AS365
 

Just one quick question. What is that tiny T-shaped thing on top of the rotor head? I don't see it on any other dauphin pictures just on the Coast guard ones.
Just wonderin' :confused:

The USCG Dolphins have standard pitot tubes under the chin and also have this small mast ontop of the rotorhead. This is the Air Data Sensor which is largly outside of the aerodynamic effects of the aircraft during flight and so gives the best indication of wind speed and direction. This data is fed to the autopilot for flight and hovering.

The low airspeed sensor is driven around by a small motor, and it gives very accurate information when the helicopter is below 40 KIAS. It gives side and rear wind, and for a helicopter that hovers over the water in the middle of the night, is nearly essential.. .Every helicopter that flies IFR, and probably every other helicopter should have such a system, but we don't because we've never had them before, so we think we don't need them.. .Bit of a pet peeve of mine - I used it to very good effect on the HH-65 when I was instructing at the Naval Test Pilot School to show hover performance. . .Since it calculates the side and rear wind components and feeds them in to the navigation computer, it gives very accurate wind calculations.

Alright, thats pretty cool, thanks for clearing that up guys.

How come it doesn't get affected by the induced flow through the rotor? Or is it factored for that?. . <img border="0" title="" alt="[Confused]" src="confused.gif" />

The Apache has a similar system mounted above the rotorhead. It is used to compute wind direction in order to correct for the basllistics of the 30mm Chain Gun and the missiles.

The low airspeed system is calibrated (or perhaps characterized would be a better term) to account for the inflow effects. . .The way this characterization would be done is to fly the helicopter at different weights, in and out of ground effect using a pace vehicle to obtain exact airspeeds. This data is then fed into the computer to compare with what it saw, and make the system display the correct values of wind.. .It doesn't work particulary well when doing rapid transitions to and from the hover, but it is way better than nothing.. .We have one of these systems on our ex-Canadian Forces Bell 212 (it was a fully instrumented aircraft from the Canadian test center at Cold Lake)and it is very useful.

The Bell AH1-J and the Agusta A-129 had a similar device in that it measured the direction of the airflow around the helicopter as well as the airspeed. It would align itself with the relative wind in relation to the center of the fuselage. In a hover it would align itself with the downflow measuring air velocity. Like the Apache system it was used to correct for wind for the gun and the missiles.. .. .Unlike the Apache system and that used on the HH-65, which were mounted on top of the rotor system this unit was mounted on the right side of the fuselage immediately next to the pilot position.

All the airspeed systems below the rotor, such as those on the side of the Cobra, are at best a bad approximation of the airspeed during low speed cases. The calibrations of those systems is nearly random where it counts, mostly because the downwash contains strings of high speed tip vortex air that is easily at 40 to 60 knots of energy. If that vortex strikes any pressure sensor (a pitot, or a fancy pressure transducer) the results are chaiotic.. .. .The S-76 pitots, and the Sea Hawk's, are located in the nose so that the blade tip vortex sweeps above them at speeds above 30 knots or so. When we developed the S-76 system (I flew one prototype that had 10 pitots -it looked like a B-17!), we had to track the tip vortex pattern as it swept across the nose at 30 knots, across the pilot's door at 50 knots, across the upper doghouse at 80 knots and finally across the transmission/swashplate fairing at 120 knots. Since the FAA airspeed calibration must be accurate down to 30 knots in level flight, we chose the nose position for the type design.. .. .The sensors above the rotor are affected by inflow, but those are relatively predictable, and much smoother than the hash below the rotor. The first airspeed above the rotor was the S-61 bullhorn system, which uses a common pitot, but is quite accurate and reliable down to 30 knots. The rotating systems above the mast are as a class quite accurate, and also read the azimuth of the airspeed, a boon to weapons shooting.. .. .Comanche uses sensors in the blades to read the dynamic pressure continiously. A computer sorts out the phase and rpm effects, and leaves the airspeed data and azimuth as a very accurate result. The blade sensors are used on Comanche because all the other systems contribute too much radar return.

