Design queries / Mew Gull and German types

[Krystal n chips]

I have a couple of questions please for those who know more about the design criteria than I do.

When I visited the RAF Museum Hendon recently, I / we ( all engineers ) noticed there is a balance horn on the left aileron of the Mew Gull on display...so I / we are curious as to why as it's a fairly unusual location. We were also struck by the size of the compass on the right hand side of the cockpit.

The second concerns the German u/c designs, notably the legs off-set from the vertical position and how much surface area of the tyre is in contact with the ground as a result....again, we were curious as to why.

All and any replies appreciated please. :ok:

[Speedbird48]

Krystal,

I can answer a little of your questions regarding the Mew Gull. I believe the one that you saw is a replica?? The aileron mass balance was similar to others of the period and I think there should have been one on both sides?? Never seen anything without a pair when they are fitted.
As for the compass, look at other British aircraft of the period and for WW2 and you will see that they all have the same or similar P9 series compasses fitted. The Chipmunk had them as well so they were still in use well after WW2. I learned to fly on a Miles Magister and it had two, one for each cockpit, and they are very accurate which in turn makes you rather accurate, or lost!!

I am guessing that you were a younger bunch of engineers??

Speedbird48

[GQ2]

I haven't seen the Mew replica at Hendon in the flesh, but it should have had a mass-balance on each aileron. Maybe you missed it...? External mass-balances were quite common at that time. It's more usual now for such weights to be faired-in to the control surface itself or be hidden in the flying surface. As well as statically balancing the control surface, they can also damp-out flutter. They are also fitted to the rudder on the Mew, but not, interestingly, to the elevators.
As for the compass; This type is known as an 'aperiodic' compass. In the days before decent radio navigation and GPS they were the best you could get, as they were much more accurate and stable than other types.
I presume that the undercarraiges that you were refering to were in types such as the Me108/109. Certainly in the '109, the reason is simply that the u/c was attached directly to the fuselage near the wing root. This meant that construction was simpler, loads were transferred directly to the primary structure and all linkages and actuators were similarly compactly located. The a/c, sans wings, could also be moved around easily. Since the attachments were so close to the centreline of the a/c, the u/c was splayed-out to crudely widen the track and add basic stability. The tyres were of a round section, so the contact angle didn't really affect the area in contact with the ground. Since the wheels were quite large diameter and attached to the legs at a very similar angle, this arrangement did lead to problematic ground handling. As a direct result of this, more '109's were lost to ground-handling accidents than to actual combat. The Spitfire, which had a seemingly similar u/c (Though fixed to the wings main-spar.) had it's wheels angled in relation to the u/c legs to give a roughly perpendicular contact with terra-firma, thus avoiding such severe problems.

[Krystal n chips]

GQ2.....my apologies to you for the delay in responding to your answers.

I was remiss in not stating there were indeed two balance horns. It was the fact they were located on the upper surface that grabbed our attention and hence I / we were curious as to why, rather than the lower surface.

As for the u/c, again we were curious as to the rationale behind the concept.

For yourself, and Speedbird 48, I should add we are all experienced engineers, thus whilst we are more than familiar with the theory, we were, as I say, professionally curious as to what the reasons were hence, if you don't know or are unsure...ask...:)

My thanks to both of you therefore for your answers...:ok:

[Fareastdriver]

Just to clear up the compass bit.

The P9 consisted of a bowl with a top filled with alcohol, The magnetic bit would swivel around in the fluid and the presentation on top of it was in the form of a T. The top glass could be whizzed around and that had all the degrees marked on it plus a hollow T to align with the T on the inside.
When that was done the magnetic heading would be shown in line with the aircraft and the gyroscopic DI (direction indicator) would be turned to agree.
You would have to do this every time after aerobatics as the DI would have toppled and normally every fifteen minutes in the cruise.

People getting confused and not lining the Ts up correctly was quite common as they blundered off onto the distance.