Time in seconds to retract flaps after takeoff.

Always wondered why the F-16 has a tailhook, or how big a bigmouth F-16's mouth really is ? Find it out here !
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MVSGas

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Unread post22 Oct 2016, 18:24

basher54321 wrote: And I am reading that between 240kts and 370kts the Flaperons are set down at an angle (under 20 degrees) depending on airspeed.

AFAIK, yes


saberrider wrote:Carefree handling at low speed and FLCS drop off the flaps by itself no pilot input. Like a F18 Hornet?

No, flaperons only deflect down 20°with LG handle down or Alt Flap switch to extend below 240kts as mention above.
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35_aoa

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Unread post23 Oct 2016, 05:14

basher54321 wrote:Hi 35 - I don't suppose you ever cared about what was happening here but if Alt flaps was left in extend at takeoff (for whatever reason) that should cause a delay in full flap retraction based on speed should it not?


I think what has been posted is perhaps the best conjecture, however I really don't know what would happen in that case. FLCS would be stuck in TO/Landing gains, and while there is surely a flap blowup speed, I would imagine weird things would start happening once you got too fast. It isn't an exact system equivalent, but GAIN ORIDE in the F/A-18 freezes the FCS into fixed gains depending on flap switch position. The further you get away from the assumed flight regime (i.e. flaps AUTO and you get real fast or slow), the less controllable the jet becomes, since the gains are based on a specific airspeed/mach number and AoA. Like I said, not an exact analogue, but I'd imagine controllability would degrade once you start accelerating on takeoff to the 300+ knot range.
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basher54321

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Unread post23 Oct 2016, 10:46

Thanks 35 - I think I had also misunderstood the OPs original post because I was thinking he had seen a video where the flaperon full retraction had been delayed after the gear was fully retracted compared to other videos.
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jbgator

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Unread post23 Oct 2016, 18:41

On FCFs we test flap blow up speed of 380 KCAS (I do not recall what the acceptable range was). We would select ALT FLAPS EXT and accelerate out to 380+ visually verifying that blow up occurred by 380. I do not recall any variation in how the aircraft handled but this test was done in a straight ahead acceleration.

As far as I know the flaps retract at a standard rate commencing with gear handle raised. I do not recall observing if the gear or flaps came up faster, mostly because I didn't care. It was wise to not retract the gear too fast when heavy weight (very heavy) as the jet would settle but this was not a big concern during normal ops. You computed a rotation speed and most pilots rotate at or above that speed so there is plenty of flying speed by the time you get to the gear handle. The one time I would notice it was a very hot day TO at Incirlik with full combat load and it would feel mushy during gear/flap retraction. On FCFs I did an AB takeoff in a clean jet. Rotation speed came so quickly that I was usually airborne well before the approach end cable which is 1,000 feet down the runway and I did not start at brick 1 so I would say the TO roll was about 800 feet. I would raise the gear real quick to avoid overspeed and let the jet settle slightly into an almost level run down the runway. 450-500 KCAS by the end of our 10K runway and then 4-5 G pull to the vertical leveling off at 15,000 shortly thereafter. I was very conscious of the flaps retracting and did not push to level off but just let the flaps retract cause the level off.
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johnwill

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Unread post23 Oct 2016, 21:11

The design specs call for gear up, locked, and doors closed within seven seconds. You may have noticed the main gear retracts at two different rates. To meet the specs, the gear would have to retract at a high rate that would slam into the uplocks too hard, causing excessive fatigue damage. So about 75% of the retract motion is at a high rate, with the remainder at a much lower rate, easing the impact into the uplocks.

I don't know what the flap retract rate is, but I would guess it is faster than seven seconds.

I had never heard the term "blow up speed" for the flap retraction from Alternate Flap selection. It sounds like it means air flow over the flaps actually blows the flaps back into a retracted position. In fact, there is a control law in the computer that programs the flap to retract as speed is increased from 280 kt up to 370 kt (approximately, as I don't remember the exact numbers). That control law is to prevent flying with flaps down at higher speeds that could cause weird things to happen to maneuverability and structural load distributions the airplane was not designed to encounter.

There is a similar term "blowback speed", applied to the speedbrakes. If you try hard enough, it is possible to get enough air pressure on the speedbrakes to partially close them.
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jbgator

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Unread post24 Oct 2016, 00:19

Well I don't know if it is blow up or command up, it didn't really matter to me but we called it flap blow up speed and was a test point on the FCF to check it. It worked as I described. ALT FLAPS EXT, visually check they extended, then accelerate to above 380 confirming they were up at 380. As I recall the TO&LANDING CONFIG light came on when you selected ALT FLAPS EXT. Other than an FCF I cannot imagine a situation where you would accidentally have them down. Now leaving the AAR door open happened a few times and has an interesting affect on handling.

The only place I would have been in a position to monitor gear retraction that closely would have been as wingman on a formation takeoff and I was concentrating on flying the proper position not watching the gear come up. This whole discussion has been somewhat in the WHOGAS for me as I don't really see the significance of any of it, but am concerned about baseless conjecture which I know you never give us JW. For everyone else, understand this type of stuff is like the standard airshow question you get as a pilot: "How fast will it go?" Who cares. Ask me what the ITR and STR are. Ask about acceleration from low speed situations, ask about anything but how fast it will go or how high it will go. I don't really care unless I am trying to chase the space shuttle.

I have extended the speed brakes many times at supersonic speed and I know they open, not sure how far or for how long. It is like hitting a brick wall when you do.
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johnwill

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Unread post24 Oct 2016, 00:40

I agree, WHOGAS. Forgive my rambling on about stuff that really doesn't matter, I thought maybe you had observed a gear retraction from the ground and noticed the somewhat jerky motion of the main gear and wondered why.
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jbgator

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Unread post24 Oct 2016, 01:59

Didn't mean to chastise you, I appreciate your insights, just seems to be a lot of threads about silly stuff. 9Gs at Mach 2.....why?
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35_aoa

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Unread post24 Oct 2016, 03:42

I'm not a VIper "pro/FCF" pilot, jbgator is the man to listen to here. I just fly them here and there, and hope that nothing goes wrong. Seriously. Put me in a Hornet, and I'm 1000 percent more comfortable.
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jbgator

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Unread post25 Oct 2016, 20:23

Just occurred to me that I have seen EPAF F-16 airborne photos where obviously ALT FLAPS EXT has been selected to allow for slow speed flight behind a photo aircraft without lowering the gear (I do not think this would be approved in USAF but maybe it has). Also ANG ADF units have used it for slow speed intercepts. That could explain someone seeing a low approach where the flaps retract slower than the gear (although I am still not sure that isn't the normal sequence). Personally I think the flaps have a standard retract rate in normal ops that may, or may not, occur faster than gear retraction. I just fail to see why it makes so much difference to someone. I recall we did gear extension and retraction tests on FCFs with a target time for each (don't recall what they were but if someone has a Dash-6 its in there) but there are no flap indicators in the jet like other airplanes so no way to test/verify ext and retract beyond looking at them.
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35_aoa

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Unread post26 Oct 2016, 07:28

Yeah, I'd put money on the fact that the flaps schedule more slowly than the gear. I've never looked over my shoulder to check, but the gear come up pretty quickly and depending on how slow you are when that happens, there is some accelerating to do before the FLCS gives you full flaps up.
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saberrider

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Unread post27 Oct 2016, 08:34

35_aoa wrote:Yeah, I'd put money on the fact that the flaps schedule more slowly than the gear. I've never looked over my shoulder to check, but the gear come up pretty quickly and depending on how slow you are when that happens, there is some accelerating to do before the FLCS gives you full flaps up.

Thank you , this is what I believe is happening
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saberrider

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Unread post27 Oct 2016, 08:42

jbgator wrote: I just fail to see why it makes so much difference to someone.

Just tried to do a realistic modeling of the F16 A early blocks and the question's i putt are specific to my needs , to respond to your queries.
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