This question may have been asked before - my apologies. My question is: Does the Angle of Attack indexer (Chevrons with Doughnut in middle) act in harmony with the HUD AoA Indexer?
The graphic shows the AoA Indexer showing FAST (lower RED chevron pointing UP). The HUD indication in GREEN markings shows the indicator at the TOP of the range, in direct opposition to the AoA Indexer. I would have thought that the Green HUD indication would mimic the AoA Indexer by being in the extreme lower part of the scale (indicated by the red path arrow). In that way (if you follow) when the aircraft is FAST (at 178KIAS) the RED Lower Chevron would show this as well as the Green HUD indicator being at the Lower End of the scale.
I have no idea what the HUD shows because any HUD film of a landing does not show the AoA Indexer at the same time. However my guesswork would indicate that the AoA Indexer and the HUD do mimic one another relatively speaking in the way suggested, rather than what is shown in the graphic. Any help appreciated to sort this out. Thanks.
Last Edit: Jul 31, 2009 22:31:25 GMT 12 by FlyNavy
A 13Mb .WMV video shows mostly the AoA Indexer showing SLOW (green) with the HUD indication being at the low end of scale (or off scale sometimes). The doughnut ORANGE indication for both is harmonised, but not SLOW or FAST:
The HUD AOA stall indication was definitely at the top of the scale with low AOA at the bottom. In the screen shot above, the HUD is showing 178 KCAS. Unless you've just pulled the stick back into your stomach, the AOA should be showing around 5 units, with the LOWER AOA chevron illuminated in GREEN (these lights were only active with the gear handle not in the up position).
If in fact you were at the stall, the HUD AOA indication is correctly showing being at the stall AOA. This "AOA too high" condition should also be reflected in the TOP chevron being illuminated RED. The chevron lights were set up to show what was required from the throttle to fix the problem when in the landing config e.g. Top red chevron on? Push the throttle forward to speed up.
The A4K HUD also had an "Optimum Bracket" centred around the flightpath marker to show when on speed. It was also shown when the landing gear lever was not in the up position (same as the AOA indexer lights). To confuse the matter, it would be above the flightpath marker when fast and as you'd slow down it would lower down to centre on the FPM when on-speed. This logic makes sense from a performance instrument point of view as when when AOA was too high, the FPM needs to be lowered to regain the centre of the bracket.
Barnesy, thanks for link to utube, good explanation videos (that seem to have come from the Skyhawk Selling Video?). I could have explained more about how the graphic from the KAHU FSX was made but thought to keep it simple and allow the video to explain things - perhaps. One can assume too much though. As it turns out there was misunderstanding between the KAHU model maker with my conviction that the AoA Indexer (being primary - like it or not because it is indicating correctly) should be reflected/mimicked in the HUD. Seems like that is the case and it will be corrected in the sim. The model maker had assumed I was referring to the FPM - words eh.
The graphic was made from the same video indicated. The aircraft was being flown at 1G at low angle of attack even though the airspeed is high the climb angle is horrendous at 1G at low altitude at FULL power (why no burner for the KAHU?). So the graphic shows FAST on the AoA Indexer which is correct. Yet in the graphic the HUD green pointer is at the top of the scale (above the Optimum Bracket) which in reality should indicate SLOW/stall. The RED Arrow drawn in is showing where that green pointer should be (at bottom of scale) to show fast (mimicking the AoA indexer).
The aircraft is at 1G in a very unusual situation only for the purposes of making an illustrative video clip against what I had hoped would be a clear blue sky; but then the cloud formed (in the sim). I have been in the situation of making cloud at high altitude in reality, which can be very frustrating if three other Skyhawks are also making cloud, trying to join up at high altitude at the same time. It actually meant we had to all go home because the sortie parameters could not be met on that sortie. I think we did formation practice at low level where we were not making cloud and then conditions were such we had to do two formation landings in the rain - due to unusual weather conditions at the time. ;D
Reading Barnsey's explanation about throttle and AoA indexer again I beg to differ. It has been a while and I don't claim to know how RNZAF pilots were taught. Yet I still remember the silly ditty that helped me remember my pretakeoff checks in a Winjeel from forty years ago. These aide memoires are important.
However the AoA indexer chevron colours are correct (from A4G era anyway). I think this explanation that follows is in the NATOPS but may not be. RED indicates FAST (low angle of attack with wheels down/dirty) to remedy it the nose should be pulled UP, in the same direction that the RED lower chevron is pointing. Hope that makes sense.
Conversely if the GREEN chevron is showing then the A4G is TOO SLOW and quite dangerous if aircraft is in a turn dirty. One could now wonder why this condition is not shown in RED but remember the system follows a pattern set before the A4 for carrier landings when going TOO FAST is possibly MORE DANGEROUS than going slow - to arrest going too fast can break everything, the arrestor gear, the aircraft and people. So that is why FAST is red (only a possible explanation though for using red - perhaps it relates to a previous convention which origins are now lost in the mists of time).
So in GREEN SLOW high angle of attack condition the nose must be put down to regain the optimum angle of attack as shown by the orange doughnut (reflecting the 'meatball in the mirror' condition). The Green Chevron points down, put nose down.
Always when flying a Skyhawk two things must be co-ordinated in the landing configuration, especially for carrier landing and why Navy pilots practice ad nauseam ashore to workup to go to the ship. Any movement of the nose requires throttle movement and vice versa. The third factor is angle of bank and even wing waggles to get back on line up on finals. All these movements require corresponding movement in the other two.
For example when deck landing a late lineup over the ramp can cause loss of lift without a corresponding nudge of power that then requires nose up to retain optimum angle of attack to counter the loss of lift from the wing waggle disturbance which also throws the hook to one side decreasing the chances of an arrest. So don't wing waggle on finals OK? ;D [Whether or not that sequence of events is accurate I'm not quite sure but you get the picture I hope that nothing can be done in isolation except a long way from landing - for a precision carrier landing there is no such thing as a steady state, everything is in flux in an effort to remain on centreline, on glideslope, on optimum angle of attack. Unlike a regular 'air force' landing or GA landing there is no smoothness in the same way that has connotations. A carrier pilot is moving all parameters like you might imagine a duck paddling on the surface looks smooth but underneath those waders are working like crazy - same same carrier landings can look smooth on the outside but they ain't like that from the inside.]
Another addition: Have been thinking about what Barnsey has said, whatever he was taught or remembers applies to that situation, I just want to clarify for this forum what 'flying the meatball in an A4' is about. If we take the aircraft on final with a centred meatball (on glideslope) with aircraft at Optimum Angle of Attack (OAoA) and lined up correctly there is no way in the world the aircraft will remain in that condition until touchdown. Always there is something that will take it away from the ideal flight condition - whatever that is - so for example the A4G pilot is constantly changing, power setting and nose up or down to stay on the meatball. Then throw in the wing waggling effects and you have someone working hard to stay on the three parameters to get an OK pass and a safe touchdown/arrest on the carrier. This level of detail could not be gained without a mirror on a runway so for Barnesy some techniques may have been different especially when using all the gizmos available on the HUD of the KAHU.
At NAS Nowra there was always a portable mirror to land by. If that was missing then our eye would have been trained quite well for each runway to have a good idea about correct glideslope but nothing detracts from having a mirror aid to do (simulated) deck landings. I believe Hornets can use the HUD to land without the aid of a mirror on a ship but it is also an emergency and not likely to happen given the back up mirror devices and other aids available on USN carriers today. Carrier landings are precise while the LSO will tell everyone how unprecise they were in reality. SIGH.
Barnesy I ignore the Flight Path Marker (FPM) I'm old school dinosaur OK? ;D I'm told that the model maker will make a huge effort to explain the workings of the HUD, especially as it is excellently modelled in the sim (not that I understand but I like pushing buttons - preferably all at the same time - to see what blows up).
This is such an excellent tutorial video on how to deck land a Hornet it is mentioned here again. Although a different aircraft the principles poorly pointed to above are clearly explained in this video: fsxblueangels.com/videoscreen%20ok3.html(115Mb .FLV video)
I have apologies to make to you Phil.... I was wrong, wrong, wrong regarding my continued bleating about the error/difference in Kahu AOA indexer colours, both in this thread and others. I was out visiting the one and only Kiwi female pilot and her family the other day and she happened to have a cockpit photo of the jets while in storage in Woodbourne, and... it shows the upper indexer colour of GREEN... Hopefully she'll send it thru and I'll post it on here.
There's one thing I can guarantee - that your approaches and AOA control would've been (and had to be!) many orders of magnitude better than mine ever were!!
Yes, front and back seats. Where-as the Skyhawk only had it in the front seat in the T-bird (the view out the front from the back seat wasn't too flash!).
Barnsey, Thanks. Any photos would be terrific. No worries I have been living and breathing the dynosaur for the last several years making the 4.4GB PDF online so there was a big re-learning/remembering curve for me after all the years. Different AirForces (not USN) can have different colours for their AoA Indexers (we had discussed that on another thread).
Tell Kelly that she features in the A4G 884 section (just because) and that at least Kiwis oughta download the now 600Mb PDF (archivable on CDrom) at:
"592Mb PDF about RNZAF Skyhawks taken from larger 4.4GB PDF about the A4G, Skyhawks & RAN FAA fixed wing aircraft:
I have apologies to make to you Phil.... I was wrong, wrong, wrong regarding my continued bleating about the error/difference in Kahu AOA indexer colours, both in this thread and others. I was out visiting the one and only Kiwi female pilot and her family the other day and she happened to have a cockpit photo of the jets while in storage in Woodbourne, and... it shows the upper indexer colour of GREEN... Hopefully she'll send it thru and I'll post it on here.
There's one thing I can guarantee - that your approaches and AOA control would've been (and had to be!) many orders of magnitude better than mine ever were!!
There was quite a bit of discussion off-line about the indexer colours for the Sim Barnsey. There were conflicting references about it from various sources, but in the end a Kahu cockpit photo with power applied solved it for me too (at least for that aircraft!). The colours could be changed by changing a filter between the bulb and chevron and I'm not convinced all Skyhawks were the same. In some photos the dohnut is white, others yellow, others orange! The red appears orange in some photos, but that could just be the photo (or the filter was faded).
Don, would not there be some documentation of a standard for the AoA Indexer colours (for the KAHU?). NATOPS is handy in this respect as are standards across the USN for obvious reasons for all Navy AoA Indexers. Just today I made a Super Hornet Indexer graphic lifted from their NATOPS for another website. I post it here. It mimics the Skyhawk Navy range including the A4G (except for any erroneous [for Super Hornet] AoA degree numbers) the concept is the same though.
Thanks for the pics Barnsey, did you say there was one with the AoA indexer lit up? I guess we can see the green upper chevron colour in two photos (after zooming in). Is that what you meant?
Fancy that, USAF different to USN (and RNZAF) with AOA colours and AOA bracket position in the HUD. The relative indexer position is the same at least!
From 3:00 in this video, you can see the AOA bracket in the A4K HUD. When fast, the HUD bracket is above the FPM and drops down to the FPM when on optimum AOA. Ref my comments about "power for AOA", once the FPM was on the touchdown point and at -3 deg, then the remaining approach variable is AOA (directly proportional to speed and weight) so continue to hold the aim point while driving the correct on-AOA indication with power. Gross AOA errors are solved with adjusting pitch, but this means that aim point and glide path angle will become incorrect.
Last Edit: Sept 24, 2018 12:32:39 GMT 12 by Barnsey