Translational lift flying backwards

[Wigglyamps]

As an interested outsider in the world of helicopters, I was wondering if it is possible to enter translational lift whilst flying backwards, and if so is that a bad place to be, I assume the back end would want to swap places with the front and a whole host of other nasties.

Thanks for any replies

Wigglyamps

[Ascend Charlie]

You can get it forwards, sideways, backwards, whenever the airflow across the disc is about 12 kt.

The directional stability will become a problem when you get towards the limits of tail rotor authority, and it will want to weathercock into wind. Also when going backwards the horizontal stabiliser will cause you to tuck the cyclic back into your intestines, and again you will run out of cyclic authority and have a windscreen full of ground, somewhat scary.:eek:

[Wigglyamps]

Thanks for the reply

[John R81]

I must admit to never having considered the question that there might be a good reason to try this kind of manoeuvre. Backward departure through translational lift? Military skill to depart-from-dodge quickly?

Anyway, the backward manoeuvre can be even more interesting, if you are not careful. I have not tried to fly that profile myself, but someone did demo it to me recently (very windy day).

When you increase speed and pass through translational lift, as the disk flaps back the direction of travel means that it lifts the tail (it would have been the nose in fwd flight, and we simply push through with the cyclic). Going backwards, as the tail lifts the air-flow then gets under the horizontal stabilizer (if you have one) and lifts the tail further. That creates a positive-feedback loop as the angle of attack on the stabilizer increases. The ship will rapidly adopt a "very severe" nose-down attitude. If the pilot is not anticipating this event there is a natural tendency for him / her to pull-back on the cyclic which - particularly in a teetering head rotor machine - creates a severe risk of amputating the tail. The control input reactions are therefore not intuitive.

Glad to have been in the demo, and even more sure than before that I will not be trying to effect a departure backwards.

[Devil 49]

from the pad entry area? Used to be a common situation in the Gulf of Mexico after a cold front. Pax exiting and loading the aircraft, especially on break day weren't always completely 'in the moment' and lots of pads with only a single access point and it could well be on the downwind. A pilot feels helpless watching somebody chasing something downwind towards towards a low tail rotor...

Allowed to routinely operate in winds up to 40 knots, being above ETL was common in the hover. As mentioned, one might have the cyclic well aft, even bouncing against the aft stop, depending on CG and aircraft being flown. Technique was slow turn, evaluating control authority all the way. The real trick was getting the nose slowly back into the wind after loading.

[Dennis Kenyon]

Not sure if it adds much but some might like to know I frequently demonstrate various Enstrom models in rearward flight at speed ... (28/280/480) In fact with a 15 knot following breeze, I've recorded a 70 knots groundspeed on the GPS. A good example can be seen on my North Weald Enstrom 28F display sequence. (video on the opening page of my web site which includes the loop) ... I've often thought it would be nice to have a rearward reading ASI fitted for display flying. There is an open secret.

To obtain anything over 50 knots the airframe needs to be flown fairly rapidly through the translation lift and associated flap-forward area using aft cyclic to achieve a steep disc angle relative to the surface. The technique is to replace a high percentage of conventional translation air flow with the good old induced airflow. Not sure what it proves though! Perhaps to say the usual ... "Don't try this without a good FI/DAE on board." Happy flying to all pps. Dennis K.

[Non-PC Plod]

I remember , it used to be part of a check test flight on the Sea King for tail rotor. When you want to stop going backwards and you push the cyclic forwards, you really get a windscreen full of ground as you get the flapping disk action plus the forward cyclic. Even expecting it, it makes your bum start eating the seat!

[Helilog56]

Hit 82kts with a Notar during flight testing in Mesa years ago...fun it was ;)

[Aucky]

Hit 82kts with a Notar during flight testing in Mesa years ago...fun it was

I bet the VSCS loved that! I hadn't considered this before but they would be acting in the opposite sense presumably with a rearwards flow across them...? Did you turn them off?

[Helilog56]

It was tested on both sides....only about a consistent difference of about 3 kts....not a happy aircraft with it on at those speeds.

[Art E. Fischler-Reisen]

During the Whirlwind course we were given a QHI demo of the effect of recovery from fast rearwards flight, in a backwards hover taxi. The old bird used to kick up her heels quite rapidly (about the only time it did anything rapidly).

I used rearwards translational lift during my time displaying the Puma HC1. One manoeuvre was to climb at full power from the hover whilst flying backwards at the fastest controllable speed. On reaching 450 feet agl, leveling off allowed the airflow to suddenly build under the horizontal stabiliser. Applying forward cyclic allowed the tail to rise (rather than the nose to drop) until the pitch attitude reached 90 degrees nose down. This was followed by a downwards vertical roll through 180 degrees, allowing the aircraft to be flown away in the opposite direction. A full 90 degrees nose down was needed, otherwise after the 180 degree roll the aircraft came out more nose down than vertical.

During one display practice the nose tucked right under to an estimated 120 degrees nose down at the top of the manoeuvre (estimated by the ground observer, my Squadron Boss) That one was bit exciting (you can't see the sky at all until you've rolled through and the ground is very rapidly approaching!) but at least after the 180 roll we were away from the vertical.

