Pete737

How do you know when you have adequately pressurized your on board gas tank?

Do you pressurize it for a days flying or just one start at a time?

Thanks! Pete

SpiderJets

Propane/butane gas liquifies at a certain pressure, given a temperature. (and vice versa)
If your pressure drops, means rather that the tank is fully empty. Theoritically speaking, pressure should remain stable until all liquid has transited into gas condition.
Transition from liquid to gas condition draws a lot of energy (=temperature !) hence cools the bottle even more (which results in even lower gas pressure). Therefore, too small size gas container in cold temperatures could mean problems when you use large volumes of gas (repeated attempts to start,...).

Technically speaking, best would be to have a rather big gas tank on board, under condition it is allowed by the local authorities, you do not have gas leaks/losses, and weight factor does not matter.

Pete737

I have the stock gas tank with the FEJ Rafale. I don't knoe the exact volume, Probably 6-8 oz (1 1/4"d x 3 1/2"l) Somewhere in that ballpark. Im filling via a small compressor needle (basketball needle) with a small peice of festo tubing epoxied to it, The tubing goes into the one way valve and then I puncture the powermax bottle with the needle. Im just conerned because I have no idea how much is in the tank or how fast it's filling etc...

Thanks! Pete

Vincent

My Feedback: (61)

There is no way of telling how much gas is in the onboard tank. If you give it a 2sec burst or so that should give you a few starts. If you are in doubt just pop a little gas in there each start.
V..

SpiderJets

Just use the stock gas tank and refill each time. Use transparant festo tubing, then you can see if there's still (liquid) gas moving into the tank...

rcpete347

My Feedback: (251)

HI, the best thing to do is not the a bomb on board, keep your canister fastened to your powermax bottle, so when your jet crashes, their is less chance it catches fire.
Rcpete

JMCJET

A gas container is always full. Even when there is no more pression the container is full.
The gas is always in balance: one part liquid other part gas When you open the container the pressure drops, the liquiq pass to gas. The formula is P+V=rT.

So, respond to your question: Use cristal tube in your gas conection. Be sure you are filling your inboard container with liquid gas. When the liquid gas stops flowing from the main container to the inboard container, you will have all the gas you need.
A small amount of liquid gas gives you gas enough for several starts.

BE SURE YOU ARE NOT FEEDING YOUR ENGINE WITH LIQUID GAS

KC36330

if you use clear tubing you can see the flow slow down when filling, that's an indication that the onboard tank has filled or the PowerMax can has exhausted.

myself i much prefer offboard starting, not becasue of the so called 'bomb' but it saves weight and frees up that $75 solenoid for latter use elsewhere.

jimbo1846

I to prefer offboard starting I do have the solenoid instaled and use a regulator on the propane bottle.

olnico

Even easier.
I just have a male Festo plug connected to the on board start valve.
The on board start valve stops the engine pressure from flowing backwards through the start line.

The stock white gas tank does not stay on board. I just connect it to the system for start and remove it after the start.
The one way female Festo valve is connected to the tank.

To check how full the tank is, I just shake it in front of one ear. As long as there is a bit of liquid gas that flows in the tank I'll have enough to do one start...

This method works perfectly well and I know exactly how much gas I have in the tank.
Minimum flying weight, maximum security.

Boomerang1

Do you just turn the gas on at the bottle & turn it off when you think all is good or have you mounted the solenoid on the bottle somewhere & plug it into a lead connected to the ECU so it works as part of the autostart process?

I agree with leaving the gas tank off board, no 'bomb', save a bit of weight & one less thing you have to find room for. Once your engine is started it serves no purpose & is just along for the ride. - John.

olnico

Check my thread above.
The advantage of keeping the start valve on board and connected to the ECU is the ease of use.
Also there is no risk of torching the engine during a start.
Plugging the mix bottle directly to the gas line upstream the valve is quite risky. Send too much liquid gas and you'll torch the engine.

Having the stock gas tank plugged to the start line and hanging head up outside of the model during the start sequence completely eliminates this risk. Also when you remove the tank after start, the line will purge from the gas left ( since the male Festo plug is a two way valve ).

Jim Cattanach

Onboard gas tanks are the cause of most jets going up in flames when they crash.

Boomerang1

THe question was for KC36330, he may have hit upon a new idea that we should consider.

Yes & no. Most mix bottles (I use the small Coleman cylinders) only feed gas, unless you are silly enough to hold them upside down.

Really, the gas solenoid is only fitted to make the start process idiot proof. My manual start Wren 44 has no solenoids at all on fuel or gas & after a bit of practice you learn when & how much gas to give it. - John.

causeitflies

I believe Powermax may be the only one with a clunk and you have to hold it upside down to get just gas.

jetnuno

Hi

I doubt that... I think the main cause is fuel contact with exhaust after tanks break because of crash. Gas explodes and what we do see in videos is a slow combustion proper of quero.

I usually fly the small gas can onboard. But in case of crash I would be more concerned with the 5,5 liters of quero (at take of)

Regards

Nuno

mr_matt

My Feedback: (10)

FYI, on a JetCat you can set the ECU to slowly drain the gas during the run, so by the time you are taking off the gas can is empty, just an FYI, I don't know about any other brand.

jetnuno

Hi Matt

I used to have it turned on on my P160SE, but then I realised that this feature, all it does is to open the electronic gas valve and that way gas is burned inside the turbine because it as a higher pressure.. You're right, after a 30second period or something like that, the gas can is empty, but the gas valve remains open, thus allowing combustion somke to pressurise all the gas compartment.

Try to open the gas valve with the turbine running and you'll see that. After a period of 30sec, the ECU should close the gas valve, but that does not happen, so I disabled this feature and do my flight with a small quantity of gas inside the can.

I have the can in the front of the fuselage away from the turbine. In the event of a crash the fuel tanks should get there firstHope not.....

Regards

Nuno

KC36330

sorry about the late reply, i was out buring some Jet-A


the only connection onboard is i have a short length of 3mm festo line from the turbine to a 3mm - 4mm festo fitting, then a short length of 4mm tube connecting the 3-4mm fitting to a festo check valve. when i initiate the start when the GSU says IGNITION (it'll flash up shortly after START goes away) i open the valve on the off board regulator bottle that is connected directly to the check valve, the ECU has nothing at all to do with my propane control.

when the yellow standby LED goes out on the IO board/GSU i turn off the regulator and unplug it from the check valve, the check valve keeps the high pressure hot air from back flowing out of the turbine melting the fittings and tubing.

EDIT: here is a pic of what is attached to the turbine on my setups, this is a pic of my P-70 as you can see only a length of 3mm festo tube, a 3-4mm adapter and then a 4mm tube and check valve.

Pete737

Ok, I used my needle setup and it worked, Kind of. I gave 3 short bursts and saw the gas go in. Maybe Ill give it a few more before I go outside. I was just a bit nervous about the whole getting gas vs. liquid in the start bottle. I saw an aerosol go through the tubes. When I wasn't inserting the needle far enough into the powermax bottle I saw a little bit of liquid, But that was just a test to the atmosphere to see if the needle would work.

Im gonna give it a few more bursts and Ill wait to hear back from you guys before I go out in the garage and fire it up.

This is my first time starting a turbine. Ive had some good long conversations with Eric and some others and I feel pretty confident, Anything els you would like to tell me would be appreciated.

After I run it, Ill let you know how it went.

Thanks! Peter

causeitflies

You want liquid in the bottle, but not in the engine. The liquid in the bottle will turn to gas and keep the pressure up. If you only put gas in the can it won't last long enough for spool up. Just don't put so much liquid in the can that it then gets in the lines to the engine. A small amount in the tank to engine line will likely vaporize but too much and you will have liquid reaching the engine and get flames. If you can see it flowing, it is liquid.

Good luck on the start and don't be alarmed if the tail cone turns read in the dim light. The first turbine start is a rush!!

Pete737

Hmmmm, I did see it flowing in the clearline from the PM bottle to the onboard bottle...? How do I know if there is going to be liquid in the line when the solonoid opens? How do I know if I put too much gas in the can?

Thanks! Pete

KC36330

Peter,

just shove the fitting fully down into the PowerMax can, with the can sitting right side up (so you get liquid, it's got a clunk) watch the clear line, you'll see the flow slow down, when it does, pull the fitting out of the PowerMax and you're ready to go.

the trick with this setup is to make sure the length of tube between the PowerMax fitting and the check valve is short, the longer it is the more it blows back when you pull the fitting out of the PowerMax.

don't worry about liquid in the line, the brass 4mm to 3mm fitting in the line going to the turbine will take care of any liquid that gets there.

olnico

Mark is correct.
No liquid gas in the turbine or you'll overheat it at each start.
The turbine internals and especially combustion chamber liners will age quicker.

I strongly advice you to put the gas tank vertically in the model. If you can't, then put it outside of the model as described above.
Using the drain function is mandatory when you have the can on board. but what a waist of gas. My Powermax mix bottle lasts about 3 months.

There is a start valve that is controlled by an ECU. This valve pulsates at a given rate. There is a reason for this. This is why I'll never have a mix gas directly plugged to the start line.

causeitflies

Fire that sucker up!!