Donut effect on the EH 101

[Rotorbee]

I have never heard of this before.
Has somebody an explanation why only the EH 101 should have this "feature". How does it work?
Life-Saving Features: No More Brown-Outs
And the Royal Air Force pilots operating the EH101 in Iraq discovered a life-saving feature of its main rotor blade which even its developers hadn’t counted on. They found a solution to a pilot’s worst nightmare when flying in the desert—“brown out”—which is a dense cloud of swirling sand and dust, virtually blinding pilots as they’re trying to land. To counteract this, the EH101’s ‘winged-tip’ rotor blades create what its pilots call the “donut effect” – a circular window of clear air inside the dust storm that allows them to see the ground as they come in to land.

LINK (http://blogs.nationalgeographic.com/channel/blog/2005/11/explorer_superchopper.html)
:confused:

[Flyting]

Quite incredible. It was apparently one of those lucky unplanned discoveries. I saw it on the documentry on the heli on the Discovery Channel one night. The down draught blows all the dust out and away from the landing spot under the heli allowing the pilot to see where he's going. Viewed from above it looks like a donut or the eye of a cyclone... Wish I had some thing like that now and again...

[donut king]

The "donut effect"!
I knew this all along! I take full credit!
Lappos, Coyle, and all........where were you guys on this?
Ha Ha Ha Ha Ha !!!!!!!
DK

[SASless]

Nick was busy wandering about looking for the Krispy Kremes and coffee pot.

Perhaps the Chinook has a "Honey Bun" effect being a tandem rotor design.

[NickLappos]

That effect exists on all helos, it can be plainly seen when looking from above. I have hovered an S76 for hours in complete whiteout while looking through clear air at plywood panels placed within 6 feet of the cockpit, in the lower windshield and chin, and have used small stones and features in Black Hawks in dust. The issue that might be different in the 101 is that the "clear" area is a bit farther ahead of the pilot's windows.

In many kinds of wind conditions the dust flows outward ahead of the machine, then upward with the roll cloud, then it blows downwind toward the helo into the center "hole" from above. This then feeds dirty air that obscures the pilot's view. I contend that this effect is not nirvana, it is a case where in low wind there is a bit more usability. I would bet dust landings are still horrible, and this is where the problem lies for all helos.

[Heli-Boy1]

The BERP blades fitted generate far more lift at the tips. This coupled with the considerable down wash (high mass helicopter) means that recirculation occurs further away from the fuselage.

There is still a huge amount of recirculating dust and to say there is no brownout is not really true. Rather the effect is a 'bubble' of relatively clear air close to th aircraft.

That is my view - having said that, Westlands themselves did not have a real answer to the effect whn this question was asked of tem recently!

[NickLappos]

Heliboy,
I dont believe the idea that the berp blades contribute to this by having less lift inboard - otherwise those crewmen being winched up would have no downwash, and the dents on their helmets suggest otherwise.

Add this wonderful concept of dustless helos to the long list of BERP myths!

BERP Myths:

1) The BERP blades are the best lifters known to man.

2) The BERP blades are great at high speed, making stall much less in an EH101

3) The BERP blades are so advanced, nobody comes close

4) The BERP blades would increase the lift of any helicopter lucky enough to have them

5) The BERP blades move air in strange ways so that dust runs and hides.

Give me a break! There is only one true BERP statement:

The BERP blades are the only blades to ever employ a PR agent

[dangermouse]

the only defence the blades need is this...

400.25 kmh / 215 kts in level flight

world absolute speed record since 1986

it's just an ex Sikorsky man getting jealous again

DM

[NickLappos]

dangermouse,
we go thru this each time! The record is a marvelous achievement - I have a signed print of it in my office!

The BERP blade is 1984 technology, a poor blade by 92/225/carson 61 standards, and those who think otherwise are simply wishing for the stars.

If you think the BERP blade is an answer to blade stall, I will send you the atrocious EH101 blade stall chart, which shows that it is about 10 knots slower than a modern helicopter at the same blade loading, showing that the blade is a dog.

That marvelous record was set with raw power and raw blade chord, and raw courage.

[heli1]

Sorry Nick but the Lynx world record,set up 20 years ago now, was not down to "raw power" or "raw courage "as anyone who was present at the time or has flown with Gem engines would know.Although they squeezed a bit of extra power out by water methanol injection it was still an awful lot less power than other contenders have generated,like the "Hi Speed" Dauphin with newer blade Technology or the Boeing 360 ditto,neither of which got even close.
However old the berp blade may be it was streets ahead of its time and the proof is in its performance since....and look out...they're working on Son of Berp.
That should cause a big hiccup !!!

[slowrotor]

I read somewhere that the Piasecki Air Jeep could hover without any dust problem. Because of the dual shrouded rotor. Not sure why the shrouds help.

[TwinHueyMan]

"Although they squeezed a bit of extra power out by water methanol injection it was still an awful lot less power than other contenders have generated,like the "Hi Speed" Dauphin with newer blade Technology or the Boeing 360 ditto,neither of which got even close."

Interesting fact though, the Dauphin holds the 3km course speed record at only 15 knots slower than the Lynx record.

Also, the Gems in G-LYNX were Gem 60s, which were not only bigger than the Gem 2s in the standard AH1, but were cleared to operate at max contingency power (OEI) for the run, plus the water injection. Thats a jump from 750shp from each burner on a stock AH1 at MCP to 1577shp each on the hot Gem 60s. More power than adding 2 more engines.

The Dauphin record was set with the Arriels pushing 820shp each. The lynx had almost twice the power. Dauphins aren't THAT much lighter than a stripped out, slicked up lynx, are they?

-Mike

P.S. in response to the original thread, I've only lost sight of the ground a handful of times looking straight down from the back seat of a UH-60, and dust has gotten pretty soupy before. Give it a few seconds and you'll start seeing the ground up front too. One of the dust landing techniques the Army teaches these days is to hover down slowly from a decent altitude -- works great on loose dust that goes away, but in use we can do the same thing on a confined LZ, as we get a cone of relatively clear air straight down the center.

[Graviman]

I thought it might be interesting to compare EH101 BERP tips against 92 anhedral tips:
http://www.b-domke.de/AviationImages/EH101/Images/EH101_Merlin_HC3-10353.jpg
http://www.etribes.com/sites/etribes.com/files/images/4_DSC00045.preview.JPG
Last one from
http://www.b-domke.de/AviationImages/Rotorhead.html#AgustaWestland

Not intending to fan the flames, but aerodynamics has undergone a serious revolution in the past 20 years. A more recent blade will inevitably benefit from the latest 3D CFD flow visualisation techniques. That said, i can't wait to see son of BERP. ;)

Mart

[dangermouse]

First I agree with Nick, we always go through this discussion, each believing the other is wrong (after all everyone is entitled to their wrong opinion).

Nick, you kindly offered to show me the EH101 stall envelope to justify your views, as this may answer some questions I will take up your offer and hope to see you 'evidence' shortly. But at the same time can you supply a comparison for a 'modern' helicopter (S92?) to show how far behind we poor europeans are? BTW the Lynx CMRB has the same as the normal blade chord except for the tip so 'raw blade chord' doesnt make sense.

no doubt further discussions will ensue

DM:ok:

ps twinhueyman; although the Dauphin as the 3km record, by definition the Lynx could have ALL the speed records, thats what 'absolute' means

[NickLappos]

dangermouse (I like the way his friend says Banana Man!),

The fact is that the EH-101 would gain over 2000 lbs of hover performance if it had the blades off the S92 (or the EC 225 or the Carson blades), even if all were held to the same blade chord. (I don't think it is a "poor Europeans" issue, unless you guys have finally tossed out the French!)

I will dig up the EH-101 blade stall chart, it is an eye opener!

The point I like to make is that the blade has a PR agent (brilliant thing!) and so I have been asked more than once "Why doesn't the S-92 just use BERP blades?" to which I respond, "Because we want to actually carry some payload, and so can't afford the performance loss." This "donut" theory is drawn from the same pool of PR thought!

[nimby]

It seems AW continues to BERP...

(from an AW press release dated 27 Sept 2006)

The first flight of a high performance variant of the AgustaWestland EH101 fitted with new technology British Experimental Rotor Programme (BERP) IV main rotor blades, more powerful CT7-8E engines and a new integrated cockpit display system took place at AgustaWestland’s Yeovil facility yesterday. Following an initial flight in the morning the aircraft performed a second flight later in the day operating at speeds up to 135 knots and performing a range of manoeuvres with all results as predicted.

Speaking after the successful initial flights Alan Johnston, AgustaWestland’s Managing Director of Military Programmes said “This event brings together the technology that will give the next variants of the EH101 even greater mission performance. The additional capability these improvements will bring, especially increased payload in demanding hot and high environments, will be of great benefit to our customers who are experiencing ever increasing operational demands.”

