Vehicle Design: Jet engine fuel

[Sturn]

I think the vehicle design system needs to point out that some propulsion systems don't work with certain power plants. I know some of this should be obvious. Others aren't so obvious.

The rules point out that they make no distinction between mechanical and electrical power, assuming generators/alternators are swapping power back and forth. I have no problem with this. The Jet propulsion seems to be my main issue. A Wind Power powerplant could power a jet engine with the rules as written (unless I missed something). This is one of those obvious issues that I figure people will understand and not pair togather. Here are some a little less obvious:

Ex1: With the current rules you could have a jet engine powered by solar power and using no fuel? I'm no engineer, but isn't some mass in the form of fuel needed to make a jet work? I could make a jet airplane powered by solar panels and batteries using no fuel whatsoever.

Ex2: Jet engine powered by a fission or fusion plant. I understand that fission rockets and fusion rockets are possible and have no problem pairing these up. But, fission/fusion plants require little or no fuel. Some sort of reaction mass is needed in the form of "fuel".

The examples in Civilian Vehicles seem to pair up Turbine power plants with Jets. If it was intended to not allow fission/fusion/solar/wind to power a jet this should be stated. If it is allowed, shouldn't there be some sort of additional rule to add a fuel requirment to the jet propulsion? Any engineers with a copy of the Civilian/Military Vehicles design system care to speculate how to fix this? The easiest fix is probably stating only Turbines can power Jets.

I actually like the design system MGT came up with. It's fun creating vehicles. Not too complex and still gives you lots of options. But, I think a few tweeks are needed.

 

[rust]

Another unlikely combination would be air breathing power plants and
submarine drives.

For example, the "Submergible Plane" on page 94 of Civilian Vehicles
with its jet and turbine is not exactly a good idea. :lol:

 

[Lord High Munchkin]

You can have an air-breathing power-plant and submarine drive (early subs did)... but you have to have a "snorkel" accessory.

 

[rust]

You can have an air-breathing power-plant and submarine drive (early subs did)... but you have to have a "snorkel" accessory.

True, but the main purpose of the air breathing engines of the early sub-
marines was to recharge the batteries that provided the power while the
submarine was diving.

Without an additional air independent power source, like those batteries
used by the early subs, a vehicle cannot dive deeper than the reach of
the snorkel - and I would very much hesitate to call a vehicle that has to
stay within meters of the surface a submarine.

 

[Lord High Munchkin]

Well, they were underwater....

 

[alex_greene]

For example, the "Submergible Plane" on page 94 of Civilian Vehicles with its jet and turbine is not exactly a good idea. :lol:

It works for Sky Captain.

"Dex fixed it for me."

 

[Sturn]

If it is allowed, shouldn't there be some sort of additional rule to add a fuel requirment to the jet propulsion? Any engineers with a copy of the Civilian/Military Vehicles design system care to speculate how to fix this? The easiest fix is probably stating only Turbines can power Jets.

 

[BP]

Don't have these books and ain't an engineer - but I also haven't seen any posters allude to being engineers of this nature... so you may be out of luck getting that type of answer. Besides this is fiction.

Are characters developing the vehicles that this is an issue? Otherwise go with your gut.

As to a 'power plant' for 'jet' propulsion - if by jet one is referring generically to propulsion that includes that from thrust via high speed exhaust gases, the energy does not neccessarily have to come from fuel burning - if the atmo supports it. Exotic, corrosive and tainted would be good candidates for this...

Like ramjets though, this would probably not work well at low velocities (or have to suck so much of the environment in that it would be impractical).

Above certain TL (prob. 8) the jet could be plasma (the most abundant state of matter in the universe and with characteristics of liquids and gases - IIRC normal jet exhaust is treated like a liquid) - in which case it doesn't matter the power source (just the amount) in order to take the atmo gases and use them (such as Nitrogen using a MHD type device for instance).

 

[Sturn]

Thanks for the response.

Lengthy sorry!

I didn't mean literal engineers, just one of the many smart folks here that are educated enough in this area to give some ballpark game figures. My sociology and criminal justice degrees don't help me much when trying to figure out jet engine reaction masses. My physics education is one class in college and scifi RPGs.

