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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.
 

pegasus

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ugly helicopter very nice thread thank you nice pictures
 

pegasus

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ugly helicopter very nice thread thank you nice pictures
Ugly? You should check out Boeing's entry. :eek:
the thread is good, i like it very informative but the helicopter is not beautiful, true is not that ugly but for an american design it is ugly, the Cobra, Apache comanche and Cheyenne are nice looking, personally i like more the Augusta Mangusta, but it is a nice thread i like it and well still this helicopter is a theme i will look every time they post new pictures like Mirages, F-16 or Sukhois or MiGs thread

I think this is truely beautiful thanks it looks like an Apache
1568715078026.png

this is nice looking, S-67

1568715442137.png

the AH-56 was ok


1568715532944.png


but this looks too coarse YAH-63

1568716034742.png

1568715702581.png
 
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