The BERP IV Technology Demonstration Programme (TDP), which is jointly funded by the UK Ministry of Defence and AgustaWestland, was launched with seven key objectives comprising reduced first cost, reduced life cycle costs, reduced rotor vibration at high and low speeds, improved hover and forward flight performance, improved damage tolerance, increased erosion resistance and reduced signatures. The TDP is delivering the technology for the next generation of advanced composite rotor blades which will deliver significant improvements in whole life costs and operational capability of future helicopters including variants of the EH101.

... I think every blade should use a PR man

Nimby

[Graviman]

OK, Bunford Lane - but it doesn't sound as good. ;)

Interesting Nimby. Any tech details, or is the design still doing lots of whirl-tower time?

Mart

[NickLappos]

Considering the expertise of the A-W aero team, I would bet the BERP 4 blade will be a good one.

[BIT]

For Graviman, yes the BERP and SK tips look similar, but its not just about the tip and the BERP "bit" applies to the whole blade too with the tip being the obvious change over a conventional aerofoil section. Nick may be able to shed some light over how the SiK blade section and twist varies across the blade diameter.

Nick, Like Dangermouse (here the similarity ends!) I too would be very interested to see how the BERP blade stall lines change with altitude and compare that with S92.

Do you think that the BERP blade stall line will be a problem for the Merlin crews when flying? Its just that I thought that retreating blade stall was pretty serious and that if it was common on the 101 it would have emerged by now.

It appears that the S92 has evolved a tip very similar in appearance to the 101? I think its right that the 92 is somewhat noisier than the 101 due to high mach tip effects but that is in the rumour world unless anyone can comment. Cant wait to see what son of BERP looks like.

[SARBlade]

I agree with nicklappos on this one. I have included a link to youtube with a video showing the "Donut" if you will. In the SAR world in Canada we refer not to the "Donut" but rather the Turbulent Flow Zone (TFZ), the area of intense airflow from the MRBs. Penetrating this with a person on the winch/hoist can be somewhat challenging.

If the wind is calm in the hover, then height of hover over the ground can make a big "donut", however, as wind increases, the "donut" moves downwind and can be quite challenging to keep someonw in it when hovering.:eek:

Merlin Hovering (http://www.youtube.com/watch?v=-oV5VHsoffk)

[NickLappos]

BIT, they aren't a bit alike, the old BERP blade has a thick, forward bulge at the tip that is almost ax-like when seen from above. In other words, the blade chord increases markedly at the tip.

The S-92 (and UH-60M) blade is a swept, anhedral tip that thins out in thickness and droops down the last 5% of blade span.

The S-92 blade has a figure of merit that is about 4% better than the BERP blade (which means that for the same horsepower, the S-92 blade lifts about 5% more weight than the BERP.)

[BIT]

Nick, thanks for the FOM data and the detailed design differences between 92and 101 tips, I appreciate your input.

I fly at highish density altitude as fast as possible a lot so what about the blade stall line data comparison?

[Heli-Boy1]

To try and get back to the point -

the BERP blade operates at a relatively low NR and creates a greater proportion of its lift at the tip (as too I suppose does the 92?). The 'Donut Effect' has been routinelly commented on by operators in Iraq - not an absence of brownout, but rather a bubble of relatively better vis within the disc.

In light of the lack of other reasonable suggestions I propose this as a solution - but would be delighted to be corrected (I am certainly not an aerodynamicist...and certainly not a Westlands agent!!)

Anybody got a better answer?

[Matthew Parsons]

It's so easy to get into aerodynamics theory and arguments about who's got the better tip that its easy to forget what matters.

The line pilots that reported this effect are happy with it. They are probably experienced pilots who have flown similiar conditions in different types (all of which blow dust into a donut, yet don't seem to offer the benefit they've reported). Lets respect them by agreeing that perhaps they have found something unique.

-----------
As far as the blade tip argument, here's my 2 cents. The S92 has about 20 years of development and technology that BERP didn't have. If S92 isn't better then something is very wrong. Similiarly, BERP IV has the advantage of potentially being better than the current S92. That's just how technology develops.

As far as timing and design similiarities, that's easy to explain. Physics doesn't stop at political boundaries. The physics that gives benefits to the BERP blade also work for the S92. As far as timing goes, the demands of the helicopter are very similiar because they are competing in the same global market. This means that the desired performance enhancements are quite close. The timing of producing similiar designs has much to do with the technology that's available. As more is known about composites, and more confidence is generated with their use, designs will start using them. I expect that making a tip like these out of wooden blades would have required so much weight that the gains in performance were lost to AUW.

