JET-POWERED - Maverick Blackout V2
Discussion
MBBlat said:
Chrysler, Rover, General motors would disagree.
http://en.wikipedia.org/wiki/Chrysler_Turbine_Car
http://en.wikipedia.org/wiki/Rover-BRM
http://en.wikipedia.org/wiki/General_Motors_Firebi...
http://en.wikipedia.org/wiki/Fiat_Turbina
Even ships do it
http://en.wikipedia.org/wiki/Combined_gas_and_gas
And before you quibble those are gas turbines not jets, a jet is just a specific type of gas turbine.
http://en.wikipedia.org/wiki/Gas_turbine
No quibbles - glad to be edified!http://en.wikipedia.org/wiki/Chrysler_Turbine_Car
http://en.wikipedia.org/wiki/Rover-BRM
http://en.wikipedia.org/wiki/General_Motors_Firebi...
http://en.wikipedia.org/wiki/Fiat_Turbina
Even ships do it
http://en.wikipedia.org/wiki/Combined_gas_and_gas
And before you quibble those are gas turbines not jets, a jet is just a specific type of gas turbine.
http://en.wikipedia.org/wiki/Gas_turbine
Slight technical update - it kept on stalling (flaming out) under hard acceleration - there's me stressing that the most reliable engine about is not being reliable for me - turns out that the fuel was chucking to the back of the tank, leading then of course to bubbles in line & flame-out. And at full tilt, it'll get through the whole tank in a few minutes or under, so it will almost always have space to let the remaining fuel gather to, away from the pick-up. The same will then happen on steering. Now I see why a lot of other models have tall tanks! Evian bottles will have to serve as a stop-gap.
Well done op, I have only just seen this thread! I did something similar a few years ago and it was fun for about an hour. You'll find that as you throttle up the car doesn't accelerate as fast as a conventional model. Then in that microsecond between your brain registering the lack of acceleration and your thumb subconsciously administering more power on the throttle control, the car will have begun to reach silly speeds and then the panic sets in. 
My advice, find a big, big flat car park, any obstruction or debris and the car will find it. The FOD guard will stop largish debris but not the fine stuff like sand, which can cause problems, particularly if it is ingested into the bearing cooling flow. Model helicopters operating in dusty conditions will often lower the bearing life due to this, something like you car may have the engine sucking in a lot of dust all the time.
Your problem with fuel pick up would be helped by using a felt clunk pick up, basically a big wad of felt, which acts like a sponge. It may also be worthwhile looking at some kind of bubble trap too.
I love small gas turbines, built my fist engine when I was 15 waaaay back in 1995. Built on the order of around 60 engines in total, both commercial and my own designs. Even made my own lathe when I was young and had no money. I keep a few engines and parts in my desk at uni so when I teach the undergraduate engineering jet engine lab, the students have the chance to hold and inspect real engines. We have some nice sectioned full size engines in the dept as well as a small engine that the students use to take measurements, but they're not allowed to touch them, and much of it is hidden away. The Wren engine you're using is a great engine, I have owned several of them, still have a much modified MW54 that's been constantly upgraded. Here's an old engine of mine that puts out around 130N of thrust at 120k RPM and a picture of a combustor along with compressor/diffuser from a variation of the first engine.
My advice, find a big, big flat car park, any obstruction or debris and the car will find it. The FOD guard will stop largish debris but not the fine stuff like sand, which can cause problems, particularly if it is ingested into the bearing cooling flow. Model helicopters operating in dusty conditions will often lower the bearing life due to this, something like you car may have the engine sucking in a lot of dust all the time.Your problem with fuel pick up would be helped by using a felt clunk pick up, basically a big wad of felt, which acts like a sponge. It may also be worthwhile looking at some kind of bubble trap too.
