Strange Robbie Cyclic(s)

[HollyCopter]

Just going through my (real) mail this evening, saving the helicopter related stuff till last, to savour as usual.
Normal batch of sales blurb, mostly heading toward the bin, but suddenly, something caught my eye. Something I can't explain, but maybe someone here can...

One of the advertising flyers is from Tech-Tools. They make really cool full-view doors for the R22 (and I wish they did them for the R44 too... grrr...).
Anyway, what caught my eye is that the R22 in the picture has seperate cyclics, very similar in shape to the B206. Not a 'T' bar in sight ?! Didn't know such a thing existed. I've looked closer at the pic, and as far as I can tell, it's really a '22, and there's no sign of a photo touch-up. There's 2 different views of the ship that show it clearly.
A tall order, I know, but can anyone verify my sanity?

HollyCopter

[Kyrilian]

I'm not at all familiar with the company about which you're talking. However, I did peek inside a hangar at Norwood (OWD, near Boston) where there was a similarly configured Robbie. I was told that Altair Avionics (maker of HUMS and that sort of equipment) which is located on the field, had done the conversion and possibly were seeking an STC??
I recall noticing a horizontal bar that connected the central control point of the standard R22 to the base of the two sticks, just behind the calf of one's leg. It was kind of ugly and obtrusive, but for someone who wants the 'real' helicopter feel, this seemed to fit the bill. Of course, you'd then have to strap a turbine or two onto it, increase the MGW a few thousand pounds, redesign the rotor system, etc ;)

[SPS]

Holly,

I have JUST the thing for you !

Two days ago I loaded up a new section to my
website, www.helicopterpilotsguide.com (http://www.helicopterpilotsguide.com)

The section is called 'Unusual products and accessories' It is reached from the left bar.

I too had heard about the conversion many times but had never seen one. Last Friday I got to photograph it and fly it! Now it is pictured on the site for all.

Kyrilian's memory has served well, the description is good.

Your sanity is preserved! If you need any more info. keep an eye on the page, I will be naming the maker when I find the precise details.

And by the way, NZer's get up to all sorts with an R22. Give us a visit and find out....
The 'deerhunting' section is worth a look, and 'slingloading'.

BFN SPS ;)

[collective bias]

A company in Auckland, NZ currently operates one of these 'normalised' R22's for training and private hire. Personally I think its a waste of time but it does suck in the odd student who likes the feel of a real phelic shape between their legs...
As a matter of further interest, they also hire it with panniers or 'helipods' which are mounted on each side and supported by the skid. This is interesting because my understanding is the skids on a robbie are not designed in any way for load support in the horizontal plane ie. a force pressing in on them (if you get what I mean..). The undercarriage on the r22 is designed to collapse and absorb the impact G's(as most are)This hopefully saves some damage to your back and I suspect that these pods may impeed this. I may be incorrect, but the R44's suffer the problem of a lack of carry area and the kiwi's and aussies have scratched their heads for ages trying to figure a way to make these aircraft really commercially useful. If we could legally fit litters, we would've.
For those who drive R44's this query. To my thinking the R44 is the Daihatsu of the sky. It is well constructed and real fast but lacks an inherent feel of solidity around it. This I notice particularily at 100 - 130kts when the aircraft seems prone to buffeting and a lack of yaw stabitilty. This is further evidenced in moderate turbulence. Don't get me wrong, I'm definately no test pilot but I have wondered if the negative pressure area generated behind the engine at the exhaust outlet, is disrupting the clean airflow over the vertical stabiliser?
To contradict my theory - I recall that removal of the semi-circle cone on the rear of the MD600's notar, improved the yaw stability significantly. This section now is completely removed.

[JoePilot]

It is a retrograde step.

The T-bar is a superior system because:

One set of linkages only
more reliable
less weight
less expense

No obstruction to entry and exit -can be significant

Cylcic grip can be held at a height which suits the dimensions of the pilot - can rest arm on leg more easily.

Against: adjustment period required for pilots who learnt the old fashioned way!

[SPS]

It looks like Joe read my article on the 'conventional' R22 cyclic as he has mirrored just about all I had to say on it. It also looks like Collective Bias didn't read it (and that's OK, no obligation to visit, it was posted in reply to Holly). The only thing I would add to what has been said is that the conversion IS grip height adjustable, there is a turn and lock device about 1/2 way up the curved portion of the stick itself which (when unlocked)results in the grip rising and falling. Then it is locked at the desired height. One drawback that I might mention is that the grip travels an arc as it moves up and down(whilst adjusting grip height) moving closer to the pilot or further away (in relation to the root of the stick). That, for me, was a less attractive feature. It didn't take me five minutes to get used to it (20kt wind) as it was very close to some other types in feel and position, but it has many disadvantges.

Am I sounding defensive of it? NOPE ! I would not buy it for all of the reasons I listed on the page and all of the reasons both of you list, quite properly, too.

Interestingly enough the conversion was photographed at that very same company in Auckland. It was included on the website as a 'general interest' item as people that fly Helis are normally interested in different uses and configurations of the type they fly. It wasn't put there to sell it and the Company mentioned do not make it or supply it. It was put there to satisfy just the sort of curiousity that made HollyCopter post the post! Hopefully it did.

Yes, they also make pods but they are not 'supported by the skid'. Their weight is
hung from the fuselage attachments, they do not apply force that would tend to make the skids move toward each other. Anyhow, it matters not, it is a preference issue as they do have approval for licenced engineer fitting in most Countries, ie a UK 'AAN' number.

It may be correct to say that you can't legally fit litters because they would exert force in an unacceptable direction (on the skids) but the pods do not do this. The UK and NZ CAA must agree that they don't, because they have certified them for installation?

And me? Well, I'm more accustomed to having anything that cannot go in the seatbox on the end of a strop and being able to 'button it off' when I want. Again, just preference.

Collective, your theory on the exhaust and its effect on the V stab. is interesting but
I have misgvings on it. Why 'negative pressure' when exhaust gas comes out positive? Why would it have a such a great effect on the stabiliser when the tail is far higher than the exhaust outlet at the speeds you mention? Would exhaust gas even get there? I have to say I doubt it because I do not find evidence when cleaning the 44's tail, not as you would with other Heli.
types. I think the only time the stabiliser would be in exhaust outflow is in a flare.

Make no mistake, I do not disagree with your description of 'lack of yaw stability' at 100-130Kt but I doubt that exhaust gas is the cause. Anyone have ideas what else could be the cause......?

[rotorque]

SPS,

I don't think he was refering to the exhaust gases per se, just the fact that there is a large flat area at the back of the engine cowl that would act as a negative pressure area. The exhaust is only a piddly little thing and probably dosn't do anything but pump out green house gasses. Who knows ??

Now if you were into H500's on the other hand.............

[JoePilot]

H369: 5% forward thrust from exhaust.
Lynx: Depends on application! ( :) )

[SPS]

Yes, OK, that would cause negative pressure
as the 'end' of the 44 has been 'blanked off'
(and it does not even look so good..!)

Then again, what else would? extending it a couple of feet and bringing it to a point would make the fuselage look too long in proportion.

The Hughes 369 designer ( and many others)must have wanted to stem the effect when you look at the shape of that area but began with things in differnt places and no squirrel cage.....

But I still think the tail (and the stabliser)are too high at those speeds to suffer from any low or negative pressure created?

[collective bias]

Yeah,
I intended that the flat panel from which the exhaust protrudes is the cause. My thoughts come from performing the same excerise as you SPS - Removing the leftover hydrocarbons to prevent corrosion in the rivets along the tail. The film buildup on the panel is the evidence of the pressure change. It is only a line of thought and I am sure frank has checked it out....
I remember now that the Appollo spray rig is attached to belly mounts, so of course it would work for the pods.

[Lu Zuckerman]

Is it possible that the yaw instability is caused by a phenomenon called vortex shedding? As air flows along the fuselage it will due to the pressure differential want to flow into the low-pressure area created by the flat plate form on the fuselage. Once it fills the void it will break away and form a vortex behind the helicopter and then it will happen again where air from the other side of the fuselage will want to fill the void and then it is shed forming a vortex behind the helicopter. When the air flows in from the other side the opposite side has a higher pressure on the fuselage surface and the pressure difference can cause the fuselage to move in the direction of the lower pressure. This pressure differential theory is what makes the NOTAR system work.

But then again it is only a theory.


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The Cat

[Hughes500]

JoePilot, so you have obviously got the plack hand syndrome from handling a 500 lower fin when pushing it out for the day.

Lu I like your theory here but surely at high forward speed this effect would diminish, is this not why they use moveable fins on Notars ???

[Capt PPRuNe]

Closing this thread until HollyCopter sorts their email out. All notification of replies to this thread are being bounced to me because of a problem with your email. Please notify me at [email protected] when you have fixed it and I will re-open the thread.


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Capt PPRuNe
aka Danny Fyne
The Professional Pilots RUmour NEtwork