As far as I know, BERP was the first (at least commercially, not sure about development). That makes it exciting. Bragging about its performance now could sound a lot like bragging about the speed of my 75 MHz Pentium. At its time Pentium was impressive, now I'm left behind with an 866MHz Pentium III. AW appears to understand this, hence the development of a new series of BERP blades.

Matthew.

[Graviman]

For what it's worth i believe the mechanism for the '92 anhedral tips is that tip vortex associated with producing lift is spead out (to make it weaker) and pushed away from the tip path. Helicopters produce lift by ingesting static air and accelerating it downwards through the rotor, so that downwash speed is twice speed through rotor. By pushing the tip vortex away the rotor effectively ingests air from 4% larger area than it otherwise would. So effectively disk loading goes down, or FM in the standard calc goes up.

I won't bore y'awl with the Biot-Savart law applied to vortex fields, and anyhow CFD has made this academic.

BERP I (or II?) was really designed for high speed, by having shaped tip profile stay within transonic Mach cone on the advancing side (sweepback), and incidentally pushing retreating stall up by letting the shed vortex developed during initial stall remain attached to profiled leading edge. Not sure it would make any difference in hover, but have seen no evidence to support or refute that claim.

I would be interested to see Nick's stall data, but my guess would be that once the already shed vortex is lost lift dropoff is severe.

BERP IV will likely be as much a step from BERP I as I was from 0. :ok:

Mart

[BIT]

Nick, I think a number of forum members would now like to see the BERP stall data you have told us about. Please keep it simple though!

[Avnx EO]

I'm still trying to understand Nick's remark
have used small stones and features in Black Hawks
.... I never realized it required small stones to hover in a black hawk:} ....Would have tought it required large ones to extend hover in such an efect.:ok:

[BGRing]

I think the Green Helis blade would fair better in FF Flight. not sure yet. I would like a better picture. or info on which blade that is.

the tip kinda looks like it would be less likly to stall at higher angles. (Is there a Chart that shows info on this? any data?
I would like to look at a chart which shows a line to indicate stall, with AoA up one side, and Air speed along the bottom, or something to that effect)

[dangermouse]

Hey Nick, can we see that 101 blade stall data you promised? (it's been nearly a month....)

I am willing to be converted.

DM:confused:

[NickLappos]

danger,
I am looking for it - haven't forgotten! If you know any EH drivers, the chart I refer to is in the flight manual.

Most flight manuals are not copyrighted, but each document tells you.

[dangermouse]

Nick, do you mean that the Flight manual is in the public domain ? (and by EG do you mean EH and it's a typo?)

If so is there a S92 equivalent for comparison?

DM

[Matthew Parsons]

Nick, I've looked through my AFM and can't find blade stall data. Would the information be available on a chart of a different name?

Matthew.

[NickLappos]

Vne vs alt and temp at Gross weight has the stall data on it, as I recall.

[Matthew Parsons]

Nick, the cruise charts show that vne (indicated) decreases as pressure altitude increases when ambient temperatures are very low. As it warms up, vne doesn't affect max speed in level flight at heavy weights because of approaching transmission limits.

I think the information you're talking about may be embedded in the charts, but it would require quite a bit of effort to draw it out, and I would want to check the legality of posting proprietary information.

If anyone wants to spend $25, AIAA-1990-3008 might have some relevant data. Go to http://www.aiaa.org.

[OnePerRev]

Agree with Lappos. This dust donut phenomenon is so old, it appears in photos in an early Army Report published in 1967, written by Sheridan. Maybe that does not ring a bell, but the report was used as the reference to a mil spec on global climactic data, which was then used in another, etc.. until the actual sand/dust density in air around helicopters used for most comercial and millitary test applications came from the same. Not surprisingly once you read it, but dust concentration is highest with higher downwash velocity:8 Heck, Prouty has this in one of the first chapters of the big red book.So the real question in a hover, is at what blade radius is the peak velocity? More to do with disc loading, so then, gross weight than blade design, as long as you are actually flying that is.
BERP blades sure do look funny, maybe better at something, but I bet the axehead costs more, and may even increase blade stress from CF.:oh:

[sbdorset]

Sounds like this thread on BERP has lost the reason the blade was designed. Remember your basic theory of flight? What factors limited forward speed in a conventional helicopter;
1 Limit of fwd cyclic due to flapback
2 Compressibility on advancing blade
3 Airflow reversal - retreating blade
4 Retreating blade stall
BERP blades were designed to compensate for 2-4, focused on forward speed not hover efficiency due to the fact that the 101 role as envisaged was to be a passive sonics helicopter spending most of its time in forward flight. Composite material allowed for exotic shape to the whole length of the blade and the tip has gone through several iterations.

