model turbine egines gas guzzlers

[stevejet66]

As you know model turbines need a fair size tank for a few minuets flight. Looking up at the sky this morning many jets fly by and im just amazed that the fuel tanks in the wings can take you anywhere in the world, just on two wings full of fuel, Looking at it the wing area is fairly small compared to the engines that stick out a fair bit, Although the core of the engine is small, Very economical when you think about it, But just amazed at the rate of fuel a model turbine uses. Again every evrything around civil avation is based on economy and the engines have been devolped for better fuel consumption, Maybe it will happen in the model turbine world, A good tank of fuel and longer flights.

[avtur]

Stevejet66 what a great topic you have started here ... you might live to regret it !!!

I think you might be surprised at how much fuel you can get into "just two wings" of a modern commercial airliner.

Firstly you are quite correct about the wings holding fuel but 'most' aircraft have at least three tanks, one each in the wings (although sometimes two each) and a centre tank in the wing root/centre fuselage (between the wings). You might be surprised at how deep a wing section is and this means that they can hold quite considerable volumes of fuel.

A couple of examples … A Boeing 737, as used by Ryan or Thomsons, each wing holds 4,700 litres and the centre tank holds 16,400 litres … An Airbus A320, as used by easyjet, each wing holds 7,800 litres plus 8,200 in the centre tank… A Boeing 757 as used by First Choice, 8,200 litres each wing plus 27,000 litres in the centre.Whatever the aircraft type fuel is always loaded into the wings before the other tanks. I suppose I should also add the figures for the Airbus A380 ... 11 fuel tanks with a combined capacity of 320,000 litres!

When fuel is loaded onto a commercial aircraft it is almost never “filled up”. There is a complex set of calculations around the fuel requirement but it can be summed up as … “as much as is necessary but as little as possible”. Given that everything around aircraft performance hinges on weight then the heavier the aircraft the more fuel is needed to move it, so the airlines want aircraft to fly as light as possible, which means they do not carry excesses of fuel.

These days that does lead to some conflicts between the airline “bean counters” and the pilots. Most pilots will tell you there is no such thing as too much fuel (unless you’re on fire!). Pilots always like to carry ‘a bit more’ to give themselves scope for changing conditions. The bean counters will tell them ‘no’ it costs too much.

A few years ago I remember fuelling a Boeing 747-400 on a transatlantic flight from New York to Amsterdam, it had to divert into Manchester for a fuel stop. Being a diligent type I was in place to fuel the aircraft as soon as it arrived on-stand. I opened the fuel panel and made a note of the gauge readings (part of the fueller’s job), I did this in preparation for the Captain coming to instruct me on how much fuel to load. When he arrived the captain was horrified to find that I had already recorded the fuel readings … there were 7 tanks 4 were empty and the total remaining in the other three was just over 5,000 litres; if for any reason the approach to MAN had been aborted, requiring a ‘go-around’ it is debatable if he would have had enough fuel!! I think the figures recorded by the crew might have been more generous than mine (for legal reasons!), he was just seriously unhappy that anyone else knew what the gauge readings really were.  ...

When you look up in the sky and see all those aircraft moving think about the combined volume of fuel they are using … some years ago I remember seeing a figure for Heathrow’s annual usage, it was in excess of 6 billion litres. If you multiply the figures up around the UK, Europe and the World the figures are simply eye watering …

I’ve recently been made redundant after spending over 22 years in the aircraft refuelling industry … as you can see I have one or two tales to tell and I have a photo library of around 10,000 pictures taken at fuelling operations around the world  maybe I should write a book !

Edited By avtur on 26/07/2013 03:10:36

[stevejet66]

What a great thread! Very interesting, I didnt realise they had so many tanks, I new the wing sections had tanks but not the belly of the aircraft, I was given a tour of heathrow 2 years ago by my best freind who works at heathrow, Doesnt look as though we are going to get better fuel consumption from model jets reading your thread, Thats just an amazing amount of fuel thats used for the aircraft industry.

[Greybeard]

I remember a “fact” quoted by the press when the Comet came into service that it used 1000 gallons to taxi a mile and wondered if it were true or just a headline grabber.

[Mowerman]

You have to remember that the engines on the modern airliner are the result of 60 plus years research and development.and are mostly high by-pass turbofans.

The model size engines are basicly the same design of the very early full size engines with centrifugal compressors which are much less efficient than the modern axial type.

Full size engines efficiency is measured in lbs of fuel per pound of thrust per hour it would be interesting to see the comparison figures for full size versus model size.

[kc]

Go ahead Avtur write the book! Refuelling may be the only aircraft subject without a book yet. Looks like you have the basis for one chapter written already.......

[Stefan Hafner]

I think a major difference that needs to be considered too is the type of engines being used by airliners. The turbines that we have for models at the moment are just that, turbines, whereas the the engines on airliners are high byppass ratio turbofans. For example the Trent 900 on the A380 has a bypass ratio of around 8.5, and these engines are much more efficient than a pure turbojet. Also with small engines I doubt the temperatures that can be achieved are anywhere near as high as in a large engine, so that will reduce the efficiency more, and then theres also the engine design, model engines still use centrifugal compressors while large turbines use axial compressors, and usually multiple turbine and compressor stages.

It all adds up to make them a good bit more efficient, but no doubt with time the model turbines will become more efficient too

[Frank Skilbeck]

Wikipedia and RC Jet International are you friend, here's some examples of specific fuel consumption for full size and model turbines

Concorde Olympus 953s at Mach 2 cruise - .0338 grams per Newton/second

Boeing 747 CF6-80C2B1F turbofan - 0.0171

Jet Cat P80 - 0.0518

Wren 160K Pro - 0.0527

Probably a little unfair on the model engines as the measurements are static while the full size are in flight and hence more efficient, but also bear in mind that if you were to take a model to height flew on cruise in a striaght line then the fuel consumption would drop, but doing airshow type manouvers is always going to burn more fuel.

[avtur]

Posted by Greybeard on 26/07/2013 08:09:33:

I remember a “fact” quoted by the press when the Comet came into service that it used 1000 gallons to taxi a mile and wondered if it were true or just a headline grabber.

Don't know about the accuracy of the figure, but it is true to say that jet engines are most inefficient when used to taxi; and back in the Comet era engines were far less efficent than now, so the figure might be in that region.

The issue of engine ineficiency during taxi is such that alternatives are being sought. One option is to 'drive' the undercarriage with elelctric motors powered by on board batteries, there is an A320 operating with a prototype systems installed.

[Richard V-D]

Then there is always "fuel on the ground may be expensive, but in the air, it's priceless!"

Works for models too

[avtur]

Thanks R V-D, not heard that one before but will certainly use it myself in future ... the price of aviation fuel (Jet or Avgas) is so topical these days I'm sure it is a much used phrase!

Edited By avtur on 26/07/2013 10:44:21

[Steve Holland]

I fly light planes for a living, the other day I was held on the runway whilst a 747 cargo taxied past and took off. Whilst I was waiting my turn I worked out his fuel load vs our rate of fuel burn, we could fly for 27,000 hours on his one tankfull. I did recheck these figures and they are correct!