Threshold Speed
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Caveat: I have never flown with a throttle…um…let’s just say I have never truly flown in Falcon.
The staple is not backwards if you think in terms of throttle. Push the throttle up (forwards) and the FPM goes to the top of the staple. Pull the throttle down (back) and the FPM sinks to the bottom of the staple.
AOA is for checking attitude
Staple is for checking glide angle or rate of descent.Then again, I could be wrong.
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Landing really isn’t as complicated as people make out. Why do you need to be working things out? Just fly the fpm in the centre of the staple and at the runway threshold and land. This takes into account any weight variables and you touch down at the appropriate aoa and speed for any given weight. Keep it simple and you free up any capacity for malfunctions.
+1
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The HUD staple couldn’t be any different provided that it is fixed in relation to the gun cross. The FPM has to move otherwise it’s not an FPM. AOA is practically synonymous with the angular difference between the gun cross and the FPM. It’s theoretically possible to design a moving bracket symbol which also moves such that the lower mark represents less AOA and the higher mark more AOA. Here’s how it would work:
At 10° the bracket would have to be fully above the FPM. As AOA increases the FPM naturally falls relative to the zero sight line (ZSL, aka gun cross). To indicate increasing AOA the bracket symbol would have to fall faster than the FPM to meet it from above. At 11° the lower mark on the bracket would be even with the FPM. As AOA increases to 15° the bracket would pass the FPM so as to line up its upper mark to the FPM. The motion of the bracket would be the sum of the FPM’s motion relative to the ZSL and the change in the bracket’s position relative to the FPM to indicate AOA. I guess it could work but it seems unnecessarily complicated compared to the fixed symbol and letting the FPM be the moving “needle” on a static HUD “dial face.”
FPM-ZSL relationship pretty much is AOA. The true AOA indicators show the air flow angle relative to the airframe datum while the FPM shows the path of the airplane relative to datum. It’s easy to understand that the air flow is going to be approximately anti-parallel to the direction and magnitude of travel. If you are driving 200 knot into a 100 knot headwind you will find that AOA and FPM-ZSL angle are different. But 100 knot wind isn’t normal and FPM-ZSL and AOA are often so close as to be the same.
I like my reduction of the “landing problem” to 4 elements to align. The runway and -2.5° dashed reference line shows correct position. FPM-reference line alignment shows correct motion. Bracket-FPM alignment shows correct AOA. The indexer and strip gauge reinforce the last item. Step 1 is to fly to a correct position. Step 2 is to fly from any correct position toward the runway. Step 3 is to adopt the approach AOA. All three indicators we’re talking about are all helping you do step 3. Any single one is sufficient and they all show the same information.
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The staple is not fixed - it floats in relation to the gun cross because on-speed AOA varies with gross weight…so it has to move, and so does attitude to capture/maintain.
The indexer in a Viper and the indexer in a Hornet do in fact indicate the same way…I think the one in the Hornet (the real one) will light an arrow and half the circle to give a finer reading, though - “slow/slightly slow” for example. From what I understand from my time working on the T-45A Navy pilots are trained to rely on the indexer as primary (nobody looks at the round gauge unless the indexer and HUD are both out) and cross-check the bracket…anyway, that’s what I do in the Viper because of the bracket being backwards - I don’t even care about airspeed as long as I am on-speed. Then I put the dashed line though the VASI, capture runway center line, and fly the FPM to the touchdown point of my choosing. I also use Navy “flare” technique - squeek on power just prior to touchdown to arrest sink rate. If you’re properly trimmed you don’t gain speed…just arrest the rate.
…which shows up again why the bracket is backwards when you do think in terms of throttle - nose in the direction of the arrow; throttle in the direction of the light - to make corrections using the indexer. Very easy to recall and use, because the indexer really does show and tell you what to do and how to do it, graphically. I find the bracket in the Viper to be about useless…but I’ve had a lot of time in the T-45A Fleet trainer.
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The staple is not fixed - it floats in relation to the gun cross
This is not correct. The HUD AOA bracket does not vary in position relative to the gun cross, with gross weight or anything else. It is always 11-15° below the gun cross.EDIT: The staple does float but it has nothing to do with the airplanes weight or drag. It’s a dynamic display but the bracket tick marks are fixed values.
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The staple is not fixed - it floats in relation to the gun cross because on-speed AOA varies with gross weight…so it has to move, and so does attitude to capture/maintain.
If AoA at a given speed varies with weight, then the staple can either move or not move. Given that the AoA is roughly equal to the angular relationship between the gun cross, the FPM, and the pilots head, then speed varies for a given sight picture with gross weight.
The only way that the staple would be forced to float, would be if AoA was indicated only by the staple, and not by the position of the FPM within the HUD. If the position of the FPM was dictated only by speed and not the instantaneous direction of velocity, then to indicate AoA correctly the staple would need to float.
