Why fabric and wood materials were used on F4Us

[ppopsie]

I found this morning in a book that as of 26th Nov. 1942 there were 2013 crewmenber on the IJN carrier Shkokaku;

691 i/c of ship
136 aircrews
653 maintenance (all belong to the ship)
352 engine room
55 carpenters
24 medical and
88 cooking and accounting

no specific mentioning about emergency crews was attached to the data.

[Macchi]

Not intending to hijack, but the old Martin Mars....

Martin JRM-3 Mars Airtankers

[HoHun]

Hi Ppopsie,

>I understand the control surfaces in general had been fabric covered for the reason of weights on many aircraft types.

It's my impression that the reason was not really weight, but mass. That's a very subtle difference and it really only counts because the mass could be a concern as it made control flutter more likely while the pull of gravity could be - and often was - balanced around the hinge line.

Control flutter (a resonance phenomenon) could make control of the aircraft difficult or epen rip the control surfaces off the aircraft if it got too violent. The greater the control surface mass, the greater the forces involved, and thus the potential destructiveness of flutter.

To highlight the point with an anecdote: The RAF discovered that the ailerons of high-speed aircraft like the Spitfire would encounter flutter (or its incipient stage, "aileron buzz") more readily when the RAF roundels were painted on the wings so that they extended on the ailerons too. The very small mass of an additionally coat of paint made a perceptible difference - so they issued an order to restrict the size of the roundels to the main wing area. What inevitably happened was that some squadrons overpainted the "excessive" roundel area on the ailerons with camouflage paint, adding even more mass and inadvertently making matters worse!

(This is from memory, so it might be inaccurate in the details. I wish I'd remember the original source of the anecdote!)

Regards,

Henning (HoHun)

[ppopsie]

Thanks HoHun-sama,

Thats right it is mass. That was my ignorance. I never knew even a slice of a RAF roundel did that but it is understandable. If a pilot flew in different individual aircraft of same type then he/she would percieve very subtle difference on the controls of the each aircraft. That is quite possible to occur, from my own experience.

What I only knew about the Spitfire ailerons was that Jeffrey Quill wrote in his great book "Spitfire," about the ailerons of some of the Spitfire Mk Vs became a lot heavier at high speed but was later made lighter .

Since after I started this thread, I have found the following test report from naca about the TBF Avenger. It is rather scientific but one can skip the part which is too academic. Even though one can know what was it like to do with very very(?) sensitive part of an airplane.

Best regards,

p-popsie AJ-P

NACA UK Mirror report description page

[DOUGRD]

Originally Posted by FLYBOYJ

EXACTLY!
AC 43.13-1B Chapter 2 section 4 for fabric repairs, Chapter 4 section 4 for metal repairs. I deal with fabric and sheet metal repairs on an almost daily basis.

What aircraft do you work on that are using Grade A cotton or Irish linen?

[ppopsie]

>Grade A cotton or Irish linen

In MY case I used them on German built gliders in early 70s. I don't have experiences on any modern systems like Dacron.

It is interesting to note that the German gliders built in 1973 still had seemingly the same fabric covering system consisted of cotton fabric, clear dope, alkyd based sealer and paint as in the case of Me110, according to a detailed technical report by Vultee Aircraft in 1941 which can be downloaded from the Technical section.

In that case fabric covering procedures in the AC43 weren't very much useful.

[HoHun]

Hi Ppopsie,

>Since after I started this thread, I have found the following test report from naca about the TBF Avenger.

Highly interesting!

From the summary: "Flutter did not occur when the installation was stiffened to prevent chordwise motion or when the bending frequency of the aileron system was appreciably higher than that of the wing as in the complete airplane installation."

The bending frequency of the aileron system depended on its stiffness and its mass - so keeping them "light" (mass-wise and weight-wise would generally result in a high bending frequency.

Regards,

Henning (HoHun)

[ppopsie]

Thanks HoHun,

I have never imagined the c/g position of aileron ABOVE hinge line affects like that. It was probably because the TBF lacks trailing edge bolt at the wing folding position. According to the report wing tortional stiffness was adequate but cordwise rigidity was not enough.

It is interesting to me too.
Best regards,

Nao (Ppopsie)