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

overscan

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YAH-63

In the second pic you can see the proposed change of the cannon to a lower mounted "chin turret" with the sensors moved to the front of the nose. As Hughes had noted, it was better to crush a $20,000 dollar gun in landing or crash than a $200,000 dollar sensor.
 

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elmayerle

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overscan said:
Source: Air International March 1977
I'm told that huge two-bladed rotor led to some canopy strikes, which was one reason this design lost.
 

sferrin

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elmayerle said:
overscan said:
Source: Air International March 1977
I'm told that huge two-bladed rotor led to some canopy strikes, which was one reason this design lost.
I seem to recall reading that one of the Cheyennes did that too.
 

yasotay

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As promised here are some pictures of the YAH-63. As you can see from the photos the airframe has seen better days. I will send copies of the ~1meg photos to those who requested them.
 

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yasotay

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Less Gregory and Antonio, if you would like the larger photo's I was able to get of the aircraft, please PM me with the address you wish me to post them too. Each pic is ~ 1 meg.

Al
 

Tailspin Turtle

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elmayerle said:
overscan said:
Source: Air International March 1977
I'm told that huge two-bladed rotor led to some canopy strikes, which was one reason this design lost.
Actually, it wasn't the two-bladed rotor but the requirement for air transportability dictating a very low rotor placement, and it wasn't canopy strikes, but at least one slight tail rotor drive shaft strike during slope landings, which eventually resulted in a tail rotor drive shaft failure while in high-speed sideward flight during Army pilot training. Ron Erhart, the Bell test pilot providing the training, almost recovered from that very awkward situation (he wasn't on the controls so he lost a few precious seconds before he realized that the Army pilot didn't initiate the resulting yaw) but crashed. Since the upcoming Army evaluation at Edwards AFB (for which the training was being accomplished) required two aircraft, Bell created a replacement in only 30 days from the static test article, spare parts, hardware off the crashed AAH-63, and some new parts.

Neither the Bell nor the Hughes AAH was ready for prime time, (e.g., Hughes had potential canopy strike problems and had to raise their rotor too) but the Army evaluation team believed that the Hughes design deficiencies were more likely to be correctable than Bell's at less penalty to hover and cruise performance and maneuverability.
 

airman

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Tailspin Turtle said:
elmayerle said:
overscan said:
Source: Air International March 1977
I'm told that huge two-bladed rotor led to some canopy strikes, which was one reason this design lost.
Actually, it wasn't the two-bladed rotor but the requirement for air transportability dictating a very low rotor placement, and it wasn't canopy strikes, but at least one slight tail rotor drive shaft strike during slope landings, which eventually resulted in a tail rotor drive shaft failure while in high-speed sideward flight during Army pilot training. Ron Erhart, the Bell test pilot providing the training, almost recovered from that very awkward situation (he wasn't on the controls so he lost a few precious seconds before he realized that the Army pilot didn't initiate the resulting yaw) but crashed. Since the upcoming Army evaluation at Edwards AFB (for which the training was being accomplished) required two aircraft, Bell created a replacement in only 30 days from the static test article, spare parts, hardware off the crashed AAH-63, and some new parts.

Neither the Bell nor the Hughes AAH was ready for prime time, (e.g., Hughes had potential canopy strike problems and had to raise their rotor too) but the Army evaluation team believed that the Hughes design deficiencies were more likely to be correctable than Bell's at less penalty to hover and cruise performance and maneuverability.
At the end Hughes won the competition ! ;D
 

overscan

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Who wrote the YAH-63 article?
 

Antonio

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Alexis Rocher
 

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Image of two Bell Model 409 (YAH-63) prototypes from Huey Cobra Gunships
by Chris Bishop, Osprey Publishing Limited, 2006.

A competent design, the Bell Model 409 lost out in the US Army's Advanced Attack Helicopter competition to the [Hughes YAH-64]. Several senior officers did not like the two rotor design, and doubts were expressed about the stability of the tricycle landing gear.
 

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Maveric

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...not Boeing-Vertol YAH.63, this is the Bell YAH.63!
 

Antonio

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YAH-63 from behind view

Source: Aviation & Marine International
 

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flateric

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Full-Scale Crash Test of the Bell YAH-63 Helicopter
In 1981, a full-scale crash test of the YAH-63 prototype helicopter was conducted at the IDRF
[37]. This helicopter was designed and manufactured by Bell Helicopter Textron as its bid in the
competition for the Army’s Advanced Attack Helicopter (AAH) program. The crash test was performed
to evaluate the energy-absorbing and load-limiting features of the airframe, landing gear, and seats. A
pre-test photograph of the YAH-63 helicopter in the impact position is shown in Figure 16(a). A
photograph of the YAH-63 during the crash test is shown in Figure 16(b). The Bell airframe did not win
the award, which went to the Hughes Helicopter (now Boeing) AH-64 Apache.
A History of Full-Scale Aircraft and Rotorcraft Crash Testing and Simulation
at NASA Langley Research Center
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.75.1605
 

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Colonial-Marine

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As I understand it Hughes selected the XM230 chain gun from the start while Bell went with the XM188. So was the YAH-63 ever fitted with the XM230 or the YAH-64 fitted with the XM188?
 

overscan

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YAH-63 article by Bell from Army Aviation Digest, May 1976. Some nice photos and details.


This issue has detailed articles on UTTAS and AAH finalists.


http://www.rucker.army.mil/avjournal/1970/1976/AVN_DIG_1976_05.pdf
 

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fightingirish

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flateric

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Sundog

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Nice pic, thanks. :)
 

Colonial-Marine

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Jettisonable ammo drum for the XM188? What's the point of that feature?

Overall I'm not certain what about the XM230 sold the weapon over the XM188. With the XM188 you have the heat buildup divided among three barrels on the XM188 and the possibility of a higher rate of fire for A/A engagements with other helicopters.
 

Abraham Gubler

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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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Two questions.

What; if any, was the advantage/disadvantage of using a two bladed rotor?

What was the intended location for the fire control optics and the flir, I presumed that it would be over the cockpit but there is no sign of it on the prototypes.

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Abraham Gubler

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

JohnR said:
What was the intended location for the fire control optics and the flir, I presumed that it would be over the cockpit but there is no sign of it on the prototypes.
The gunner’s sight is the turret between the nose wheel and the gun turret. Bell placed the sight and gun in this arrangement because having the gun in the nose actually increased its firing arcs when in forward flight and placed the muzzle blast away from the helicopter so it didn’t damage the optics or anything else.
 
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