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Now here's a thing

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Now here's a thing

Old 27th Dec 2014, 11:14
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Now here's a thing

Here's a press release from Airbus that I thought might interest a few people, a bit late for the Christmas wish list.



Airbus Group has completed successful flight tests on a fiber-optic, eye-safe, [email protected] sensor system that delivers accurate airspeed information in three axes at low and negative airspeed for rotary wing aircraft. This range of capability generally is not possible with pitot tubes, the industry standard for airspeed sensors.
The sensor system was developed by Virginia-based Optical Air Data Systems (OADS) and was installed on an Airbus Dauphin 6542 helicopter for flight tests that were conducted in France by Airbus Group's helicopters division. Airbus Group now will work with OADS for certification, with the ultimate goal being commercialization aboard rotary wing aircraft.
The OADS system measures airspeed as low as -20 knots with an accuracy of more than 2 knots over the entire flight envelope compared to standard pitot tubes, which are not functional at airspeeds below 30 knots. The system measures the air 50-60 meters away from the aircraft. This factor can be significant in rotary wing applications, where airspeed measurements may be affected by the downwash effect.
The OADS system is not affected by icing, which can form in the sensor openings of pitot tubes, blocking their ability to accurately measure airspeed.
The OADS technology can measure wind and turbulence several thousand feet above and below the aircraft, allowing pilots to select the most favorable flight altitudes, resulting in fuel savings and a smoother ride.
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Old 27th Dec 2014, 20:41
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Been around for a while. Surprised it hasn't caught on - but then again, knowing how the 'we haven't needed it before so we don't need it now' mentality is so prevalent in our industry, perhaps not so surprised.
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Old 28th Dec 2014, 01:47
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Yes indeed the technology has been around, it was the subject of my graduation research project in 1995. Two (phase shifted) [email protected] cross each-other a some distance ahead and create an interference pattern. As particles cross the pattern they will blink, all that is left to do is use a camera sensor tuned to see these and relate the blinking to speed.


it does require the air to have particles in it (which it almost always has)
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Old 28th Dec 2014, 13:59
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Interesting thing, but isn't it ground speed - an then of course also in all three axes - that's more relevant, when in low speed mode (i.e. hovering either IGE or OGE)?
As far as I know, with radar altimeters/varios, only one "ground related" speed is currently measurable while on low speed.
Do I know too little?

Thracian
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Old 28th Dec 2014, 15:31
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cost benefit

I guess I am old school so someone younger and smarter please tell me why I would need this tech? When I am flying at low airspeed, my attention is completely outside the aircraft. I am judging my speed and the need for more or less speed visually and have no need for an accurate airspeed indicator. There are certainly other technologies I can think of that I would much rather have in the cockpit for the money. An accurate wind direction indicator would be awesome as I fly into many remote areas. I would love to have my ops person be able to send coordinates directly to my GPS so I am not punching a lot of buttons at night, head down instead of outside where it should be. How about voice command for GPS? I want to be able to press a button on the cyclic and say "Direct so and so hospital" or any other preset waypoint, and boom, there it is. That would be awesome. Goggles with an 80 or more degree field of view, now that would be nice. If I was making a wish list, this [email protected] airspeed indicator would not show up. I have lots of instrument time and even in that mode of flight, knowing these low airspeeds accurately is not that important because again, by the time I am slowing to 30 knots or less, I am already outside. Fixed wing or rotor, not necessary.

edumacate me on this.

cheers

Last edited by grumpytroll; 28th Dec 2014 at 15:33. Reason: for some reason my computer put an @ symbol in the word laser!
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Old 28th Dec 2014, 16:08
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On police ops at night in a high hover it would be nice to know my relative airspeed. It is sometimes necessary to hover downwind to keep the rear seat observer 'eyes on' with the 'person or vehicle of interest'. It would also be handy when doing tail rotor handling checks during airtests. How many of us have to 'guess' what sideways and backward speeds we are doing when checking tail rotor authority. Doppler and GPS can help, but both give ground speed and you have to compensate for wind. I would like to see this technology asap.
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Old 28th Dec 2014, 17:09
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Grumpy:
it's important for maximum angle of climb in a twin engine machine that's suddenly lost one in the hover - currently there is no way to show airspeed repeatedly below 40 knots, and for many twins, that gives away a lot of performance in an engine failure situation.
It's also important for limitations such as side and rear wind at night. Like many other things, we've survived (sort of ) without it, but once we have it, we like it.
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Old 28th Dec 2014, 18:05
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For those who fly on the presumption that their helicopter does not suffer from VRS, it could be coupled to the instant VSI and when the tested parameters start squeaking, have it coupled to a large sign on the dashboard that flashes "More airspeed idiot". Might save the odd military bingle at least.
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Old 28th Dec 2014, 19:51
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Remembering the rather vociferous discussion on asymmetric VRS for tiltrotors, maybe it could come in handy there.
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Old 30th Dec 2014, 01:44
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It's also important to tell you what the angle of sideslip is - minimizing drag in the cruise can save fuel, and you have no way of knowing sideslip (unless you fly Airbus helicopters, of course).
Also significantly improves climb rate when sideslip is minimized - the slip ball tells very little of any use below about 60 Knots (except that one was installed).
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Old 30th Dec 2014, 04:20
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OADS vs. Slip String vs. Slip Ball

Shawn,

Could you offer some further explanation with regards to how the system tells you about the angle of sideslip? Is it a separate read-out or something you simply derive from seeing the improvement of climb performance at lower airpseeds?