All very interesting chaps, can I digress from the initial query for a moment....how did the USCG come up with the name 'Dolphin'?.....did they not like the manufacturers name? True, the military have always assigned differing names but I wonder if anyone has any idea on this one.

Prob could not pronounce Dauphin correctly so It came out like Dolphin. Ever heard a Texan trying to get their lips around Ecuriel ??. .edited for bad spelling.. . . . <small>[ 14 March 2002, 12:31: Message edited by: widgeon ]</small>

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica">Comanche uses sensors in the blades to read the dynamic pressure continiously. A computer sorts out the phase and rpm effects, and leaves the airspeed data and azimuth as a very accurate result. The blade sensors are used on Comanche because all the other systems contribute too much radar return. </font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">I had heard about that, very , uh .. Kewl !

Dolphin, Dauphin same thing. The early 365C's had a large Dolphin sticker on the side of the gearbox cowlings with the word Dauphin. I've still got one somewhere. I sent a fax of it to R&W some time back when sombody started burbling on about the origin of the word Dauphin and it's relationship to Dauphin.

Correction that last Dauphin should be Dolphin

Doesn't 'Dauphin' mean 'Prince' in english??. .. .Excuse my year 10 public school education....

Dauphin is the French for Dolphin.. .. .Dauphin was also used as the French term for a Prince.

AS 365
 

Hello again rotorheads,
Is there somebody here who is operating an AS365N or N2 with an HUMS (or IHUMS) retrofit ?
Are you happy with it ?
I am a bit disapointed about the operational reliability of the model my company has decided to buy .... Lot of money for almost nothing but trouble.
I don't think, in these conditions, that the retrofit of a such complex system on a relatively small (and old) helicopter already stuffed with other electronic gadgets is a + to safety and maintenance costs.

I'm a HUMS engineer, and I've dealt with dozens of AS365'S with retrofit HUMS, there should be no problems whatsoever. What sort of trouble are you having??

I dispute your point regarding safety and maintenance, HUMS is not a fail safe early fault detection system, however, and the CAA will back me up on this, it definately IMPROVES safety and reliability, and on a machine with so many single critical load paths, that is justification enough for its existence my friend.

Remember, the fact that a good HUMS will save you a few beans in terms of maintenance costs by allowing better maintenance planning and spares procurement, not to mention helping your direct operating costs through reduced downtime due to in depth fault investigations, or unnecessary assembly changes when a small component is at fault, is a side issue. The name of the HUMS game is safety, when you are flying out to the ship, or the rigs, the one sound you do not want to hear is "Splash".

E-mail me privately if you want more in depth chat regarding your specific problems, happy to help. :ok:

Thank you for your answer Flytest, and believe I completly agree with you about a normal operating HUMS efficiency in improving safety and maintenance costs (i.e enhancing preventive maintenance, permanent monitoring and component life times)
And I believe this system works well when fitted on an helicopter from factory.
The problem seems to come from the retrofit operation itself, and the result, with the HUMS my company has chosen, is rather disapointing compared to the investment. Basically, in the best of cases, we can use it for track and balance of main and tail rotor :ugh:
For obvious reasons I cannot give too many clues here, but I am going to try an email now (I wasn't lucky last time I've tried it here) but I cannot garantee my words will be able to find your mailbox through the "cyberspace".
Sorry, I am nothing else than a miserable pilot

;)

CPT

Am interested to hear specific problems with HUMS, especially retrofit, after all none of us are perfect. That said there are a few of us out here who believe whole - heartedly in the future of such systems, whether they are made in Toulouse, Eastleigh, Fareham or wherever. One of the biggest problems with HUMS is false alerts, when a system detects a "fault" that isn't really a helicopter problem. This can happen from alert thresholds being incorrectly set, faulty sensors or corrupt data files. All I can tell you is that manufacturers, operators and regulatory authorities are aware of this, and are constantly working to reduce false alerts, without compromising the ability to detect real faults... its a fine line :ok: