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  #11  
Old 02-03-2008, 10:40 AM
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groucho groucho is offline
 
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I've been flying velocity vector's around for about 10 years & absolutely love them. They are great for many things other than IFR flying. However, a velocity vector alone is not enough, IMHO, for IFR flying. For IFR work, I still want a bank angle displayed along with pitch attitude of the plane & mag heading. If everything is displayed correctly, you can get ground track easily by comparing the VV to the heading. Is the current standard of displaying attitude & VV the best? Maybe, maybe not. I like it, but I could be swayed if someone can make something better.

Alex, great question - many people haven't flown with a velocity vector, so this is worth talking about. To describe what a velocity vector (sometimes also called a flight path marker) does, I'll use this generic EFIS screen (that I happened to program up for my homebrew EFIS...it does look somewhat similar to a "Brand B" EFIS ).



In that picture, the heading tape is shown across the bottom. Airspeed is on the left & altitude is on the right. Vertical speed is shown as a while bar with text just to the left of the altitude. The black "W" represents the waterline (aka Whisky line) of the airplane (i.e. where the nose is pointed) and is fixed on the screen. The velocity vector is the green circle with little wings & tail. Things can be moved around, but the generally accepted EFIS/HUD layout is airspeed on the left, altitude on the right & heading either at the top or bottom. Heading can also be displayed along the horizon line - that works fine too.

The "W" shows where the nose of the airplane is pointed. That works just like the aircraft reference on an old-school attitude indicator. The shape of the "W" symbol is not critical & can, in fact, be changed to include flight director type information & more. Aircraft heading and pitch attitude are shown relative to this symbol.

The velocity vector moves around the screen relative to the W and horizon to show where the airplane is actually going. In the above picture, the aircraft's pitch attitude is about 5 degrees up (see where the "W" is on the pitch ladder). The velocity vector shows that the airplane is actually descending at about -5 degrees (center of the velocity vector circle). The vertical (i.e. pitch) difference between the "W" and the velocity vector conveniently works out to be the airplane's angle of attack (if you define zero AOA as aligned with the "W"). So, the above picture shows the airplane at about 10 degrees AOA. If the airplane is moving level, the velocity vector is drawn on the horizon. If the airplane is descending at 3 degrees, the velocity vector is drawn 3 degrees below the horizon (ILS anyone?). If the airplane is moving straight down, the velocity vector is drawn at 90deg down.

That's pitch...half of the velocity vector. Yaw (sideslip, beta, track - whatever you want to call it) is the other half of its job. The above picture doesn't really show this well, so here's one that should help.



The display here is roughly the same except that the velocity vector is yellow. Here my airplane is flying level, but with a significant crosswind from the left. Since the airplane is flying level, the velocity vector is drawn on the horizon (that's the pitch part). Since there is a crosswind from the left, the airplane is actually moving (drifting) to the right of its nose. So, the velocity vector is drawn to the right of the "W." The difference between your "W" and velocity vector here is your drift (the difference between your heading & ground track).

Displays should be programmed so that a degree up or down is equal to a degree left or right on your EFIS. So, this shows that I have about a 20 degree difference between my heading and ground track (it was freakin' windy). If the EFIS has a heading tape instead of just a digital readout, the ground track can be read by drawing a line from the velocity vector down to the heading tape (when your wings are level).

For day VFR-only flying, I still like having an attitude reference, but you certainly don't need one. For night VFR flying, I REALLY like having an attitude reference. I flew a VariEze around for about 5 years without any attitude reference (except the huge attitude indicator out the front window). (note: I don't count that 2" turn & bank as an attitude reference...paperweight) Love it:



(on soap box.) Without getting too caught up in the source of the info, I think it's important to think about what the pilot is actually being shown. Pitch based on vertical speed & bank based on turn rate are not actual "control parameters." While you can fly around & maintain level with a VSI & turn & bank, they can't be relied on in all situations - especially dynamic situations. I still feel that attitude derived from a gyro source is a safety critical item for IFR flight (gyro source: EGI, INS, AHRS, MEMS, mechanical gyro, etc). A non-gyro device might save your life if you get in a bind, but complacency around using it might kill you. (off soap box.)

