CowAnon
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Posts: 83
Joined: Fri Nov 03, 2017 12:03 am

Coanda effect and propeller aircraft

Tue Nov 12, 2019 1:02 am

The DIE WELT article below mentions the Antonov An-70's application of the "Coanda effect," stating that its contra-rotating propellers blow air over the top of the wings to increase lift and reduce takeoff and landing distances. Does this use of Coanda help the aircraft during cruise phase? Are there other propeller aircraft (like the A400M, ATR, Q400, and Saab 340/2000) that apply the Coanda effect in the same way? If not, what's preventing those designs from making use of it? Single rotation, dihedral vs. anhedral/flat wing slope, or anything else? And would this type of design be incompatible with active or passive laminar flow wings, if those ever get implemented?

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SheikhDjibouti
Posts: 1859
Joined: Sat Sep 30, 2017 4:59 pm

Re: Coanda effect and propeller aircraft

Tue Nov 12, 2019 6:07 pm

CowAnon wrote:
The DIE WELT article below mentions the Antonov An-70's application of the "Coanda effect," stating that its contra-rotating propellers blow air over the top of the wings to increase lift and reduce takeoff and landing distances. Does this use of Coanda help the aircraft during cruise phase? Are there other propeller aircraft (like the A400M, ATR, Q400, and Saab 340/2000) that apply the Coanda effect in the same way?
I haven't got a direct answer to your question(s), but you may find the GAL38 Fleet Shadower of some interest.
These were attempts in early WWII to develop an aircraft capable of following (shadowing) enemy naval units, flying for hours at a time at extremely low speeds.
The two rival designs both opted for FOUR small engines to help generate more lift over the wings
Wikipedia wrote:
An innovative use of the "propwash" generated by propellers directed over the full-span flaps led to an impressive minimum speed of 39 mph (63 km/h) which would have allowed the Fleet Shadower to cruise effortlessly above an enemy fleet.

And yes, I'm fairly certain that in a strong wind, the aircraft could actually fly backwards... :lol:
Image
https://en.wikipedia.org/wiki/General_A ... t_Shadower

The key thing I take away from this is that the increased lift comes from propwash not just over the wing, but also over the flaps. And the fact that it is most beneficial at low speed.
As regards the An-70, I do wonder if there is an accidental benefit in terms of cruise speed, not because of extra lift in the cruise, but because the whole wing design is less constrained by low speed (take-off & landing) requirements.

But I'm not an engineer (not officially.... ;) ) so please forgive my naive contribution.
Nothing to see here; move along please.
 
spacecadet
Posts: 3484
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Re: Coanda effect and propeller aircraft

Wed Nov 13, 2019 7:42 am

Basically all modern props blow air over the tops of the wings to help generate lift - it's got nothing (or little, at most) to do with the "Coanda effect". It's got to do with Bernoulli.

The reason turboprop airliners don't use contra-rotating props is cost. There are advantages to using them, and there are advantages to using counter-rotating props too. But most airliners don't do either due to cost. If you don't need the additional lift, then there's no reason to stock two different sets of engine parts, or four sets of propellers for a two-engine plane.
I'm tired of being a wanna-be league bowler. I wanna be a league bowler!
 
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jetmech
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Re: Coanda effect and propeller aircraft

Wed Nov 13, 2019 7:54 am

CowAnon wrote:
Does this use of Coanda help the aircraft during cruise phase?]

Coanda effect is the phenomenon of a fluid following a concave surface and as such, I don't think it would be overly beneficial in the cruise as the wing is in the clean configuration.

CowAnon wrote:
Are there other propeller aircraft (like the A400M, ATR, Q400, and Saab 340/2000) that apply the Coanda effect in the same way?

Any design with propellers blowing across the wings would probably benefit from Coanda effect to a certain extent.

SheikhDjibouti wrote:
The key thing I take away from this is that the increased lift comes from propwash not just over the wing, but also over the flaps.

The article mentions super-circulation which means the stagnation points are closer together on the underside of the wing and / or flap than would naturally occur. It suspect it is the forward stagnation point that is moving aft under the leading edge of the wing and / or flap.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
CowAnon
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Posts: 83
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Re: Coanda effect and propeller aircraft

Sun Nov 17, 2019 9:30 pm

SheikhDjibouti wrote:

spacecadet wrote:

jetmech wrote:

Thanks everybody. I was thinking the An-70's design as described in that article would result in air smoothly coating the top of the wings, flowing off toward the wing tips (and helped by the downward slope in the outboard direction). Judging from your responses, it sounds like the flow is just smoothed directly backward over the wing, further toward the trailing edge and the flaps, and air swirl (or lack of it) and wing curvature/slope don't have much positive or negative effect.

Here's another snippet about the An-70, from https://www.flightglobal.com/pdfarchive ... 00332.html:

    The An-70 has a maximum payload of 30-35t, with a range of 4,000-5,000km (2,200-2,700nm). Its take-off weight will be 100-130t, depending on the mission. The can be operated from concrete runways, 1,800-2,000m (5,900-6,500ft) long, or on unpaved airstrips of just 600-800m.

    The aircraft has a high-aspect ratio high-mounted wing, supercritical airfoils, with airflow blown onto the wing by counter-rotating propfans. This combination has previously been researched by Antonov, together with TsAGI, the central aero/hydrodynamics institute of Russia. It is intended to provide the An-70 with high lift:drag ratio and exceptional takeoff/landing characteristics. The supercirculation phenomenon, resulting from high-pressure airflow from propfans meeting the deflected flaps, doubles the lift in take-off and landing configurations, according to Antonov.

    The Progress D-27 10,440kW (14,000hp) propfans provide 119kN (26,8001b) of thrust on take-off and have been developed by the Ukraine's Zaporozhye design bureau, with substantial co-operation from TsAGI and TsIAM, the central aircraft engines institute in Moscow.

Doubling the wing lift sounds very impressive, but it results in a 6,500-foot takeoff distance for a 130-ton aircraft -- a good but not spectacular improvement, it seems to me, especially since you're using twice as many engines sized in the 150-200 seat airliner range.
 
Zeke2517
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Joined: Wed Jan 09, 2013 4:29 pm

Re: Coanda effect and propeller aircraft

Sun Nov 17, 2019 10:06 pm

I, for one, would like to welcome our new Russian overlords.

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