Control harmonisation

[spicmart]

With the war ongoing control harmonisation on war planes became increasingly important, is my impression.
The first plane I read of that had excellent control harmony was the Fw 190 which designer Kurt Tank seem to put more emphasis on than his counterpart Willy.
And later Allied planes were then developed with good harmony.

Can you tell more about this topic in general, its technical side and with regard to WW2 fighters/planes?

 

[Trilisser]

I think Eric Brown put it like that if control forces are rated from lightest to heaviest as 1-3, a good control harmony is 1 ailerons, 2 elevator and 3 rudder. A comfortable stick force per g is about 2.5 - 3.5 per g.

Not a fighter, but an example of really high control forces is the DB-3/Il-4. Like a wheelbarrow. First, before take-off, the elevator trim had to be set very nose heavy and still raising the tail on take-off might need two men pushing the massive wheel-type stick. Yet, on getting airborne, the pilot had to wind back the trim, otherwise the plane got so nose heavy while gathering speed that it was very likely to crash on the ground as the elevator was too heavy to counteract the change of trim.

 

[Shortround6]

the Hawk 75 is supposed to have had very good control harmonization. Better than the Spitfire it was flown against (1939) as the Spitfires elevators were too light. That is to say it didn't take much force to move the Spitfires elevators. Flip side of that is that the Spitfire's elevators were too powerful The pilots were over controlling the elevators in a turn and it was hard to do a smooth turn, which made it hard to fly near the limit as a small correction to the pilot (flying at 4-6 Gs) could over control the plane and make it stall.
On the Spitfire they made things much better by installing a bob weight in the control linkage/circuit which increase the amount of effort needed.

Trouble is a lot of this is subjective. Not all planes gave the same result for the same effort on the stick (or pedals) and the result(effect) varied with the speed with the alerions seeming to be the most notorious. Many tales of the alerions almost locking up at even max level speed let alone diving while responding vey well at low speeds.

 

[Jabberwocky]

As aircraft speeds increased with the arrival of stressed skin monoplanes in the late 1920s/early 1930s and control forces went up as a result, the amount of work on control harmonisation also increased.

This went into overdrive in the second half of the 1930s as the war approached and various air forces put very high performance fighters into service. And, then accelerated again as people began to get REALLY interested in the comparative flight characteristics of fighter aircraft for some strange reason.

There's a bunch of studies from the NACA on control balance/harmonization, control forces, control surface effectiveness and the general stability of aircraft. The University of North Texas has most (all?) of the NACA studies catalogued and PDF'd:

National Advisory Committee for Aeronautics (NACA) - UNT Digital Library

EDIT: Cranfield University might also have some stuff that UNT doesn't:

Community List

I know that there's also plenty of work on the same topics from the RAE and A&AEE that can be found at the UK National Archives site:

Research and development in the Royal Air Force and civil aviation - The National Archives

1. Why use this guide? Use this guide for advice on records of research and development in the Royal Air Force and in the civil aviation industry now held by The National Archives. You can find out what kinds of records we hold and how to search for them. As with all of our records, […]

www.nationalarchives.gov.uk

There's also the occasional (translated) German or Soviet technical report from the 1930s floating about, but mostly in the forms of random .PDFs. Maybe the Technical sub-forum here is the best place to look?