Why design a passenger aircraft with a high wing?
 

The vast majority of multi-engine passenger aircraft have low-wings, while relatively few (for example F-27, Herald, Dash-8, An-24, Bae 146) have high wings.

I can see the benefit of a low floor height for a cargo aircraft, but from a design point-of-view, what other reasons are there to choose a high wing layout?

High Wing Vs Low Wing
 

India,

One reason may be FAR 25.810 (Escape routes). Basically if the exit is more than six feet from the ground with the LG extended, then a means to reach the ground must be provided (i.e. an escape chute). This adds complexity and weight to the door design, complexity and weight to the Flight Test program, and complexity is generally directly proportional to increased cost during the service life of the aircraft.

So, in order to lift xx number of pounds/pax off the ground we need a given amount of lift, therefore wingspan. In order not to get a tip strike on landing you need to make sure that the geometry of the undercarraige is right i.e. a short stroke undercarriage sits lower to the ground, therefore beyond a certain length of wing a tip strike is a given - like the U2 for instance.

Therefore in order not to incur the penalty of heavier and more complex doors, resulting in a decrease in the amount of payload, one design workaround is to sling the fuselage low and the wing high, thus allowing a short stroke undercarriage, a low step down height and still maintain a long span wing.

That's my two cents anyway:)

Also, the aircraft you mention - Dash 8, BAe 146 etc are designed to allow operations from austere airfields - keeping the wing high also keeps the engines high and reduces the risk of fodding an engine.

There are a number of advantages for having a high wing. First, they have what is known as 'pendular stability' which means that the wings don't necessarily have to have dihedral, which means that the wing can be made as a one piece unit with a straight spar for ease and cost of production. The wing is simply mounted on top of the fuselage. Secondly, look at the Shorts 330/360, the fuselage accounts for a large proportion of the lift, something that cannot be done too easily with a low wing aircraft. The wing can thus be either shorter, or thinner for a higher aspect ratio and thus more economical with regard to performance and that also increases the payload capability, or allows the manufacturer to use smaller engines. Everything in aircraft design is a compromise. A high wing is often used for rough field operations, since it is well out of the way and is less susceptible to damage from debis on badly prepared runways. Often aircraft with high wings do not need fuel pumps, because they have the advantage of gravity feeding, all these little things ad up to a cheeper aircraft.

Another reason, for the majority of the aircraft you quote, is that they're all derived from military transports with rear ramps. Dash 8 followed on from the Caribou (via the dash7) and the 146 was a civilian rework of the HS681 V/STOL transport with twin Pegasus originally. The Shorts aircraft all came from the Skyvan & went back to the Sherpa.

But the ATR 42/72 series aren't are they?

ICT SLB, I think that you are mistaken re the origins of the Dash 8 and BAe146.
The 146 evolved from UK studies into RTOL and STOL. Both concepts had high wings. RTOL was the larger project (200 pax) and used 2xRB 211; STOL was the smaller project (but larger than the 146) and used 4xRB410.
From the documentation that I have, the driver for the high wing appears to be performance with good handling – including steep approach.
A low wing appears to offer lower cost of operation, but the high wing would be better on short sectors in conjunction with a shorter field length – also a better climb gradient in the 4 engine case.
There were noise advantages in placing the engine ‘well’ below the wing, i.e. not like 737.

Freighter studies were based on the larger RTOL project (2xRB211), but the airliner lineage dropped the ‘RTOL’ concept and became the UK Airbus (via BAC 3-11?), the final proposals resembling the A300.
The 146 was a smaller version of the STOL project (108 pax reduced to 80). Subsequently a true military version of the 146 was considered (not the STA), but never built.

You can have larger radius props with a high wing design.

Can't think of many modern prop driven aircraft with a low wing other than the ATP :D

Safety,
I worked on BAC 1-11 when the HS146 was launched & I assure you the baseline aircraft was definitely the HS681 - the reason for the 4 Lycomings is that the blown flap needed 4 jets to replace the twin peggies (think QSTOL Buffalo).

I also did the outline wiring harness for a very early 3-11 concept. It was the competing rear-engined European JET design to the Airbus 300. If anything, the 3-11 came about after the great performance numbers from the RB-211 testbed VC-10 (twin Conways replaced by a single 2-11). Just have to wonder what a straight twin 2-11 VC-10 would have done.

Cargo,
Saab 340/2000?

Cargo: Presumably the Swearingen Metro/Merlin have such tall undercarriages because of this
I remember the HS681 proposal (about '64 ish?) Wasn't it killed off by Labour at the same time as TSR 2 so the americans could sell us Hercules instead? It definitely had a similar layout to the later HS 146 which Labour first refused to back, so Hawker Siddeley put it on the back burner, then Wedgie Benn re-discovered it and it was resurrected when HS were by this time part of BAE.
I'm sure there were other proposals at the same time as the '681 one being with normal engines rather than Pegasus.

ICT SLB, thanks for you assurance. Although I flew the 1-11 and in a very small way was part of the 3-11 concept, my information comes from being very much closer to the 146 project.
The reference document was “A summary of the work and conclusions arising from the 1972/73 joint HMG/BAC funded programme of R/STOL studies.” 18th July 1974.

Surprisingly the STOL project in the studies always had 4 engines, whereas the RTOL/conventional aircraft (CTOL) evolved from a high wing, 2 eng aircraft to the low wing 2/3 eng ‘Airbus / 3-11’ idea.
Whilst my information does not refute an association with the HS 681, I suggest that some of the essential components were not the same as the 146, e.g. fuselage diameter, wing sweep, and pontoon main gear.
Many of these aspects were discussed in the research document. In particular, the ‘blown flap’ (internal and external) aspects of STOL performance and gear shape / location. Whilst the 146 might have a very small ‘blown flap’ component of lift, it is miniscule in comparison to what was considered in the research. Some of the concerns were with pitch control, this required very large tail surfaces, possibly powered controls and leading edge flaps.
The simpler, lower risk concepts were followed, which I suggest are considerations in the choice of wing location – 146 manual controls, no leading edge flaps.

A simpler fuel system was another advantage of the high wing; emergency gravity feed to under wing engines and no fuel pipes in the cabin – unfortunately the 146 failed with the second aspect.

Maybe the simple answer to this difficult question is:


BECAUSE IT IS POSSIBLE AND IT IS NOT UNSAFE?

As it will often depend on the likes and dislikes of individuals which design is utilized rather than any real reasons? (But that is only my opinion)

VG300

High wing vs low wing was a raging argument during the conceptual design phase of both the Dash 7 and the Dash 8. All of the foregoing points certainly tend to favour a high wing over a low wing layout for any aircraft with pretensions to austere runway operations.

An additional, but important factor is the reduced touchdown dispersion of a high wing aircraft during landing, due to diminished ground effect in the flare with a high wing configuration.

Dornier 228, 328 and 328J??

It's simply a matter of prop clearance, isn't it? Most high-wing aircraft are propeller-driven, and some high wing jets are derivatives of prop-driven aircraft. (See above?)

Low-wing prop aircraft fuselages must be high off the ground, therefore needing big ladders, cargo-lifters etc, and even then they have very little prop clearance off the ground, so they pick up all sorts of stuff to damage the props, especially on un-paved strips.

Quote: I worked on BAC 1-11 when the HS146 was launched & I assure you the baseline aircraft was definitely the HS681 - the reason for the 4 Lycomings is that the blown flap needed 4 jets to replace the twin peggies (think QSTOL Buffalo).

Er, no.
If there had been any carry-over from that generation of military VTOL aeroplanes, it would have been from the DH129 not the HS (né AW) 681 as the 146 was a Hatfield product .

The progression from DH126 small feederliner via the HS136 rather less small one (with RR Trent engines - no not the later huge ones, nor the earlier turboprop ones!) and other project aeroplanes to the AVCO-Lycoming powered high-wing 146 was the result of shifting targets for size, range and complexity being matched to shifting availability of suitable power units.
The 146 has not and had not blown flaps. The flaps are behind the engines, and there is doubtless a bit of fan-induced extra velocity but blown flaps as normally understood are very different.
The 146, although the most numerous British-built airliner, seems to be very poorly understood if this thread is anything to go by.:)

Interesting bunch of views with respect to the origins of the 146.

My input is that when I was interviewed by HSA in 1966 for a test flying job at Dunsfold it was made clear to me by Harry Broadhurst that if they did not eventually get a contract to produce what became the Harrier I would have to go to Hatfield and do the 146. John Stamper took me through the design philosophy and said that it was intended as a hub and spoke aircraft to open up Africa. At the end of the spoke was just going to be a strip - not what we would recognise as an airfield – with negligible facilities. This meant that the aircraft had to have four small engines because they needed a three engine ferry capability to return to the hub to do the donk change. The high wing was to get the engines as far away from the FOD issues of strips as possible. Everything else stemmed from these two criteria.

In the event as we know HSA decided not to launch the aircraft. That was left to BAe many years later.

Very interesting, John. Surveying the ramp at Los Angeles International in the late 1980s and seeing 146s in a variety of liveries, everywhere, one could be forgiven for thinking the aircraft had been intended to open up the West Coast of the USA! :)

The four small engines had conferred another benefit - low noise - which made the 146 acceptable in Orange County and other noise sensitive areas. A case of "not quite what the designer intended, but jolly good anyway". The massed ranks at LAX of a British design were a pleasing sight.

Graham Perry

John,

A very interesting point, it reminds me a lot of Neville Shute Norways's books, after he founded Airspeed - as to the early 146 designs, I like yourself have seen them supposedly mounting 2-4 vectoring Pegasus engines on proposals - presumably only proficient piano players need apply !

I can't help wondering if the good old as became the norm' 146, with it's STOL capability ( & hopefully the freight version ) would be very usefull now in sandy places, if only to insert/ recover some people & kit...

Double Zero

There may be some confusion between AW681 and the original HS146 in some peoples minds. I am not aware of any connection between the two beyond the choice of a high wing for both

JF

Later, in service, the HS 146 was frequently referred to as "the best three-engine plane built" due, no doubt to the choice of engines-Lycoming ALF502. Obviously, the three-engine ferry was a good idea for a rather ironic reason. A friend of mine called them hand grenades disguised as jet engines.

GF