[Gomer Pylot]

Be careful of a downwind departure, which is sometimes necessary. Especially if you're near max gross weight. You can go from translational lift from the rear to out of it on takeoff as you accelerate, and suddenly you can be out of ground effect, out of lift, out of power, and out of ideas simultaneously. It's not that you should never do it, it's that you should always think and plan carefully before you do it.

[Delta Torque]

When I was younger and quite stupid, I tried rearward translational lift in a 365C. The rapid flip to a 90 degree nose down attitude certainly caught my attention, and reinforced the fact that even the most docile of aircraft will bite you if mishandled.

[GipsyMagpie]

As a wise instructor once pointed out to me, translational lift occurs at all speeds above a perfect zero wind hover. Its all about whether you get any benefit from it.

[RVDT]

And life gets even more interesting on a Bell with a "sync elevator". (47, 204/205, 212 etc)

Hence the placard "Protracted rearward flight prohibited".

It works against you when flying backwards like a canard in reverse.

Then again on a Bell Medium translating rearwards can be beneficial.

Forwards, backwards, sideways is of no consequence to the main rotor, its more about the pieces hanging below it that becomes a "piloting" issue.

[cattletruck]

I assume the back end would want to swap places with the front

Yep, even happens to aeroplanes when they return back to base :E.

[Thud_and_Blunder]

Most advantageous wind direction - to make maximum use of translational lift - in the Chinook was taught as from the 9-10 o'clock position.

Main problem with rearwards flight at speed in that aircraft wasn't the aerodynamic effects, it was the reversal of airflow through the engines. Folk watching the Chinook display may occasionally have heard the rapid popping sound associated with the early stages of compressor surge/ stall.

[[email protected]]

John R81 - a much more useful manoeuvre (especially in a strongish wind) is - starting from an into wind hover, climb slightly as you move backwards keeping straight initially with pedals then, at a groundspeed that retains translational lift, yaw the aircraft gently round, maintaining the cyclic moving in the desired direction of travel (so it starts in the 6 o'clock position and gradually comes round to the 12 o'clock) until you are now flying in the opposite direction to the initial hover.

This is useful in mountain valleys, areas where there are obstacles ahead or just for handling practice.

You could just turn downwind and do a downwind transition but you might not have enough TR control in 30 to 40 knots for that.

The skill is to maintain translational lift throughout so you don't get any Tq spikes or run out of power.

Best practised on a 15-20 knot day before attempting it in a stronger wind.

The yaw is best done with power pedal so that any weathercocking doesn't cause Tq spikes (shouldn't happen if you keep ETL).

[Arnie Madsen]

.

Somewhere there is a video of a full down auto done backwards , including flare and landing .... was a 206 or maybe Enstrom

[Dennis Kenyon]

Ref the above ... it doesn't have to be somewhere.

I've actually sat alongside a highly type experienced and especially competent UK pilot who demonstrated a rearward entry into autorotation from 400 feet and the following descent terminating with a full skids-on touch down while remaining in rearward flight. The type was a Robinson! DRK.

[[email protected]]

I just can't for the life of me think why on earth you would want to do that.

How many times did he get it wrong before he got it right and turned it into a party trick?

[Gomer Pylot]

My IP demonstrated backwards auto entries in flight school lo those many years ago. The only safe landing area might not be in front of you, and you might not have enough altitude for a turning auto to it. We never touched down backwards, we transitioned to forward movement in time to touch down going forward. I'm not sure the TH-55 would do a successful backwards touchdown, but I suppose anything is possible.

[[email protected]]

Entering auto but bringing the speed right back - even to negative IAS - is a good technique with valid application as you say GP.

Trying to do an EOL to a piece of land you can't see however, is likely to cause more problems than it solves.

[Gomer Pylot]

Depends entirely on the land, or lack of it, and what is or isn't on it. Sometimes you have to take the lesser evil, because that's all the other evils are worse. In an ideal world, there is a runway dead ahead, in the right place for landing. But we don't live in ideal world.

[[email protected]]

We are in complete agreement Gomer Pylot - going backwards in auto so you can get visual with somewhere to touchdown is taught widely and is especially useful in a strong wind.

My question is about trying to to a 'flare, check, level cushion' EOL backwards which means you never see the LS - nothing but a party trick.

[311kph]

The real fun is at 0:30 and 1:30.
Useful or not, GREAT skill, and I'll bet that girl is impressed too.

Autorotations - YouTube

:):*

[[email protected]]

There is a person who is going to end up owning a crash site at some point in the future:ugh:

[Paul Cantrell]

Yeah, but at least the stinger won't be all scraped up!

[Miklavz]

Look impressive - for a airshow display. My personal surviving instinct tells me - don't try this with a big birds. Me, personally, from the experience, am always taking in calculation - what else can go wrong.
Even in perfect conditions - with a nice, smooth infinite big landing spot right in front of me - would never play fool of myself and odds of fortune to do something like this.
But, again, what can I know? I am bus driver.
M

[311kph]

Me, personally, from the experience, am always taking in calculation - what else can go wrong.