I love small gas turbines, built my fist engine when I was 15 waaaay back in 1995. Built on the order of around 60 engines in total, both commercial and my own designs. Even made my own lathe when I was young and had no money. I keep a few engines and parts in my desk at uni so when I teach the undergraduate engineering jet engine lab, the students have the chance to hold and inspect real engines. We have some nice sectioned full size engines in the dept as well as a small engine that the students use to take measurements, but they're not allowed to touch them, and much of it is hidden away. The Wren engine you're using is a great engine, I have owned several of them, still have a much modified MW54 that's been constantly upgraded. Here's an old engine of mine that puts out around 130N of thrust at 120k RPM and a picture of a combustor along with compressor/diffuser from a variation of the first engine.
The compressor on an average turbocharger (approx 60mm dia) requires around 7 Kilowatts of shaft power to spin at 120k+ RPM so I suppose you could use a model tubo-shaft engine and use it to drive a second compressor. However the design and construction of such an engine wouldn't be a trivial task. A turbocharger is simply a gas turbine where the heat source is the piston engine instead of a combustor.
Have you heard of hyper-charging? Essentially it is a combustion chamber attached to a turbocharger, so at low engine RPM the turbocharger runs like a jet engine and most of the air bypasses the engine and is burned in a combustor, as you throttle the car engine a valve diverts the high pressure air to the piston engine. So you have maximum boost at any engine RPM. However it is not very fuel efficient as you can imagine, but for something like a hill climbing car then it's worthwhile. These small gas turbines will use around 200 to 300ml of fuel per minute at full chat, 2 litres of kerosene usually lasts around 8 to 10 minutes of fairly spirited flight in a model plane.
The reason I think apu's are used, is that you could possibly bleed some compressed air from the system without incurring temperature or running problems in the gas turbine.
Have you heard of hyper-charging? Essentially it is a combustion chamber attached to a turbocharger, so at low engine RPM the turbocharger runs like a jet engine and most of the air bypasses the engine and is burned in a combustor, as you throttle the car engine a valve diverts the high pressure air to the piston engine. So you have maximum boost at any engine RPM. However it is not very fuel efficient as you can imagine, but for something like a hill climbing car then it's worthwhile. These small gas turbines will use around 200 to 300ml of fuel per minute at full chat, 2 litres of kerosene usually lasts around 8 to 10 minutes of fairly spirited flight in a model plane.
The reason I think apu's are used, is that you could possibly bleed some compressed air from the system without incurring temperature or running problems in the gas turbine.
Fugazi! DUDE!! I gotta be at work right now (paid work/day job) - but will revert later with a deluge of further questions! I worshipped at the altar of jet power ever since I discovered it!
...
(But - P.s. that fuel filter dongle thing, I know it well from two-stroke - but wouldn't it restrict flow to the point of straining the pump's sucking? I hear that the fuel can be sucked so hard and fast that even a solid line of it can be 'pulled apart' releasing the air dissolved in it (cavitation). Hence - anything restricting flow would be a bad thing, no?
It does have a filter within the green housing - and my instinct it to have one at fuel pick-up - what what's your thought on pump-strain?
...
(But - P.s. that fuel filter dongle thing, I know it well from two-stroke - but wouldn't it restrict flow to the point of straining the pump's sucking? I hear that the fuel can be sucked so hard and fast that even a solid line of it can be 'pulled apart' releasing the air dissolved in it (cavitation). Hence - anything restricting flow would be a bad thing, no?
It does have a filter within the green housing - and my instinct it to have one at fuel pick-up - what what's your thought on pump-strain?
Edited by Arif110 on Monday 7th July 13:56
Fugazi said:
Well done op, I have only just seen this thread! I did something similar a few years ago and it was fun for about an hour. You'll find that as you throttle up the car doesn't accelerate as fast as a conventional model. Then in that microsecond between your brain registering the lack of acceleration and your thumb subconsciously administering more power on the throttle control, the car will have begun to reach silly speeds and then the panic sets in. My advice, find a big, big flat car park, any obstruction or debris and the car will find it. The FOD guard will stop largish debris but not the fine stuff like sand, which can cause problems, particularly if it is ingested into the bearing cooling flow. Model helicopters operating in dusty conditions will often lower the bearing life due to this, something like you car may have the engine sucking in a lot of dust all the time.
Your problem with fuel pick up would be helped by using a felt clunk pick up, basically a big wad of felt, which acts like a sponge. It may also be worthwhile looking at some kind of bubble trap too.
I love small gas turbines, built my fist engine when I was 15 waaaay back in 1995. Built on the order of around 60 engines in total, both commercial and my own designs. Even made my own lathe when I was young and had no money. I keep a few engines and parts in my desk at uni so when I teach the undergraduate engineering jet engine lab, the students have the chance to hold and inspect real engines. We have some nice sectioned full size engines in the dept as well as a small engine that the students use to take measurements, but they're not allowed to touch them, and much of it is hidden away. The Wren engine you're using is a great engine, I have owned several of them, still have a much modified MW54 that's been constantly upgraded. Here's an old engine of mine that puts out around 130N of thrust at 120k RPM and a picture of a combustor along with compressor/diffuser from a variation of the first engine.
A quickie (to help with further work on it tonight): Debris. Say grass seeds. Now - where exactly does it go? Does it go 'straight through' and get burnt - or does the fact of radial compression mean that debris will get thrown up and into areas you really don't want them, at all? Will it 'hit' things like the igniter? Block the tiny fuel jets? I can be quite anal about mitigating this risk - have bought a load of Halfords car bodywork alu-mesh - but I need to know what harm debris actually does, more than you've noted so far. I don't anticipate ever letting it near sand (not even as a two-stroke) - so out-&-out abrasion/abrasives I'm less concerned about. My advice, find a big, big flat car park, any obstruction or debris and the car will find it. The FOD guard will stop largish debris but not the fine stuff like sand, which can cause problems, particularly if it is ingested into the bearing cooling flow. Model helicopters operating in dusty conditions will often lower the bearing life due to this, something like you car may have the engine sucking in a lot of dust all the time.Your problem with fuel pick up would be helped by using a felt clunk pick up, basically a big wad of felt, which acts like a sponge. It may also be worthwhile looking at some kind of bubble trap too.
I love small gas turbines, built my fist engine when I was 15 waaaay back in 1995. Built on the order of around 60 engines in total, both commercial and my own designs. Even made my own lathe when I was young and had no money. I keep a few engines and parts in my desk at uni so when I teach the undergraduate engineering jet engine lab, the students have the chance to hold and inspect real engines. We have some nice sectioned full size engines in the dept as well as a small engine that the students use to take measurements, but they're not allowed to touch them, and much of it is hidden away. The Wren engine you're using is a great engine, I have owned several of them, still have a much modified MW54 that's been constantly upgraded. Here's an old engine of mine that puts out around 130N of thrust at 120k RPM and a picture of a combustor along with compressor/diffuser from a variation of the first engine.
Never had a problem using felt clunk pick ups, I think you could run into trouble if you had one that was too dense and restricted the fuel flow too much.
This is the kind of thing I used: http://alshobbies.com/shop/lookupstock.php?pc=4489
You should also get into the habit of checking fuel, these days I only do research stuff, (developing my own testing and evaluation software for small gas turbines in my spare time) so I don't require gallons of kerosene anymore and just buy small quantities of paraffin from B&Q, (smells lovely, unlike JetA1). Anyway that fuel is generally clean, however if you buy from an airfield then you should really be filtering your fuel before you use it. I only use a single filter between the pump and engine, but make sure it's clean as sometimes you get a bad batch of fuel and it's full of crap and can sometimes lead to running problems.
This is the kind of thing I used: http://alshobbies.com/shop/lookupstock.php?pc=4489
You should also get into the habit of checking fuel, these days I only do research stuff, (developing my own testing and evaluation software for small gas turbines in my spare time) so I don't require gallons of kerosene anymore and just buy small quantities of paraffin from B&Q, (smells lovely, unlike JetA1). Anyway that fuel is generally clean, however if you buy from an airfield then you should really be filtering your fuel before you use it. I only use a single filter between the pump and engine, but make sure it's clean as sometimes you get a bad batch of fuel and it's full of crap and can sometimes lead to running problems.
Grass is actually quite harmful to jet engines, what tends to happen is that grass sucked into the engine wont really damage the compressor, even at high speed but will start to accumulate around the diffuser, (the thing with blades and wedges in my earlier picture). Then due to the high temperatures it gets baked on and can start to affect the aerodynamics within the engine. I also believe it can become corrosive, something to do with the chlorophyll. But the odd grass seed, insect or bit of dust wont affect your engine. I've even seen an engine that had hardly any damage after somebody stuck their finger into it at almost full throttle. Prolonged use in dusty, sandy and poor environments would have an effect though as some of the air is bled from the system and used to carry a fine mist of lubrication and cooling air through the bearings. If this air contains fine dust then it can accelerate bearing wear significantly. These engines run at very high speeds and the slightest problem with bearing lubrication can often mean things go wrong, very quickly. Here is a couple of pictures after a bit of dirt clogged the lubrication line during an engine test, the engine data shows that it went from 80k RPM to zero almost instantly, the turbine gouged a 1mm deep line into the turbine housing and the bearings themselves had fused together.
As to where it goes if ingested, well some debris may pass through the compressor and get burned within the combustor, something like a small screw may get lodged somewhere after taking a chunk off a compressor tip. It's hard to say, if you where to track an air molecule flowing through the engine I'd be surprised if it took longer than a few milliseconds. It wont block fuel jets however, these are located within vaporiser tubes and are quite simple and are usually nothing more than hypodermic needles and so they're safe from FOD damage.
I'd be careful if you make an extra FOD guard from aluminium mesh, the FOD guard used by Wren on their engines actually impacts on the performance and you lose a little bit of thrust from the turbulent flow entering the compressor. Compressors are very sensitive to changes in inlet conditions and restricting flow further with a finer FOD screen could mean you end up with an engine that starts to surge as the mass flow rate drops.
This is why the land speed record teams will spend days FOD'ing, picking up stones and debris, before they run the car. If you can find a a quiet car park that's well kept you should be okay. Don't forget though that the wheels my throw things up into the air!
As to where it goes if ingested, well some debris may pass through the compressor and get burned within the combustor, something like a small screw may get lodged somewhere after taking a chunk off a compressor tip. It's hard to say, if you where to track an air molecule flowing through the engine I'd be surprised if it took longer than a few milliseconds. It wont block fuel jets however, these are located within vaporiser tubes and are quite simple and are usually nothing more than hypodermic needles and so they're safe from FOD damage.
I'd be careful if you make an extra FOD guard from aluminium mesh, the FOD guard used by Wren on their engines actually impacts on the performance and you lose a little bit of thrust from the turbulent flow entering the compressor. Compressors are very sensitive to changes in inlet conditions and restricting flow further with a finer FOD screen could mean you end up with an engine that starts to surge as the mass flow rate drops.
This is why the land speed record teams will spend days FOD'ing, picking up stones and debris, before they run the car. If you can find a a quiet car park that's well kept you should be okay. Don't forget though that the wheels my throw things up into the air!
Fuel-tank upgrade...! Calling them fuel towers!
I was testing them for leakages. Obviously, am drilling 1mm holes in the caps to prevent a vacuum.
Not sure that's quite in line with what Brita had in mind for their product!
The brainwave came to me at night while putting the little one to bed - she was drinking from her own Brita bottle (no filter - we just use it as a washable bottle), and I had my Eureka moment.
She loved that just by filling the one up, the other fills up to exactly the same level!
I think now the fuel-starvation-on-acceleration issue will have been resolved. I'll take pics once installed.
I was testing them for leakages. Obviously, am drilling 1mm holes in the caps to prevent a vacuum.
Not sure that's quite in line with what Brita had in mind for their product!
The brainwave came to me at night while putting the little one to bed - she was drinking from her own Brita bottle (no filter - we just use it as a washable bottle), and I had my Eureka moment.
She loved that just by filling the one up, the other fills up to exactly the same level!
I think now the fuel-starvation-on-acceleration issue will have been resolved. I'll take pics once installed.
Fugazi said:
...You'll find that as you throttle up the car doesn't accelerate as fast as a conventional model. Then in that microsecond between your brain registering the lack of acceleration and your thumb subconsciously administering more power on the throttle control, the car will have begun to reach silly speeds and then the panic sets in. ...
In-fecking-deed sir! Panic is the word! I've taken the 2-stroke engine out now, to make space for the new fuel units - so it should exhibit less inertia/slightly more predictable behaviour....Thankfully also - the Spektrum transmitter has some very elaborate settings, and so here we're talking throttle 'Expo' or I guess 'rate' as we'd call it in the car world.
In Low Range, my Defender's throttle pedal would go 'long' - same thing here - allows a good margin of security of control.
Fugazi said:
...You should also get into the habit of checking fuel, these days I only do research stuff, (developing my own testing and evaluation software for small gas turbines in my spare time) so I don't require gallons of kerosene anymore and just buy small quantities of paraffin from B&Q, (smells lovely, unlike JetA1).
Good stuff - I use Bartoline paraffin - just bought a few bottles today! Key question: two-stroke oil addititive - I'm happy (want) to spend as much as necessary for the 'best' thing - so am currently using Castrol Actevo. Is there any drawback though with using this - as it's fully synthetic? (I'm used to asking the question, as once toyed with the idea of dosing my actual car's diesel with two-stroke, whereby lots of warnings over wrong type of oil).Paul sir (Fugazi),
Any thoughts then on top speed, with 10kg of thrust? The thing weighs about 13/15kg now.
I'm also worried that the car will go out of transmitter range, if actually allowed to get to top speed. I'm suspecting 80mph at least?, based on a very short burst of high power.
Thankfully idle (50,000RPM/300g of thrust) is perfectly balanced with the car's own inertia - so it equates to not moving at all. It begins to move at about 80,000RPM - and it gets rapidly scary at 120,000RPM onwards.
Arif
Any thoughts then on top speed, with 10kg of thrust? The thing weighs about 13/15kg now.
I'm also worried that the car will go out of transmitter range, if actually allowed to get to top speed. I'm suspecting 80mph at least?, based on a very short burst of high power.
Thankfully idle (50,000RPM/300g of thrust) is perfectly balanced with the car's own inertia - so it equates to not moving at all. It begins to move at about 80,000RPM - and it gets rapidly scary at 120,000RPM onwards.
Arif
Fugazi said:
The compressor on an average turbocharger (approx 60mm dia) requires around 7 Kilowatts of shaft power to spin at 120k+ RPM so I suppose you could use a model tubo-shaft engine and use it to drive a second compressor. However the design and construction of such an engine wouldn't be a trivial task. A turbocharger is simply a gas turbine where the heat source is the piston engine instead of a combustor.
Have you heard of hyper-charging? Essentially it is a combustion chamber attached to a turbocharger, so at low engine RPM the turbocharger runs like a jet engine and most of the air bypasses the engine and is burned in a combustor, as you throttle the car engine a valve diverts the high pressure air to the piston engine. So you have maximum boost at any engine RPM. However it is not very fuel efficient as you can imagine, but for something like a hill climbing car then it's worthwhile. These small gas turbines will use around 200 to 300ml of fuel per minute at full chat, 2 litres of kerosene usually lasts around 8 to 10 minutes of fairly spirited flight in a model plane.
The reason I think apu's are used, is that you could possibly bleed some compressed air from the system without incurring temperature or running problems in the gas turbine.
You could even use a turbine to spin the turbo in a hillclimb car and then utilise the turbine exhaust to power a blown diffuser. You'd have to be a bit nuts though...Have you heard of hyper-charging? Essentially it is a combustion chamber attached to a turbocharger, so at low engine RPM the turbocharger runs like a jet engine and most of the air bypasses the engine and is burned in a combustor, as you throttle the car engine a valve diverts the high pressure air to the piston engine. So you have maximum boost at any engine RPM. However it is not very fuel efficient as you can imagine, but for something like a hill climbing car then it's worthwhile. These small gas turbines will use around 200 to 300ml of fuel per minute at full chat, 2 litres of kerosene usually lasts around 8 to 10 minutes of fairly spirited flight in a model plane.
The reason I think apu's are used, is that you could possibly bleed some compressed air from the system without incurring temperature or running problems in the gas turbine.
Arif110 said:
Paul sir (Fugazi),
Any thoughts then on top speed, with 10kg of thrust? The thing weighs about 13/15kg now.
I'm also worried that the car will go out of transmitter range, if actually allowed to get to top speed. I'm suspecting 80mph at least?, based on a very short burst of high power.
Thankfully idle (50,000RPM/300g of thrust) is perfectly balanced with the car's own inertia - so it equates to not moving at all. It begins to move at about 80,000RPM - and it gets rapidly scary at 120,000RPM onwards.
Arif
How fast, very fast, stupidly fast.. a simple, back of the fag packet calculation gives a rough estimate of 90 mph. Biggest factor is the drag of the car, which is probably huge as it has the aerodynamic qualities of a chest of drawers. 90 mph may not sound 'that' fast but if you're stood still then it will disappear into the distance at a rate of knots. However I found my car, (looked very similar setup to yours) was very, very twitchy as the speed increased and I ended up just letting it accelerate for a few seconds before spinning it around to dump the speed. If you had a quiet road and followed in a car, you might have better luck Any thoughts then on top speed, with 10kg of thrust? The thing weighs about 13/15kg now.
I'm also worried that the car will go out of transmitter range, if actually allowed to get to top speed. I'm suspecting 80mph at least?, based on a very short burst of high power.
Thankfully idle (50,000RPM/300g of thrust) is perfectly balanced with the car's own inertia - so it equates to not moving at all. It begins to move at about 80,000RPM - and it gets rapidly scary at 120,000RPM onwards.
Arif
As you've noticed the thrust curve isn't linear, so you can program the transmitter to give a better profile. One thing to remember though, if you do get high speeds is the engine, even at idle, is always producing thrust. Some of the first rc jet engine powered models were unable to land unless the engine was shut down due to this residual thrust. My car wouldn't move at idle, but once rolling the thrust at idle meant it didn't stop. But looking at those tyres I think you'll be fine.
Edited by Fugazi on Tuesday 8th July 11:58
Arif110 said:
Good stuff - I use Bartoline paraffin - just bought a few bottles today! Key question: two-stroke oil addititive - I'm happy (want) to spend as much as necessary for the 'best' thing - so am currently using Castrol Actevo. Is there any drawback though with using this - as it's fully synthetic? (I'm used to asking the question, as once toyed with the idea of dosing my actual car's diesel with two-stroke, whereby lots of warnings over wrong type of oil).
I use either Mobile DTE or Castrol Power TTS 2-stroke depending on the engine. The commercial engines use the good stuff, my own use the 2-stroke. This is just down to servicing and warranties on the commercial engines, as some companies will know from the deposits in the combustor whether a synthetic turbine oil was used or not. Personally I prefer the 2-stroke stuff as it was designed to be burned off, the turbine oils are designed to be recovered and there is some uncertainty as to their effects on health. But as long as you don't breathe vast amounts of exhaust, you'll be ok. Fuel wise I've used white spirit, JetA1, Parasene (B&Q paraffin) and I also have experimented with Diesel. Just stick with good quality paraffin or JetA1 (if you can get it, it's often cheaper than buying the same quantity of paraffin, it just doesn't smell as good) and a decent oil and you'll be ok.Gassing Station | Scale Models | Top of Page | What's New | My Stuff