I can only imagine that this means you are under the impression that the FPM does NOT normally indicate AoA, which it does.
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What is backwards about the Viper E bracket (and it’s true in the real airplane as well) is that it in fact indicates in reverse from the indexer wrt what to do with the nose of the airplane - as a rule of thumb for using the indexer it’s: nose in the direction of the arrow, throttle in the direction of the light. Try that gouge with the Viper bracket and you will get totally gooned up - you have to reverse the logic…though the indexer operates the same in both USAF and USN jets. It’s a “nose-centric” vs “throttle centric” orientation thing…if that makes any sense…
If you get a chance to fly a properly set up Navy sim (T-45, Hornet, etc.) you will find that the FPM (or Velocity Vector) is at the top of the bracket when the upper indexer light is lit and at the bottom when the lower light is lit, and as such the technique for capturing on-speed becomes quite different if you are just looking at the HUD…what I personally do in the Viper is hit the break fast, pull power, and let the FPM fall into the bracket - then I push the throttle up until I get a green indexer. Then I totally ignore the bracket and fly on the indexer only.
The Bracket (it is not a E ) is not inverted at all, It is totally logical that the more AOA you have , the more the FPM is goind DOWN the bracket , how could it be otherwise ???
NOw the question is : is the AOA indexer (the one in colors left of the HUD ) inverted in up / center / down position vs what would be needed in term of action.
i would say YES eveything is logic
Yellow = AOA too low , arrow up : PULL (increase AOA)
Green = AOA OK , CIRCLE : do nothing
red = AOA to high , arrow down : PUSH (reduce AOA)that means the F16 indexer has to be seen more as a STICK ACTION than a THROTTLE action and colors fits the AOA indicator stripe
PERIOD.From that perspective indeed, the NAVY AOA indexer is not working the same , IIRC colors are not the same and arrows are about THROTTLE ACTION rather than STICK action…
IMHO , i prefer the logic of the F16 : RED = DANGER AOA too HIGH
PS : for your information , if the Bracket Moves down from a certain AOA , this is only because of a problem of Scaling between the bracket (from 10 to 15 IIR) and the HUD degree values and visibility . Indeed, the Bracket size is NOT 5 degrees but 2.5 degrees (it would be huge in the hud ), so to scale the AOA on the Bracket, the Bracket has to move down with FPM from a certain AOA …In reality, the bracket is not associated with the HUD or Ladde but only with FPM. The logic says : AOA = 10 : put the Bracket top on the FPM , AOA 15, put the bracket Bottom on the FPM , and interpolate between those positions for AOA between 10 and 15…no matter where the FPM is on HUD
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5 pages about this!
… Train to land your F-16 without this (so essential for too many virtual F-16 pilots) HUD by using only the indexer and you will never have any more questions about FPM and bracket stuff … eveything will become much easier.
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Mav-jp, I see how the AOA bracket is a dynamic symbol. It scales and stretches based on the AOA or FPM position. The top mark is always 11° and the bottom 15° but the position of the marks relative to the gun cross aren’t fixed. It’s compressed which is plain to see simply because the staple isn’t 4° tall compared to the pitch ladder despite representing values 4° apart. Doubly interesting I thought the top mark was fixed 11° depressed from the gun cross that it was possible in strong winds for the top mark to represent an angle that wasn’t the same as AOA. This turns out to not be the case. The staple actually shows AOA. It’s entirely possible to be at 11° AOA and the angular distance between the FPM and the gun cross to be more (headwind) or less (tailwind).
I still disagree with Stevie’s statement that the correct AOA changes based on weight. The indicators always align and illuminate at the same values of AOA if the plane is at 25,000 lbs. or 45,000 lbs. The AOA indicators are fixed in numerical value just not display position.
I did find that the cockpit gauge & indexer indicates about 0.55° less AOA than the info bar and HUD bracket. If the AOA gauge shows 11.0° the indexer is right on the transitions between lights but the HUD bracket and info bar will show 11.5-11.6°.
One thing I never studied closely is the behavior of the FPM beyond 13° in landing mode. I always thought the “X” meant the FPM was off the HUD only. However if AOA is 14° it gets the X even if the FPM is still displayed on the HUD as a valid path indicator. Additionally the AOA bracket is still reliable in the 13-15° range even if the FPM isn’t valid for path. If you want to fly a 14° approach you would place the FPM 75% down the bracket despite the FPM having a superimposed “X”.
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Of course the correct landing AOA does not depend on weight. The speed to get this AOA depends on weight!!
That is why we don’t give a shit to speed or weight when landing. If you have correct AOA and slope you are just good to land.
Speed only matters then for runway length and brake energy
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AoA depends on speed and speed to get this aoa depends on weight: conclusion aoa depends on weight!
Knowing the speed in advance by means of a formula like a the original poster showed is valuable, maybe not to all, but to some.
