the Intermeshing Configuration is Best [Archive]

Dave Jackson

26th Aug 2001, 08:55

Fool on the Hill

>Loose one gearbox and the whole thing really intermeshes quite spectacularly.<

I think that this fear is more physiological than factual. To my knowledge, no intermeshing helicopter has had an accident due to the failure of rotor synchronization. The intermeshing helicopter must have the rotor-rotor portion of its gearbox as simple, as strong and as reliable as possible.

The final stage of a single rotor helicopter's gearing has a degree of criticalness as well. This is because its on the rotor side of the overrunning clutch, so it can drive the tail rotor.

> If you must have two rotors why not go upper lower contra-rotating like the Hormone and Helix. <

The intermeshing configuration has a number of advantages over the coaxial, such as a lower disk loading and true symmetry in forward flight.
________________

ACORN

True. The tandem configuration of the Chinook does result in more clean air through each rotor, particularly in forward flight.
________________

heedm

I agree that no one aircraft can serve all tasks. But; the intermeshing helicopter is perceived as only being good for lifting heavy loads because Kaman, the only manufacture of intermeshing helicopters, elected to build their craft that way.

The Germany patent on the intermeshing helicopter will be 100 years old, next year. Up until the mid-forties, the intermeshing configuration had as much chance of becoming the preeminent design as any other. In fact it was, questionably, the best helicopter when WW II ended. At the end of the war, the only surviving FL 282 was brought to the States, and evaluated by the Prewitt Aircraft Company. The report praised it and the craft was offered to American helicopter manufactures for testing, should they wish. I do not know whether others tested the craft or not, but it was eventually destroyed. I suspect that reduced government funding and, more importantly, the inherent pride of inventors in their own ideas resulted in the demise of the intermeshing helicopter.

> What exactly are your reasons why you believe an intermeshing rotor is better than a tail rotor? <

I believe that the only obstacle to the proliferation of the helicopter is the difficulty and cost in learning to fly it.

The intermeshing configuration offers symmetry of flight. The symmetrical FL282 even had a rotor (not engine) governor and thereby had automatic entry into autorotation. The cost of the helicopter is not a concern since the cost of supply will come down when the demand goes up. As per the Ford model-T.

Cyclic Hotline

26th Aug 2001, 10:33

Dave,
You might want to investigate that last statement a little more.

The worst civil helicopter accident that has occurred to date was a British International Chinook that desynchronized. 45 of the 47 souls died in this accident, after the fwd gearbox failed. That anyone survived was a true act of god!

Date: 11/06/1986
Location: Sumburgh Head, Shetlands, Scotland
Airline: British International Helicopters
Aircraft: Boeing-Vertol Chinook
Registration: G-BWFC
Fatalities/No. Aboard: 45:47
Details: Crashed due to rotor failure.

Columbia Helicopters have lost at least 2 BV 107 helicopters from shaft failures leading to desynch's.

I cannot vouch for all the military accidents, but I know of a number that have occurrred. These accidents tend to be of a catastrophic nature.

Link to the Mannheim CH-47 accident. http://www.aviationcrashes.com/photo/military/p135CH-147C.jpg

All well and good until it comes unglued. There is no comparison between a tail rotor failure on a conventional helicopter and a tandem rotor system.

The main obstacle to the proliferation of helicopters is the ability (cost) to design and build quality machinery and the lack of control over the people operating them.

Edited to remove image and replace with link. (Apologies for posting that, it was innapropriate).

[ 26 August 2001: Message edited by: Cyclic Hotline ]

collective bias

26th Aug 2001, 12:25

A K-MAX in europe recently (1-2yrs ago?)had a catastrophic failure in the lift generating dept.
Those are really yuccky pics CH. Keep that up and I'll have to stop reading prune before beddybyes... :eek:

Fool on the Hill

26th Aug 2001, 13:52

One incident that I do know of is the loss of two RAF chinooks in one day. Both were on first test flights after maintenance, one in England and one in the Falklands. As the aircraft lifted it to the hover there was a bang and the front rotors slowed down and mingled with the rear rotors. It turned out that the techs had put the drive shaft to the front gerabox in backwards on both machines. both were written off but no lives were lost :cool:

sling load

26th Aug 2001, 14:58

Dave Jackson,

You obviously don't read much about helicopters, if you did, you would know about the problems encountered by the Marines when the CH-46 was introduced. They experienced synchronised shaft failures that caused many accidents and many fatalities. Before you make such claims, you want to get your head out of your computer and do some research.

Your opening of your post "with the hope and pleasure of starting a controversy" is not in the spirit of pprune. All helicopters perform specific functions relative to their design, each has its advantages and disadvantages, each has its unique role in aviation.

Thud_and_Blunder

26th Aug 2001, 19:07

F-o-t-Hill,

Just to return some of the loyalty our techs in the RAF show us, I should point out that at least one of the transmissions involved in the 2 1989 incidents had been incorrectly assembled by contractors (at Perth?), not RAF groundcrew. It may well be that both came from the same source, but time and distance prevent me from verifying...

I couldn't do the techies job, I'm just glad they're willing to.

Nick Lappos

26th Aug 2001, 20:03

Guys,
I fully support Dave Jackson's wish to start a controversy. If it degrades into an on-line slasher flick, it is our fault for failure to exercise decorum, not Dave's fault for stating a premise that might prove interesting! "It's Johnnie's fault I hit him! He said something I disagreed with!"

Regarding syncropters, tandems and such:

The standard single rotor helo has stood the test of time, but as technology moves forward, small changes in metalurgy, computers and other esoteric fields can change the balance and make old ideas appear new. The helicopter itself was held from development by the need for an engine light enough to allow the relative inefficiency of the rotor to be over come with brut force. Similarly, the tilt rotor and vectored thrust had to wait until engines got light enough to allow gobs of power to be pissed away while they hover.

I'll bet an electrically motored dual rotor system helicopter, with no interconnect shaft, but with computer controlled digital synchronization could trigger new development. The ways that technology reviels new doors to walk through is almost completely unpredictable. Who would have inagined that lasers (I remember back in 1958 when the first ruby lasers were developed) would revolutionize communications via fiber optics? That they would be used as supermarket scanners, eye surgery tools and fancy pointers for professors, enormous money wasters for US politicians trying to shoot down missiles while terrorists truck the bombs in via Budget rent-a-truck?

I think the complexity, weight, drag and control issues with today tandems and synchropters relegate them to the role of interesting sidelights to the helicopter world. Over 95% of all helos having Igor's trusty tail rotor, the best single test of what works. After all, like Beta vs VHS, it isn't what is best that always counts.

