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

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.
 
JohnR said:
What; if any, was the advantage/disadvantage of using a two bladed rotor?
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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 - 2449.html

and the 409 had 40-inch-chord!


Edit: also, high inertia for auto-rotations!
 
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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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.
 
In this case it was all fat and slow.
 
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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Great photos thanks fightingirish!! :p

Does anyone know if the 'air transportation capability' of the AAH RfP was for a Lockheed C-130 or was it for the C-141?



Regards
Pioneer
 

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I am GUESSING it was 2X per C-141.
 
ugly helicopter very nice thread thank you nice pictures
 
sferrin said:
pegasus said:
ugly helicopter very nice thread thank you nice pictures
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Ugly? You should check out Boeing's entry. :eek:
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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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I always wondered about the tail rotor driveshaft. Whys is it exposed? granted, a thin aluminum cover around it is not going to protect anything from ground fire, but other Bell helicopters aren't like that. Was it for maintenance?
 
The aircraft was massively overweight. While I am not sure this was the cause (ridding the aircraft of any weight not critical), it certainly could have been the reason.
 
Brochure attached as PDF. Interesting drawings are attached as JPG.
 

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second brochure attached.
 

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Abraham Gubler said:
There are two good reasons to have a jettisonable ammo drum on an attack helicopter. First and most likely reason it was installed was to provide an instant reduction in aircraft weight in case of an engine out emergency. This would function like dumping pylons and stores and jettisoning fuel to lower weight in an emergency.

The second reason is perhaps they were thinking of installing a caseless propellant gun? USAF required a jettisonable ammunition supply for the FX (F-15) project and its initial caseless 25mm gun requirement. At the time of the state of art of caseless propellant meant the ammunition was more vulnerable to explosion from excessive heat and damage compared to conventional ammunition. So the fighter was required to be able to expel the entire magazine if needed. This is however a much harder thing to do in a fighter jet with far more extreme performance than just a comparatively lumbering attack helicopter.

As an interesting tidbit in Dan Raymer’s autobiography (Living in the Future) he mentions that the FX jettisonable magazine was the inhouse reason given as to why North American Rockwell lost the project. The ‘old timers’ at the company told Raymer that they had included the jettisonable magazine with all its extra weight and complexity in their FX tendered design (NA-335) as required by the specification. But rivals McDonnell had got wind that USAF was unhappy with the 25mm and in their tender left out all the weight of the jettisonable magazine and just provided a design with the conventional M61 20mm gun and ammo drum. So their F-15 was lighter and cheaper than the rivals who actually meet the specification as originally set by the customer.
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Wow thanks Abraham Gubler, I for one appreciate that 'interesting tidbit regarding the FX jettisonable magazine and was the inhouse reason given as to why North American Rockwell lost the project'.

Regards
Pioneer
 
yasotay said:
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.
Click to expand...
How are two blade systems lighted? I was around Hueys at my local airport for 25 years and never saw any lighting on the rotors.
 
famvburg said:
yasotay said:
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.
Click to expand...
How are two blade systems lighted? I was around Hueys at my local airport for 25 years and never saw any lighting on the rotors.
Click to expand...
I suspect that the meant to write LIGHTER. Two-blade rotors are simpler and have fewer parts.
 
From this book
 

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Abraham Gubler said:
Lower weight as two of something is usually lighter than four of something. The wide blades of the AAH and a few other Bell helos of this time were also designed to provide a lot of lift at lower rotation speeds. The slower the rotor spins and the less noise it makes (usually).
Click to expand...
Funny, the wide blades are what are said to give the Huey/Cobra and Chinook their thunderous sound, while thinner blades end up quieter.
 
FighterJock said:
I just had to search for Boeing’s AAH entry on Google, and sferrin is right, it is the helicopter equivalent of the X-32. Well and truly ugly.
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Nah, the X-32 is nowhere near as fugly as the Boeing BV-235. The BV-235 fell out of the ugly tree, hit every branch on the way down, then bounced back up to hit them all again!
 
BV-235 demonstrates why Boeing 'cherry picks ' designs from outside the company. Their internally designed platforms tend to be adverse to the aeronauts eye. Enthusiast tend to have adverse reaction as well.
 

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