Those graphs do exist for the real deal for a reason. -
No, that is incorrect. You aim to land at a given, constant AoA. Your AoA varies with a number of things, but ideal landing AoA does not vary with GW.
Knowing the speed in advance is part of the procedure - you should be able to cross check the speed against your actual speed to ensure the systems are working correctly.
Given that cockpit G is 1, AoA varies with weight and speed. As speed rises, AoA falls - and as weight falls, AoA falls.
Actual AoA then depends on weight. The ideal AoA to land at does not depend on weight. However to set the correct AoA will require varying speed based on weight.
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Cool, so can we say that this formula is usable? Given the limitations and incorrect weights etc of the sim?
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The Bracket (it is not a E ) is not inverted at all, It is totally logical that the more AOA you have , the more the FPM is goind DOWN the bracket , how could it be otherwise ???
NOw the question is : is the AOA indexer (the one in colors left of the HUD ) inverted in up / center / down position vs what would be needed in term of action.
i would say YES eveything is logic
Yellow = AOA too low , arrow up : PULL (increase AOA)
Green = AOA OK , CIRCLE : do nothing
red = AOA to high , arrow down : PUSH (reduce AOA)that means the F16 indexer has to be seen more as a STICK ACTION than a THROTTLE action and colors fits the AOA indicator stripe
PERIOD.From that perspective indeed, the NAVY AOA indexer is not working the same , IIRC colors are not the same and arrows are about THROTTLE ACTION rather than STICK action…
IMHO , i prefer the logic of the F16 : RED = DANGER AOA too HIGH
PS : for your information , if the Bracket Moves down from a certain AOA , this is only because of a problem of Scaling between the bracket (from 10 to 15 IIR) and the HUD degree values and visibility . Indeed, the Bracket size is NOT 5 degrees but 2.5 degrees (it would be huge in the hud ), so to scale the AOA on the Bracket, the Bracket has to move down with FPM from a certain AOA …In reality, the bracket is not associated with the HUD or Ladde but only with FPM. The logic says : AOA = 10 : put the Bracket top on the FPM , AOA 15, put the bracket Bottom on the FPM , and interpolate between those positions for AOA between 10 and 15…no matter where the FPM is on HUD
…it’s backwards…every USN Test Pilot I know that has flown the Viper agrees that it is backwards. From their training…and I agree with them.
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5 pages about this!
… Train to land your F-16 without this (so essential for too many virtual F-16 pilots) HUD by using only the indexer and you will never have any more questions about FPM and bracket stuff … eveything will become much easier.
Actually very good gouge…
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AoA depends on speed and speed to get this aoa depends on weight: conclusion aoa depends on weight!
Yes, given a speed and weight (and some other stuff) the AOA the airplane adopts naturally is determined by these. We’re confusing the AOA that results from given inputs with the desired AOA. We’re saying the desired AOA for approach is constant. I’m at 30,000 lbs. what AOA do I want on landing? 11°. I’m flying at Mach 1.3 at 31,528’ inverted, what AOA do I want on approach? 11°. There’s a 4 knot headwind… 11° AOA. You see that no matter what the airplane is doing, the AOA that we strive for is unchanging.
Cool, so can we say that this formula is usable? Given the limitations and incorrect weights etc of the sim?
I think so. If you didn’t have reference to AOA indications (HUD, horn, gauge, indexer) at all and had to use a computed approach speed this rule of thumb would likely allow a safe landing. Would it be exactly precise? No. Would it be close enough for landing distance and brake energy calculations? Yes.
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Yes, given a speed and weight (and some other stuff) the AOA the airplane adopts naturally is determined by these. We’re confusing the AOA that results from given inputs with the desired AOA. We’re saying the desired AOA for approach is constant. I’m at 30,000 lbs. what AOA do I want on landing? 11°. I’m flying at Mach 1.3 at 31,528’ inverted, what AOA do I want on approach? 11°. There’s a 4 knot headwind… 11° AOA. You see that no matter what the airplane is doing, the AOA that we strive for is unchanging.
Yes indeed, I think most on here agree that what you desire for AOA to land the viper and how to achieve that are two different things. My comment was regarding that for whatever AOA yo desire, you need to fly a certain speed that is dictated by weight among other things.
I for one think it’s useful to know how to calculate that approach speed, regardless of HUD failures etc. So I thank the OP for this and you Frederf for “confirming” the method.
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and poor Red Dog doesnt get a thank you, for including it in your install folder?
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and poor Red Dog doesnt get a thank you, for including it in your install folder?
Including the formula? I must have missed it then. What doc and what page is it on?
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It’s got some interesting information in it and people might find it useful, especially when you lose your HUD in the video game due combat damage.
I tired to make this more obvious in the original post but everyone here is so fast to try shoot anyone else down around here you guys can’t see it. Chill
So much fuss about the bracket that’s not an E or C, when the OP is calling BMS a video game when in fact is a simulator.
Video game = HAWKS :uham: