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auto rotation recovery 300CBI


RHS1
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whats ups,

 

Training in CBI for CPL and I was just wondering how other cbi drivers do the power recovery at the bottom of your autos. I have been taught to "crack the throttle" not roll on right before the flare due the fact that the correlator fully joins the needles when u pull in collective to cushion . I was under the impression this is done this way to prevent an engine overspeed in the recovery. some guys do this more like R-22 recovery which i do not like to do . would just like to know what the majority does.

 

Thanks

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When you enter the auto you should lower the collective while maintaining a fixed grip on the throttle... this should split the needles and maintain @2300 ERPM ... if it doesn't you will need to crack the throttle slightly to get them to split to that level... then don't do anything until you're ready to pull collective and as you raise collective the correlator will join perfectly.... as you raise, maintain fixed grip again so as to not roll off rpm...

Perfect!!

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When you enter the auto you should lower the collective while maintaining a fixed grip on the throttle... this should split the needles and maintain @2300 ERPM ... if it doesn't you will need to crack the throttle slightly to get them to split to that level... then don't do anything until you're ready to pull collective and as you raise collective the correlator will join perfectly.... as you raise, maintain fixed grip again so as to not roll off rpm...

Perfect!!

Will Give that a try seems like a very smooth and easy way to recover.

Thanks for the info

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Just did my first auto's in the 300C today...a few hours ago...we did like 8 of them.

 

The way I'm being trained is collective down, maintain attitude and heading (60kts, pedals, rpm check...etc.), then roll throttle to detent, maintain attitude, proceed with glide, bring throttle to 2500rpm during end of glide just before flare...begin flare...then raise collective for power recovery and fly out of it...or come to hover. The correlator joins the needles at this point.

 

Don't know if this helps...the ship is a 300C...not a 300CBI...

 

Either way...what a ride...that was the first time I've experience an auto-rotation. I even did a few myself...(instructor close by...of course)

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Nobody mentions slighty pulling the cyclic back when entering the auto here. Is this being taken for granted and not mentioned or something that is not being done?

 

Roger- very important point on the R22 due to how fast the rotor rpm decays...a lil back cyclic gives you that cushion to get rotor rpm in the green..then you can adjust your airspeed where you want it..

 

Maybe not being emphasized on the 300 due to a slightly higher blade inertia??

Edited by Goldy
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I know it is done routinely but I would not recommend rolling throttle to the detent in power recovery autos....Throttle chops in all piston helicopters have a greater risk of a real emergency when the engine dies.

Why put a greater risk on the "simulation"? Everything else is going to be the same in the auto if you don't roll to idle. Now if you're practicing full downs ... go for it.

 

All the 269/300 series coorelators are set up the same that if you are at (or near) gross weight at full down collective lifting the collective will produce an approx 500 erpm rise.

I've noticed two methods taught out there in the 300 series in startup/liftoff:

 

One says bring rpm to 500 rpm below flight rpm (I didn't list what rpm as that depends on the model...ie C, CBI, A, B) then lift collective and the coorelator will bring rpm into the green... there is alot less turning of the throttle with this method and it is preferred for the piston pilot.

 

The other says roll to green then lift and roll off throttle to maintain green range at liftoff. I hate this method. People teach it because if you are going to fly turbines you MUST have the rpm in the green before you lift the collective, so they think they are teaching good habits..... I say they are teaching to monkeys who can't figure out how to operate a particular aircraft and need a "one size fits all"

just my opinion.

Edited by apiaguy
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Thanks for the input Goldy. I am sure on the R22 its even more pronounced (rotor RPM decay) if the cyclic is not pulled back when entering an auto.

 

As far as rolling off the throttle, we normally did not roll off the throttle for auto's because of the remote chance of an engine failure. The school lost a ship (300c) a few years ago during a checkride when the examiner rolled the throttle off during the checkride to simulate an emergency and the engine quit.... All were ok after completing an auto, aircraft did not survive though.

 

We did practice full down auto's a few times (to the runway/taxiway) with the throttle rolled off completely and not used. Instructor was hovering over the controls when we did this becuase after entering the flare and waiting to pull collective is all about timing: to late or to early and things can go wrong quickly. An adrenaline rush knowing you only have one chance to do this, just like in a real emergency.

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Thanks for the input Goldy. I am sure on the R22 its even more pronounced (rotor RPM decay) if the collective is not pulled back

 

Edited for Roger...for any students reading this...he meant to say cyclic..you know...that thingy hanging around between your legs.

 

Goldy

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Nobody mentions slighty pulling the cyclic back when entering the auto here. Is this being taken for granted and not mentioned or something that is not being done?

 

Sorry...I was unclear...I was just trying to write it quickly...however aft cyclic is part of the training in the 300C. That's what I meant by keep a 60kt. attitude...we started our auto's at 70kts, hence the need for slight aft cyclic. The chant, per say, is "DOWN" (collective) "RIGHT" (pedal) "AFT" (cyclic) when entering from 70kts, which is what we were practicing.

 

However, we haven't done hovering auto's yet (we're doing some later today) but I don't see how AFT cyclic would be the procedure if you want to build your speed when entering under 60kts.

 

For example...if I entered an auto at 40kts...wouldn't I bring the cyclic slightly forward in increae my airspeed and catch and maintain a 60kt. attitude? Again...we're doing that today and I'm sure the instructor will explain it to me...so just a curious question.

 

Either way...hope that clears up your question brushfire21...that was a good point.

Edited by zemogman
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All the 269/300 series coorelators are set up the same that if you are at (or near) gross weight at full down collective lifting the collective will produce an approx 500 erpm rise.

I've noticed two methods taught out there in the 300 series in startup/liftoff:

 

One says bring rpm to 500 rpm below flight rpm (I didn't list what rpm as that depends on the model...ie C, CBI, A, B) then lift collective and the coorelator will bring rpm into the green... there is alot less turning of the throttle with this method and it is preferred for the piston pilot.

 

The other says roll to green then lift and roll off throttle to maintain green range at liftoff. I hate this method. People teach it because if you are going to fly turbines you MUST have the rpm in the green before you lift the collective, so they think they are teaching good habits..... I say they are teaching to monkeys who can't figure out how to operate a particular aircraft and need a "one size fits all"

just my opinion.

Our 300C has a significantly more than 500 RPM increase. Green Range is 3000-3200 ERPM, on startup/liftoff you can pretty much set the RPM at 2000-2100 and lift collective and you will pull it off the ground with the RPM in the green. Same thing applies for autos, don't roll the throttle off more than 2000 RPM, and you will only have to pull collective while maintaining your grip on the throttle to recover in the green range.

Edited by flyby_heli
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However, we haven't done hovering auto's yet (we're doing some later today) but I don't see how AFT cyclic would be the procedure if you want to build your speed when entering under 60kts.

 

For example...if I entered an auto at 40kts...wouldn't I bring the cyclic slightly forward in increae my airspeed and catch and maintain a 60kt. attitude? Again...we're doing that today and I'm sure the instructor will explain it to me...so just a curious question.

 

Either way...hope that clears up your question brushfire21...that was a good point.

No, No, No....common mistake, specially amongst fixed wing pilots.

When you lower the collective the nose WILL drop and, depending on how fast you lower it, you will end up seeing only green grass out the windshield if you don't pull aft cyclic. At the same time your rotor RPM will decay because the airflow up through the disc is insufficient to keep the RPM up. Now you are in a diving situation with low RPM. When you realise this, you will pull alot of aft cyclic, because of the nose low attitude, and your RRPM will go through the roof. You are now chasing both your airspeed and your RPM, which will make you busier than a cat covering sh*t to get it sorted out and stabilized before entering the flare.

Correct entry is always DOWN, AFT, RIGHT, until established in the glide, at whatever airspeed, and then you can adjust your attitude (for airspeed) and pitch settings (for RPM) as appropriate.

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Correct entry is always DOWN, AFT, RIGHT, until established in the glide, at whatever airspeed, and then you can adjust your attitude (for airspeed) and pitch settings (for RPM) as appropriate.

 

Cool...thanks for the input...if the weather holds-up we'll be practicing those today...

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just wanna second apiaguy:

 

I was taught to hold the throttle into detent on all autos. While working as a cfi we had that discussion wether or not to roll the throttle into detent, because I was under the impression that when you have to check the collective to prevent an overspeed (in 180's in particular), the correlator will kick in and join the needles. Needless to say that that adds to the distraction of the student.

 

Anyway, I personally saw the remains of hard landing due to a stopped engine (apparently happend during a private checkride, everybody walked away - but how embarassing for the examiner :blink: - they flared too high - no engine - ups!). After that I was convinced that you should better be sure your fulldown skills are up to par and you are not overshooting your spot!

 

We even called the factory and I spoke to the Chief Testpilot; he said that in their (testing-) environment they never roll off to idle on power recoveries.

One little problem remains: how should I surprise my students now without giving those nasty throttle chops? :o I think the old "simulated engine failure" and starting to roll of, works ok too... :(

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All the 269/300 series coorelators are set up the same that if you are at (or near) gross weight at full down collective lifting the collective will produce an approx 500 erpm rise.

I've noticed two methods taught out there in the 300 series in startup/liftoff:

 

One says bring rpm to 500 rpm below flight rpm (I didn't list what rpm as that depends on the model...ie C, CBI, A, B) then lift collective and the coorelator will bring rpm into the green... there is alot less turning of the throttle with this method and it is preferred for the piston pilot.

 

The other says roll to green then lift and roll off throttle to maintain green range at liftoff. I hate this method. People teach it because if you are going to fly turbines you MUST have the rpm in the green before you lift the collective, so they think they are teaching good habits..... I say they are teaching to monkeys who can't figure out how to operate a particular aircraft and need a "one size fits all"

just my opinion.

 

Hey all! I'm a new guy, great website! :)

 

Thats a good tip apiaguy has, to start with lower RPM than flight rpm as it builds quite a bit, but are you shure that is because of the corellator rigging?

I think this is the reason: as you pull pitch and increase the lift produced by the blades and they start to take the weight of the helicopter, they will cone and because of the conservation of angular momentum they will speed up. the sprag clutch does off course allow the blades to speed up, but this offloads the engine and with the amount off throttle we have put in at that point it will not continue at its present ERPM but go up along with the RRPM. I can't see how the corellator could be rigged to give that effect, but I'm no mechanic. any opinions anyone?

 

About the throttle chops: We always practiced autos with the throttle in detent. and it does scare me a bit. Not only do you have a greater risk of your engine dying, but if you have an overloaded and tense student gripping at the throttle it like mad and forgetting to roll on early enough you could get quite a throttle kick on the bottom when you slam the engine back in. So I'll definetively try your firm grip method next time, thanks apiaguy. (I'm a PPL doing my instrument rating, so i haven't been instructing autos yet, but I have been an overloaded student ;) hehe, ah the memories of those first autos)

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Guest pokey

my 1st initial lift-off is always with the rotor RPM in the green & roll throttle off as required. After a few pick-ups/set-downs,, then maybe let the correlater do its job-you want to see that the engine can produce full RPM/power, initially tho.

 

auto's? just split the needles & pay attention to the engine tach-- NO to full detent unless you plan on a full on. ( always plan on a full on anyhow)

 

 

petter? as far as the coning to increase RPM? i'de say it's negligible- the correlater is on the job. The overrunnig clutch has nothing to do with the speed, other than allowing the engine to NOT drive the blades when there is an RPM difference.

 

Here is an interesting note, (about the 300's) We ALL know that "declutched operation is prohibited above 1600 RPM", rite? Do we know why? AND? from the stand point of auto rotation AND above 1600 RPM? do we need to do the overspeed inspection of the short shaft? ( i never did quite figure this out NOR get a straight answer from the factory) WTF is joker when we need him? :huh:

 

lots of "interesting" stuff in this thread

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We ALL know that "declutched operation is prohibited above 1600 RPM", rite? Do we know why? AND? from the stand point of auto rotation AND above 1600 RPM? do we need to do the overspeed inspection of the short shaft? ( i never did quite figure this out NOR get a straight answer from the factory) WTF is joker when we need him? :huh:

 

lots of "interesting" stuff in this thread

This is what I've heard....When engine is running declutched there is no load on the short-shaft, so it is free to "wobble" if it is not centered perfectly. This can cause oscillations that can be damaging to the short-shaft, therefore the inspections if this happens. In an auto you still have the belt tension, so the load on the short-shaft makes sure it is centered. So even though the ERPM is higher than 1600, no inspection is needed.

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Yep, this thread is interesting! I've been following it, but not really able to comment. Currently at Flight Safety on S76 sim course. Plus, there are already some great comments that cover most everything.

 

Thats a good tip apiaguy has, to start with lower RPM than flight rpm as it builds quite a bit, but are you shure that is because of the corellator rigging?

 

This is due to the correlator action. The pitch on the blades (thus coning) is so low / neglegiable as you first start to raise, yet the RPM still goes up. It continues to rise until the drag is enough to counter the correlated throttle input, and therefore RPM stays steady. Remember, the correlator is calibrated for flight...not sitting on the ground at flat pitch. On the ground the 'correlation' is too much for the low drag, thus RPM rise. Hope that helps!

 

The easy way to test this, is to raise the collective holding the shaft, not the grip (thus not allowing the correlator to work.) If the RPM doesn't increase, then your answer is 'correlator'. - Note: Ask your instructor before you try anything different to what you have been taught.

 

Petter, if the rotors sped up 'ahead' of the engine, you would surely see this by a split in the needles. RRPM would momentarily be ahead of the ERPM. Have you seen this?

 

Starting - I haven't got my checklist handy, but I don't recall anything saying, "Increase throttle until 500 below flight green arc." From a teaching point of view, surely you have to keep with the RFM. Nothing wrong with giving students tidbits though. Each to their own I suppose. I know what you're saying with this, but it is unnecessary if the pilot has a good understanding of the correlator system.

 

What's wrong with simply rolling throttle on until green arc. Then losening your grip (pull the shaft only) on the trhottle grip as you raise it for flight to get over that little time where the RPM increase is too much for the drag. Raise until the RPM wants to start drooping, then 're-ingage' your grip (and correlator) as normal. It becomes second nature after a while. I think that's how I did it.

 

The way you hold the collective is important here. It won't work if you grip it like a motorbike handle. I found the best way is to wrap pinky finger and ring finger (two furthest from thumb) around the shaft and manipulate the throttle grip with only my thumb, index and middle finger.

 

Autos

 

NO to full detent unless you plan on a full on. ( always plan on a full on anyhow)

 

Interesting paradox! Does that change the way we think of this? Could there be a problem if you roll off to say 2000, and the engine starts coughing just as we are in the flare? So we try to full down, but it is all happening so late in the auto that we forget to roll to detent. Then, just as we raise to cushion our landing, we get another engine cough. Hmmm....just thinking aloud.

 

RPM over 1600 - Flyby_heli has this exactly right. The belt tension in flight secures the shaft from the destructive harmonic resonance.

 

Joker

Edited by joker
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Thanks Joker. Makes more sense, a pitch increase in flight would require more throttle than on the ground before liftoff. :)

 

Sprag clutch thing: the way I see it, if the blades speed up because of coning the enginge would follow simultaneously, so you wouldn't see much or any needlesplit. if you have enough throttle to drive the heavy blades at 2700 rpm and they suddenly spin faster, the engine isn't going to maintain its RPM with that amount of throttle input and a lot less mass to push around , it's going to rev up as the load decreases..

Edited by Petter
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I wish to add to this topic a couple of recommendations.

 

The general thought that you will always add a "gentle bit of aft cyclic" is not always correct. In most single engine helicopters, a ballpark airspeed of 60 knots in autorotation will work. With this in mind, if you are above 60 knots, a bit of aft cyclic is beneficial. If at or below 60 knots, especially at the apex of H/V, aft cyclic should be avoided as a gentle but deliberate cyclic movement to attain proper airspeed pitch attitude is paramount.

 

For the original question of throttle increase at the end of the power recovery auto. I can't think of a helicopter that I don't like to see engine response prior to the leveling of the helicopter and subsequent pitch pull. All to often, the recovery (level, collective increase, and throttle) items all happen simultaneously. This puts the instructor in a potentially dangerous situation. If the engine fails to respond (which will happen to you), you have already increased collective pitch taking away from your rotor and potential rotor rpm needed for successful landing. I prefer to increase engine rpm during the flare to verify engine response. I then feel assured the recovery will be successful.

 

Please note that adequate planning with regard to surface texture is equally important. If the engine fails and your a going to wet grass, etc...it makes for an interesting ride.

 

Just a bit of a Randy-ism!!!

 

Take care all,

 

Randy Rowles

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One note about airspeed in an auto I 've found that alot of people fixate on the airspeed indicator. Try to learn to look at your tip path plane attitude and go to you 60kt attitude and your airspeed will stay there, this also alllows you to keep your head up in the auto and looking out not focusing inside the cockpit.

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OK ya'll... was trying to leave it simple but It is good there has been so much interest.

 

The POH doesn't say anything about the coorelator use..... just says "use ---- rpm for take-off" (I left out the rpm numbers again as they are different for the different models).

 

The HMI (handbook of maintenance instructions) gives us lots of useful information on the correlator, how to set it up properly and adjust it if it isn't quite right.

 

Section 8-78 helicopter rigging of collective control: "Normally an engine speed increse of approximately 500 rpm can be expected if the throttle remains fixed when going from flat pitch to hover at gross weight"

"If throttle bellcrank adjustable extension is not set correctly, the change in RPM from hover to ground with fixed throttle will be less or more than 500 rpm normally observed."

 

If we use the above information in autorotation we can see that simply lowering collective to the stop while maintaining a fixed throttle position the needles will split pretty dang close to what the POH says to use for power recovery autorotations...... this high rpm keeps the engine from loading up or stalling....

 

From the 300C POH: "split the needles by lowering the collective while maintaining throttle setting. The throttle correlation will establish a high idle rpm (approximately 2500 rpm) which will aid in preventing the engine from loading up or stalling during recovery. Conversely, when the collective is raised without increasing throttle, the correlation is such that only minor throttle adjustments will be required to perform a smooth recovery without exceeding 3200rpm."

 

And the A & B POH "When performing practice autorotations with power recovery, maintain 2400 rpm during stabilized autorotation"

 

From all this, if you re-join the needles before the flare and pitch pull you will be all over the place trying to avoid an overspeed.

 

Petter: the correlator is a very simple mechanism attached to the collective and throttle cable that merely pulls more on the throttle cable as the collective is lifted. Ask your mechanic to show you sometime between the seats... is is very easy, but much more difficult to explain the correlation. With less load on the blades the engine does not need as much throttle/power to maintain rpm. When you pitch the main blades and put a load on the rotor system it would tend to drag the rpm down but the correlator increases the throttle setting as you lift on the collective...... clear as mud??

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OK ya'll... was trying to leave it simple but It is good there has been so much interest.

 

The POH doesn't say anything about the coorelator use..... just says "use ---- rpm for take-off" (I left out the rpm numbers again as they are different for the different models).

 

The HMI (handbook of maintenance instructions) gives us lots of useful information on the correlator, how to set it up properly and adjust it if it isn't quite right.

 

Section 8-78 helicopter rigging of collective control: "Normally an engine speed increse of approximately 500 rpm can be expected if the throttle remains fixed when going from flat pitch to hover at gross weight"

"If throttle bellcrank adjustable extension is not set correctly, the change in RPM from hover to ground with fixed throttle will be less or more than 500 rpm normally observed."

 

If we use the above information in autorotation we can see that simply lowering collective to the stop while maintaining a fixed throttle position the needles will split pretty dang close to what the POH says to use for power recovery autorotations...... this high rpm keeps the engine from loading up or stalling....

 

From the 300C POH: "split the needles by lowering the collective while maintaining throttle setting. The throttle correlation will establish a high idle rpm (approximately 2500 rpm) which will aid in preventing the engine from loading up or stalling during recovery. Conversely, when the collective is raised without increasing throttle, the correlation is such that only minor throttle adjustments will be required to perform a smooth recovery without exceeding 3200rpm."

 

And the A & B POH "When performing practice autorotations with power recovery, maintain 2400 rpm during stabilized autorotation"

 

From all this, if you re-join the needles before the flare and pitch pull you will be all over the place trying to avoid an overspeed.

 

Petter: the correlator is a very simple mechanism attached to the collective and throttle cable that merely pulls more on the throttle cable as the collective is lifted. Ask your mechanic to show you sometime between the seats... is is very easy, but much more difficult to explain the correlation. With less load on the blades the engine does not need as much throttle/power to maintain rpm. When you pitch the main blades and put a load on the rotor system it would tend to drag the rpm down but the correlator increases the throttle setting as you lift on the collective...... clear as mud??

 

 

"if you re-join the needles before the flare and pitch pull you will be all over the place trying to avoid an overspeed."

 

Thats why I started this this thread because thats what Ive seen when someone trys to auto the 300 like a robbie. thanks for all the info guys this thread has become very informative and has answered a few other important questions I had like the ERPM above 1600 when free wheeling.

 

As far as the aft cyc on entry pretty sure this is done because of the negative pitching moment that occurs on entry as a result of the rapid change in flapping atleast this is what ive been told.

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I wish to add to this topic a couple of recommendations.

 

The general thought that you will always add a "gentle bit of aft cyclic" is not always correct. In most single engine helicopters, a ballpark airspeed of 60 knots in autorotation will work. With this in mind, if you are above 60 knots, a bit of aft cyclic is beneficial. If at or below 60 knots, especially at the apex of H/V, aft cyclic should be avoided as a gentle but deliberate cyclic movement to attain proper airspeed pitch attitude is paramount.

 

For the original question of throttle increase at the end of the power recovery auto. I can't think of a helicopter that I don't like to see engine response prior to the leveling of the helicopter and subsequent pitch pull. All to often, the recovery (level, collective increase, and throttle) items all happen simultaneously. This puts the instructor in a potentially dangerous situation. If the engine fails to respond (which will happen to you), you have already increased collective pitch taking away from your rotor and potential rotor rpm needed for successful landing. I prefer to increase engine rpm during the flare to verify engine response. I then feel assured the recovery will be successful.

 

Please note that adequate planning with regard to surface texture is equally important. If the engine fails and your a going to wet grass, etc...it makes for an interesting ride.

 

Just a bit of a Randy-ism!!!

 

Take care all,

 

Randy Rowles

I always crack the throttle 200 ft AGL for response check and to bring ERPM up a little for the needle rejoin.Usualy goes (throttle crack, flare, level , collective ) didnt go into specifics on performing the maneuver because I was basicaly asking guys that fly 300s if they perform the power recovery the same way I was taught to do it.

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