Three years ago you kindly took the time to try and explain the vagaries of slip balls and slip strings to me(http://www.pprune.org/rotorheads/424...ip-string.html). It now looks like I might have a third system to worry about trying to comprehend!

Simon
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Old 30th Dec 2014, 13:13
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Shawn says:

It's also important to tell you what the angle of sideslip is - minimizing drag in the cruise can save fuel, and you have no way of knowing sideslip (unless you fly Airbus helicopters, of course).
I dunno Shawn, after many years of teaching, my back has developed into a very sensitive indication of sideslip angle... which students seem to be able to keep pegged for the entire flight!
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Old 30th Dec 2014, 15:14
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grumpytroll - it is very useful when you are flying at speeds below 30 kts when there isn't anything to look out of the window at - night or IMC overwater SAR for instance, dust landings or snow landings as well.

Can this system be used to give groundspeed as well as that would be the mutts nuts?
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Old 30th Dec 2014, 21:04
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Good point from SC almost about Best Angle of Climb Speed OEI :

"it's important for maximum angle of climb in a twin engine machine that's suddenly lost one in the hover - currently there is no way to show airspeed repeatedly below 40 knots, and for many twins, that gives away a lot of performance in an engine failure situation."

Vtoss or Vtosh ?
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Old 30th Dec 2014, 21:37
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grumpytroll
An accurate wind direction indicator would be awesome as I fly into many remote areas.
Isn't that exactly what you might use accurate airspeed data to help compute and display?
The aircraft I fly has a great wind direction/speed indicator, but at air speeds below about 40, it becomes much less reliable, mainly because the airspeed information is pretty useless that slow.
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Old 31st Dec 2014, 08:26
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AnFI - Vtoss is not the same as as the best rate of climb speed and a cat A helo operating to PC1 would not transition to forward flight if it lost an engine in the hover unless it was above TDP.
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Old 31st Dec 2014, 17:50
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Paul:
To be very precise - what you're sensing is side force - not sideslip. The Slip ball does not measure sideslip - a common mistake.

For others...
For the first part of the climb following an engine failure, the item of interest is angle of climb, not rate of climb. You want to get away from obstacles that might be near to you, and hence the use of Vtoss instead of Vy.
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Old 31st Dec 2014, 19:03
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Your own words from a 2005 thread Shawn
A term that's missing in helicopters is Vx (best angle of climb speed).
The reason it's missing is that if you can climb vertically in the hover, Vx is obviously zero. But in other cases, (like after an engine failure), Vx would be
a) so variable that it would be a nightmare to caculate
b) probably be below an airspeed that would indicate reliably
So, the term Vtoss was developed - it's below Vy, and a repeatable airspeed and gives a better angle of climb than rate of climb, because for the time you want to use it, you're more interested in clearning the ground in a short distance than in a rate of climb.
For what it's worth....
So, Vtoss is neither Vy, Vx nor Broc and in order to comply with the RFM for PC1 procedures you make your first segment climb at Vtoss, not Vy, Vx or Broc - simples
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Old 2nd Jan 2015, 11:38
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Crab - not sure why you are lecturing me again, on something I know.

I think you miss the point.

The choice of Vtoss is an attempt at Vx but taking other factors into account.

Best angle (Vx) is what you need for avoiding obstacles ahead, Vtoss is the proceedure's 'attempt' at that. As SC says using Vtoss instead of Vx gives alot of performance away (in exchange for other benefits, repeatability, control etc), and the suggestion is that this invention might help get closer to Vx. (but it would need ground speed too, GPS (with 'augmentation') could do this).

Hence Vx, Vtoss or Vtosh?

HNYr
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Old 2nd Jan 2015, 15:34
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I have flown several systems like this, the RAH-66 Comanche had one (albeit a vastly different technology). It will be a boon to pilots in many ways.

AnFI, there really is no such thing as Vx for a helicopter. There are families of angles available, depending on the speed you chose to get to, and there is a distance needed to accelerate to that speed, which changes the resultant achieved angle. This entire complex thing is simplified by providing one speed, one angle and one solution known to work.
With the advent of a real 360 airspeed system, it would be possible to show a graphic presentation of the many families of procedures available to the pilot, so an appropriate one could be selected.
Better yet, we could just provide the power to be a helicopter, go straight up and make it simple again!
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