Aircraft Main Antenna - Quick Question

[jamesinnewcastl]

Hi All

I'm putting the main aerial wire on my Stirling 3D model but can't find how thick it was.

It would have been about 60 feet long and quite straight so I assume it would have been under tension.

Anyone hazard a guess?


Cheers
James

7 strands of 16 gauge came out of my head, no idea why. Is that 3D as in aerobatics?

[jamesinnewcastl]

Hi Merlin

3D as in computer modelling!

Google makes that 1.55mm dia or 0.061 ins.



James

That means 7 strands would be three times that overall.

[jamesinnewcastl]

Hi Merlin

That was for the 7 off according to this site:

http://www.te.com/catalog/Overview/WireCalculations.pdf

(2nd Page)


James

[Herald1360]

Sounds like that would be strong enough to stay put in a 300mph breeze

End on, anyway.

[jamesinnewcastl]

Hi Herald

Oddly enough that's just higher than the max speed of the Stirling so wind speed would be a factor.

Oh you've reminded me that the aircraft also a trailing antenna! That is going to be a reasonable guide to the wire diameter. (I once asked a WWII gunner if he could hear the sound of the trailing antenna slapping against the sides of the aircraft - he answered rather dryly "well, not above the sound of the engines.....")


James

[Radio Wrangler]

There's no reason why an aircraft antenna can't be steel or steel cored for mechanical strength. The electrical difference is small.

The biggest problem with trailing antennae was people forgetting to wind them back in before landing.

David

That was for the 7 off according to this site:

Ah, that would be the equialent to a solid conductor, I was thinking 7 16 guage wires. About 6 guage on the PDF. I was also thinking in SWG rather than AWG, close enough though.

[jamesinnewcastl]

Hi All

Found a pic of the trailing aerial with a rule next to it - looks like twisted steel about 1.5mm in diameter.

I think that I had been thinking of tinned copper wire but of course steel is so much stronger!

Thanks all


James

[GMB]

It would have been about 60 feet long and quite straight so I assume it would have been under tension.

I don't think so.

I recently researched this although I was mainly looking at slightly later radios.

There was a rule of thumb that appears in notes of this era that they used one foot of aerial wire for every metre of wavelength. So more like 150 feet for the Mk-1. Later valve-based technology worked at lower frequency and uses a loading coil (sort-of) to reduce the aerial length. They standardised on 120 foot at this point it seems.

I have only read a description of the spark installation but have actual drawings for later ones which sound similar. From those it looks like the aerial is wound on a wooden reel at the back of the 2nd crew member. It feeds vertically down through a structure that is well described - and consists of a disc and a tube. The disc carries brushes to contact the (bare) aerial wire which is indeed stranded (but I don't know the exact details). The tube sticks through the floor and guides the wire out of the plane (downwards). The wire carries a weight at the end so as you wind it out the weight, which has an aerodynamic shape, pulls the wire down and then is swept back by the slipstream. You can imagine how it ends up, curving down and back away from the aircraft.

Having seen how it was drawn it looks like the weight on the end of the wire was the big hazard when aircraft forgot to retract their aerials!

[GMB]

Wait a minute, by "Sterling" did you mean the aircraft?
I read that as the Sterling transmitter.

So my reply may have been talking about the wrong era?
I was talking about ~1916.

In the WW2 era the aerials on big bombers were much longer. It mentions 250 feet in notes on the T1083

[turretslug]

Originally Posted by GMB

The wire carries a weight at the end so as you wind it out the weight, which has an aerodynamic shape, pulls the wire down and then is swept back by the slipstream.

Colloquially known to aircrew as a "fish"- for obvious reasons!

[jamesinnewcastl]

Hi GMB

Yes the original question was in regard to the Stirling Bombers 'main aerial' being the one hung between the post near the cockpit and the tail. I was after some idea what diameter this was likely to be.

Then I realised that the trailing aerial might give a clue - The mechanism for this in 1941 is the same as you just described for 1912 except for the radio technique. I've been looking at this system this morning, the tube leading the aerial out of the aircraft is called a 'fairlead' apparently, an interesting name without any obvious derivation.

I am about to ask you for some remaining dimensions, in the meantime here are some pics on my progress with the radio systems on the MKI Stirling. Many of these dimensions being kindly supplied by yourself!

Sadly the pics are a little dark!


Cheers
James

[GMB]

the tube leading the aerial out of the aircraft is called a 'fairlead' apparently, an interesting name without any obvious derivation.

Yes, that is exactly the term used in the WW1 documentation which I think is basically a nautical term for a thing like that.

Wouldn't surprise me that it was the exact same device as it seems that not a lot changed between the wars except for a few extra valves in the TRF receivers!

[majoconz]

Not quite so old but may give you a clue. The Fokker F27's and HS 748's I worked on had twin HF antennae from the cockpit to the top of the tail. The antenna wire was copper coated steel in a reasonably hard insulation of about 1/4" diameter. The fairlead over the cockpit had a toothed gripper the you inserted the bared conductor into and slid a cover over. At the tail end a spring tensioner, an insulator and a similar gripper. In my old paperwork I found the part numbers for the tensioner (Chelton 8-1), the insulator (0712670009) and a different tensioner (6131 or 6132). This was in the early 90's before the internet - they may have gone out of business. Newer aircraft have tuned fibreglass rods or matching devices (trombone?) to tune the whole vertical stabiliser as in the Boeing 737/767.

Found a pic of the component parts....

http://www.sea-avionics.com/lc/cart....&mode=research

[Radio Wrangler]

You'll find the word 'fairlead' used for the guides for ropes onto winches, both the nautical ones and those bolted onto land-based vehicles. So its application to an antenna wire on a mini-winch seems logical.

David

[jamesinnewcastl]

Hi Majoconz and David

Thanks for your replies! I eventually went for 5mm in a twisted steel, that has the right thickness to look good close up and the ability to disappear from view at any distance.

More esoteric questions to follow soon!


Cheers
James

[G4YVM David]

Originally Posted by jamesinnewcastl

Oddly enough that's just higher than the max speed of the Stirling so wind speed would be a factor.

Why would wind speed be a factor? Remember that the aircraft flies at an airspeed regardless of windspeed: it flies at 300mph (or knots) whether its flying in a breeze or a gale, only the groundspeed changes. cf Lancastrian "Stardust".

David

[jamesinnewcastl]

Hi David

Ah - while interested in aircraft I'm not enough into flying to spot that correct distinction - I really just meant wind as in how hard the antenna would be 'hit' by the aircrafts passage through air.

I'm trying to produce a fairly accurate animation of the Stirling and any moving or flapping of the long thin antenna would be a feature of this.

The tighter the antenna wire the less it would flap but the thicker it would need to be. While in straight and level flight the wire is hit 'head-on' however any turns or dives would subject the wire to sideways forces.

It's bit of an esoteric question but better to get opinions and you guys are the only people I know who put up great long wires!


Cheers
James