Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by nickec, Jan 29, 2014.
See the link below.
There's a whole list of issues with that one. Actuation forces and drag when open are just a few of the issues.
Above version has fixed rear section. Less drag when open - than first version. Lower actuation force - than version in post 1.
Other variations possible.
There is not much more drag by leave part of the wheel out. Why go through the trouble.
If you're worried about the drag of the wheel exposed below the pant, what about attaching a stiff bristle brush? It can be just forward of the wheel, projecting at an angle toward the wheel and ground (like an air dam); since it is a brush, it can extend to touch the ground or wheel without detriment, as long is it doesn't touch both at the same time (to get pulled under hte wheel on the ground). Alternatively, a brush can be installed around the perimeter of the pant opening, extending inward toward the wheel to completely close off the gap but still allowing the wheel to roll.
For those who missed it, we had an interesting discussion on lower-drag wheel pants a few months ago. Here it is.
I think the gaps around the wheel in a typical installation probably do make for a lot of drag. The trick is to find a way to make things smoother without introducing more complexity or hazards than it is worth. I think some kind of fabric "window shade" that pulls over the exposed portion of the wheel/tire might offer a good combination of low weight, simplicity, and "forgiveness" if the thing is closed when the airplane touches down. The brushes also seem very low risk and easy.
Thanks for the link Vigilant1.
It looks like my suggesting of a brush seal is nearly identical to Toobuilder's story here:
How do you brake (well, cool the brake discs) if you completely seal off the pant?
We would complicate it further by installing a cooling system. Maybe we could design it so we get more thrust out of the heated air, like the silly stories about the P-51's cooling system. Except we would direct the thrust backward so as to aid braking.
Most airplanes have plain old wheelpants for good reason. Anything more complex isn't justified by the small gains in drag reduction and the large gains in weight and complexity and tendency to fail in the hostile environments a wheel encounters.
Retractable gear makes more sense.
There I disagree. Folding away the lower half of the pants seems to solve all issues of both retractable gear (weight, consequences of failure, trouble in sealing gear doors) and those of tighly streamlined pants (brake cooling, filling up with dirt/wet grass, access for maintenance), for as low or lower drag as either.
Posted about this on the "tailless model characteristics' thread --gear doors in pant are easier a la Bede -only need cooling when they are open . Measurements with recumbent bicycles showed that air leakage around a wheel opening WAS significant in terms of drag and the same was found with solar challenge vehicles (the Delft Uni "Nuna" was it ? should be able to ask about their results. )
Yeah. Every time you seal something, you gain a few knots. Pretty soon, your airplane can go supersonic. :nervous:
Hahahaha. This has to be the funnest post today.
In some radio control model airplane competition formats the rules stipulate a fixed non faired undercarriage.
If drag is important, like in pylon racing, the competitors first select the minimum number of wheels allowed.
Then competitors start playing with the wheel size. Because of this the rules usually specify a minimum wheel diameter. If the minimum width is not restricted the entrants chose very narrow wheels. Therein lies an important detail, a very narrow wheel might have less drag than a wider wheel even if it for practical reasons do have to have a greater diameter.
One of the issues of very narrow tires/rims is stall due to yaw. A biggie on the Nuna (they got fwd thrust from a sidewind...), but a very thin cover (like on a bicycle wheel) will stall with very small yaw angles, causing a lot of extra drag.
What about gear strut fairings? Do they cause a lot of drag from a sidewind?
Just a guess here, but as long as they are not too wide, I would think not. Fairings would normally be used on round tubes, and since round tubes already generate significant drag, the addition of a little more area will probably not have a notable effect on side load.
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