BTW, I understand that two Kamov KA-50 coaxial types (the awesome Russian gunship that eats Tigres for breakfast, and Long Bows for lunch) have had catastrophic accidents due to self midair.

Give me the old fashioned kind of midair, thanks, and make mine a single rotor helo, to go. :cool:

Gash Handlin

26th Aug 2001, 20:21

This is probably a stupid question and please go easy on me as I have almost no knowledge of rotary types other than being able to point and say helicopter :D

As the failure of the gearbox on an intermeshing design causes such "spectacular" results is there any particular reason why the cabin isn't stretched the extra 10 feet or whatever to provide physical seperation between the blade tips?

I realise there are probably aerodynamic reasons why the rotors have to be synchronised but at least the physical separation would prevent contact between the blades if the synchronisation is lost, wouldn't it?

or should I get me coat?

Nick Lappos

26th Aug 2001, 22:17

Gash Handlin asked why we don't just prevent intermeshing by lengthening the fuselage the extra 10 feet or so.

(I edited this post, as I looked up the Chinook and found that it has 20 feet of overlap, the below corrects the original post that was up for an hour or so)

Really, the problem is the integrity of the system, since a connecting shaft break, even without intermeshing problems, will lead to loss of the machine anyway, since either each rotor must have its power supply, and perfect speed control, or the game is over anyway.

The amount of overlap is a ticklish thing, since the weight of the fuselage goes up a lot as the body is lengthened (maybe 150 pounds per foot, plus the loss of lift due to downwash on the greater fuselage area (maybe another 125 pounds per foot). The cost of the extra 20 feet of length might be 3000 pounds weight plus 2500 pounds lost hover performance, total about 5,500 pounds, maybe 11% of the total gross weight, 22% of the payload.

The lift of tandem rotors actually increases as they are separated, so the two play off against each other. If we completely separate the rotors of a Chinook we can drop the power required to hover by about 10% (which would improve the hover performance by 10% or so), but we'd have to lengthen the fuselage by the 20 feet. So we'd gain 10% and lose 12% for a minus 2% net and a much larger, more expensive to build machine (you pay for empty weight).

You can bet that the designers placed the rotors right where they wanted them!

[ 26 August 2001: Message edited by: Nick Lappos ]

[ 26 August 2001: Message edited by: Nick Lappos ]

Fool on the Hill

26th Aug 2001, 22:27

Thud and Blunder,
Apploigies to the techs. I realise that they do a very complicated and often unrewarded job. My source was the RAF flight saftey mag Air Clues so I wrongly assumed the crews were RAF. Just to assure you, if I didnt have complete faith in the techs working on my aircraft I wouldnt fly. However I believe they do a great job, but it was interesting that two machines were lost on the same day. :) :)

Cyclic Hotline

26th Aug 2001, 22:38

There is no such thing as a stupid question - stupid answer maybe, but not the query! :)

The main reasons for the development of the tandem rotor system, was the ability to counteract torque whilst providing all the power solely to provide lift. A tail rotor uses a considerable amount of power, detracting from the available horsepower for main rotor lift performance.

The designs that evolved coupled a compact airframe with an excellent lifting capability. The drawback, was that in order to achieve both goals, the rotor systems would have to intermesh. In the instance of the Chinook, the rotor system is 60 feet in diameter (no metric crap here!), but the distance between rotor centres is 39.17 feet. The Chinook is hardly a compact helicopter to start with, but if it were to be built with the rotor systems not intermeshing, the distance between rotor centres would have to be at least 60.1 feet. If you now combine all the additional airframe thay you would require (say, 50% stretch) you are starting to look at a massive increase in empty weight, hence payload reduction and useability.

Like most things in life, the result is a compromise between risk, performance and design.

The K-Max is actually quite an efficient design, in so far that it is a compact, efficient little single seat airframe. Generates a lot of lift for that T-53!

There were many other experiments with dual rotor system, the Bristol Belvedere was an interesting machine.

The Russians also built a large number of intermeshing and non-intermeshing tandem designs. The ultimate was the the Mil V-12. If you look at these photo's you will see the physical scale of separating the rotor systems. It takes a lot of horsepower to run one of these! http://www.duffeyk.freeserve.co.uk/mi-v12.htm
http://www.royfc.com/mi12001107-3.html

Of course, like so many great innovations in the helicopter world, Igor Sikorsky was the leader. Here is Igor's early attempts at solving the problems of helicopter design, forerunner of everything in the rotary field! Don't forget the ABC, Sikorsky's more recent venture into this realm. http://www.russian.ee/~star/vertigo/sikorsky.html

The Yak-24 kept up the development work; http://www.russian.ee/~star/vertigo/jak-24-r.html

All the Kamov products are here: http://www.russian.ee/~star/vertigo/kamov.html

All the Mil's: http://www.russian.ee/~star/vertigo/mil.html

Not to be outdone, that famous manufacturer of chainsaws McCulloch got in on the act with a couple of small tandems! http://www.russian.ee/~star/vertigo/jov.html
http://www.pimaair.org/mcc_mc4c.htm

There are many more examples, including a number on the website below. Just another interesting topic relative to overcoming the practicalities of building helicopters.

Lots of credit to whoever put this website together. It is really quite excellent: http://www.russian.ee/~star/vertigo/helicopters.html

http://bestanimations.com/Military/Helicopters/Chinook-01.gif

inthegreen

26th Aug 2001, 22:57

Not to speak for Dave Jackson or anything, but I think there's been some confusion in terminology. He spoke of an intermeshing rotor, which is usually understood to be a synchropter design such as the H-43 Kaman Huskie. Although a Ch-47's rotors do intermesh, they are usually referred to as a Tandem rotor and not an intermeshing rotor. And yes there have been many spectacular crashes in the CH-46 (bv107), CH-47 (bv234) family.
Like Dave, I believe the intermeshing design was a great idea because of it's overall efficiency. It has two advancing blades and the weight of only one gearbox, without the power loss of a separate antitorque system.

1) Vs. Tail rotor:
A tail rotor equipped helicopter uses 15% of total power in a hover to counteract torque, which is power unavailable for lift. Plus the obvious advantage of not having a tail rotor to lose.

2) Vs. Tandem:
A tandem rotor helicopter requires a second gearbox and synch shaft which adds several thousand pounds to the Ch-47. Plus the aforementioned problem of desynch.

3) Vs. Coaxial:
The lower rotor has a higher induced velocity and therefore higher induced drag and lower lift. Coaxial helicopters generally have much higher downwash velocities, making them difficult to use in all situations.

4) Vs. Notar:
The Notar spends just as much power on antitorque as a tail rotor aircraft, maybe more. It has the added disadvantage of not gaining any of that back in forward flight the way a tail rotor unloads at cruise speed.

I agree with the bit about rotor danger when approaching from the side. That is a serious drawback. There are also cyclic and pedal combinations that can cause unusual effects, although training and time can overcome that.
It may not be the best aircraft design for the jobs that we do, but from a pure engineering standpoint, it is the most efficient.

Cyclic Hotline

26th Aug 2001, 23:32

Well I guess you might have a point there! However, the initial statement was that The intermeshing configuration is better then the single rotor configuration
(No stupid questions, only answers! :eek: :) So I think that the response to the initial question posed was pretty reasonable.

I did a quick search for intermeshing rotors and just got a lot of information about food-mixers (honestly)! :D :)

However, there was one reasonable hit, and an excellent site for information about much of what has been discussed in this thread.
http://www.aerospaceweb.org/aircraft/question/helico pter.shtml (http://www.aerospaceweb.org/aircraft/question/helicopter.shtml)

However; A subgroup of twin non-coaxial rotors is the twin intermeshing rotor system, seen only on a few helicopters made by the Kaman company, including the H-43 Husky and K-MAX. The principles by which intermeshing rotors operate are the same as those previously discussed for other twin rotor helicopters. The difference is that the rotors are mounted very close together and actually intermesh, i.e. the blades on one rotor travel through the rotor disk of the other rotor. Of course, the intermeshing of the rotors is carefully timed to keep the rotors from chopping each other to pieces :eek:.

Whilst the Kaman products have seen some success, it needs to be noted that the most succesful helicopter produced by Kaman was the Seasprite - a conventionally configured helicopter with a tail rotor.

Not a flame. Interesting topic and an interesting response (as always). :)

[ 26 August 2001: Message edited by: Cyclic Hotline ]

Dave Jackson

27th Aug 2001, 00:34

Sling Load

There appears to have been a slight misinterpretation of the opening statement in this thread. It was a specific reference to the intermeshing configuration.

There was absolutely no intent to say that the other multiple rotor configurations, which includes the tandem, coaxial, interleaving, side-by-side, and quad, are any good, at all. :D
__________________

collective bias

I believe that the accident with the K-Max in Germany was due to the failure of an oil pump.
______________

Nick Lappos is by far the best person to comment on the following, but in my limited way, I do find the potential marriage of the intermeshing configuration and Sikorsky's Advancing Blade Concept very intriguing.

Nick Lappos

27th Aug 2001, 00:48

Let me answer inthegreen's points in turn: I used carrots to mark his points.

>>>1) Vs. Tail rotor:
A tail rotor equipped helicopter uses 15% of total power in a hover to counteract torque, which is power unavailable for lift. Plus the obvious advantage of not having a tail rotor to lose.

NL - I think you overstate. A typical tail rotor eats about 3 to 6% in steady hover, where it counts. (More in maneuvers, quite up to the 15%) The loss of efficiency for overlapped rotors is at least 10% in steady hover, so they are worse where it counts.
Regarding mechanical failure, the loss of synchronization is utter disaster when compared to the loss of a tail rotor (although a tail rotor loss is perhaps slightly more probable.)

>>2) Vs. Tandem:
A tandem rotor helicopter requires a second gearbox and synch shaft which adds several thousand pounds to the Ch-47. Plus the aforementioned problem of desynch.

NL - The transmission for a co-axial or synchropter is more complex, and actually approaches the complexity of that dreaded second transmission. Desynch is also a disaster. No free lunches!

3) Vs. Coaxial:
The lower rotor has a higher induced velocity and therefore higher induced drag and lower lift. Coaxial helicopters generally have much higher downwash velocities, making them difficult to use in all situations.

NL - The overlap area of the synchropter is nearly 100 %, so the effects mentioned on induced power are shared by it. The twin heads of the synchropter have all the forward flight drag of the second rotor of the co-axial. No free lunches!

>>4) Vs. Notar:
The Notar spends just as much power on antitorque as a tail rotor aircraft, maybe more. It has the added disadvantage of not gaining any of that back in forward flight the way a tail rotor unloads at cruise speed.

NL - No argument there! The Notar eats lots of power, and has only tail protection as a virtue, which the synchropter has as well.

What didn't get discussed:
Problems in autorotation with yaw control, and the need for more rudder area and controls with extra weight and complexity. Need for twin rotor controls, with two of everything - swashplates, servo sets, control mixers, etc. Lots of maintenance weight and cost.

>> (stuff snipped)It may not be the best aircraft design for the jobs that we do, but from a pure engineering standpoint, it is the most efficient.

NL - I don't think so, I think it is a wash with a single rotor. Of course, a wash means either will do, so let the buyer chose!

:cool:

H-43

27th Aug 2001, 01:05

Nick you state that the transmission on an intermeshing helicopter is much more complex. I disagree after having worked on and worked with both the Kaman H-43 and several models of Bell products. The transmission in the H-43 is basically a large truck rear end where output is driven up instead of out. These transmissions are extremely strong and quite simple (if you can consider any helicopter component simple). Also the extra gearbox(es) going to the tail rotor are eliminated thus removing complexity so I feel that the argument of more complex is not really a factor.

Also having logged under both the Huskie and the UH-1H with identical powerplants I can say from experience that the Huskie is more efficient. Especially at high temperatures and altitudes.

Just my $.02

Brian

Nick Lappos

27th Aug 2001, 02:13

H-43:

I hear you, but doesn't the trannie have two different outputs, with the associated gearing for the opposite direction drives, extra thrust bearings, output housings, swash plates and collective mechanisms? I assume (could be wrong, won't be the first time! especially since I haven't looked inside one of those trannies ever) that all this stuff is "about equal" to the added burden of a tail gearbox system.

Regarding efficiency, I'll bet you are right, the H-43 is more efficient than an H-1. That has a lot to do with its disk area, which is great, because it was designed in the late 40's for a heavy piston engine, so low low disk loading was needed to get it off the ground. Toss in a turbine, and you have a real screamer. Not necessarily an attribute of its twin rotors, more due to the turbine slipped into the ancient design.

Dave Jackson:
The ABC was a great machine, with its counterrotating system and its very high agility. It weighed about 5% more than a single rotor helo but made that up with excellent maneuverability. Also, it could get to almost 300 MPH (with aux thrust) and pull lots of g at high speed, since retreating blade stall was not an issue.

Dave Jackson

27th Aug 2001, 02:58

I do not think that the intermeshing helicopter can be equated with the coaxial when discussing induced velocity. Many of the Russian coaxials were intended for shipboard operations and therefore a small 'footprint' was advantageous. The Kaman intermeshing helicopters were promoted based on their low disk loading.

1/ The Huskie has a 23.5' radius and a 3.7' stagger. Its combined disk area is exactly 10% greater then the area of its individual disks. This represents a 10% improvement over a comparable coaxial or 4-bladed single rotor disk.

2/ The tip path of the upper blade when at 90-degree azimuth is 9'-8" above the plane of the lower blade. This is a much greater gap then a coaxial has and therefor the convergence of the upper rotor's downwash will put even more of the lower retreating blade in free air.

3/ The outer portion of the retreating blade imparts the greatest (blade element) lift and this is the portion of the blade that is operating in free air.

If the payload of a helicopter is 50% of its gross weight, then the above represents at the very least a 20% increase in payload.

Conversely, for future faster intermeshing helicopters, the total disk area and rotor drag can be proportionately smaller for a given thrust.

Nick Lappos

27th Aug 2001, 04:07

Dave Jackson's points, in turn:

>>1/ The Huskie has a 23.5' radius and a 3.7' stagger. Its combined disk area is exactly 10% greater then the area of its individual disks. This represents a 10% improvement over a comparable coaxial or 4-bladed single rotor disk.

NL- True enough, but it also shows 90% commonality with a co-axial, clearly within the accuracy of our "PPRUNE Engineering" According to the data I looked at today (This web site makes me work on Sunday!!) the negative effects get large at 50% overlap, let alone 90%. While it would be better than a straight forward coaxial, the diffecence would not be thundering.

>>>2/ The tip path of the upper blade when at 90-degree azimuth is 9'-8" above the plane of the lower blade. This is a much greater gap then a coaxial has and therefor the convergence of the upper rotor's downwash will put even more of the lower retreating blade in free air.

NL- This takes the extreme of course, but the rotors have zero clearance at the hub, so the average is probably half that, or perhaps 5 feet, which is about what a typical coaxial uses as its separation. No points scored here, Dave, I think.

>>>3/ The outer portion of the retreating blade imparts the greatest (blade element) lift and this is the portion of the blade that is operating in free air.

NL - Sounds plausable, I wonder if there is any data to describe

>>>If the payload of a helicopter is 50% of its gross weight, then the above represents at the very least a 20% increase in payload.

NL- The data gets muddy here, mostly because there is little to quantify the one possible advantage from above. The H-43 is so very hover efficient because of its extremely low disk loading, where the 48 foot rotor(S) lift about 9000 pounds of aircraft (5 pounds per square foot for 1 rotor, 2.5 pounds for both, the reality is somewhere in between). A Bell 412 is 6.5 PSF so it would use 40% more power just because of the disk loading, not the planform.

H-43

27th Aug 2001, 04:14

Nick:

I don't know if you understood my point in saying that I think there is little difference in complexity between either the "conventional helicopter" and the "intermeshing helicopter" they both have their simplicity and complexity. You pointed out correctly that the Huskie was designed with piston power in mind and had a much bigger power plant installed. However, it still has the same power plant as the UH-1 and will still out perform the UH-1. I will also add that the Huskie is still limited to the same transmission input power as it was when the T53-L1A engine. The larger engines were simply added for more altitude performance.

Brian

Arm out the window

27th Aug 2001, 04:55

Slightly off the topic, the great photo links listed above by some of the contributors put me in mind of a spectacular contraption that the Americans put together quite some time ago.

It had the front ends of 4 single-rotor helicopters positioned at the corners of a large square lifting frame.
As I remember (saw a photo of it somewhere) it had four pilots all setting power on command from the chief pilot who was sitting in one of the airframes.

A brave effort to come up with a heavy lift machine, but too many problems to be successful, I think.

Does anyone have links to pictures/information about this machine, whatever it was?

Thanks.

Cyclic Hotline

27th Aug 2001, 05:34

The machine was the Piasecki Helistat. By attaching four H-34's (Sikorsky S-58's) to the device. I guess they figured they had a good means of removing all those old ships from the desert and putting them to use. The project was funded by the US Forest Service and US Navy :confused:, who believed there was a need for a new heavy lift capability.

The following is the NTSB transcript of the sole flight undertaken by the craft. Sadly one of the pilots was killed when all four machines broke loose, after they lost control of the entire device. :(

This Russian site (again) seems to be the sole source of a photo of this machine. http://www.russian.ee/~star/vertigo/piasecki_helistat- r.html (http://www.russian.ee/~star/vertigo/piasecki_helistat-r.html)

Frank Piasecki is still around and Piasecki Aircraft recently won a US Airforce contract to produce a compound helicopter version of the H-60 Blackhawk. (The web site above has some pictures of the evolutionary models).

Lakehurst N.J was the center of US naval airship operations (collosal airship hangars), and is probably better known in infamy, as the site of the loss of the Hindenberg.

NTSB Identification: NYC86FHD01 . The docket is stored on NTSB microfiche number 32618.

Accident occurred Tuesday, July 01, 1986 at LAKEHURST, NJ
Aircraft:PIASECKI HELISTAT 97-34J, registration: N1897Z
Injuries: 1 Fatal, 3 Serious, 1 Minor.

The helistat, a hybrid a/c with 4 H-34 main fuselages attached to a frame along with a zpg-2 helium filled envelope had just completed it first hover test flt successfully and landed. A pwr loss was noted on the No. 3 helicopter and the test was terminated and the mooring mast called for. Prior to re-mooring a wind shift caused an uncommanded left turn which the pilot could not control with the flt controls. With a tailwind, no wheel brakes or gnd steering a takeoff was attempted. The 4 main landing gear which had no shimmy dampners started to shimmy. The four helicopters started to react to the shimmy with ground resonance. As the helistat finally lifted off, the four individual helicopters broke off and fell to the ground. One pilot received fatal injuries, 3 received serious injuries and one minor injuries. The helistat was destroyed. The prw loss on the no. 3 helicopter was traced to a missing throttle linkage correlation pin. Why the pin was missing was not determined.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:-

Throttle/power lever,linkage..disconnected
Rotorcraft flight control..inadequate
Acft/equip,inadequate design..manufacturer
Acft/equip,inadequate handling/perf capabilities..manufacturer

Contributing Factors
Landing gear,main gear..vibration
Rotor system..vibration
Landing gear,normal brake system..lack of
Landing gear,steering system..lack of

[ 27 August 2001: Message edited by: Cyclic Hotline ]

Arm out the window

27th Aug 2001, 06:00

CH, thanks very much.