You must be a cheerful guy!!!


- don't try this with a big birds.
That is why you take it there gradually...

Amazing Landing - YouTube

[ShyTorque]

What amazing point is the video supposed to highlight?

[311kph]

The thread is called Translational lift flying backwards.

[[email protected]]

And that wasn't.

[Arnie Madsen]

Here ya go girls

ATU Helicopter taking off backward from football field. - YouTube

[JohnDixson]

Perhaps if he takes a look into this thread, Mons. Lappos could paste in a video of himself doing a very interesting bit of backward flying with a modified S-76B that he flew in conjunction with the 1995 Paris Airshow.

[Vertical Freedom]

It's just toooo Hard :mad: (backwards flight) :yuk: hmmmmmm what is the actual useful purpose for flying backwards???? :ooh: (backward Auto from a good height to eventually get 65knots fwd ASI- OK) :ok: But....If there isn't a good reason for flying low level at high speeds with ETL+ in reverse, bar challenging one's (superior?) Skills :confused: then.....otherwise Airmanship dictates taking the Safest, or at least more Safer options, thus avoiding that area of flight; as it has additional risks, challenges & (potential) dangers :8

OmOmOm ;)

[Miklavz]

At some point I have a feeling that here is a splitted discussion between backward flight transition (than can be usefull in certain condition) and circus flying and opening beer bottles with helicopter...
Are the pilots flying in Red Bull race best FW pilots in the world? If so, than rearward AR is essential thing in every heli pilot training.
If not - than it is good to know that it is possible; essence of flying helicopter is to do your job safely and correct with high enough safe margin.
That is my opinion. Doesn't mean that I wouldn't be able to do something simillar in helicopter like this. But, at the end of the line, good pilot is living pilot.
Mike

[NickLappos]

JohnDixson hinted at a story about the Paris air show that fits perfectly with this thread about flying backwards.

First, some aerodynamic background. The rotor does not know which way it's going, so that flying backwards is actually no different to the rotor than flying sideward, or forward. Where the rotor not attached to a fuselage you would feel perfectly comfortable at hundred knots backward. What does get you feeling funny on the controls is the effect the sideward or rearward flight has on the horizontal tail, the vertical tail and tail rotor. Basically, those tail feathers are like the feathers of a dart, and they try to force the aircraft to point its nose into the wind. Try throwing a dart backward, feathers first, and note how it flips forward. About halfway into its journey, it goes point first and sticks its nose into the wall. Your helicopter does the same thing, and you spend most of your effort in rearward flight fighting the horizontal and vertical tails. This makes your cyclic and pedals workload very high. Any missed timings on the controls, and the aircraft literally tries to swap ends. If it does so, it does so quickly and you are a passenger for a few seconds, usually an anxious passenger..

The most disturbing thing about rearward flight is how the horizontal tail tries to take over. Because the horizontal tail stabilizes your pitch axis in forward flight, it destabilizes the pitch axis in rearward flight. You can tell how strong this effect is when you recover from rearward flight and the nose pitches way down during the deceleration. While it's generally foolish to fly rearward at appreciable speed, doing a pedal turn in a brisk wind is the same thing.

Now on to Paris! It was 1993, and JohnDixson & I had brought our latest toys to the air show. He had the latest model UH 60L and I had the experimental demonstrator that we called the Fantail. A quick Google search of the Sikorsky fantail will show you a picture of the modified S 76B with the fan. It was the prototype for the Comanche, which proved the effectiveness of the yaw device.

We were at the Le Bourget heliport and flying back to Issi Les Moulineaux, diagonally across Paris. Flying with me in the fantail was Etienne Herrenschmidt, a fine test pilot – my counterpart at Eurocopter. We took off in formation with the Black Hawk, JohnDixson in the lead. I asked John to hold steady at 80knots, and then pressed full left pedal and popped the aircraft into rearward flight. As we trimmed in formation with the Black Hawk, he going forward, and we going backwards, Etienne whistled under his breath "Formidable!" We flew two thirds of the way around Paris backward!

I didn't feel brave enough to shoot a backward approach to the Issy heliport (not from a courage standpoint, more from a "Will he get thrown out of France?" standpoint) and so I swung the aircraft nose first on long final. Etienne was grinning ear to ear as we settled into a hover!

So much for backward flight transition!
how important is it to fly backward? For civil helicopters probably not very important, for military helicopters, it means you can point your weapons in seconds perhaps twice as fast as making a bank, so that large rearward flight speed envelopes might buy you the ability to finish your mission.

A vanilla video of the Fantail: Sikorsky H-76 Eagle FANTAIL Demonstrator - YouTube (http://youtu.be/JAzqShF9EAI)

JAzqShF9EAI

some Comanche sideward flight, similar to that we proved on the H76 Fantail: RAH-66 COMANCHE - YouTube (http://youtu.be/J-qitMUW38U)

J-qitMUW38U