DiscoWings

My Feedback: (76)

what size tygon are you running 5/16? Also are your running 5/16 tees?

I have P-240 in a jacknife my p-240 uses the almost the same amount of fuel as the B300F full power so fuel consumption is going to be similar.

Here are are the T's I needed, and MARC is correct the 260 CAT is plenty for the B300F I think you issue is the center tank

http://www.autozone.com/autozone/acc...ntifier=102899

DiscoWings

My Feedback: (76)

Also in flight the B300 needs a good 15-20 seconds to start making good power its not going to be like the P-200 you have to do a nice big round lap to prep it up, then .... WATCH OUT! Luckily the UB has no gear doors.

DiscoWings

My Feedback: (76)

Here is the tube I use:

http://www.grainger.com/product/TYGON-Tubing-12X205

olnico

Your engine must have a problem. Acceleration time from idle to full power is 6 seconds. You get 300 N+ after these 6 seconds.

DiscoWings

My Feedback: (76)

OLI I will take a video on a test stand, reaching full RPM vs making full power are completely different on these big turbines. At 6 seconds my 300F was only making 53 Lbs of thrust, it took it 11 seconds to get to 64 lbs and that is where it topped off. This was at 75% humidity and 91 degrees farenheight.

My P-240 is the same way, full rpm in 7 seconds but full power takes longer 12 seconds total, I don't believe just because you are at full rpm you are making full thurst.

LA jetguy

Is it possible that altitude and barometric pressure makes a difference in thrust output??

DiscoWings

My Feedback: (76)

Well I use to think, FULL RPM = FULL POWER but I don't believe that is the case as turbines get larger, I think something has to happen with the airflow perhaps? All I know at 104,000 RPM at 6 seconds 53 LBs of thurst, 104,000 RPM at 11 seconds 64 lbs of thurst.

olnico

A gas turbine is a very simple device. The thrust generated is proportional to the mass flow going through it. The total mass flow is a combination of the air mass and fuel mass used.
The fuel mass is proportional to the pump RPM and and air mass is proportional to the engine RPM ( drawn by the compressor ) .
For a given RPM, the air mass is constant.Thus the thrust generated, since pump RPM stabilizes faster than the engine RPM.

I am using a lab grade dynamometer bench to check the engines. There is no such thing as a progressive increase of thrust once max RPM has been reached when I test them on my bench. What you are experiencing is either a drift or slow reading or hysteresis on your test bench.

ravill

My Feedback: (11)

Disco,

Thanks for the suggestions on the T's . You can see the one "T" I use in my set up. It was the biggest I could find at an autoparts store that was fuel and heat resistant.

The tygon I have is the biggest you can buy from Todd:

http://www.dreamworksrc.com/catalog/...uel-Tubing-316

And no, it does not have 5/16 ID, only 5/16 OD. I think I'll pick some up.

What size clunks are you using? And, where did you get those clunks?

Thanks!

DiscoWings

My Feedback: (76)

I'm using some 5/16 ID clunks I got at a local lawn mower store, they are the STONE type, plenty of FLOW, But you need 5/16 ID tubing.

http://www.dreamworksrc.com/catalog/...uel-Tubing-316

This is generic tubing available at ANY lawn mower shop, and is a quite a rip off at dreamworks, I paid $24.00 for a 50 foot roll of 3/16 ID yellow tubing.

You may need to go to a motor cycle shop to get the 5/16th ID tubing, but any large lawn mover shop should have it too, it may be in clear or black color though. I bought yellow online for $85.00

DiscoWings

My Feedback: (76)

Here is some on ebay if you need a small patch:

http://www.ebay.com/itm/Tygon-Fuel-T...item19ef3c7012

remember vent lines should have the same diameter!

ravill

My Feedback: (11)

So I tried a new experiment last night.

Since I was getting cavitation no matter which bubble catcher I used and no matter how I hooked up my tanks, parallel, series, one at a time, etc...

I wanted to bypass all the UAT's and try running the fuel pump directly to my header tank with ALL my tanks hooked up regularly. And for good measure I turned up the pump voltage to 6v (61W) and ran it.

Two things:

1. The pump temperature didn't even raise up 1/10th of a degree after this run (see the pic below). It had the same thermal reading before AND after. Nice piece of machinery there Oli.

