larry11

My Feedback: (6)

I know this probably has been asked before but I am going to ask it again as I didn't find it on a search.

How critical is it to use a hopper tank with a p20?

The only one I have is a 4 ounce and it will not fit in the model I'm putting it.

Will I probably have issues not running one?

Thanks in advance
Larry

Jetkopter

My Feedback: (1)

Check with Tam, hes has a smaller one

larry11

My Feedback: (6)

I know there are smaller ones available.

Just wondering if I'll have issues without.

Henke Torphammar

I don't run a P20, but I have other small engines. I never use a hopper, only a large felt clunk. In theory this makes the engine have the fuel it needs except when going straight down with full power. However in real life that is not a problem as you seldom use alot of power when diving down and when you do the fuel splashes around in the fueltank still making the felt clunk pick it up without bubbles.

There are alots of meanings about feltclunks, but one thing I do know is that they work very well for this application.

marc s

Whilst I do make a CAT specifically designed to be used with P20 and Kolibri turbines my view is if you have room to fit one - fit one.

The CAT or hopper will if fitted provide you with some added benefits, it will help if air enters the fuel line from the main tank and it adds a little extra fuel capacity and provides that 'reserve' margin.

marcs

Justflying1

As you know most people run bubble traps with turbines.

Henke Torphammar

Yeah, better with a correctly setup hopper, but not critical if useing a felt clunk :-)

Justflying1

Just something to keep in mind is that Jetcat does not recommend you restrict the intake on the pump.

Justflying1

Henke Torphammar

Yes, in theory it would not work, common sense But as the clunk holds fuel + the fuel splashing around in the tank keeping the clunk wet even when going downwards. It does work :-) The engines I use used to have the same pump as the P20 before changing to an in house design. That pump had no problems handling the restriction of the felt clunk. But we are careful always putting the valve and additional fuel filter after the pump.

Testing this in my funjet a sinterd clunk provided about 30sec of flight time before flaming out, a fuel magnet known from RC helicopters did empty half the tank ~3min flights, while the felt clunk empties the tank to the last drop every flight.

As I mentioned, there are alot of minds about feltclunks, but in this case it fills about the same task as the hopper. Only time I have had flameouts with a felt clunk is in my Swist racer when chickin out, ie going vertical up for about 2secs until it is a spec then diveing back nose down without any stick input. This puts the rules of nature back on track making the gravity hold the fuel from the clunk at the back of the tank.

Jgwright

It is a popular myth that you have to use UATs with jets. I have made loads of jets of various sizes and with single or multi engines. None of my planes or the planes of my pilot Dave Wilde have ever used a UAT. I have made my own pleated paper pickups but they are commercially available

http://www.gbr-jet.com/catalog/produ...products_id=83

I started with felt pickups but found they tended to shed hairs and were more prone to blockage than a pleated paper clunk.


John

siclick33

My Ducty/P20 has about 8 hours on it with no form of bubble trap and it has been faultless. A UAT isn't needed.

alasdair

Like John, I normally use a pleated paper clunk in the big tank.
In my O/D JayTee, and the Falcon 120 (Wren powered) and the CARF Rookie I used a single tank with a pleated paper clunk, straight to the pump. In my Wren powered JLGripen the last tank before the pump has a long narrow felt clunk, and normal unrestricted clunks are used in the two side tanks that feed in parallel into the centre tank.

The only time I had a problem with bubbles was when I switched to an Orbit clunk.

I have also used a UAT, in my first jet (Boomerang Intro) and my second hand CARF Lightning and CARF Eurosport and not had a problem.
But the simpler the fuel system, the less there is to go wrong and the less the restriction to the flow.

Henke Torphammar

I wonder if a hopper tank with it's tubeing or a felt clunk makes the most restriction.

ticketec

My Feedback: (2)

I've run my Wren 54 and K-80 without a UAT an use a sintered bronze pickup have had no problems either.

Thanks

Dave

Dr Honda

My Feedback: (4)

I have a wren 44 in a small T-45... and I was having bubble issues. So... I took out a BIG hanson bubble trap, and installed a felt cluck. (I found the Hanson was leaking) It was fine, and it flew it's first 4 flights on it, without a secondary bubble tank.


BUT......


Somewhere in the back of my head... I just didn't feel safe. The 44 is very susceptible to a flame-out, with the smallest bubble. And... since the fuel tank is so small the clunk line doesn't move much, and I feared that a long dive could kill it. So... I made a small header tank from a 2oz DuBro tank. I took the felt clunk out of the main tank, and replaced it with a standard cluck. Then... I put the felt clunk in the header tank.

In total... it cost me $10 to make the 2oz bubble tank. (with a felt clunk, and "Gas" stopper) And... it has been running great.

Jgwright

Tony

None of my various 44 powered planes had UATs or a header tank. You just need faith and a pleated paper filter. Many of my planes have had only 1 tank.

I have found more problems with flameouts due to electrical reasons than bubbles in the fuel. The more tanks you install the more likely that there will be air in the fuel pipe.

John

BaldEagel

I am also running a P20 without a header tank, just use a paper pleated filter as above, been faultless without the header.

Mike

bidrseed2

My Feedback: (2)

Ive used the orbit clunk as pictured by Alasdair in post 12 in my P20 model, without any problems.

You need a clunk anyway and i felt ( no pun intended) that it was a good half way measure between a clunk and a UAT.

larry11

My Feedback: (6)

Wow,
Great answers, information, and explanations!

I'm going to my local hobby store today, if they have what I need to make a small one I'll do that. If not, I'll just run without.
I'm leaning toward just going without though.

Thank you very much.

Dave Wilshere

No jet needs a bubble trap...but

Tank shape is everything...its how I decide on pick up type.

I generally add a hopper not as a bubble trap, but as a "use all the capacity" device. I use Felt clunks in 95% of my models, NEVER cleaned a filter yet.

My Airworld Cougar which started all of this with the first ever Lambert T32 #1 produced had no hopper, just an Stil/Orbit clunk. When I added the JetCat P-20SE in the summer of 2010 I still didn't add a hopper and it was fine. When I built my Habu 32 turbine I used a MAP Mini BT and in 139 flights it never flamed out. Felt clunk in the 20oz Kavan and the paper pick up MAP use. I could land with 6mm of fuel in the tank and hardly a bubble in the hopper.

To answer your question...depends on the fuel tank shape!

Dave

tamjets

My Feedback: (2)

I had over 150 flights using my 2oz air trap tank without a single flame out.

larry11

My Feedback: (6)

Hi Dave,
It's a 20 oz dubro on top of a ducty

marc s

Dave interested to know what this statement is based on, just personal experience or some documented paper? - if the latter I would love to see a copy.

From personal experience of working with Boeing and NASA they seem to think there is a good reason to use bubble traps with turbines we use in this hobby and I suspect have also done many trials and tests to have arrived at this conclusion.

I appreciate each will have their own view based on experience but it seems a like a very bold sweeping statement................

marcs