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Bell Model 409 / YAH-63 attack helicopter (AAH contender)

Stargazer2006

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Thanks to you all for the great recent posts! :)
 

yasotay

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Having had opportunity to see YAH-63 up close I can tell you the huge blades were probably the heaviest wide cord blades I have seen. Then they were designed to take multiple 23 mm and keep working. I have an alternate idea on the jettisonable ammo drum. Given that the helicopter was design to hover and shoot at Soviet tank divisions go the a refuel/rearm point and repeat, the jettisonable drum might have been a proposal for rapid rearm. I say this because at the time of this effort US Army helicopters only flew at nap of the earth. Time between engine fail and landing was minimal.

I agree that two blade systems are usually lighted and with the lift from the wide cord probably meant slower rotation speed and less transonic noise from the tips.
 

Kiltonge

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JohnR said:
What; if any, was the advantage/disadvantage of using a two bladed rotor?
My aerodynamics are second-hand but I believe the factors are:

1. Gives a more solid disk and hence more lift than multi-blade of equivalent diameter: better for hovering and low-speed but poorer at high-speed
2. Less drag
3. Less complicated hub, very useful for maintenance and reliability

and as yasotay points out:

4. Greater ballistic tolerance as the individual blade structures are larger

This diagram shows the 214ST's huge 33-inch-chord blades well. The only hubs more simple than that are the rigid and semi-rigid hubs on Eurohelis.

http://www.flightglobal.com/pdfarchive/view/1979/1979%20-%202449.html

and the 409 had 40-inch-chord!


Edit: also, high inertia for auto-rotations!
 

flateric

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https://apps.dtic.mil/dtic/tr/fulltext/u2/a125642.pdf
 

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Mark Nankivil

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Good Day All -

I have become the happy and grateful caretaker of a significant number of 4x5 negatives of models that were tested in the LTV/Vought Low Speed Wing Tunnel (LSWT) along with a number of the test reports. As I sort thru the whole lot (guessing 4,000+ negatives), there is plenty there to share as they get scanned and identified.

Here is a YAH-63 wind tunnel model (Bell is just up the road from Vought - makes sense they tested there) along with different components of the airframe.

Enjoy the Day! Mark
 

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AeroFranz

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Very cool. Those are all hard components to get a good indication of the drag coefficient (lots of separated flow).
Makes sense to do a wind tunnel test to refine the assumptions.
 

yasotay

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In this case it was all fat and slow.
 

yasotay

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From Dr. Mike Scully's Book (Adventures in Low Disk Loading VTOL Design, NASA/TP—2018–219981)

The specification requirement for cruise speed (level flight airspeed at MCP) was 145 to 175 KTAS. The GCT cruise speed for YAH-64 was 141 KTAS; see Table 3 in the AEFA final report [28]. The YAH- 64 Phase II proposal included some modifications to overcome small performance shortfalls so 145 KTAS seemed possible. The GCT cruise speed for YAH-63 was 122 KTAS; see Table 2 in the AEFA final report [27]. The original YAH-63 Phase II (P2) proposal included no performance modifications. We now anticipated a modified YAH-63 P2 proposal with major changes to overcome such a large performance shortfall. This shortfall was a surprise to the SSEB...
While we continued to work on the YAH-64 evaluation and other YAH-63 performance issues, YAH-63 cruise speed now consumed most of our effort.
 
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yasotay

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I am GUESSING it was 2X per C-141.
 
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