Nick Lappos

27th Aug 2001, 06:08

Brian,

Not to take away from the excellent performance of the H-43, but to explain why it has it, the reason is the disk loading. The Huskie was layed out when heavy piston engines were needed so the power came at a steep empty weight. This made the designers thrifty with power, and the best way was to use big rotors that needed less power. Thus, the H-43, with a 48 foot rotor disk weighs in at about 9000 pounds. The piston engine was replaced by a turbine, which could develop the transmission rating up to high altitude, but just as inportantly, it weighs about 1/3 of the weight of the piston, so all that weight savings gets to become payload.

Another example is the S-55, which has a 53 foot rotor diameter for about 8600 pounds gross weight. The Black Hawk has the same sized disk for 24000 pounds!

The lift advantage of light disk loading is awesome. The power needs of the rotor are proportional to the square root of the disk loading, so a 6.5 pound per square foot rotor (Bell 412) needs about 40% more power than a 3 pound per square foot rotor (H-43). This means that for the same power, it lifts 40% more.
In other words, the efficiency of the H-43 is not because it is a synchropter but because it has a great big rotor!

The downside of the old machines is that they also beefed up hover performance by having skinny blades with low rotor solidity (ratio of blade area to disk area). With low solidity, the blades are near optimal lift to drag in a hover, so more weight can be lifted, but the downside is that the rotor stalls at slower speeds.

The Huskie has a max speed of only about 110 knots, if I recall correctly, which is part payment for that hover efficiency.

Nick Lappos

27th Aug 2001, 06:14

Cyclic hotline,

Some background on the Helistat is that Frank Piasecki did little dynamic analysis of the big airframe, a factor which perhaps contributed to the mishap. The chief pilot he had during the development told me that virtually no computer analysis was done to study the low frequency modes of the structure, which is a big problem area on all larger machines (and a major contributer to the problems with the largest helicopter that ever flew, the V-12).

Cyclic Hotline

27th Aug 2001, 07:00

Nick,
There was a published engineering report prior to the first flight, that predicted exactly what occurred.

I think it is also very revealing, as you note, that so many of these huge machines were constructed but were totally impractical and had no viable application - they simply weren't thought out thoroughly. Once it was flying, you were sometimes left with more problems to tackle than the initial design work itself! ;)

Although I never saw this machine in real life, I do know a couple of people who did and they said that they were not surprised at the outcome just from looking at the way it was constructed.

The evolution of large helicopters was spectacular and rapid, considering the short period between the first production helicopters and some of the gargantuan models that followed. Of course, like all Aviation development, the lack of suitable powerplant's was really the controlling factor in all of these developments. The Sikorsky CH-37 (S56) was unbelievable in both complexity (and maintenance demands) ;), but the very last of the large piston engine helicopters as they struggled through material and technological change, must have been one of the most exciting times ever in the helicopter business.

Piasecki Vertol were of course in the midst of this. During the transition period between piston and turbine engines, so huge boundaries were passed. I think that one of the most amazing looking helicopters ever produced came out at that time. Although not a success, the Piasecki YH-16 epitomises 1950's design, architecture and style. Not only does it look like something from a science-fiction (or Godzilla) movie, it clearly demonstrates the amazing resources and drive that was apparent in the post war aviation industry.
http://www.russian.ee/~star/vertigo/piasecki_h-16-r.html

Not meaning to detract from Dave's original thread - amazing how these topics take on a life of their own!

sling load

27th Aug 2001, 13:26

Dave Jackson,
Apologies to you, I misunderstood your real intent, I beleived you meant tandems.My hope was that your hope to start a controversy wouldn't end in slanging matches, I concur with Nick.

[ 27 August 2001: Message edited by: sling load ]

vorticey

27th Aug 2001, 17:27

i would have thought the russian "shark" helicopter would have been the most efficient design.
should go faster because retreating blade stall being reduced by the opossing blade wake (less rotational flow) which would also help when hovering, but a stronger induced flow would be the downer.
i would think votex ring state would be less of a problem too. (less rotational flow) or do you think it would be worse? comments??
:eek:

tgrendl

27th Aug 2001, 18:13

I think the russian shark design was pretty efficient in some regions of flight but not in all.

Big long bendy blades with not that much hinge offset.(compared to the ABC)

As forward speed increased flapping did likewise. Add some g forces to it and clearances got smaller. A low speed heavy lifter great but a high speed attack helicopter no.

A few years back I sat in a similar rotored aircraft during runup. It had a video camera setup that looked down one of the blades while it rotated. (The blade was fixed in the line of site and the horizon spun around)
The big worry was that these blades would meet each other inflight at the higher end of the envelope. Apparently that's the speculation on what happened to the russian general in the shark. :(

Nick Lappos

27th Aug 2001, 23:23

I agree with tgrendl, the Shark KA-50 can't do much retreating blade stall magic, as the tip clearance problems this would induce are too much for it to handle. The ABC has very stiff blades to allow the retreating blade to get into deep stall without much motion.

Dave Jackson

27th Aug 2001, 23:24

tgrendl'

Not to stay off topic, but a little trivia; and a regret.

It is my understanding that the ABC had a rotor separation of 30", and they set the minimum allowable tip clearance at 10".

Unfortunately, like the Russian helicopter, it appears that the first ABC also crashed because of blade-blade contact between the rotors.

Nick Lappos

28th Aug 2001, 00:10

Dave Jackson,

The first ABC had a hard landing due to a combination of issues, none of which were at all associated with blade clearance. The aircraft basically ran out of longitudinal control due to very conservative rigging based on simulation data that was seriously in error.

To the best of my knowledge, blade clearance was monitored in flight test, and no close calls were ever recorded on either ABC demonstrator.

Two KA-50's have been lost so far due to blade contact, I am told. Perhaps this is due to the sporty envelope proposed for an attack helo as opposed to the relatively benign envelope of the ASW missions flown by other Kamovs.

tgrendl

28th Aug 2001, 00:14

Dave,

Nick actually flew the ABC so I think he'd have better information than I do.

I believe part of how they solved the retreating blade stall/bending problem was with a huge hinge offset (25-30%?)and very stiff blades.

There's some other magic wrapped up in that aircraft that nick would know.

And I didn't know that it had inflight blade contact, thanks I guess and sorry several years too late.

tom

tgrendl

28th Aug 2001, 00:25

Dave,

Back to your intermeshing discussion,

Do you or does anyone know a valid way to model the drag effects at the combined rotor mast/ fuselage area?

I have a feeling that this region may be a "try it and see" area in your testing. I've tried thinking of ways that it might be done but have come up empty handed.

This could, of course, be due to my walnut sized brain. :D

Dave Jackson

28th Aug 2001, 03:42

Nick,

Thanks for setting me straight about the first ABC. The information that I posted had been given to me in a telephone conversation with a retired executive in the helicopter industry, so I just assumed it was correct.

Sorry about that.

Kyrilian

28th Aug 2001, 03:51

Dave,
A few people have pointed out that overlapping rotors (coaxials, intermeshing, tandem overlapping) lose some power from induced losses because of the increased induced flow. Let's talk numbers.

Since induced power losses are in the range of 60% of rotor power, with profile power taking up another 30%, the reasons for adding a second rotor need to be pretty good. Adding another rotor will increase profile power (more blade area being spun through the air), but more importantly, it will increase induced power loss--the overlap induced power loss will be up to 41% (100% overlap). Of course, an intermeshing rotor will have some separation (say 10% of rotor span) which means that the loss will be less than 41%--by my calculations approximately 33%. If you want to have a 25% span overlap then the overlap fraction is .68 and the loss in power is 23%, still quite substantial in my opinion. Add the .3*(difference in profile power) to .6*.23 (14%) and you probably have something like a 16-20% loss. This doesn't include the small (1-2%) loss due to the fact that the lift vectors are not vertical or the extra frontal and and vertical blockage of such a wide separation.

While it is true that you can get a smaller footprint and won't have to worry about dissymetry, you pay for it in power and controllability. I've never flown anything but conventional (tail rotor) helicopters, but from what I've heard the coaxials and intermeshing rotor helicopters leave something to be desired when it comes to yaw control, especially in low/no power conditions. Someone with experience please correct me if I'm wrong, but the tail rotor or fantail still seems to be the best in terms of yaw control.

As for a helicopter in everyone's driveway, I really doubt it. I don't think the lack of helicopter proliferation has much to do with simplicity of control. It's cost and insurance requirements. Why can't new pilots go out and fly turbines or get a job as a heli pilot? In the US at least, you can solo in 10 hours, get your PPL with 40 hours (less if you've got other ratings already), and have a comercial ticket in as much more (150 if you don't have any other time) and then wait until you've got 1000 hours before you can fly a turbine for hire. I really don't think that would change if everyone flew an intermeshing helicopter. Do the 1000 hour requirements of insurance companies reflect on the ability of relatively inexperienced pilots to keep a steady hover? I think it has much more to do with judgement, insight, and experience.

In any case, I'd love to see your toy if you go about developing one :D I just don't think there's anything that will have the effect on rotorcraft the model T had on automobiles. Good luck!

Dave Jackson

28th Aug 2001, 04:04

Nick,
>NL- True enough, but it also shows 90% commonality with a co-axial, clearly within the accuracy of our "PPRUNE Engineering" According to the data I looked at today (This web site makes me work on Sunday!!) the negative effects get large at 50% overlap, let alone 90%. While it would be better than a straight forward coaxial, the difference would not be thundering.

I still believe that the lift distribution of the intermeshing configuration cannot be equated with the coaxial. This will be particularly true in fast forward flight. Please remember that we are not talking of the Kaman synchropter. We are talking of a 'head to head' contest between comparable single-rotor and intermeshing-rotor helicopters.

The intermeshing may only offer a 10 to 15% advantage over the coaxial in hover, but in forward flight, the difference will be significant. The following is a sketch showing the lift distribution for an intermeshing helicopter in forward flight. http://www.synchrolite.com/Lift_Distribution.html

This difference becomes even more significant at very high forward velocities, and if flapping is reduced, or eliminated. (ref: Figure 3.15 Helicopter Performance, Stability and Control ~ Prouty). This is where the [intermeshing & ABC] marriage comes into effect.

If you agree with the above, please don't let Sikorsky patent the idea :) . My long-standing position on this particular idea and any others on my web site is that they are, and will, remain open and available to all.

______
Sketch revised

[ 28 August 2001: Message edited by: Dave Jackson ]

Comments revised

[ 28 August 2001: Message edited by: Dave Jackson ]

Cyclic Hotline

28th Aug 2001, 04:52

Dave,
Getting back to the topic of Intermeshing rotor desynch's (sorry to keep bringing this up).

NTSB Identification: MIA83FA183 . The docket is stored on NTSB microfiche number 22314.

Accident occurred Thursday, July 14, 1983 at NEAR CLERMONT, FL
Aircraft:KAMAN H-43B, registration: N57996
Injuries: 1 Serious.

The helicopter crashed in an uncontrolled descent from a hover. A witness stated that the helicopter was slowing descending to position a 150 ft line for the ground crew when he observed something separate and the helicopter came down in a vertical descent. Investigation showed that the transmission and rotor assemblies separated in flight. The engine continued to operate after the crash and had to be shut down. The pilot sustained a head injury and does not recall the accident.

The national transportation safety board determines the probable cause(s) of this accident as follows.

Rotor system..separation
Rotor drive system,main Gearbox/transmission..separation

NTSB Identification: SEA93LA105 . The docket is stored on NTSB microfiche number 50380.
Accident occurred Wednesday, May 12, 1993 at ANATONE, WA

Aircraft:KAMAN HH-43F, registration: N846D
Injuries: 1 Fatal.

The converted military helicopter was in a hover lifting an external load of logs when the main rotor pylons separated in flight, resulting in an uncontrolled inverted descent into the ground. On-scene examination revealed that the transmission rotor input gear shaft, Pt/no: K774515-5F, had fractured. Safety board metallurgical examination showed that the fracture was characteristic of fatigue failure, and indicated repetitive high loads. The FAA type-certificate, based on military configuration, lists the approved engine as 1100 shp, and the external load limit as 2,300 lbs. The FAA had approved installation of a 1400 shp engine, and operations with an increased external load limit of 4,000 lbs.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows.
Fatigue failure of the rotor transmission drive system, resulting from the improper certification/approval of the aircraft modification by the federal aviation administration.

I cannot quantify the overall number of accidents in commercial operation as I do not have access to the hours flown. However, from a very small fleet, there seems to be quite a number.

The same is true with the K-Max. A recent news report states that the the fleet leader has recently turned 10,000 hours. So with a relatively small fleet and overall low hours, I would not rush to too many assumptions.

H-43 is correct, they are really stout and simple machines - certainly Kaman's trademark, and one which is hard to beat in the real world of making money. The longevity of the aircraft is a pretty fair testament to that.

I have a number of acquaintances who have both flown and operated the H-43. One told me that when firefighting for the State of Washington Department of Natural Resources(DNR) they would always arrive on the scene of the fire at the same time as everyone else left, as they were so slow! (made for a very casual and relaxed summer) :)

I thought that the funniest comment however, was a mechanic who told me that there was no doubting that the machine was built by a bearing company. "You've never seen so many Kaman bearings in one place before, nor a piece of equipment that can use 'em up so fast!" :)

Now, about that weird control reversal deal - can't say I've run into that to many times before! :)

Dave Jackson

28th Aug 2001, 08:42

Help! You guys are ganging up.

tgrendl

>Do you or does anyone know a valid way to model the drag effects at the combined rotor mast/ fuselage area?
I have a feeling that this region may be a "try it and see" area in your testing.<

Your "try it and see" appears to be the answer of the professional designers, as well. All the books seem to mention that the mathematical and the testing methodologies can produce fairly different results. Mind you, some of these books are a few months (years) old and things sure change fast.

There appears to be a strong consensus that streamlining the rotor hubs and associated control linkages is very beneficial in reducing drag. One book mentioned the additional advantages of locating the hub close to the fuselage, then streamlining them together.

Here again, Nick is probably at the cutting edge.
__________________

Kyrilian

You've covered a lot of territory. So here goes a weak attempt at a rebuttal.

Thrust:
There are virtually no calculations available on the intermeshing. Much of the work must therefore be 'guestimates'. The side-by-side configuration is the optimum for thrust. In fact, it has been reported that an adjacent side-by-side give more than twice the thrust of its individual halves. The synchropter will come somewhere between the side-by-side and the coaxial. Hopefully, my sketch to Nick shows that the intermeshing is significantly better than the coaxial.

It might also be noted that in the early forties weight to thrust was very critical and yet Sikorsky and Flettner were able to produce comparable helicopters, with the Flettner being the alleged faster of the two. The image of the Kaman synchropters must be put aside.

>Adding another rotor will increase profile power (more blade area being spun through the air),<

If the two sets of blades are identical then the profile power of a 4-blade single rotor and that of twin 2-blade rotors should be very close.

>from what I've heard the coaxials and intermeshing rotor helicopters leave something to be desired when it comes to yaw control, especially in low/no power conditions.<

I have spoken to the Canadian pilot of a Russian coaxial, which is used for logging. The helicopter uses differential collective for yaw and he makes any minor trim adjustments that are required before taking off. He said that the helicopter was quite responsive and that there was automatic pedal reversal in the event of an autorotation.

I understand that the K-Max has an extended empennage to provide better control that that of the Huskies, and they uses differential longitudinal cyclic in addition to the differential collective. Of course, the pilots of the Huskie can provide the best answers.

It may be of interest to know that the Flettner intermeshing helicopter supplemented it rotor control with elevator and rudder control.

______________

Cyclic Hotline

Oops! Two failures.

Your comments on the drive train and yaw control aren't too good.

Mine you, this is offset by your jokes, which aren't too bad.

[ 28 August 2001: Message edited by: Dave Jackson ]

tgrendl

28th Aug 2001, 21:30

Dave,

Thanks. I've gotten the feeling that Nick was right much earlier (different thread) when he said that a lot of science goes into the design and then a lot of engineering gets applied to it (variable cams, trial and error etc).

It seems as if this is a repeated cycle of development in most helicopters that make it to the flightline. Idea, refinement, mathematical modeling, refinement, scaled modeling, refinement, full scale, testing, refinement, envelope creation, production.

If you have a list of things that are holding you back on yours could you share the particulars? I would guess the people on the forum would be happy (time permitting) to put their brains to use on identified problem areas. Or at least to try.

You never know, you may get something good out of it and I'm sure the problems you pose will help educate everyone.

Always enjoy your posts,

Lu Zuckerman

28th Aug 2001, 23:10

To: tgrendl

I would like to add to one of your statements.

It seems as if this is a repeated cycle of development in most helicopters (or any other complex systems) that make it to the flightline (or the road or, whatever). Idea, refinement, mathematical modeling, refinement, scaled modeling, refinement, full scale, testing, refinement, envelope creation, production and final wringout of overlooked problems by the operator.

tgrendl

29th Aug 2001, 00:30

Hi Lu and you're right. The wringout feedback loop was left off by accident.

I know that Macdac tried to do this with the IKPT on the apache but they still overlooked a few things.

BTW, your helo pilot joke wasn't complete.

It ended by that lady looking down at me and saying "now, who could you make happy with that?"

My answer, of course, was me.

Dave Jackson

29th Aug 2001, 03:06

tgrendl

>If you have a list of things that are holding you back on yours could you share the particulars? <

Thanks for the offer of assistance. It would be hard to think of where to start. :rolleyes:

These discussions are very informative and interesting. This specific thread has highlighted numerous concerns, such as mechanical synchronization reliability and a reevaluation of the rotor efficiency.

Nick and many others would be surprised at the number of times their nuggets of wisdom have been clipped and posted in my scrapbook (web site).

Nick Lappos

29th Aug 2001, 04:01

Dave Jackson,
Regardless of what we kibitzers here may think and ponder, the credit goes to the guy who builds and flys the machine! Go and do it, and tell us how it went.

I suggest a scale model, with a good rc system and a tie down phase as a great way to model the aerodynamics. A pair of electric motors (with a simple synch gear set to maintain order) could serve as the power plant. You could measure power consumed through the tether/feed line as you test it.

Good luck :)

heedm

29th Aug 2001, 10:09

Dave, lots has been said about efficiencies of the intermeshing rotor. One problem I can see is the rotor disks are tilted from the horizontal (12.5 degrees in your design). This means that only a fraction of the lift is countering gravity.

It works out to 97.6% for a 12.5 degree tilt, but that still means there is a 2.4% loss due to design, not yet accounting for aerodynamics. With tail rotor losses of 3-6% I think that this number is significant.

Of course, all rotor disks tilt from the horizontal, but there is a purpose to that tilt. In this case, the lost power just works against the lost power from the other rotor.

Another area where I see a loss for the intermeshing rotor is when you compare it to a single rotor, "head to head", with the same engines, same disk loading, and same fuselage, you would need a smaller rotor diameter for the intermeshing rotor. The loss is found in that there is a greater percentage of fuselage blocking the disk.

I think you may be right that it is a more efficient design, but it won't be any easier to fly. The four axes of control will still be required, the "inherent instability" is a result of the required agility to precisely hover. The only thing that will make it easier is you won't have to change your yaw inputs when you change your power...that part isn't that tough.

The rotor governor will make things safer for engine failures in a particular envelope, but unless the pilot can instantly override it, there are some flight regimes where a governed rotor will kill you in an engine failure. Granted, for the commuter taking off and landing in open area pads, the restricted envelope should suffice.

Time to stop rambling.

Matthew.

tgrendl

29th Aug 2001, 21:28

Dave,

At your target weight a ballistic recovery system (or two) should alleviate some of the concern regarding reliability, at least for test flight.

A well designed safe area for the squishy thing (pilot) operating the controls will help too.

I'd think also that a rotor governer could be replaced by a sprague clutch setup at the right place.

Engine power direct to main gear reduction and then a sprague prior to splitting the mechanical power. The only differance would be that the rotor rpm would have to be adjusted to allow it to drive a small set of gearing in autorotation. This would also allow for any mechanical power taps you needed in growth.

What powerplant(s) are you looking at?
Output shaft speed?
Output torque?
Final rotor rpm?

If you have time, not ganging up on you.

I'm trying to imagine what your helicopter will sound like. :eek:

Dave Jackson

29th Aug 2001, 22:22

A general overview. http://www.unicopter.com/7up.gif

No single helicopter can be best for all missions, but, based on ease of piloting and a resultant popularity, I claim that the intermeshing configuration is unquestionably best. The intermeshing is the only realistic configuration that can provide the symmetry of an airplane. Even the coaxial does not have absolute symmetry.

The question of the intermeshing helicopter's thrust to empty weight has been raised. The single rotor may well have a slight advantage in this department, but consider the popularity of the automobile. Only 10% of the BTU's that a car consumes go to propel the vehicle, and only 1% of the BTU's are actually use in transporting the occupant. Maybe the Dutch and the Chinese are smarter then most of us since they tend to use the much more efficient bicycle :)

My positive attitude toward the intermeshing configuration has little to do with the design and functionality of the current synchropters. It is based on Flettner's helicopter and the direction that he and Hohenemser could have taken it.

A gentleman has assimilated a considerable amount of material on the Flettner FL-282. He has even produced the construction drawings of the fuselage and cockpit, with the intent of building a full scale operational replica. He has been very generous in passing on, over a period of time, copies of much of this material. The more I read, the more impressed I became at the technological beauty of this helicopter and its configuration.

Few people would question the technical competence of the German's preceding and during WW II. It might be of interest to know that there was an alleged contract with BMW for 1000 FL-282's. Unfortunately for Flettner, he faced a few obstacles that most of his contemporaries didn't, such as having his manufacturing facilities bombed on two separate occasions, plus being on the loosing side.

I believe that the 3-bladed self-stropping Kellett helicopters and Kaman's use of the Italian servo-flap did little to advance the development of this configuration.

_________________

For those who are still following the 'hype' :) and would like to dig deeper into the Flettner FL-282, the following page may be of interest: http://www.synchrolite.com/0474.html

_________________

heedm & tgrendl

Thanks for your concerns. Intelligent response coming ~ hopefully.

[ 29 August 2001: Message edited by: Dave Jackson ]

t'aint natural

29th Aug 2001, 23:17

Any MD people on this thread...? Earlier inthegreens and Nick Lappos dismissed the Notar as requiring substantial antitorque power even in the cruise. I always thought the offset vertical stabilisers unloaded the tail in cruise and the compression fan pretty well idled along in flat pitch. Am I misinformed?

Dave Jackson

30th Aug 2001, 01:49

Thanks for the constructive criticism.

heedm

>One problem I can see is the rotor disks are tilted from the horizontal (12.5 degrees in your design). <

This should not be a serious problem. As you mention, the vertical component of thrust is still a healthy 97.6%. The 'theoretical' UniCopter has rigid blades and therefore its current angle is 9-degrees, resulting in a vertical component of 98.8%

In opposition to the western perspective ;) ~ " .... the single-rotor helicopter's tail rotor power consumption accounts for 10-12% of total power." ~ Eduard Petrosyan, Deputy Chief Designer of the Kamov Company

>you compare it to a single rotor, "head to head" .... would need a smaller rotor diameter for the intermeshing rotor<,

This is an important but difficult area to discuss since there is no rotor performance data available on the intermeshing configuration. The downwash on the fuselage is not a serious problem because the intermeshing rotor cutout is quite large. My earlier downwash chart to Nick L. makes it appear that, theoretically, the synchropter is not too bad, particularly in fast forward flight. Ivo, of Ivo Props built a simple little intermeshing helicopter years ago and although it never left ground effect, he was surprised by the small amount of power it required.

The following web page should be informative to anyone who has an interested in the coaxial helicopter, and it may be of particular interest to Nick L. http://www.kamov.ru/news/petr11.htm

> ... it won't be any easier to fly. <

Symmetry of flight controls is a given and cross-coupling should be reduced, but your point is well take, particularly in respect to SynchroLite. It was this concern that prompted the UniCopter development. The intent here is that the rigidity of the rotors will give a faster and more precise response; which is an extension of Nick L. comments on piloting the ABC.

> The rotor governor will make things safer for engine failures in a particular envelope, but unless the pilot can instantly override it,
<

The pilot has the ability to instantly override the rotor governor. My understanding of the 'basic' difference between an engine and a rotor governor is, that with one; pilot input is required to put the craft into autorotation, whereas with the other; pilot input is required to prevent it from going into autorotation. Some additional 'dry' information is available at: http://www.synchrolite.com/Governor.html

_______________

tgrendl

> At your target weight a ballistic recovery system (or two) should alleviate some of the concern regarding reliability, at least for test flight.<

The current method is to hang a St. Christopher medallion. :) Your idea may work, as long as it is possible to 'get around' the intermeshing rotors.

> I'd think also that a rotor governor could be replaced by a Sprague clutch setup at the right place.<

A Sprague (overrunning) clutch is definitely needed, where you suggest. The rotor governor would serve somewhat different functions and would be a later add-on.

>I'm trying to imagine what your helicopter will sound like. <

Probably like a lawn blower.

> What powerplant(s) are you looking at?
Output shaft speed?
Output torque?
Final rotor rpm?<

Since you asked. :eek:
http://www.UniCopter.com/UniCopter_Reciprocating.html http://www.UniCopter.com/UniCopter_PowerTrainAccessFor m.html (http://www.UniCopter.com/UniCopter_PowerTrainAccessForm.html)
http://www.SynchroLite.com/Reciprocating.html http://www.SynchroLite.com/PowerTrainAccessForm.html

[ 29 August 2001: Message edited by: Dave Jackson ]

[ 29 August 2001: Message edited by: Dave Jackson ]