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.
But would those shorter blades produce enough lift? Would they have to have an incline line the V-22′s rather than the flatter surface of existing blades?
I am uncertain with this idea, the logistics advantage is minimal I think.
Good post nonetheless, good to read peoples ideas c:
Not entirely sure if it work as planned, but like the alternative thinking!
Sorry, four blade main rotor or not, the shortening of the blades would require them to spin faster to beat the air into submission – so while I don’t have a PhD in Aeronautics, I am pretty sure this would lift LESS than a standard Chinook, not more – sorry
By the way – what exactly do you see as the requirement to lift heavier loads ?
If you want a smaller cabin just buy new Merlins. If you want to lift 20 tons, just buy MI-26T off the shelf.
I think changing the sectional density would effect fuel efficiency.
The only thing our new Ch47 need are folding blades. Kept in one squadron. And used in conjunction with CVF.
“Sorry, four blade main rotor or not, the shortening of the blades would require them to spin faster to beat the air into submission”
Much depends on how much lift is lost by shortening the three blades versus the lift provided by a fourth blade.
http://www.youtube.com/watch?v=KMJ68DWtpdc
You don’t need the audio because it is in Welsh.
Oh! And our new Ch47 need AAR gubbins too.
Interesting idea though I’m not sure it may quite work out like that. The lifting power of a helicopter is determined by rotor diameter and engine power not by blade numbers. The number of blades increasing can reduce performance if you don’t change the blade profile and add engine power. The addition of another blade can reduces noise and make the overall system more efficient for the lift generated but it will not offer anything like the performance drop associated with reduced rotor dia. Tandem rotors are better for lifting heavy loads as no engine power is required for a tail rotor all purely for lift. Is this proposal not really a ch-46
@ Mark,
Providing the blades were selected correctly the additional two blades should be sufficient to maintain the same lift, surely?
Chrisb
You are I guess thinking a long the lines of more blades means more lift so more payload but in helicopters it not really the case. Helicopters create lift by moving a lot of air slowly and that is down by engine power and blade diameter these are the only real variables in the equation. Addition blades add many other benefits like better cruise performance and ride stability, rpm speed enhancement most critically reduced noise and better efficiency but not anything significant to lifting power.
Not an increase in lifting power, just maintaining approximate lift for what is now a lighter helicopter, so increasing payload fraction, which I believe is what Richard desires from his concept?
Can’t find an accurate blade length for the Chinook, but let’s just say we’re talking about shaving off the same blade length as Richard wants to remove from the fuselage (77 inches, 6.41 ft per blade) that’s 19.23 ft of lost blade per rotor. Surely the extra blades he wishes to add back on would give more blade area now than before, but accounting for the lost diameter, balance out and re-install roughly the required lift, though perhaps a touch less than before?
I agree with Mark, it seems like a rehash of a Sea Knight. BTW during the Vietnam war, the problem was not really with lift but with the fact that the Chinook had so much internal cargo space that people were often tempted to load more into the aircraft than it could carry. It’s a bit of a human thing, if you wanted to move cargo, your instinct is to fill up every bit of space regardless of load calculations.
Shortening the aircraft also reduces troop carrying capability due to cutting down of space. Troops per man isn’t really that heavy in terms of sectional density, you just need space.
@Chris
The amount of air pushed down is the rotor diamater, adding a blade won’t do much as the area of air pushed down doesn’t change. To increase lift, you’ll need to increase blade length = increase area of air pushed down.
I see where you’re coming from, but surely the blade area would increase lift? Otherwise it would make little sense for something like the Mi-26 to have 8 blades?
To clarify, I’ve always been under the assumption that air deflection is only good for about 25% of the lift contribution, while aerodynamic lift generated from the blades makes up the other 75%.
Does this sound right?
Chinook rotor diameter of 18.3m according to wikipedia. Chop 2m from aircraft and from rotor diameter for 16.3m rotor diameter. Disc area of Chinook is 520m^2, max weight 22680kg with total power of 9466hp. A smaller rotor disc area would need to move air faster to support the same weight. Smaller rotor disc area is 418m^2.
The original disc area is 25% bigger so the smaller rotor discs would need to move the air 25% faster? I don’t know the precise relationship between power and rotor disc area but I’ll make a guess that that 25% more air would require at least 25% more power so you’d be looking at 12000hp. And if you can get engines that powerful onto a Chinook you might as well keep it the same size and be able to carry more weight.
Could an additional pair of engines be put at the front?
Well, the Chinook already has a pair of turbofans at the back, it’s what makes the chopper so nasty to board, you’re actually walking in the jetwash.
Besides speed of air being pushed, there is also the problem of once you push it down, the top is empty until it refills, you’re not pushing infinite air, you’re pushing, refilling, pushing ad infinitum. Not sure how it works out, but once you start, the top of the blades are going to be constantly at a lower pressure than the bottom = more work. Not to mention the blade tips speed increase is geometric, not linear. Have to ask Mark for more details.
What exactly will it be lifting? 10t is enough for artillery, light vehicles, palletized cargo internally (you lose this is you shorten).
I think @TD was working on the assumption that things like CVR(T) and BVs10 are getting heavier, while we would in practice prefer not to carry 50+ troops in a single helicopter
Chrisb
If your so wish you can read thru this page 85 talks specific to reasons for increasing blades.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720015374_1972015374.pdf
Thanks for your comments, there are some interesting ones, unfortunately I also lack a PhD in Aeronautics, .
With regards to the shortened blades I should clarify that it wouldn’t be just a case of lopping of the ends to make them fit. This would as some have commented reduce the lifting capability. What I’m suggesting is a new blade design taking into account profile, chord width and wash out etc. If you look at the Bell U-1H and the 412, they are aircraft of a similar size and weight but with different numbers of blades of differing designs, with both types providing similar lift. If the 412 was given an additional main rotor blade, rotating at the same speed (NR) and a more powerful engine it would produce greater lift and subsequntly greater lifting capability. There would be an increase in Torque through the main rotor gearbox though, and the resulting downwash would increase ground erosion.
Jed, re: the lifting of greater loads, I was toying with ideas on the back of TD’s post, how could you increase payload capability of the Chinook without spending a fortune or buying a fleet of Mi-26′s.
@ Mark,
Cheers, I’ll have a read later. I found this a while ago so I’ll return the favour with something to keep you busy over the weekend; http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&ved=0CF4QFjAA&url=http%3A%2F%2Fwww.vtol.org%2F64627BD0-E86D-11E0-AE6C0050568D0042&ei=-1_bT-3jBqKM0wXo4OmACw&usg=AFQjCNGLIyeokU0wLtzdXBolBRNyGA0OlA&sig2=jSOE9WrvO-cPL2do3obwIg
Richard ref: “Jed, re: the lifting of greater loads, I was toying with ideas on the back of TD’s post, how could you increase payload capability of the Chinook without spending a fortune or buying a fleet of Mi-26′s”
OK – thanks
TD – why ? What do you want to carry ? (other than a 15 tonne CVR(T) MK3)
Maybe we need some kind of Skycrane version of the Chinook? Remove most of cabin fuselage aft of the front doors (or thereabouts) and move the side fuel tanks to the where the cabin roof was (might be a safer place for ‘em too) with some downward pointing long pylons for the rear wheels somewhere beneath engines? It would then have some cool container capabilities.
http://www.aviastar.org/helicopters_eng/boeing_hlh.php
Mentioning time and cost factors in the development of a composite fuselage and fitting more powerful engines seems to imply that there are no time and cost penalties in shortening the existing body and rotors. I’m sure there are plenty of dodgy garages that will chop out a section of bodywork and saw off the wings, but it won’t necessarily fly again.
When cutting up your rotor blades, remember that the weight and velocity of those blades imparts the force that keeps them rigid in flight. Cut 2m off the Chinooks blade, and the much lighter section that’s left is going to be travelling remarkably slow – they might just bend upwards under the weight of the chopper. Either that or the reduced drag overspeeds your transmission.
You’re going to need probably all new gear boxes, shafts and blades which won’t come cheap. I expect you’ll need a new flight control system and engine management system too.
If you want to keep the same hook spacing, bear in mind that the hooks are positioned towards the rear at the moment, so you’ll get a relative shift in the centre of balance if you try keeping the distances apart. The helicopter currently hovers in a nose-up attitude and dips its nose in flight, moving the hooks forward relatively in ‘shortbus’ Chinook could screw up your balance completely. Also, the forward hook is currently rated seven or eight pounds lower than the centre hook in order to maintain balance.
Also… got to go.
@Brian, I envisinged chopping the airframe would be at a manufactures level, anyone else doing it would still need the design signed off by Boeing, as they are the lead design authority. I’m sure any Chinook operator isn’t going hand over a major piece of multi-million dollar hardware to a back street cut and shut merchant. Sure, its going to cost, but not as much as developing an all new aicraft. Boeing trialled a 4-bladed rotor back in the 70′s, so we know its feasible.
In the article I mentioned that the main rotor head and blades would need to be replaced, and the four-bladed head should provide sufficient mass and drag to prevent over-speed, also it just suggests modifying an existing design as a cheaper alternative, admittedly its not a full design review or appreciation.
I’d be suprised if the flight control system would need any alteration before the swashplates, also I see the main rotor speed, NR, being the same, so the engine governors (FADEC?) speed should remain unchanged.
Good point about the CofG though, to prevent this the frames with the cargo hooks on would need to repositioned further back.
The BV-347 prototype offers more ideas. Why didn’t variable-incidence wings on helicopters catch on? I assume it was just one more maintenance job but didn’t Westland propose a similar Lynx ACH prototype in 1998?
Me: “I’d be suprised if the flight control system would need any alteration before the swashplates”
What was I thinking? Of course the flight control system would need to be altered, and significantly due to the change in fuselage length. It was a long and trying day!
Brian, compound helicopters have come on gone repeatedly over the decades, I guess the cons outweighed the pros but interesting to see Eurocopter resurrecting the idea with their X3
@ Brian – Thanks for the link; I had heard of the BV-347 but didn’t realise the wings could rotate.
Chinook with ducted fans:
http://www.flightglobal.com/news/articles/piasecki-reveals-new-look-for-hot-rod-chinook-321544/
Just had a look at the Chinook ducted fans article, on the face of it it looks feasible, but it doesn’t say if the 30% increase in payload includes or excludes the weight of the fans. Also, looking at the diagram it looks as though the drive system would intrude into the cabin area, if its mechanical, unless they’re considering some giant bolt-on electric motor driven fan. In this case they will need to significantly upgrade the alternators!
One of the problems with pushing a chopper faster is that the rotor blades lose their ‘flat track’ at higher speeds causing higher than acceptable vibration levels. Unless they’re got some form of active vibration damper they can put in the project will stall. Also, would it suffer from retreating blade stall? It can be countered with contra-rotating rotors, but does the distance between the rotors create any unique problems?
Alternatively, if you’re thinking with fans why not go for a x-22 style aircraft using the Chinook fuselage as a base.
http://en.wikipedia.org/wiki/Bell_X-22
Or a V-22 style aircraft with four props on tandem wings, eg the Boeing Quad Tilt Roto,r an idea borrowed from the Curtiss X-19, I understand.
Isn’t it the convention to include in any discussion about a Chinook replacement the suggestion that the Fairey Rotodyne is reincarnated?
@ Brian – for the record, you started this…
“The Rogers Board had declared that the ideal transport aircraft would combine the best attributes of the CH-47 helicopter and the CV-2 fixed-wing transport aircraft in a V/STOL airframe, but since these were then new aircraft, the Board deemed it too early to specify a
replacement. As a result, the Army became involved in a tri-service V/STOL research program designed to yield what the Board described as a medium tactical transport (MTT) V/STOL aircraft which it hoped would replace the CH-47 and CV-2 around 1970.21 …
The Board also anticipated a light tactical transport (LTT) V/TOL aircraft which might use similar technology and which would replace the entire UH-1 utility helicopter fleet from about 1973 onwards.”
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA460480
Something like the Rotodyne?
http://en.wikipedia.org/wiki/Fairey_Rotodyne
Modern version of MTT?
http://www.groenbros.com/images%5Cgyrodyne_tech_clip_image006.jpg
and the LTT version?
http://www.aviastar.org/helicopters_eng/groen_gyroliner.php
@Gareth,
Many thanks for those links, especially the paper on “Inter Service Rivalry” that I hadn’t seen before. CV-2 is the old pre-MacNamara reforms Army designation for the DHC Caribou or C-7.
Here’s another link from Carter Aviation Technologies for a gyroplane/heliplane concept aircraft. They also have other gyrocopter projects on their website.
@ Brian – There’s a few different designs out there for autogyros/compond helicopters, the Groen Brothers are my personal favourite.
Another idea mentioned in the above book was a flying artillery platform:
“Most radically, the Board anticipated the development of an entirely new type of aircraft: the Artillery V/TOL platform, essentially a flying artillery piece it would provide the airmobile formations with indirect fire support from ground sites from which it could be rapidly re-deployed. To be available in the mid-1970s, the artillery V/TOL platform would have a secondary mission of providing direct fi re support for ground units, both from the ground and from the air, furnishing the Army with yet another combat aircraft.22″
When I originally looked on-line for any info I didn’t find anything but recently I came across what could be an attempt to design it:
http://forum.worldoftanks.eu/index.php?/topic/77377-artillery-does-give-a-flying-frak/
http://sobchak.files.wordpress.com/2009/09/aerial-artillery-design-study-two-externally-mounted-xm204-howitzers-on-a-ch-47c-helicopter.pdf
If I have learnt anything from working with helicopters this last couple of years it is to keep it simple. The aircraft themselves must be simple so they can be fixed quickly and easily in the field, desert or snow. The aircraft also need to be able to get in and out of small spaces quickly unlike the Ospreys. They need to be equally comfortable operating hot and high or low and cold.
The only aircraft we operate that fit this criteria are the Apache and Chinook although the Puma 2 is likely to be an excellent all-rounder. The Merlin is excellent in the cold, useless in the heat and requires too much engineering support. The Lynx and Wildcat cant handle the heat and have poor endurance and payload.
Sadly, I think military helicopters are going to only get worse as people seem hell bent in computerising everything and increasing the need for OM support. A moving map is an excellent tool but if the gobbins that make the screen work fail you can’t use the aircraft, if a paper map fails you print then fablon a new one and go flying.
Wibble, thanks for this one “The only aircraft we operate that fit this criteria are the Apache and Chinook although the Puma 2 is likely to be an excellent all-rounder. The Merlin is excellent in the cold, useless in the heat and requires too much engineering support. The Lynx and Wildcat cant handle the heat and have poor endurance and payload.”
I keep guessing about the factors driving the helo fleet plan past the mid’20s and engine commonality (going with your themes)seems to be more limited than what it could be… also you define the “go-anywhere” part of the fleet (the first 3) and the rest (another 3)
-the newest 22 Lynxes (half of them about to get other than engine upgrades) and Wildcat share the engine type. It is also the same one as one of those on Merlins? These upgrades would suggest that combined 9A/Wildcat fleet will be kept over the same time horizon that the Puma LEP is aiming for
- however, all of the above restricted to the latter half of the fleet, as you define it
Any thoughts on this? By 2025 the uprated Chinook (with 50% more power) will already be flying. No point trying to put those monster engines on any other airframe (if we ever are going to buy the upgrade in the first place)
I am not really into engines but would appear to me to be the complicated and bulky component that is crucial to having (or not) maintainability in the field/ on a smaller ship with a tight hangar?
The Chinook does not need more power and is rarely operated close to its limits in terms of passengers or payload as it is. The issue, as the USN Seals found out last year, is there is huge risks in putting too many people on one aircraft and that goes for equipment too.
I believe the Lynx and Merlin engines are different; the Merlin is not limited by engine power but gearbox and tail rotor strength.
A new Merlin with the original Westland designed gearbox plus better engines (might as well if you are going to new build) combined with a simplified avionics, better ramp and overall weight decrease could work.
The Lynx/Wildcat does not seem to offer value for money in terms of land use. In hot and high (Afghan) configuration it is restricted in speed, payload and endurance. I do not believe it has a live data link, or full live data link, in ISTAR mode making it an expensive video camera. It is good for airborne mission control but the Apache can do that an a lot more.
@Richard
Re number of blades…… an increase is an advantage up to a limit
- from the NASA study……………
“Contemporary main rotors have perhaps from 2 to 6 blades. Most often there are 3 -4 blades on light helicopters and 5 -6 blades on heavy helicopters.
The space factor has a value from .04 to .07. This means that 4 -7% of the area swept out by the rotor is taken up by the blades. The larger the space factor, within the limits indicated, the larger the thrust developed by the rotor. But if the space factor exceeds .07,then the forces of resistance to rotation are increased and the blade efficiency of the main rotor is decreased.”
I think this is a great idea for the future maritime use of Chinook
we get a lot of “Chinook capable” decks but with a reduced airframe / blade length we could also get “Chinook capable” ship hangers and the extra payload would be very useful for amphibious operations and for use on the QE carriers etc
I believe the Chinook was touted as a ASW platform in the past… and if it can carry pallets it could carry palletised loads like those of the C-295?
@RW, I did consider the idea as a CH-46 Sea Knight alternative for amphibious ops or at least a ‘poor man’s MV-22′ alternative. Although I’m sure Boeing wouldn’t want to produce anything that took sales away from the Osprey! At least they could get the blades on the CH-46 to fold away in a compact manner, unlike the Chinook.
Gareth,
The Chinook can carry pallets but the issue is the on/offload as you need some sort of mechanical help (forklift). This is fine at a main base but troublesome at a PB for both time and practical reasons. It also requires the engineers to re-role the cab which is not a quick as it would be in a C17 (for example)
Having read through the postings above I request some help I am looking to purchase between 2-4 CH47 New or Used Helicopters if anyone can point me in the direction of a Seller I would be most grateful.
Many thanks,
Helen