"Lift-Planks" - 2 or 4? which, why and wherefore?!

[SoundBarrier]

Lift-Plank = Wing! :)

So the question is, why would you have 4 wings on an aircraft, as opposed to 2. What benefit did the bi-plane have and why don't we build em too much any more? Comparing the initial bi-planes such as the Fokker DVII vs the Bristol M1-C AND of course the Pitts vs the Extra.

Some answers I have discussed with fellow "lift-plank" users we have the following ideas :-

1) Initial bi-planes were built for the extra lift with more wings (of course more drag)
2) The wings of bi-planes could be strung together to create extra strength. (is this true?)
3) More control surfaces in the airflow (Pitts?) therefore giving more authority.
4) The monoplane would have a better roll-rate would it not?
5) Better visibility in the monoplane as well

One last question, I notice from a plan view of the pitts the wings seems swept a bit, what is the reason for this?

OK So I haven't been to a flying club bar for a while, and I'm curious!

[barit1]

The primary reason for a biplane is structural. The cross-braced wires are strategically placed to carry lifting loads very efficiently. A cantilever-wing monoplane needs a relatively heavy spar to carry the loads; a braced wing can be lighter.

http://i.pbase.com/t6/05/783705/4/83392010.jlz4lcJf.jpg

And a well-designed biplane can have a very good roll rate. The Waco Taperwing of the late 20s had tapered-chord wings (wing mass concentrated near the fuselage centerline, thus low roll inertia) and ailerons on four wings (lots of roll power), and was famous as an aerobatic ship.

http://www.goldenageair.org/images/1930gl2.jpg

A ship with sweepback (Pitts, Great Lakes, Ryan PT-22) will snaproll faster, because one wing has its sweep effectively cancelled, while the other wing has increased sweep and thus less lift. I inadvertently snapped a PT-22 while attempting a cross-controlled stall. Never saw the horizon rotate so fast in my life!

[Mark1234]

I would imagine the origins were very much to do with solving an engineering problem. Look at the early monoplanes, they have some very interesting posts with lots of string and bracing to keep the wing in place..

To more recent examples, the major downside is that the biplane configuration adds heaps of drag. Generally the monoplanes have a larger wing & greater wingspan to make up for only having a single plank - I guess that gives a better lever, but also more roll inertia. I don't know about the intrinsic roll rate comparison; but can confirm that in practical terms, a pitts rolls pretty damn fast, as does an extra :) The thing that strikes most if you ever stand next to a pitts is how small it is, and how tiny the wingspan is; if I put my fingers against the side of the fus, I can almost touch the wingtip with the other arm - and thats the 2 hole variety.

[SoundBarrier]

thanks barit and mark. I can show my fellow plank fliers what I've learnt!