Re: 747 with engines on the wings?

Date:         19 Feb 98 01:34:03 
From:         "jlberton" <jlberton@ix.netcom.com>
Organization: Netcom
References:   1
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Lion's Pers Agentschap wrote in message ...
> What is the reason that airliners have engines under the wing instead
>of on it?
>
> Possibly it will take a little bit more aluminium to construct
>airliners this way, but with overwing engines the wing can deflect a
>big portion of the noise for people living around airports. (This can
>be reached even without improving the engines themselves!)
> The 777 is rather silent, but could be even better with engines on
>the wing.

Yes, and with the discharge noise of today's high bypass, modern
geometry fans now dominating the overall noise in many cases,
engines mounted over the wing might become even more attractive.

Off the top of my head, here are a few pros and cons:

*Pros:
- Shorter, lighter landing gear -- a major benefit.
- Possibly better (or at least equal) interference installation
  drags.  The high lift effect of the flow over the wing may be attractive.
- Fewer restrictions on nacelle diameter, allowing the efficiency trend
  of bypass ratio growth to continue.
- Possibly a better 'wheels up' emergency landing configuration.
- Less inlet flow distortion during ground roll, resulting in
  slightly better field thrust performance and a little less fan noise
  while on the ground.
- No more ice slush or FOD ingestion from the nose gear.

* Cons:
- Maintenence issues.  New servicing rigs/lifts required.
- Increased cabin noise or more sound proofing material required.
- A 'simple' re-engining of an existing airplane is unlikely.  Engine
  mounts, wing box, and even empennage would require redesign.
- Over-wing emergency passenger egress may be more difficult.
- Potentially worse in-flight catastrophic engine mount failure and
  engine breakaway configuration.
- Possible airline/passenger acceptance issues.

Jeff Berton