Extending Flaps at High Speed
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Ive not tested it in an F-16 obviously, but every low wing aircraft Ive flown so far (and granted, its a relatively short list) pitches down when you add flap. The additional drag located below the CoG in these cases increases the nose down torque, or moment.
Wind tunnel testing would be the way to go for finding out, and that data might be in TP 1538? My initial guess would have been to expect a nose down reaction from putting flaps in on an F-16, just based on where the TEFs are located relative to where I assume the aircraft CoG would be. But then again, for the F-16 in particular, this is not so useful knowledge. Seems like OPs question would relate to conventionally controlled aircraft that actually have a flap lever. In which case, it would as you say depend on the jet and its particular design.
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I seem to recall that when I was flying the Turbo Arrow (my favorite) that I had to push the yoke forward when I put the flaps down…in general, if you increase the camber of an airfoil (by extending flaps) it produces an increase in pitching moment for that airfoil…it’s quite possible that the Arrow pitches up because it’s a high power airplane, dunno. Pretty sure I recall the Dakota doing the same, and that the effect is more notable with a higher powered airplane. Given that you can actually feel the flap loads through the Johnson bar in a Piper, yeah…but the real limiting factor is still the flap hinge moment - load transfer from the flap to the hinge…the hinge is the weakest link, and what will break first.
Something I’ve been wanting to play with is the LE FLAP LOCK switch on the Flight Controls panel…I’m interested in if they lock to where they are when you throw the switch or if they lock into some preferred position. And what - if anything - that’s good or bad for…
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can the F-16 ever be parked with flat & not deployed flaps? I couldn’t do it in F4 BMS but I saw only one picture where the F-16 was parked and flaps were not down.
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Its possible to pin the landing gear in place. If you pin the landing gear, then press and hold the DN LOCK REL button (located immediately left of the gear handle), then raise the gear handle, the TEFs should retract to the streamline positions.
This is beneficial if its necessary to fly the aircraft for an extended distance with the LG extended, as retracting the LEFs and TEFs significantly improves fuel consumption.
Something I’ve been wanting to play with is the LE FLAP LOCK switch on the Flight Controls panel…I’m interested in if they lock to where they are when you throw the switch or if they lock into some preferred position. And what - if anything - that’s good or bad for…
Should lock in their current position. Good if you have a failure of the LEFs to track to the commanded position, but they end up in the 2° up position, and you can then lock them there.
If they become asymmetric, they should automatically lock, but you can manually command lock if you want. The -1 has a section on handling characteristics, and a heading in that section is dedicated to flight with locked LEFs. You could read that if you wanted an idea of what it should look like.
LEADING EDGE FLAPS LOCKED (SYMMETRIC)
Flight characteristics for landing and low AOA maneuvering are not significantly affected by locked LEFs. At high air-speeds, LEFs locked down cause increased buffet. At high AOA, LEFs locked up reduce stability, increase departure susceptibility significantly, and cause increased buffet. Above 16-18 degrees AOA, an abrupt yaw departure may occur, producing an uncommanded roll with little or no forewarning. Do not exceed 12 degrees AOA with the LEFs inoperative. Locked down LEFs significantly reduce cruise range. During landing, floating may also be noticeable if LEFs are locked at or near full down. The aircraft may float, sink rate may decrease, and a slight forward stick pressure may be needed to fly through the ground effect. -
Flaps encountered up/down post landing can depend on then the picture was taken - if the flaps are hyd powered they may be up at shutdown but then bleed down as hyd pressure decays…if they are electrically actuated they should stay put…in theory.
Failure modes are understandable, but my wanting to play with locking the LEFs has to do with some gouge I got from a RL fighter jock concerning using the AOA indexer in the T-38 up and away…he caveated it with thinking it only holds for a hard wing, but playing around with BMS I think it may hold with variable camber too, maybe even to greater extent. I’d like to do some test flying and compare observations - but I need the gear up.
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Well, thats pretty easy to do. Increase your angle of attack, either by increasing Nz or decreasing airspeed. Once your LEFs are extended sufficiently, lock them into place, then perform your testing as desired. Perhaps considering unlocking them before landing.
Just keep in mind that part of the variable camber comes from the ability of the LEFs to move. And that unless Im mistaken about how BMS gathered lift data for the F-16, what you see in BMS with locked LEFs may not represent what you would see in the real aircraft. Im not familiar enough with the source data for the aerodynamic simulation, but unless the test figures include the effects of LEF positions being outside the FLCS commanded values, then there may be some unsimulated effects.
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Its possible to pin the landing gear in place. If you pin the landing gear, then press and hold the DN LOCK REL button (located immediately left of the gear handle), then raise the gear handle, the TEFs should retract to the streamline positions.
