AW169 quality of altitude and air speed measurement

[MeddlMoe]

Hello all,

I saw that the AW169 has the static ports of the barometric system (altimeter) integrated in the pitot tubes, which is different from Eurocopter or Bell helicopters (at least those that I know).

Do you have experience with this system?
Are there any special issues with the airspeed indicator or altimeter at slow speeds? Does the AFCS behave well?

Thanks
Moe

[rrekn]

Integrated pilot/static tubes are very common in many types including fixed-wings, the AW139 & AW189. There shouldn't be any issue with the altitude or airspeed measurements with using these against the flush-fuselage mounted types.

[[email protected]]

And the data from the pitot and static ports is fed to Air Data Computers for processing before being sent to the displays and the AFCS.

[212man]

Why would there be issues?

[JohnDixson]

212, we started the SH-60B Seahawk with the UH-60 pitot static system, but wound up moving the probes and utilizing separate static ports. The aerodynamics with relatively low but powerful rotors and the lower climb and descent profiles, combined with fuselage add-ons make for aerodynamic irregularities.
Going back to the basic UH-60 prototype, we did over 100 flights on 652 ( the powerplant integration and sub-systems test vehicle ) wherein the pitot static system was on the test card. And yes, there were all sorts of “ colorful “ suggestions as to how to fix the system.

[212man]

Thanks John - always a pleasure to hear your tales. I'm aware that various designs encounter issues during testing and often need creative solutions (I'm pretty sure the S61 didn't start life on the drawing board with its pitots on top of the mast!) but I guess my query to MeddlMoe was more around what specifically he had concerns about, and how would it have been certified if there were such issues.

[MeddlMoe]

The integrated solution is nice and compact, and you can use less tubing, so I thought that Eurocopter and Bell have a good reasons not to use them.

The front of the aircraft is ideal for dynamic pressure measurements (pitot tubes), but not for static pressure measurements. Vice-versa for the static port locations. Therefore, the total result could be worse.

The certification leaves some space for interpretation. Maybe the AW169 system is just good enough. Or it is perfectly fine. That is what I was curious about.

[megan]

pitots on top of the mast

The 61 must be unique in that regard, are you familiar as to why JD, besides it obviously being the best place found?

[gmrwiz]

These are the calibration curves of the AW169. Lev flt,climb and partial power descent are on the same curve while in autorotation the speed is slightly underestimated i.e. IAS=100kts means CAS=102kts

[JohnDixson]

S-61 Head Mounted Pitot

Originally Posted by megan

The 61 must be unique in that regard, are you familiar as to why JD, besides it obviously being the best place found?

(I signed on in June 1966). Here is what I recall being told. The original 61 was the USN anti-sub SH-3A model with cockpit roof mounted pitots. That location was also used for USAF model with the rear ramp. The USAF required that model be FAA certified and it was. The head mounted probes on the commercial model 61s resulted from the associated flight profiles commensurate with Cat A certification, which the previous military testing and the FAA certification of the USAF model did not include.

[SimFlightTest]

Just because a pitot-static system is on a certified aircraft doesn't necessarily imply that it is accurate. It simply implies that it is accurate against what is presented in the RFM. For example, the AW119 pitot-static system has massive errors (>10 kts) in certain flight regimes (mostly during low power descents, as well as during high power climbs at higher airspeeds). It's pressure ports are up above the windshield.

[Thud_and_Blunder]

ISTR the P2e version of the EC135 (or whatever AirbusH call it this week) separated the static source for aircraft instrumentation (fuselage sides) from the source for ADCs (probes under the nose, later fitted with pilot-with-wash-and-brush-proof 'guards'). There were also separate sources for the engine air particle separator systems, right next to the intakes. Interesting that Leonardo would go for sourcing all the info from the 2 tubes; chance for increasing mismatches twixt systems increased, I would think.

[gipsymagpie]

Originally Posted by Thud_and_Blunder

ISTR the P2e version of the EC135 (or whatever AirbusH call it this week) separated the static source for aircraft instrumentation (fuselage sides) from the source for ADCs (probes under the nose, later fitted with pilot-with-wash-and-brush-proof 'guards').

Those probes under the nose are Total Temperature Probes for the ADU. The ADU get their static pressure from the same ports as the standby instruments on the rear sides of the aircraft.

Ive flown and tested all sorts of variations of static ports and pitot ports and I don’t think there’s really anything particular to note about a combined sensor. The only point I’d have is that they’ve probably got a combined heat source so lose one heater means lose both pitot and static on that side whereas there might be more redundancy in a split system.

[gmrwiz]

SimFltTest,
I am wondering how you could have calibrated the airspeed system in low power descent and high power climb.

[gipsymagpie]

Originally Posted by gmrwiz

SimFltTest,
I am wondering how you could have calibrated the airspeed system in low power descent and high power climb.

Do you mean where do you get "truth" data from? Probably a trailing pilot static bomb on a sling line under the aircraft