K Max

[Bitmonx]

Would like to hear from ppruners who are or have flown the K Max.
Intersted in flight caracteristics, performance and maintenance related issues.

Thanks,

Bitmonx

[Savoia]

Bitmonx: I'm sorry there are (as yet) no replies to your query. However, with fewer than 30 operational examples in existence, K-Max drivers are something of a rarity.

I'm willing to share some speculations with you (and which I know will be a poor substitute for the comments of someone with hands-on experience .. and which comments I hope will come) but, in the meantime ..

The K-Max utilises a contra-rotating and intermeshing main rotor system which was initially developed by the German engineer Anton Fletner (designer of the FL282 Kolibri (1942) .. the helicopter used to make history's first rotary-wing air strike during the Battle of the Bulge). This same design was used on Kaman's H43 Huskie (1947).

One of the features of the K-Max's unique rotor system is that during ground ops one needs to be mindful of the different risk areas .. specifically noting that the area to the sides of the craft is where the rotor swoops lowest (the safe area in most other types).

In terms of handling .. who knows .. except a K-Max pilot but .. I'm willing to guess the following:

That based on the craft's design, downward visibility must be a dream. The fuselage tapers away beneath the pilot's seat giving the craft a 'V' shape profile (from head-on) and which must be an advantage during longline/general lift work.

The K-Max's rotor system would (I imagine) also play a part in assisting pilots during vertical reference flying as the intermeshing arrangement creates a 'dynamic equilibrium' which is inherently stable (as far as I understand it). This stability 'should' make precision work just that bit easier.

Coming to the donk .. you've got a T53-17 producing a galloping 1,400 horses .. being driven into two main rotors both of which are (obviously) providing lift to an airframe with a basic weight of around 2.3 tonnes. What does this mean? Well, I don't truly know but I remember from my days flying the MD530F that when you wanted to execute a maximum performance take-off .. the craft did not disappoint .. it could achieve 2,000fpm in a vertical climb (if required) without reaching torque or temperature limits (in a lightly loaded craft). So .. in the K-Max .. heavens only knows .. 4,000fpm ?? Lol !! On a more practical note .. what it does mean is that you have a useful load of around 2.7 tonnes, some say slightly more.

This aircraft was, so I understand, specifically designed for external load operations and I think Kaman probably accomplished what they set-out to achieve.

Like you, I'd love to hear some first-hand reviews.

Sadly (and as you probably know) production of the craft ceased in 2003 (nine years after production began). Quite why the K-Max was not more successful .. I am not entirely sure. When I first heard about the project I criticised (like many) the single-place accommodation for the simple reason that it significantly limited the aircraft's multi-role potential. It was explained to me however that if Kaman were to achieve their objective of creating an 'efficient' lifter in this size category .. all excess weight (which obviously included additional cabin accommodation) had to be sacrificed.

In recent years Kaman have found interest in their product from the US Navy (which I think were .. or are .. being used in ship-to-ship re-supply) and the US Marine Corps who have been using unmanned versions of the K-Max to support their operations in Afghanistan.

I hope this powerful little lifter still has a future. Time will tell.


Kaman K1200 K-Max HB-ZGK as seen in Brienz, Switzerland on 27th November 2008 (Photo: Matias)

[500 Fan]

It looks like Kaman have been flying unmanned helicopters for quite a few years now!

Kaman HTK-1K - the first unmanned helicopter (1953) - YouTube

It is surprising to read how few of these helicopters have been built thus far. The K-Max goes up against the Boeing H-6U in February next year for the Marine Corps' unmanned helicopter contract. Maybe the production line will be re-opened after that. Maybe future commercial sales of the K-Max are affected by the availability now of the Kamov KA-32.

500 Fan.

[Matari]

Here's an interesting case study from the logging industry, but dated from 1994:Helicopter Logging Kmax

[Nubian]

One factor may be that they had a couple fatal accident at an early stage which resulted in big lawsuits due to if I remember correctly a design flaw.

It looks like only 23 aircrafts are still operational, and 13!! has been written off

Now, having 1/3 of your helicopters crash for any kind of reason would not help boost your sales.

As for the incredible climb rate, well you don't drain XX% of your power to drive the tail rotor for a start, then if you just put a big enough engine and a gearbox that can take it, then you get unbelievable numbers.

Quite a good web-page about the machine below..

Kaman K-Max Productionlist by Markus Herzig

[helihub]

37 built, 12 written off, 3+ are UAVs in Afghanistan. So we're down to 22 including Kaman's development aircraft and a maintenance spare they have available.

[Ian Corrigible]

Three in the 'Stan? I thought there were only two deployed in-country, with one having been written-off in June?

I/C

[Savoia]

Some of the early K-Max crashes seem to have involved a recurring problem with the aircraft's sprag clutch. Later on, one or more aircraft suffered a failure of the splines on the shaft that provides turbine speed input to the turbine governor resulting in an engine overspeed. In one case the splines failed due to "a significant reduction in the flow of lubricating oil resulting from the partial blockage of an oil filter outflow orifice."

Then in 2003 there was the Keller (Washington State) crash (which I think was probably the worst K-Max crash) where the entire rotor assembly disintegrated:

The helicopter was in cruise flight when the pilot radioed "I've got a problem" and "I'm going down." Witnesses observed rotor blades departing from the helicopter. On site examination revealed that all four main rotor blades had departed from their respective rotor hub/blade grip units coming to rest in a circumferential band within several hundred feet of the helicopter's ground impact point. Both main rotor hubs also departed the airframe and were located a short distance north and east of the ground impact site. Post crash examination revealed the presence of extensive corrosion fatigue cracking in the upper half of the blade grip plate associated with blade (s/n) 27B. The crack passed through the 7th blade retention bolt hole from the inboard section of the grip leaving the blade attached at the upper blade grip plate by one bolt inboard of the crack and 5 bolts outboard of the crack. The crack displayed corrosion fatigue striations through most of its surface. The number 7 blade retention bolt bushing was also found to have corrosion fatigue cracking in line with the grip crack. With a crack through the inboard section of the upper blade grip plate occurring, the rigidity of the associated blade (27B) would have been significantly weakened in the vertical axis and dynamic imbalance would have developed leading to successive separation of all four blades. CAUSE: Corrosion fatigue within the blade retention bolt bushing(s) of the main rotor blade grip resulting in fatigue, cracking and ultimate separation of the upper grip plate. The separation of the upper blade grip plate led to a dynamic imbalance within the rotor system and the subsequent loss of all four rotor blades in flight

.

[jymil]

This one happened in Switzerland, Engine out during aerial work. Lucky guy.

http://www.sust.admin.ch/pdfs/AV-berichte//2142_e.pdf

[Savoia]

That was an interesting report Jymil. Shame that Eagle got caught-out with a loaned engine.

For our engineering brethren .. There are some good illustrations in the report linked by Jymil (above) and in one illustration (at the top of page 22 and reproduced below) it says: "The bevel pinion of the outer pinion gearshaft assembly exhibited pronounced damage and plastic deformation."



I've not come across this term 'plastic deformation' before ( .. I've lived a sheltered life you see ) but which I now understand is a standard engineering expression. One definition I have read says: "Under tensile stress plastic deformation is characterized by a strain hardening region and a necking region and finally, fracture (also called rupture). During strain hardening the material becomes stronger through the movement of atomic dislocations. The necking phase is indicated by a reduction in cross-sectional area of the specimen. Necking begins after the ultimate strength is reached. During necking, the material can no longer withstand the maximum stress and the strain in the specimen rapidly increases. Plastic deformation ends with the fracture of the material."

Could anyone provide me with a slightly more 'layman' style explanation? I've also read that before a metal can suffer 'plastic deformation' is must first have undergone 'elastic deformation'?

What I understand (from what I've read) is that a material (in this case metal) becomes deformed under stress (and which must of course have quite a bit to do with heat) and that this deformation reaches a point beyond which 'recovery' is no longer possible, ie. the deformation becomes permanent and which (I am also guessing) is the difference between 'elastic' and 'plastic' deformation?

[Peter-RB]

One term we use here in Lancashire is,

"Totally buggered" will require a new one !... oh and metal found in oil so that needs renewing as well!!

Peter R-B
Lancashire

[DaveTM]

Elastic deformation - it bent, and then it sprung back when the force was removed. Like a spring.
Plastic deformation - it bent, and stayed that way after the force was removed. Like a banana.

[heli1]

Going back to the beginning of the thread the poor sales were the result of the US Army sales of surplus Huey's going cheap and perhaps the lack of role flexibility.
One thing that is noticeable and that is how quiet it is.No tail rotor and the relatively slow turning main rotor make it probably the quietest.
In terms of the accident record one must remember that it spends much of its life lifting and carrying,usually in inhospitable locations where there is nowhere to land when the red light comes on?

[9Aplus]

@Sav

That all goes under Hooke's Law

valid only through "elastic" range (2) after that
all goes "plastic"....

[Bitmonx]

Thanks all for some very interesting facts.
Will a successive trial with the US Air Force bring production back to live for the K Max?

[whoknows idont]

yay!

Kaman restarts K-Max production on new commercial orders

At least 10 more K-Max helicopters will be produced on a revived assembly line after a 12-year hiatus, Kaman Aerospace announced on 5 June.

The production restart comes after K-Max operator Rotex Helicopter placed deposits for two new aircraft, Kaman says in a news release.

Helicopter Express is listed as another launch customer, but Kaman has not disclosed if the Georgia-based company has placed deposits.

Kaman revealed to Flightglobal in February 2014 that increasing commercial demand had prompted them to consider relaunching production of the K-Max.

“Our team has done a great job assessing the market and working with customers to secure enough orders to support the business case for reopening the line,” says Neal Keating, chairman, president and chief executive of Kaman.

The Bloomfield, Connecticut-based manufacturer expects to collect revenues between $75 million and $85 million on a multi-year production run of 10 aircraft.

The aircraft will be assembled using an existing type certificate, which should minimise costs to restart the production line, according to Kaman.

“I am particularly pleased that Charlie Kaman’s visionary design for this unique aircraft has stood the test of time,” says Kaman Aerospace Group president Greg Steiner.

The single-engined, single-seat K-Max is a unique aircraft. It features two counter-rotating and intermeshing rotors mounted above the fuselage. The dual rotors balance the torque produce by each.

So, unlike a conventional helicopter, the K-Max can use all the thrust produced by the engine to power the rotors for lift and thrust, rather than direct up to one-fifth of the available power to a tail rotor to counter the sideways-bending torque produced by a single main rotor.

Kaman produced 38 aircraft over a four-year period that ended in 2003 to mostly commercial operators, especially forestry companies needing an efficient heavy-lift aircraft.

In 2011, the US Marine Corps deployed two K-Max helicopters modified to fly autonomously to Afghanistan. Though billed as a “demonstration,” the two helicopters hauled 2.04 million kilograms (4.5 million pounds) over a three-year deployment to forward operating bases. The crash of one aircraft in 2013 did not sour the Marines’ enthusiasm for the project.

The US Army and the Marines have a long-term plan to use a fleet of autonomous helicopters to bring supplies to remote operating bases. In February 2014, a Kaman executive said that relaunching commercial production could help the company compete for a future military requirement for an autonomous cargo delivery system.

Nice to see that there will be at least a few more of these.
On the downside, it will most likely still be way to pricey to succeed in the market...

[Caboclo]

Never flown one, but I have actually seen one in person. Refuelled a logger in Wyoming a few years ago, and watched him start up and fly away afterwards. While he was sitting on the ground with engine idling, the vibration was so bad that his head was bouncing around like a bobble-head doll. Not my idea of a good time. Hope it got better in flight. Correction, it had to get better in flight; no one could possibly withstand what I saw for any length of time.

[whoknows idont]

It's not supposed to do that, just check out some videos online. It actually seems to be a pretty smooth ride when properly t&b'ed.

[Arnie Madsen]

Never flown one, but I have actually seen one in person. Refuelled a logger in Wyoming a few years ago, and watched him start up and fly away afterwards. While he was sitting on the ground with engine idling, the vibration was so bad that his head was bouncing around like a bobble-head doll. Not my idea of a good time. Hope it got better in flight. Correction, it had to get better in flight; no one could possibly withstand what I saw for any length of time.

It's not supposed to do that, just check out some videos online. It actually seems to be a pretty smooth ride when properly t&b'ed.

When stopped-parked the rotor blades go out of alignment (lead lag hinge) .... pause the video at 0:08 and you can see it

Once some rpm builds up they align and smooth out.

But Yeah ... between 0:25 to 0:50 there sure is a lot of "bobble" like you said

.

[Peter3127]

Wouldn't want my ground crew getting too used to ducking under the vertical stab like that .... Change of machine could be ugly.