Zack Morris

Why dont some of the better known engine manufacturers incorporate an alternator with/near the starter motor so we can have constant electrical supply while the engines are running??? This can maybe supply a charging current to the battery to keep it from depleting and reduce the dangers of running out of electrical juice.

Dave03B

sounds like a plan!

SJN

I think..

Extra weight
More complicated setup
RF noise
Higher price
Not a necessity

is why we dont have it [8D]

siclick33

I'm sure it is possible and I'm sure someone will do it soon.

I guess a slight problem is the RPM involved. An electric motor (alternator) will probably not stand up to 160,000 RPM. A gearbox will be required which will add considerable complexity to the relatively simple model engines. I guess it would be pretty easy on a turboprop that already has a gearbox.

Zack Morris

Another way would be to have a freely rotating light mini turbine sitting in the exhaust duct driven by exhaust gases.

siclick33

That is similar to how a turboprop/turboshaft engine works. The difference is that they are designed to convert the accelerated exhaust gases back into mechanical power.

In a turbojet (model engine) the power is gained directly from the high velocity exhaust. Anything that is put in this gas flow will significantly reduce the power output of the engine.

Zack Morris

Even if its the diameter of say 2-3 cm? Its only a fraction of the exhuast gas velocities.

JohnMac

We do not need anything so complex. Most of our engines now use a hall effect pick up which requires a small magnet in the compressor nut. If we wrap a coil of wire close to the magnet we have an alternator. I believe that David James engineering tried this with their Cobra Turbojet in the early 90's. Their problem was way too much voltage and RF noise, nothing insurmountable, but do we need it. What is wrong with batteries?
Personally I would sooner see a bleed taken off the compressor to keep my air tanks topped up.
regards,

John.

Dave03B

I've seen a kit/plan for this.....using a small, freely rotating prop. Cant find the website at the mo...will keep looking.

Zack Morris

Excellent idea(s)!

Dave03B

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siclick33

Full size aircraft use a RAT (Ram Air Turbine). This is a small windmill that sticks out into the airflow (not the jet pipe/exhaust gases). On full size aircraft this can provide electrical and hydraulic power. Personally, I would prefer this to having anything in the exhaust section.

I must admit that I don't actually know how much power you would lose by putting a propellor in the exhaust. Bear in mind that 2-3 cm is quite big in comparison with the size of the engine turbine section. (This obviously depends on which engine you are using).

EddieWeeks

During RIG testing 3200 mah pack would last over 4 hours with 8 servoes and 3 gyros..

Its just not needed...

Eddie Weeks

Javier-RCU

My Feedback: (6)

Take a look at http://www2.towerhobbies.com/cgi-bin...?&I=LXFV20&P=7

Lt. Dan

My Feedback: (21)

Now you're talking complex! A compressor bleed air system will require a pressure regulator, overpressure safety valve, and most likely a heat exchanger to function properly. Not to mention the significant power loss created!

David Gladwin

The RAT is only used when everything else has failed. Each engine has an alternator , driven by a complex and heavy CSU (constant speed unit) and a hydraulic pump. In the event of engine failure the APU (auxiliary power unit) can be used to supply electrical, and therefore hydraulic, power. When all that fails the ram air turbine is exteneded, very rarely happens !
Regards,
David Gladwin.

Lt. Dan

My Feedback: (21)

Yes, and then there was the Gimli Glider...

Kelly W

My Feedback: (2)

A friend went through the equation for an open vented line from the pressure casing and found that the losses were much less than expected. To prove it, he runs a KJ-66 with the propane circuit open through a small tube (ie not even plugged with a check valve like most) and the engine still performs as expected after disconnecting the supply. Its been running that way for over a year. To partially refill a retract system, the flow would be nearly static, so the loss in performance would likely be that much more negligible. For that same reason, its really not all that important to have a perfectly air tight seal on the NGV clamp rings or the glow plug...

