EC135 tail rotor authority

[bolkow]

I had a conversation with a lighthouse bo105 pilot last week and he queried of me whether I had a view regarding the effectiveness of the tail rotor on the proposed EC135 replacements. It was mentioned that in certain lighthouse locations tail authority is critical, and to have plenty of it. I was unable to answer the question, and just said I had'nt heard it was a problem. Any EC135 drivers able to comment or inform me? We are talking about situations offshore where the wind is considerable and likely to shift in moments. Any comments would be gratefully received.

[Shawn Coyle]

When I flew the EC-135 in 1995, part way through the flight, the safety pilot brought me back to reality when he said something along the lines of 'not bad tail rotor control for a fenestron'. Up to that point I had not even thought about it as a fenstron - I don't think there's a problem with tail rotor authority in this machine. You'll probably not even notice it's not a tail rotor in the pure sense of the word.

[timex]

Not been flying it too long but at AUM you still have plenty of tail rotor authority in most wind conditions.

[Phoinix]

I've been flying it for the last year and i have never got close to loosing TR authority. However you have to be careful with sidewind during hovering. Fenestron is somewhat less sensitive to wind gusting due to higher airflow velocity but the fenestron takes a lot of tail surface. 135 just does't like the crosswind from the right. Keeping the wind on your left solves the problem.

[semirigid rotor]

I have been flying the EC135 for 8 years now and have never hit the pedal stops.

[Phoinix]

I am puzzled from time to time; how much pedal is actually used during some maneuvers. Pedal input from the pilot is one, SEMA input on the tail rotor control is another.

[eurocopter beans]

i have about 1300 hours on 135s, never noticed any lack of tail rotor authority. ECD issued a pilot circular following an enquiry about LTE in fenestron helis, they maintained that if you have what you perceive to be loss of tail rotor effectiveness that full pedal input (to stop) will rectify the situation. Other than that im not sure what the b0-105 driver was referring to. Then again im no test pilot, seems like a question for those guys 'pushing the envelope'!!

[Droopy]

Most powerful tail I've ever flown.

[Helinut]

Obviously, it depends on what you are doing and where you are doing it, but in 7 or 8 years of EC135 flying in various roles, I have always found there was a reserve of TR authority. Lots of out of wind OGE hover and similar that would challenge some other types.

I suppose that the body of the fenestron might possibly cause an obstruction to flow in some situations, but I have never noticed anything.

[bolkow]

The bo105 driver specifically mentioned the kinds of abrupt changes and strength in wind encountered offshore, (lighthouse releif/supply) and noted that on occasions in the bo105 he had down the years encountered gusts the bo105 coped with well. He had never flown a 135 but was simply wondering (or worrying) as to whether it would compare. He mentioned that the area of the fenestron fan seemed small compared with the relatively small tail rotors of the bo105.
Never having flown it either I wondered too as it is going to replace the bo105's.
I note the comments from guys who have flown it, but has your flying been in the sort of conditions encountered offshore?

[[email protected]]

Sounds like we're back to the Fenestron Stall arguments about the Gazelle:)

[Heli-phile]

I have always found wind conditions offshore to be pretty steady (direction wise)regardless of strength as compared to urban or in locations where mechanical turbulence is a risk. Offshore, even in winds up to 55kts control is not a problem (assuming you are landing into wind) Biggest problem is passengers not getting blown off the pad!!:}

Fenestroms, like notars will always be 'mushy' compared to standard designs. As with any helicopter it only gets interesting when you try to hold it against the wind. (never a good idea in many ways) If for some reason you are obliged to just abide by the RFM and avoid the problem quarters where airframe/ M/R downwash can make life interesting, Test pilots have gone to a lot of effort so you dont need to.:)

[meat bomb]

Ive generally found the 135 to have good handling qualities all round,in high oge hover , out of wind , lighthouses , mountains ( not all at the same time ). As per the manual if you do have a problem apply a bootload of pedal and maintain till the spinning around stops.

[Fly_For_Fun]

Sounds like we're back to the Fenestron Stall arguments about the Gazelle:)


Doesn't exist. Ask the French :ugh:
...or there again ??? ;)

Never had a problem with Tail Rotor Authority of EC 135 T1 or T2 in the 6 years I have been flying it. It would be interesting to hear from the ECD test pilots that have flown some of the more interesting profiles though.

