Nov 152009
No further data than this one illustration. Clearly an early transport helicopter… late ’40’s, early ’50’s would be my guess.
11 Responses to “Bell Model D-18: Early Helicopter”
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No further data than this one illustration. Clearly an early transport helicopter… late ’40’s, early ’50’s would be my guess.
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Definitely early – the vertical separation of the contra-rotating rotors looks far too small – clashing blades ahoy!
Ah – but they aren’t contra-rotating, although it takes a close examination of the blades to tell that. The arrangement is an attempt to increase blade solidity for greater lift with the least development cost and risk. The stabilizer bar appears to be oriented at 45 degrees to both rotors although the pitch link arrangement seems to apply a different input to the top rotor than the bottom one. The open support for the tail rotor to maximize thrust is also interesting.
Look closer at the rotors…they both revolve the same way (counter-clockwise as seen from above).
I have no idea why they would design it that way, unless they were concerned the backwash from the blade would interfere with the lift from the one following it if they were closer than 180 degrees apart.
Maybe you can vary the rotational speed of each set of blades to vary lift?
It uses a conventional tail rotor, unlike a counter-rotating blade design.
Thanks for the enlightenment gents!
It looks to me as if they’ve placed two, two-bladed teetering rotors, one on top of the other, spaced 90 degrees apart.
Using technology they’re familiar with??
Robin said:
“Using technology they’re familiar with??”
Although I’ve never seen this done on a helicopter before, there were some cases where two two-bladed props were bolted together one behind the other to make a four-bladed one, like on the Supermarine Walrus.
I think Tailspin Turtle has this one nailed though; it’s a attempt by Bell to use their two-bladed rotor concept for a larger aircraft without ending up with too wide of a rotor span.
Now, the next step would be to stick two more rotors atop this gizmo, so you end up with eight blades total.
At that point a fifth rotor could be stuck on the tail to handle all the torque. 😀
BTW, anyone else note that although the visibility from the cockpit is outstanding, getting into those seats with almost zero head clearance isn’t going to be easy, and you had better bring along a six-foot-long ladder to even get into the side doors of the helicopter itself?
Tail rotor design is indeed interesting; you can almost picture a rubber or metal drive belt rotating around inside of the two pylons.
> the visibility from the cockpit is outstanding
Note that the seats are on cantilevered platforms.
> you had better bring along a six-foot-long ladder
I would assume that that would be part of the helicopter… a ladder or a ramp unfolds after the doors open.
It looks like there is a lot of wasted space under the crew seats.
Also, there are no obvious air intakes or exhausts on this thing, and it’s even hard to figure out where the engine (piston?) is located…aft of the passenger compartment?
> no obvious air intakes or exhausts on this thing
There is a suspicious grate on the underside, between the fore and aft wheels. The engine might well have been on the underside, witha long vertical drive shaft running through the troop compartment. Shrug.
Regarding the pilot’s seats… are they pretty much vertical when you get into them by leaning back against them, and does the lower half then rise up to a horizontal position?
You get into the cockpit via the door between them, but I’m a bit at a loss regarding what happens next.
It’s a very strange set-up, whatever it is.