Move forward and the wall comes down, the role changes and you end up with a helicopter that hovers with quite an element of nose up and less efficient in the hover than others. No surprise.

The AW press release cited talks about improved hover, well from a poor base! As for other benefits, it has to be the most quiet helicopter in its class in the hover....:ok:

[Peter-RB]

Was'nt the speed record 249.5 MPH for the original Lynx..! :D:D:ok:

PeterR-B

[MightyGem]

Hmmm...6 years. Is that a record?

[msmfi]

The "Donut Effect" is mentioned @ 20:16 of the following document:
Les constructeurs de l'extrême - Hélicoptères géants - YouTube

Hope You speak French .... :)

Regards,
Mirek

[OnePerRev]

Point is that the blade design should have little to do with this phenomenon, the thread title anyway, and the report shows this pictured on an H-21 way before BERP. My copy is old, and actually made of paper. No promise, but if I can scan the photo, I will. Correction to some details: Sheridan is the author's first name, and it was 1968, not 1967. Maybe someone can beat me to it. Love the gram/ cubic ft units.... but an Excellent report. Interesting that the video only simulates this condition. Too much to actually fly in it?

Accession Number : AD0669676
Title : EVALUATION OF THE DUST CLOUD GENERATED BY HELICOPTER ROTOR DOWNWASH
Descriptive Note : Final rept.
Corporate Author : MSA RESEARCH CORP EVANS CITY PA
Personal Author(s) : Rodgers, Sheridan J.
PDF Url : AD0669676 (http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=AD0669676)
Report Date : MAR 1968
Pagination or Media Count : 136
Abstract : The dust cloud generated by a tandem-rotor H-21 helicopter was studied as a function of type of soil, hover height and disc loading. A total of 98 tests were made, and three different test sites were used. Samples were collected at 25 locations on the helicopter. Analyses were made for dust content and particle size distribution. Average dust concentrations at the area of highest dust density, i.e., at rotor blade overlap, are given. The highest concentrations were measured at the site of rotor blade overlap, and the lowest concentrations were found beneath the rotor hubs. The maximum particle size decreased with increasing elevation. No particles over 500 microns were found at any elevation. Dust concentrations of 40 mg/cu ft were measured during takeoff and approach maneuvers. With another helicopter hovering in the immediate area, concentrations of 64 mg/cu ft were measured.
Descriptors : *HELICOPTER ROTORS, *DUST, *GROUND EFFECT, PARTICLE SIZE, LIFE EXPECTANCY(SERVICE LIFE), SOILS, SAMPLING, DOWNWASH, ENGINE AIR SYSTEMS COMPONENTS, HELICOPTER ENGINES, HOVERING, INGESTION(ENGINES), VISIBILITY, EROSION, ROTOR BLADES(ROTARY WINGS), PILOTS
Subject Categories : Aerodynamics
Helicopters
Jet and Gas Turbine Engines
Distribution Statement : APPROVED FOR PUBLIC RELEASE

[OnePerRev]

Aw how bout this one? no BERP around.
http://www.3at4u1.tk/uploads/chinook-in-north-african-exercise-23317.jpg

[Dave_Jackson]

Heli-Boy1 mentioned earlier;
The BERP blades fitted generate far more lift at the tips. This coupled with the considerable down wash (high mass helicopter) means that recirculation occurs further away from the fuselage.
There is still a huge amount of recirculating dust and to say there is no brownout is not really true. Rather the effect is a 'bubble' of relatively clear air close to th aircraft.
That is my view - having said that, Westlands themselves did not have a real answer to the effect when this question was asked of tem recently!


The following may support your "The BERP blades fitted generate far more lift at the tips. .........."

From:~ Art of the Helicopter, by John Watkinson;
”The presence of the rotor head and blade root cut-out area creates a hole in the middle of the disk through which air can escape upward in ground effect. This is actually another form of tip loss, which is called the fountain effect. In practice the fountain effect can be beneficial because it puts some of the hull into upflow and reduces the hull download.”

This presentation by AgustaWestland may be of interest.
Numerical Analysis of Unsteady Vortical Flows Generated by a Rotorcraft Operating on Ground: a First Assessment of Helicopter Brownout. (http://www.agustawestland.com/system/files/Brownout%20-%20abstract.pdf)

Dave