2. NO CAVITATION!!!!

So, the biggest concern is my choice of UAT that is causing cavitation. The CAT being the least prone to cavitation.

yeahbaby

My Feedback: (21)

Give the cook uat a try. Solid piece of gear!!!

ravill

My Feedback: (11)

Do you mean the JMP accumulator? I had two brand new ones I just tried. Both cavitate worse than BVM's and the CAT

mr_matt

My Feedback: (10)

Great work Raf,

I have to admit, I have never understood the how this is cavitation, in the way I learned about it.

I thought cavitation bubbles collapse almost instantly once the local pressure increased, how can they travel all the way to the turbine?

I have seen leakage (resulting in a stream of little bubbles) through hard urethane (clear) line when in tight bend radius (out of a UAT), even with safety wire, but NOT on a new install.

olnico

Hi Matt.
Have a look here:

http://www.ultimate-jets.net/blogs/f...ing-cavitation

I did lots of tests with many different airtrap to characterize the Vacuum threshold at cavitation. Not all air traps are equal on that matter.
I studied this phenomena a lot as well. What happens is that AIR bubbles are created by both a certain level of vacuum AND turbulence (this is very close to what happens in a can of beer. As soon as you open the container, its pressure drops and thousand of micro bubbles of CO2 start coming to the surface). The reason behind this is that the micro swirl in turbulence creates local point of lower vacuum where the vapor pressure of air dissolved in kerosene equals the local level of vacuum. This is where the liquid "explodes" in a micro bubbles. Thousands of micro swirls create thousands of micro bubbles. Then the high energy stream keeps on swirling passed the creation point and prevents the bubbles from re-dissolving.

The reason why the bubble does not dissolve immediately when the vacuum/ turbulence condition stops is that this is not kerosene but air. Condition for the bubbles to re-dissolve will be to agglomerate into a bigger bubble with a lower tension surface into a locally calm area of the stream. In any case, re-dissolving would take between one to two minutes. Way too slow to avoid bubble propagation into the engine.

yeahbaby

My Feedback: (21)

Yes thats at what I meant and strange to hear about JMP. I've had great success with mine using the AMT Olympus.

mr_matt

My Feedback: (10)

Hmm yes Oli. I was thinking of cavitation as an "empty" bubble so to speak. I figured the phenomena we see is actually the dissolved air coming out of the fuel, exactly like carbonation in soda

I also wondering if we are dissolving a lot more air into the fuel while pumping the fuel into the plane?

olnico

No we don't. Kerosene is saturated of air as it comes. You can't get more in.

The air solubility coefficient in % is roughly equal to the air pressure in PSI.
So it would vary between 13 and 14%, depending on kerosene composition, ie: there is about 13% of air dissolved in the carburant. One way to de-saturate it is to expose it to vacuum till it stops foaming. Not very practical at the field, especially considering the fact that it re-saturates within a couple of minutes.

BTW, cavitation is not exactly the best term for this phenomenon, but I keep using it as it involves fluid movement and vacuum in our systems.

mr_matt

My Feedback: (10)

Oli your explanation is great and I appreciated your research on air traps. I also look forward to you and Raf evaluating that UB install. I have an install with a similar tight bypass clearance and I hope to learn some tricks (and physics).

olnico

You're welcome Matt.
If I can help, this will be with pleasure.

ravill

My Feedback: (11)

So, I got the new "Hi-flo" BVM UAT and it looks like a solid piece. Nice and big connectors with the correct step downs for the fuel pump tubing. And a nice purple "BVM" logo on it.



The bad news is, my system is still cavitating.

To recap:

In decreasing order of cavitation: Large CAT, New "hi-flo" UAT, Reg uat, JMP accumulator.

The removal of the "air traps" gets rid of any and all cavitation in my system.

ravill

My Feedback: (11)

My next step is to skip the UAT (without a UAT/CAT there isn't EVEN a hint of cavitation in my system!) and use one of the LARGE pleated clunks that Marc at GBR-jets uses.

Here is the big one he offers next to a JMP clunk.

ravill

My Feedback: (11)

Included with the B300F was a felt clunk. But neither clunk will fit in the JMP fittings. This is the felt clunk. And there is the JMP tank fitting. No way, no how are either of those clunks fitting.

So, also from Marc and GBR jets (the same guys that make the CAT), is a large fuel tank fitting hardware set. It is so very cool.


Its big enough to allow these big clunks in.

ravill

My Feedback: (11)

Here is the fitting installed on my tank.

Now, its time to let the hysol cure and time to test.