Emergency Number

No En, Thanks for that, that’s interesting. What metal standard do they use in aircraft?

EN in the context of WW2 stands for Emergency Number, being, particularly, steel alloys rapidly impressed into wartime service without the delay occasioned by a committee considering the materials classification under DTD (Directorate of Technical Development of the Air Ministry) or British Standard. Most of your Stirling would be composed of BS and DTD materials as well as EN. So you would be right using EN materials and most folk over the age of 65 think of steels in ‘EN’. Euro norm, that’s something different again….

Few more guesses

I’m sure someone out there will know the answer to a question that has puzzled me for a long time;
From what i’ve seen at airshows or on videos etc , a Merlin, Allison, DB605, Jumo engine all sound pretty similar when running even a Kestrel .
So why , (when they are all V12 engines) , does a Griffon engine sound different ?
Thanks in advance.
Keefy041

I don’t definitively know but here are a few more guesses : (1) higher octane fuel, meaning more fuel energy, under higher compression, produces (i) a different quota of sound energy (ii) lower heat of exhaust gases meeting the ambient air, changing exhaust expansion effects (iii) less post combustion (flame) and sound associated with post combustion. (2) metallurgy of engine, in respect of sound absorbing qualities, if you can accept that minute
Changes to the size and tension of a guitar string can make utterly distinct sounds, this is not such an exotic idea then. (3) prop vortex affect on sound, if Griffon rotates in a different direction, perhaps sound is skewed, or, if due to more volume of air being chopped by more horsepower, sound carries differently; you would have to ask a pilot what both engines sound like in the cockpit!

New dog, old tricks

An interesting piece on the BBC website today, showing how things in the region have changed very little since the 1920s in some respects.

http://www.bbc.co.uk/news/magazine-29441383

I have pictures of my Great Uncle, stationed in Iraq with the British Army in the 1920s and 1930s in places like Basra and Fallujah, the same places that were on the news showing the British Army there once again some 70-80 years later.

The BBC article and the modern use of air power in Iraq and Afghanistan show that contemporary decision makers have absolutely not read the history of the RAF in interwar Iraq and the North Western frontier. The key contemporary doctrine is stealth. The key historical doctrine was communication.

Nineteenth century British military doctrine in Afghanistan found its basis in the disaster of the initial Afghan Wars, when ground troops march out to decimation by the Afghan tribes. The key evolution was the colonial ‘political officer’, brave, intelligent, streetwise non conformists who found good employ wandering out into the desert on a pathway to create relationships with local, indigenous authorities. No nineteenth century taxpayer found better return than the investment in the political officer, who could understand the topography of the local politics and sense out what was about to happen and why. In his back pocket he held the might of gunboats, airforces and artillery, but was entirely nuanced in finding it unnecessary to state such an obvious fact.

It is incredible to understand that the RAF ran a country, Iraq, in the 1920’s. In the post Cromwell tradition, no military force should ever run a British possession, but exceptions like this form within the weft and weave of British colonial history. In respect of a threadbare asset base in the the 1920s the RAF evolved a standard procedure, directed by the political officer. If face to face negotiations with uncooperative elements did not succeed, after the political officer had removed himself from the threat of being taken hostage, leaflets were dropped, warning that in one to two days, crops would be fire bombed. This was profound economic warfare, difficult to ignore. If this was ignored, crops were bombed, and this was often enough. If not ,the next step was to drop leaflets warning that the town/village would be bombed, with the focus on architecture sensitive to reception by the recalcitrant parties. This form of communication held the North West Frontier and Iraq in equilibrium during the interwar years, until German initiatives in early WW2 forced the RAF to more conventional warfare dealing with an Axis aligned government in Iraq.

Today, UAVs circle stealthily above these countries and visit death with ‘shock and awe’ , and the expenditure of billions of tax payer funds and act to recruit volunteers to increasingly gruesome responses to Western technical superiority. Amorally, there is nothing wrong with UAVs, and there is no difference in outcomes to being accounted for by a Vickers gun or laser guided munitions. Morally, there is something wrong in the hands that guide this technology, on our behalf, if their use is in preference to the simple human fairness of at first listening to the targets point of view.

It is too easy to criticise, so I will try and imagine something that could evolve in reference to the old tradition. Today, a UAV may, proximate to a perceived threat, transmit locally to TVs, radios and mobile phones messages explaining what might happen to a town if the positions of militants are not known. It could encourage townsfolk to use a range of methods to communicate a range of information. Hopefully this information could be interpreted by intelligence operatives who, like the political officer of old, know the area. The UAV should NEVER release a laser guided munition by surprise. This is different to conventional war, where the rules are different.

I have every confidence the lessons of history will be ignored. I am sick of this thoughtless, terrible conflict.

More guesses

Many historic aircraft, if not all initially, had fabric covered control surfaces where otherwise the entire airframe was of metal construction. I wonder why.

Could it have been simply to reduce the weight of the surfaces or was there an aerodynamic argument?

The weight saving of using fabric covering rather than a aluminium skin seems to me to have been minimal.

Great to fill this gap in my knowledge!
Mike

I don’t know but an allied query in the overflowing filing cabinet of the mind are timber flaps on the Mosquito, while the ailerons and elevators were metal. Why would you make a highly stressed component like the flaps in timber, while going to the extent of making all other control surfaces in metal ?

The postulatum given in other replies covers answers such as weight, alloy material savings etc, but I wonder if there are considered structural issues involved.

For fabric covered ailerons, one thought is that as the metal wing flexed, so the weaker fabric aileron member would flex and follow the shape of the major wing member. If it did not, the aileron hingeing might bind.

Calculating the performance of complex, new stressed skin structures in the 1930’s was an emerging science. Only practical experience could really determine what was going to happen to these novel structures. A smaller stressed skin aileron structure, composed of a skin of the same thickness as a larger wing structure, would be stiffer than the wing : therefore I wonder if the aileron was purposefully designed to be weaker, using the known performance of fabric covered members. In truth these were T50 steel tube spar structures with predictable characteristics of elongation. Only the ballooning of fabric emerging from new high speed flight factors created a new issue to resolve. So being then forced to use a stressed metal skin aileron, the first thought would be to make it a thin skinned structure more longitudinally flexible than a wing. In addition the fitting of a piano hinge would then force the aileron to follow the flex of the wing.

In applying these thoughts to hydraulically activated plywood Mosquito flaps, a different set of forces is in play to wing flex, which might be the ability of plywood to flex and distort under sudden high flap loads, while the flap spar was an extremely strong 3 inch diameter tubular member that would not distort or transfer destructive forces through the flap hingeing.

In other words control surfaces are purposefully designed to be ‘weaker’. When you look at the flaps and brakes of a modern jetliner landing, they certainly do shake, rattle and roll.