This is beneficial if its necessary to fly the aircraft for an extended distance with the LG extended, as retracting the LEFs and TEFs significantly improves fuel consumption.
but the DN LOCK REL button is not functional in BMS where you answering for the real jet? because my question was about BMS
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Ah, it wasnt clear to me that you were asking specifically about in BMS. So far as I know its not possible in BMS?
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Well, thats pretty easy to do. Increase your angle of attack, either by increasing Nz or decreasing airspeed. Once your LEFs are extended sufficiently, lock them into place, then perform your testing as desired. Perhaps considering unlocking them before landing.
Just keep in mind that part of the variable camber comes from the ability of the LEFs to move. And that unless Im mistaken about how BMS gathered lift data for the F-16, what you see in BMS with locked LEFs may not represent what you would see in the real aircraft. Im not familiar enough with the source data for the aerodynamic simulation, but unless the test figures include the effects of LEF positions being outside the FLCS commanded values, then there may be some unsimulated effects.
Yes, but AOA really doesn’t have anything to do with what I want to do other than that I want to fly to maintain on-speed using the Indexer up and away…what AOA that turns out to be is going to vary with GWT, altitude, etc. I’m not sure about the TE flaps on the T-38, but I’m thinking they don’t move up and away? The USN A-7 used to have “maneuvering flaps”…at least I think it was the A-7…meaning that one could employ them during ACM. I used to hear older RL jocks lamenting not having them in more modern jets…but I have no idea if the T-38 did/does anything similar.
So…what I’d really like to do in BMS is to lock both the LEF and TEF (you’re correct in that unless I do both I’ve still got variable camber) up, and then do my maneuvering…and see what I get compared to one and/or both in full authority. I’m expecting similar results, but at differing levels…I’d just like to know to which side of “better” in each available case. Just curious.
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Yes, but AOA really doesn’t have anything to do with what I want to do…
Well, the reason I suggest increasing AOA is to set the LEFs to the angle you desire, for testing. If you lock them at high speed, low AOA, they will be in the 2° up position. If you want to test with them down, you will need to lock them during a high G turn.
Im hopeful that Mav-JP will chime in here, and comment on whether BMS will model the aerodynamic qualities of the wing accurately with the LEFs and TEFs not in the FLCS scheduled positions?
… other than that I want to fly to maintain on-speed using the Indexer up and away…what AOA that turns out to be is going to vary with GWT, altitude, etc. I’m not sure about the TE flaps on the T-38, but I’m thinking they don’t move up and away? The USN A-7 used to have “maneuvering flaps”…at least I think it was the A-7…meaning that one could employ them during ACM. I used to hear older RL jocks lamenting not having them in more modern jets…but I have no idea if the T-38 did/does anything similar.
So…what I’d really like to do in BMS is to lock both the LEF and TEF (you’re correct in that unless I do both I’ve still got variable camber) up, and then do my maneuvering…and see what I get compared to one and/or both in full authority. I’m expecting similar results, but at differing levels…I’d just like to know to which side of “better” in each available case. Just curious.
Do keep in mind that if you lock the TEFs, you dont have much control over the roll attitude of the aircraft. Actually, Im not even sure you can lock the TEFs? You can tell the FLCS to deploy them or handle them automatically, I dont think there is an option to lock them. There isnt a good reason to lock them anyway, because if the TEFs cant move, you only have very limited roll authority (through differential movement of the horizontal tails).
As far as the A-7, I dont know much about it, but I do know that it had flaps as well as ailerons. The fact that the F-16 doesnt have separate ailerons makes locking the TEFs a dicey proposition, at best.
Im a big fan of curiousity, generally. In this case, Im suspicious that the aircraft performance might not match the real thing, although Im hoping Im mistaken on that. Depends how BMS models the aerodynamic performance of the aircraft, something I dont know enough about.
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Hmmnn…agreed on the TEFs in the F-16 case. Hadn’t really considered that, but that’s still something I’d expect the old Navy dogs would lament. I think I have to just accept them doing what they do…which I don’t think will impact my test given the design of the airframe.
I’d like to lock the LEFs at zero for what I want to try…so I guess I’d need to unload? And I’m not interested in the effect on/of G either - on-speed will be on-speed and whatever G that turns out to result in will just be what I get and that will become part of the observation. Even if what BMS does doesn’t mirror RL exactly, I should see something close to what I’m expecting…I think. Or at least some differences between configurations, which is more what I’m interested in - degree and extent of any difference. The results will at least be consistent within the limitations of the BMS aero model because I’ll be using the same aero model. I’m more curious about what BMS does vice the real jet, in this case.