I didn't want an answer that was fitting for Fire, Fusion, & Steel, but one for the simple system of MGT. I hoped for an educated person to say, "Jets should be limited to Turbines" or "Jets should add X% to fuel consumption of the power plant".

Are characters developing the vehicles that this is an issue? Otherwise go with your gut.

It might take some understanding of the design system to understand, but I was trying to build a jet powered by fusion when I noticed the issue.

Vehicle design requires a propulsion and powerplant. Propulsion + powerplant determines speed. Powerplant gives fuel consumption. Jet propulsion + Turbine powerplant seemed the default pairing. Turbines have significant fuel consumption. If I used Jet + Fission/Fusion though, the fuel consumption dropped to nothing or nearly nothing. Nearly unlimited endurance. A jet aircraft that should be burning up lots of fuel wasn't when it was designed like a "fission rocket".

I understand the scramjet concept, but if that was allowed the turbine should gain the same benefit of lower fuel consumption from sucking air and thus using less overall fuel mass. But, fuel would still be needed. (note: "scramjet" might be a nice addition to the options list of the design system that can be added to a Jet to reduce fuel consumption while giving a max speed boost).

I was also comparing a wheeled vehicle with Wheels + Fusion to a flying vehicle with Jet + Fusion. If the same sizes were used, they had the same fuel consumption. Of course the wheeled vehicle was slower, but they both had the same endurance even though the jet would obviously be burning up much more fuel per hour.

The easiest solution without changing the design system significantly would probably be just to limit Jets to a required Turbine powerplant.

 

[rust]

I didn't want an answer that was fitting for Fire, Fusion, & Steel, but one for the simple system of MGT. I hoped for an educated person to say, "Jets should be limited to Turbines" or "Jets should add X% to fuel consumption of the power plant".

It is a bit difficult because "Jet" is not well defined, the word is used for
many different types of drives, from the scramjet down to the hydrojet.
The typical aircraft jet does not need an additional power plant at all, it
is both drive and power plant itself, but some other types of jet work dif-
ferently.

 

[BP]

rust nailed it - 'jet propulsion' is a bit ambiguous...

This is the reason for my 'if by jet one is referring generically to propulsion that includes that from thrust via high speed exhaust gases' statement.

Sturn, I think you answered part of your own question - if your goal is reduced fuel consumption then add in ram/scramjet variants with reduced fuel requirements...

A fusion P.P. with a jet propulsion makes sci-fi sense if you substitute plasma for gases in the statement above. Plasma jet engines do exist even for atmo - experimentally. IIRC, just last year, some MIT guys created a Nitrogen based one (without fusion ).

In the context of the current design system - these assumptions would only make 'sense' if the TL was appropriate (though the MIT guys I believe demonstrated their tech with a softdrink can and softdrink bottle ).

 

[atpollard]

At it's simplest, all 'jets' suck in one end, heat it and expell it out the other end to produce thrust. As THISshows, burning fuel is not the only way to make a jet engine work.

I like the fact that the rules are not bogged down with lots of details on what combinations are not allowed. Leave those decisions for the designer to reason out.

So what if I want a giant blimp covered in solar cells used to heat the air and drive a small jet (turbofan) mounted in the tail?

So what if I want a submarine that extracts O2 from peroxide to burn fossil fuels and leaves a trail of exhaust bubbles as it travels?

How is Traveller improved by banning either of those ideas because that's not how it was done in 1950 or 1980 or 2010?

 

[AndrewW]

How is Traveller improved by banning either of those ideas because that's not how it was done in 1950 or 1980 or 2010?

Well, it's not really banning as anything in their is merely an option. If someone wants to use a combination that wasn't permitted they are free to do so.

 

[rust]

So what if I want a submarine that extracts O2 from peroxide to burn fossil fuels and leaves a trail of exhaust bubbles as it travels?

No problem with that, except perhaps that accidents with the extremely
dangerous peroxide already caused the loss of two submarines, HMS Si-
don in 1955 and K-141 Kursk in 2000. :wink:

 

[Rikki Tikki Traveller]

Well, I AM an Aerospace Engineer (that's what it says on my diploma anyway!).

I actually agree with ATPOLLARD on this one. Fuel is NOT needed for a jet engine as long as you have a way to very quickly heat the air to increase your exhaust gas speed.

We have not discovered a method that is more efficient than fuel, but solar panels are certainly not out of the question on a small scale at least.

Using a wind turbine to power a jet engine would be INTERESTING. If the design system works properly though, the size of the wind turbine will make it unflyable with a jet engine (haven't checked the book, but it should be that way).

The book should allow you to try whatever combinations you want, but there should be some combinations that just aren't going to make the craft you want. So efficient designs are going to drive you to certain combinations, not some arbitrary rules system.

For those of you that have read the BOOK "Hunt for Red October" the Red October used a hydraulic version of a jet engine but with water. Since the design rules don't provide for this specific type of underwater propulsion, modeling it on a jet engine might actually work...

 

[phavoc]

Well, I AM an Aerospace Engineer (that's what it says on my diploma anyway!).

I actually agree with ATPOLLARD on this one. Fuel is NOT needed for a jet engine as long as you have a way to very quickly heat the air to increase your exhaust gas speed.

We have not discovered a method that is more efficient than fuel, but solar panels are certainly not out of the question on a small scale at least.

Using a wind turbine to power a jet engine would be INTERESTING. If the design system works properly though, the size of the wind turbine will make it unflyable with a jet engine (haven't checked the book, but it should be that way).

The book should allow you to try whatever combinations you want, but there should be some combinations that just aren't going to make the craft you want. So efficient designs are going to drive you to certain combinations, not some arbitrary rules system.

For those of you that have read the BOOK "Hunt for Red October" the Red October used a hydraulic version of a jet engine but with water. Since the design rules don't provide for this specific type of underwater propulsion, modeling it on a jet engine might actually work...

The US worked on a nuclear-powered aircraft back in the 50's. They took a B-36 plane and modified it, calling it the X-6. The reactor at the time put out 3 megawatts and could fly the plane around at about 400mph.

The concept never really panned out (the plane at the time had a 12ton shield between the reactor and the crew!), and it was scrapped.

I guess a more modern design utilizing a more powerful source, say an MHD or fusion plant, might work.

 

[Rikki Tikki Traveller]

That is correct. What grounded that design was the need to shield the pilot and the weight penalty involved. So, come up with a way to shield the pilot (or not have a pilot...) and a Fission plant might be a viable, if dangerous, option for the power plant for the jet.

Power plants are about POWER DENSITY... How much usable energy do you get for a given mass/volume. The higher the power density, the better.

Wind and Solar power tend to be lower power densities while the Internal Combustion Engine has a very high PD. Fission plants have a decent power density, but with the need of shielding, it isn't practical for small applications. That is why there are nuclear powered ships and subs, but not planes or cars.

If you throw in Gravitic technology, the rules change (a lot), you MIGHT be able to get small nuclear reactors that use compressed gravitic waves to control the radiation, allowing for small fission (or fusion) plants that could be used in planes, cars or whatever.

 

[Silvereye]

I don't have the vehicle books, but there is probably an assumption behind what a 'Jet Engine' is.

Basically a 'jet engine' is essentially a gas turbine engine. With perhaps a few tweaks by Frank Whittle way back when. The principles behind a jet engine in a plane are very similar to a turbocharger in a car (exhast gasses powering a compressor to feed more air into a combustion chamber).

A gas turbine has a very large power to weight ratio which is why its used to power lots of things like locomotives, tanks, helicopters, jet planes, boats and there are some nutters that built a motorcycle around one.

Wiki has a good article on them.
http://en.wikipedia.org/wiki/Gas_turbine_engine

While it does not really help with using fusion energy to power a turbine , with sufficient handwavium the fusion plant could feasible power a modified pump-jet (jet ski) engine that works in atmosphere. Suck gas in, compress it, throw it out the back at high speed.