I'm very much for us pushing the human-machine interface (aka pilot-vehicle interface (PVI)). There are several EFIS manufacturers that read these boards, so your great ideas just might make the next round of software (get your patents filed quickly ).

Hope this helps!
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  #12  
Old 02-03-2008, 11:41 AM
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AlexPeterson AlexPeterson is offline
 
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Groucho, excellent explanation. One curiosity though - the Blue Mtn. picture shows constant altitude flight (vertical velocity vector level), but nose down (W below the white horizon line). ??
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  #13  
Old 02-03-2008, 11:50 AM
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REHughes REHughes is offline
 
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Default Classification of Velocity Vectors

The terms Velocity Vector and Flight Path Marker are often loosely applied to three distinct implementation schemes that behave very differently:

1. The symbol is caged to the fuselage boresight laterally and only moves vertically (in the same plane as the fixed Waterline.)

2. The symbol is air mass-referenced and shows actual projected path (including Beta sideslip angle) through the air mass. This is the implementation of choice for Air-to-Air weapon systems, and is most convenient for any maneuvering flight reference.

3. The symbol is ground-referenced, including drift over the ground as well as Beta, and thus shows the true flight path projection in reference to objects on the ground. This is the implementation of choice for Instrument Approaches and Air-to-Ground weapon delivery.

The most effective HUD presentation that I was able to evaluate in a sim was a "Best Of Both Word's" approach from the British for their last group of Sea Harriers. The standard 'circle with wings and a fin' symbol was displayed as an air mass reference (they called it the CDA, or Climb-Dive Angle indicator) and another small diamond symbol was shown full time as a ground-referenced Velocity Vector. The diamond was carefully mechanized to avoid clashing with the CDA when there was minimal drift over the ground.
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  #14  
Old 02-03-2008, 12:01 PM
B25Flyer B25Flyer is offline
 
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Alex,

Let me put it in warbird pilot speak, Our traditional HMI, or PVI, shows us where the airplane is pointed. VV shows where the airplane is going.

Most systems that incorporate VV info today provide it as secondary information, with pitch roll and heading primary.

Displaying VV as primary with pitch roll and heading as secondary information should result in an interface that is much easier to fly. As has been said here many times, most of us with EFIS are now the flying track carrot instead of the heading on approaches now.

I was absolutely opposed to it and I told Younkin he was on the wrong track with his EFIS interface until I figured out that only reason for an EFIS in a light sport is inadvertant IFR. (I realize I am repeating this) When I realized that a Sport pilot would have a much greater chance of survival with VV instead of tradtional pitch & roll info, then I asked myself, if it is easier for them, why isn't the industry having this discussion instead of just Jim Younkin, who by the way, has probably pioneered more flight control and insturment technology than anyone.

Repeating again, I am not interested in discussing how we derive that info and GPS failure etc. Once the industry decides what the correct interface is, then we can discuss how to get the info. There are plenty of failure modes in what we are doing right now.

Tailwinds,
Doug Rozendaal
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  #15  
Old 02-03-2008, 12:02 PM
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groucho groucho is offline
 
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Quote:
Originally Posted by AlexPeterson View Post
Groucho, excellent explanation. One curiosity though - the Blue Mtn. picture shows constant altitude flight (vertical velocity vector level), but nose down (W below the white horizon line). ??
Excellent catch...I'm pretty sure that was in an updraft, so it took some nose down to maintain level.

I set my "level" in my EFIS to correspond to cruise speed at about 8000' MSL, so it shows 0 AOA at cruise speed. Anything slower than cruise, it shows positive AOA & anything greater than cruise speed it shows negative AOA. A negative AOA at 14,500' means I was pushing forward for something (updraft!).