You're right about the heat problem though, if you assume the leak causes a significant flow rate of air. When testing a JG-100 in 2001, I hooked up a case pressure line to an off-the shelf pneumatic gage and ran the motor. The engine worked and the gage registered the pressure level expected. The pressure line we was just a simple yellow Festo hose plumed to a right angle 4mm bulkhead fitting on the diffuser cover, just like the propane and fuel lines used on other motors. I then made the mistake of switching the gage while the motor was running for a more accurate one I had on hand. Funny though, after I switched it neither gage worked... Ignorantly, I ran it for another few minutes and the performance still looked within the spec.

I shut the motor down and pulled off the fairing to see why the gage stopped working... In that few seconds of free venting through the 4mm hose, enough hot air passed through the fitting to melt the plastic right-angle portion and the section of hose immediately following it... In a lower flow rate, I'd assume we could plum the system with a length or two of aluminum or brass tubes to act as heat exchangers to the ambient air in the fuselage. Its added weight, but I don't think it would be too difficult to make it work, just don't expect to get 120psi out of it... If a leak did happen, the plane would probably still limp home. I think the AMT Netherlands engines use a system like this to propel smoke oil.

Kelly

David Gladwin

I bet they used the RAT during that incident !. They couldn't start the APU , there was no fuel in the left wing tank (which feeds the APU on the 767) or any other tanks for that matter ! A brilliant piece of flying saved the day !
Regards, David Gladwin (ex 767 capt).

For those who don't know what the Gimlee glider was, it was an Air Canada 767 which ran out of fuel because they had despatched with u/s fuel guages and had misintepreted the tank dripstick calibrations. The aircraft was landed on a disused airstrip being used for drag racing. The only damage was a collapsed noseleg !

JohnMac

Now you're talking complex! A compressor bleed air system will require a pressure regulator, overpressure safety valve, and most likely a heat exchanger to function properly. Not to mention the significant power loss created!
[/quote]

Lt Dan,
Well it has already been done. I talked to the boys fromJetworld in Germany when the visisted the JMA AGM in the UK a couple of years ago, and they showed me a prototype system. They then published details in the German Jetpower magazine.
A pressure regulation system would be required but a simple mechanical device could be used. Getting one small a light enough might be the problem. Pressure loss has already been dealt with, it's insignificant; but the point you make about temparature rise may provide a difficulty. When you compress air it gets hot, but is air bled from our compressors hot enough to cause a problem?
The lack of a commercailly available system has prevented me from going any further with this idea.
Regards,

John.

Lt. Dan

My Feedback: (21)

I never said it was impossible, just complex!

The bleed temp depends on where you bleed it from, of course, our engines are single stage compressors so you don't really have much choice. On the big jets, bleed air is taken from several different compressor stages at different temperatures. It passes through a regulating valve and then through a precooler (heat exchanger) where the heat is exchanged through cold ram air from the fan section (another valve), before it is passed on into the aircraft for use. I would love to have onboard electrical generation and bleed air, but it becomes a big departure from the KISS concept that I love!

JohnMac

I never said it was impossible, just complex!

The bleed temp depends on where you bleed it from, of course, our engines are single stage compressors so you don't really have much choice. On the big jets, bleed air is taken from several different compressor stages at different temperatures. It passes through a regulating valve and then through a precooler (heat exchanger) where the heat is exchanged through cold ram air from the fan section (another valve), before it is passed on into the aircraft for use. I would love to have onboard electrical generation and bleed air, but it becomes a big departure from the KISS concept that I love!
[/quote]

Well I agree with that, our jets are complex enough. When I anylise why I want an air bleed system it is because I have had problem with pressure loss due to my brakes. So in retrospect I think I will buy some better brakes that don't leak half the time and add simplicity.
Regards,

John.

Flyjets

My Feedback: (51)

David

I am a current 767 Capt with a US Airline was the Air Canada incident you?

I remember when it happened and it was a terrific job of getting her down in one piece.

Not unlike the Air Transat which at least had the energy vector arc for help in LPLA. Seems like u Canadian guys are good at dead sticking it in.

PM me if you want to take this private probably not something everyone will appreciate.

sengle

http://www.wadenelson.com/gimli.html

The Gimli glider story - yep the RAT saved the day!

Cheers from NZ!

David Gladwin

The A/C 767 was a good save but so was the 747 incident when all four engines flamed out and were seriously damaged over Indonesia due to the ingestion of volcanic dust.

Regards, David Gladwin