[NickLappos]

Having flown a number of fans, Eurocopter and not, it is my belief that there is no such thing as "fenestron stall" as a phenomenon unique to fans. The fan on the older Gazelles was too small and had too little thrust. It didn't stall, it just didn't have enough poop in some situations. It was fixed by changing it to add more max thrust.

The Comanche and S76 Fantail demonstrator could fly at 80 knots sideward, and point independent of the direction of travel up to well over 100 knots. No fenestron stall there. Or better yet, "it flew pretty well, for a fenestron".

I would bet the comments of the experienced 135 drivers below ("flew for 8 years and never touched the pedal stops") tell the story, build a tail with enough thrust, and you will have no problems.

[bolkow]

Thank you for all iof the responses above. I am reading it that concerns about the 135 fenestron are largely just something that afflicts the inexperienced such as myself. many thanks!

[BlenderPilot]

If you are going to have problems with TR authority it will be at the higher altitudes with high weight, it will happen.

[eurocopter beans]

Blenderpilot, your input is interesting. Could you tell us of your experience of this happening, what altitude and weight? How did it manifest itself and how did you recover?

[ron-powell]

BP said: If you are going to have problems with TR authority it will be at the higher altitudes with high weight, it will happen.

EB said: Blenderpilot, your input is interesting. Could you tell us of your experience of this happening, what altitude and weight? How did it manifest itself and how did you recover?

Just when I thought I had it all pushed into a nice pile in the corner……. I’m out here in the high desert of New Mexico USA flying an Astar B3. A machine I consider having a pretty powerful tail rotor. Then one night……..

One of our pilots was coming out of the scene a few percent under gross, maybe 6500’ MSL and 50-60F, a slight breeze of a headwind as registered on the ground, hand full of collective, low airspeed and takes a right turn home. At about 200’ AGL and 90 degrees into the turn, they proceed to spin a couple times against full right pedal before he gets it sorted out. I can only imagine what it would have looked like without NVGs.

More forceful left crosswind at altitude? Bad choice of turn direction? Not enough airspeed? Probably a little of all of them.

I’m in agreement with Blender. If you’re not careful, sooner or later she comes home.

[Shawn Coyle]

ron-
Did the pilot report this? NASA's ASRS is an ideal place to let this get known.
And if we don't report stuff like this, nothing will ever be known about it, and nothing will ever get done about it (and the something that might get done about it could be as simple as training and awareness....)

[ron-powell]

Shawn:
>Did the pilot report this? NASA's ASRS is an ideal place to let this get known.

There was an internal investigation. Incidents such as this are taken seriously by both the aviation and medical sides of PHI and the information is disseminated company-wide, but to my knowledge, that document hasn't been published yet. Beyond that, I don't know.

My take is it was a combination of factors. You will truly be amazed at the varying strength of the wind out here. A flight can be coming in from the west with a 30-40kt tailwind at 1000' AGL. Overfly the hospital and the sock is hanging limp. My personal favorite is typically 25 gusting 35-40 reported from the east at ABQ international and at the hospital 3 miles due north, light and variable.

[coorong]

In my experience, The EC 135 will hover 90 degrees out of wind up to 35Kts. with little problem. At 35-40 Kts., you wil sometimes reach full pedal with a proportionate reduction in control. At 40-45 kts., control may be lost and you need to quickly dive on speed to regain yaw control. Above 45 kts. it becomes almost impossible to retain control, especially if ther is any gusting.

This can be a bit hairy , so I would recommend plenty of height [ i.e. greater than 800'] if you need to do it. The a/c may yaw through ~130 degrees with you as a passenger:eek:

[Fly_For_Fun]

Nick

It didn't stall, it just didn't have enough poop in some situations.

I would have thought that not enough thrust to overcome relative airflow through the fan could easily be described as "fenestron stall"

[Graviman]

Don't forget fenestron might be recirculating its outwash - effectively requiring more power to overcome VRS...