Here's another possibility (not real, but to use as an example)...Suppose I just pushed forward on the stick to get that nose low attitude. Since the gyro in the EFIS outputs measured angles, the attitude of the plane is shown immediately. The vertical speed takes a few seconds to "catch up." Because of that, if a pilot is using a pitch attitude display based on vertical speed, that pilot has to give a control input & wait to see if it was right. A pilot using a "real" gyro can change his pitch attitude a degree (or whatever's required) and get instant feedback. Both can be done, but a vertical speed based system requires the pilot to fly more "open loop" (less frequent control inputs).

For inadvertent IMC, a pilot might be able to survive using either system. Whatever the sensor input to the display, (historically speaking) an non-IFR trained pilot typically doesn't stand that good of a chance. Like others in the thread say, pushing the PVI/HMI technology forward is one great way that we can increase the chances of survival for VFR pilots in inadvertent IMC.
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  #16  
Old 02-03-2008, 10:42 PM
paul330 paul330 is offline
 
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Default Thrust + Attitude = Performance

The correct technique for instrument flying is to set an attitude and a power and monitor the performance instruments (airspeed, altitude, heading, v/s) to assess. Any errors should be corrected on the attitude and/or thrust. It is extremely poor technique to attempt to fly the performance instruments which results in "chasing" parameters. Having said that, I have seen an awful lot of pilots who get away with it on a regular basis!

The VV or FPV (whatever you want to call it) is essentially a performance instrument. Whilst it is a fantastic tool it should not be used as the primary means of controlling the attitude of the aircraft.
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  #17  
Old 02-04-2008, 01:01 AM
penguin penguin is offline
 
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Quote:
Originally Posted by paul330 View Post
The VV or FPV (whatever you want to call it) is essentially a performance instrument. Whilst it is a fantastic tool it should not be used as the primary means of controlling the attitude of the aircraft.
Paul, That's a great quote from the text book, and I guess from a few hours of practical experience flying "conventional" glass. The suggestion here is that a VV, properly implemented, will provide better information for the pilot to control the aircraft. It may require some tweaking of what are thought of as instrument flying basics (I'm not sufficiently knowledgeable or experienced to say). But I would suggest one of the reasons for the current teaching is that, generally, there is no indication to the pilot where the aircraft is actually going. Once you have that, the basics of set the attitude and see what you have may be less relevant. Good technique will still play a part - and chasing anything is often a bad idea - but focusing on where you're going, while keeping the other parameters in bounds, has got to be a good thing?

Quote:
Originally Posted by REHughes
The most effective HUD presentation that I was able to evaluate in a sim was a "Best Of Both Word's" approach from the British for their last group of Sea Harriers.
Thanks for that, I had a small part to play in the design of that system. One other way to differentiate between a ground referenced and an air mass referenced system is to have 2 modes (perhaps called air-to-air mode and air-to-ground mode), but in reality won't we be interested in the ground referenced symbol most of the time?
Pete
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  #18  
Old 02-04-2008, 02:09 AM
paul330 paul330 is offline
 
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Quote:
Originally Posted by penguin View Post
Paul, That's a great quote from the text book, and I guess from a few hours of practical experience flying "conventional" glass.
Er, actually 13000+ hrs including a RAF Flying Instructor on basic and F4 and currently a IRE/TRE on Airbus 330/340...........

You don't need the FPV to tell you where the aircraft is going. Basic technique is to know the appropriate attitude and thrust setting for the phase of flight. It's as relevant on what I fly today as it always has been. I teach to set the parameters and THEN see what the FPV is giving you. It's a great tool and source of additional information but no substitute for basic IF technique. Trust me on this from one who, when young and foolish, used to fly around over the UK North Sea, low level at night at 450kts doing 4g turns on instruments!!
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  #19  
Old 02-09-2008, 09:56 PM
jeff122670 jeff122670 is offline
 
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not to hijack the thread, but what current systems on the market offer a flight path marker (velocity vector)?

Jeff
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  #20  
Old 02-10-2008, 11:24 AM
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frankh frankh is offline
 
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Default My head hurts!

The only thing I understood so far is that mechanical turn coordintaors are indeed paperweights....

Frank
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