A Guest post from Ace
In a previous article, Growth Chinook, TD had a look at the possible future growth of the CH-47 Chinook, due to its 10 tonne payload limit and the large numbers used byUKforces. In this one I shall look at the possibilities of going the other way, in shortening it. First things first, I apologise for the quality of the adopted drawings and photographs used. My access to photo editing software is limited and my drawing ability hasn’t evolved further than that of the stickman, but I hope they serve their purpose as an aid to visualising the real thing.
To dramatically improve the Chinook’s payload capability by a significant factor requires more than a tweak here and there of the engines and transmission. Consider developing the engines utilising the existing cores, strengthening the fuselage and floors to take the increased slung load and floor bearing capacity, improved transmission and new, four-blade main rotor heads. For all intents and purposes we have a new aircraft with limited commonality with previous versions and the potential of a costly development process. Going for a composite airframe and 7,500 shp engines to follow Sikorsky’s example with the CH-53K, would also add an appreciable development time factor into the equation, with a cost increase to reflect this. Going for a significantly cheaper option, especially in these financially prudent times, can add a significant advantage.
It is common in the aviation world to stretch an aircraft’s airframe to increase its cabin volume and therefore its capability. Unsurprisingly, this can have an adverse effect on other aspects of the aircraft’s performance, such as speed and range, due to the increase in weight and drag. Conversely, it is not unknown to shorten an aircraft’s fuselage, and in doing so significantly increase its performance parameters at the expense of cabin capacity. Examples of this would be the Boeing 747SP and theCarsonmodified S-61, known as the Shortsky.
On the face of it, reducing the length of the Chinook (by approximately 77 inches/1.94 metres) sounds like a bad idea. It limits troop carrying capability and would require shortened rotor blades due to the reduction length between the transmission pylons. The reduction in blade length would also require a four-bladed rotor head as mentioned above, to maintain sufficient lift from the rotor discs. With regards to rotor heads and blades, the original CH-47F was to have included a four-bladed main rotor head, but this was discounted early on due to costs. The footprint would remain the same however, as the forward undercarriage is relocated at the front of the sponsons like the MH-47E. This would help maintain stability on the ground.
As for actual weight saving, the most obvious area is fuselage weight, which is reduced by almost two metres, in addition to this would be troop seating and reduction in the lengths of hydraulic pipes, electrical cabling, fuel tanks and other items such as the drive shaft. At a guess the figure could be between one and two tonnes as a conservative estimate. A more accurate figure would require a design study by the manufacturer and not yours truly sticking his finger in the air followed by a quick study of the frog bones.
So what advantages would a shortened Chinook, CH-47S for want of a better designation, offer?
- A payload increase to match the reduction in airframe weight, say one to two Tonnes
- Improved transportation on a C-5B or C-17A
- Improved shipboard storage and maritime lift capability
- Improved rate of climb compared with a standard model Chinook to improve battlefield survivability
- The modification would help develop a four-bladed main rotor head, which could be used by standard variants to help maintain commonality
- Cheaper to develop than designing a new replacement airframe
- High degree of commonality with existing Chinook fleet
The disadvantages being:
- Reduction in cabin volume and troop carrying capability (by approximately 10 troops)
- Reduction in range due to reduction in fuel tank volume
- Requires development of a new four-bladed main rotor head and new, shorter blades
Despite the reduction in fuselage length, the three cargo hooks are still evenly spaced under the fuselage, allowing the same slung load capability. Further to this, to improve range, the larger, fatter MH-47E style fuel tanks could be utilised, as can the in-flight refuelling probe.
So there you have it, the possibility of a 10 to 20% improvement in lift capability, and therefore ‘growth’, without a kings ransom in development costs.