[sycamore]

I`ve not flown an EC135,so my comments relate to approx. 30 other types that I have flown and tested.All have limitations for certification,military and civil,being either Vne,enginepower/rotor Tq, weight,CofG,SIDEWAYS flight,BACKWARDS,and RATE of YAW. They are usually determined when the amount of control used is within 5-10% of full control authority as determined/set by the manufacturers,to allow a little margin for error. If you use ,as has been said,full yaw,whilst hovering,possibly outside the sideways/x-wind limit,and the a/c about-faces,that is your problem,and you may not have 700ft to play,or pray with!
Not only that,operating consistently outside the limits will put up the amount of power reqd,by the t/r drive shaft ,and gearbox; it may well fail,maybe it will fail with someone else,who may well be flying within limits one day.

[[email protected]]

The theory behind 'Fenestron Stall' was that even in the hover, the vertical and heavily cambered area of the tail was producing useful anti-torque lift by virtue of the fact the air was accelerated over the fin on its way to the fenestron. Therefore the fenestron itself wasn't having to work as hard it might if that lift wasn't there. Now introduce a wind from the right (about 10 kts was the quoted figure) that disrupts that flow around the fin and suddenly the fenestron is behind the drag curve, not producing enough thrust to make up for the loss of the fin lift - the yaw to the left starts and what is required is an unusually large right pedal input to cancel the yaw and compensate for the loss of lift from the fin. Most pilots would be reluctant to make such a large yaw input initially and so the yaw rate increases - all the while the selected pitch of the fenestron is less than is actually required because the pilot is having to play catch-up.

The theory was debunked by Aerospatiale because they showed that full right pedal would always stop the yaw, even if it overtorqued the transmission!

Frankly I am surprised the French didn't claim it was designed in like the jackstall due to underpowered main jacks:)

[BobbyBolkow]

Intresting thread this! So having flown Bolkows on lighthouse ops and currently flying the 135 I'm going to throw my 2'pennorth worth in.

Flying a 135 to lantern top lighthouses (which are mostly confined to the SW of the country) will be no problem. The wind, regardless of strenght, will be fairly consistant in direction and with 100'+ of open airspace around the tower, a go around is no big deal. The 135 has very good tail authority, copes well in a cross wind and, like others, I've never got near the stops.
HOWEVER, I do take issue with those that say "just put in a bootfull of pedal". At high AUW and low speed/hover, the 135's fenestron eats huge amounts of power. If at a high Tq setting you put in a bootful of left pedal you WILL overtorque (very rapidly). Most 135 pilots have had the Tq limit 'BONG', (or is that just me?). OK with consistant wind if you are aware of the possibility. The problem will come with rock station or headland lighthouses. Where the winds can vary by topography + /- 20+ knots and + or - 90+ degrees. The fin would react to the wind and corrective action could or most likely would, result in a Tq limit.

Sorry! Banging on a bit here. So, in a nutshell, and to answer the original question, the 135 would be a very capable replacement for the Bolkow for lighthouse ops. However, in certain conditions it could well be more limiting.



Does ANYBODY know how to fly this thing? :ok:

[eurocopter beans]

Previous comments of bootfulls of pedals are an obvious generalisation but are for the most part correct. The majority of the flying i do in the 135 is in OGE hovers at MAUW in windy/turbulent/gusty conditions, we often operate in crosswind hovers with plenty of spot turns etc and i have never experienced any condition where a 'bootfull' does not remedy the situation. If at MAUW, a bootfull may induce the bong (indicating you are in excess of 10 FLI, however you may pull a transient 10.5 FLI before maintenance inspection is required). Never have i reached the pedal stop either. As ECD published, pilots should be wary when operating close to the ground at low airspeed while turning right into the wind, however the pilot notice did say that if loss of tail rotor authrity is suspected to apply pedal to the stop and this will remedy the situation, if it means overtorqueing the machine in the process of saving the airframe, so be it. I think talk of fenestron ineffectiveness is giving some people unfamiliar with the machine a bad impression of it. My experience of the 135 has been very positive in comparison to other helis, if only they sorted out those damn ARIS pots (thats another thread!) other than that they are an example of excellent german engineering!!!!

[Brilliant Stuff]

Just remembered have a word with Rotordompteur who posts on here he flies the 135 amongst the windturbines offshore Holland he should know about windy conditions and tail authority.:ok: