203.104/search?q=cache...+of+a+housefly&hl=en&lr=lang_en&client=safari

As for the lift part, this might fare better in physics or engineering. I'll see if any of the other mentors thinks this thread can find a better home elsewhere here.

 

[Ouabache]

The question requires some knowledge of principles of bouyancy. I did not recall the scientific explanation of buoyancy but have certainly experienced it. [As a scuba diver, I learned to manipulate my bouyancy using my lungs, an inflatable vest and dry suit]

So I looked it up, and here is what I found: An object's buoyancy (the upward force exerted on it by a fluid) is exactly equal to the weight of the fluid it displaces. Not only are liquids fluid, air also behaves as a fluid.

The following http://www.scientificamerican.com/print_version.cfm?articleID=000DF125-5545-1C75-9B81809EC588EF21, does not address a housefly directly, but a close cousin, the fruit fly. It lends some insight into their lift mechanisms.

(paraphrased)
Biomechanic scientists have tethered tiny flies and tried to measure the forces generated. Other researchers have photographed their beating wings with strobe lights. But the aerodynamic mechanisms of insect flight have been elucive. By carefully designing a scaled model of a fruit fly's wings, researchers have simulated its movements and gained significant insight, how lift forces are generated. It turns out that flying insects utilize several distinct and interacting methods to gain lift to counter gravity. Three have been defined as delayed stall, rotational circulation and wake capture.

Delayed stall creates lift during the up and down portions of the wing stroke and may be the primary lift mechanism. The insect moves its wings in a way that creates air currents known as leading edge vortex that forms along the top surface of the wing and generates lift.
Rotational circulation As insect wings near the end of its stroke, it rotates backward, creating backspin and lifts the insect, analogous to lift generated when backspin is applied to a tennis ball.
Wake capture: As a wing moves through the air, it leaves trailing vortices of air behind it. If the insect rotates its wing before starting the return stroke, the wing is buoyed up on its own overtaking wake. Insects can get lift from the wake even after the wing stops.

Different insects use these mechanisms to varying degrees. The housefly more closely related to the hover fly than a butterfly; may share the same degree of following mechanisms. They appear to use very little 'delayed stall' and make greater use of 'rotational circulation' and 'wake capture'.

 

[Gokul43201]

From Moonbear's numbers, the density of a housefly appears to be about 100 kg/m^3. While that's low, it's still 80 times more dense than air, so buoyancy will reduce the effective weight by only a little more than 1%...fairly negligible, methinks.

 

[pervect]

I'm mainly interested in the measurements of the housefly, which I tried to google for without much luck (thanks Moonbear). The volume estimate is a little uncertain from the figures given, but a sphere 3.5 mm in radius (7 mm in diam) sounds like a reasonable estimate (probably a bit on the high side, actually). This leads to Gokul's conclusion for the importance of buyoant forces.

One thing that puzzles me is the use of mg in the referenced URL - it looks like they mean micrograms, not milligrams.

The physics of calculating the buyoant forces doesn't need any clarification in my opinion, several posters here have already noted that one need only apply Archimedes principle. The density of air at STP (standard temperature and pressure) is also fairly easily found to be a bit over 1 kg / m^3 at STP.

The interesting part of the question in my mind is what the dimensions and mass of a housefly actually are, which seems to me to be a biological question (which is why I posted it in the biology forum).

 

[FredGarvin]

I am definitely not an expert in this field, but I'll throw my 2 cents worth in. It seems that insects are, pardon the cliche, in a different paradigm when it comes to how they produce lift and control it. I always wondered if insects of such small mass take advantage of natural convection, despite unnoticeable levels on our part, to generate lift.

Leading edge vortex (delayed stall) is talked about for low Re in this paper which is pretty interesting:

http://www.math.nyu.edu/faculty/peskin/papers/Miller_Peskin_2004.pdf

This one was also pretty interesting:
http://w3.impa.br/~jair/1954.pdf

Does anyone have a good swag as to just how many different species of houseflys there are? Pervect is right on the lack of physical data for these little buggers. I could find average lengths but that was about it.

 

[Moonbear]

One thing that puzzles me is the use of mg in the referenced URL - it looks like they mean micrograms, not milligrams.

I don't think so. They start out with kg, 1/1000th of a kg is g, and 1/1000th of a g is a mg. So, there's no confusion that a mu turned into an m. 12 mg makes sense to me for something that size (I wouldn't have posted something from an uncertain source if it sounded orders of magnitude off). 12 micrograms would be like a speck of dust for most substances.

 

[Moonbear]

Does anyone have a good swag as to just how many different species of houseflys there are? Pervect is right on the lack of physical data for these little buggers. I could find average lengths but that was about it.

To the best of my knowledge, when you refer to a housefly, it means one particular species (though there may be different species in different regions that get called the same thing...that's the trouble with common names in biology, it's imprecise). When you refer to just flies, then I don't have a clue..it's a LOT, and they have quite a range of sizes, everything from those fat horseflies and botflies, down to little gnats and no-see-ums.

 

[Gokul43201]

One thing that puzzles me is the use of mg in the referenced URL - it looks like they mean micrograms, not milligrams.

I'm with Moonbear here. The weight is in milligrams, not micrograms.

If it were in micrograms, your average housefly would have the density of helium gas !

 

[pervect]

Duh. Ok. Yep. (I hate it when I make silly mistakes like that).

 

[Ouabache]

When you refer to just flies, then I don't have a clue..it's a LOT, and they have quite a range of sizes, everything from those fat horseflies and botflies, down to little gnats and no-see-ums

That's right, the common housefly is just Musca domestica. The Order http://www2.ncsu.edu/unity/lockers/ftp/bwiegman/fly_html/diptera.html is for all true flies.There are close to 120,000 identified flies.