If you don't use a UAT, what clunk do you use in the tank? I am only asking about simple single tank installations, not mulitple tanks with wing bags etc:

Mike

<span style="color: #ff0000">EDIT: Please only poll if you don't use a UAT or the results become meaningless</span>.

UAT!

<span style="color: rgb(255, 0, 0); ">EDIT: </span>Wanted to let you know I did not vote when I stated UAT as the post title does suggest.<span style="color: rgb(255, 0, 0); "></span><br type="_moz" />

I use just a 1 litre Dubro tank in a little Bobcat 50 with no UAT. Generally I have no problems but I have had a couple of flame outs which I think was engine settings rather than a lack of UAT. The engine is a manual start Wren 44 &amp; the install is super simple, tank, pump, shut of valve , filter, engine. I do get some tiny bubbles under full throttle but I posted in a thread on the subject &amp; no one came up with one, definate answer why. It doesn't seem to worry the engine. The clunk is a felt type. - John.

John

What clunk do you have in your main tank? please poll, or if the option is not there let me know and I will add it to the list.

MIke

Edited post - John.

Does it make much difference whether you use a UATor not as to the type of clunk in your final tank?

Iwant the best clunk Ican in the final tankas Idon't want air to pass through.Ifair did pass through, whether it ends up in the UAT or engine, it is not a good thing. If you want to know people's preference over clunks you will get a much bigger response if you open the question up.</p>

It make a big difference, the UAT (universal air trap) is supposedly designed to take out any air that is in the system, if you do away with the UAT you are then reliant on the clunk to do this job, I use the Orbit clunk as it is a felt and membrane clunk also designed to exclude air from the feed line, I have never seen any air comming out of my tank using this clunk.


Mike</p>

Originally I used a felt clunk but did have the odd flame out. However since discovering pleated paper filters I have only used them for my tanks, not had any flameout problems and they will suck up almost all the fuel in the tank. I have never used a UAT.I have useda pleated paper filterin single tanksinstallations in anumber of planes without any problems. I like the simple installation with one tank with the pump really close to it.I trust them enough to use them in the Fei Bao S-27 with the 2 P60 engines where I have one tank per engine and one shared tank and the Horten with 2 MW44 engines which has 2 tanks per engine. Always surprises me that more people do not use them.

The Orbit type clunk does the same job but has less surface area so may get clogged more quickly. So far I have not had to renew any of my clinks and have even reused them on subsequent models.

John

Well I have taken the UAT out of my Elan and just use the Orbit Clunk in the main tank, after four flights I have not had a flame out or even a hiccup, I will still keep an wary eye on the pipework just in case, and I also ensure that the feed to the pump is full before I start the turbine and there is no existing air in the fuel lines.

John

I understand what you are saying about the surface area, but as my fuel is filtered four times prior to getting into the tank I think I have that one covered.

Mike

We have all been using homemade header tanks will zero problems.
I use a 6oz dubro tank, the pickup to the turbine is a piece of streight brass tube in the middle of the tank, extending into the tank to about the middle also.
A fill pipe to the bottom, and the feed from the main tank is a brass tube bent to the top of the header tank, with a piece of tygon tube cut in a V, just so it can just rub against the tank top. I then draw a ring around this on the outside so I know where it is and I make sure all my bubbles go out that pipe when filling, the tank stays completly full at all times and, none of us have had a bubble related stoppage.

We also add a fuel filter in the fill pipe to the filler connection. As a mark two version the next one I do I will solder a sintered brass clunk onto the end of my centre engine pickup pipe, just for added filteration.

Xairflyer

So you are using a 6oz dubro tank as your UAT, John Wright is using a paper filter in the main tank and no UAT and I am using an Orbit clunk with no UAT, this obviously reduces the complication of the install and reduces a weight that you have to find room for.

Mike

we sell about a 1200 uat,s to endcustomers a year , for the last 4 years use for jets , helo,s , cars and boats. petrol and jet fuel
we also sell them to a large UAV-Drone company in Germany. they use 3 x 25 KG turbines and 3 UAT,s to get them asap to 10000ft without flaming out.
so i think without being biased here is my opinion

all users that purchased a UAT:

from wich about 90 % uses a brass clunk (17mm in diameter)
since the uat acts allready as a giant small particle filter. (the uat bag comes from a automotive factory and is used also in fuel tanks to dry the tanks up without bubbles to the fuel pumps..
this filter is much better then any felt or fuel filter can stop.
the orbit clunck (Skill tree saw clunck) has a to little pickup frams and CAN clog up very soon .
since SKILL they use only use a liter an hour , this is fine for them but not for us..
the Simjet uses a Husqvarna fuel clunck , works well but is to light and can give pickup problems.

i also now people that fly them without UAT , also works perfect if you ask me.
but with the UAT there is this little more protection you have.
uat in combination with multiple tanks is the most used system out there.

most problem i see with fuel pickup problems are:

1 . Chinese Tygon , gets hard as concrete after a month
2 . small fuel lines , connect your tanks wit as LARGE as possible connections )tygon or 6mm festo , from one tank to another
3. clunck in tanks DONT use Tygon it can fall forwards and wrap itself around itself , use also Festo 6mm.. (G -forces will make sure that when you are flying the fuel ALWAYS stays backwards)
4. Air to tanks use large diameter for airing your tanks!
5. to long fuel lines from and to your pump , can cause cavitation and CAN look like a fuel leak..
6. using small cluncks or to light cluncks



TIP: i hear lately about using a Pitot tube for venting your tanks , and in the same time pressuring them a little.... cant hurt! and can solve some peoples cavitation and vacuuming their tanks..

My post was more of "a simple replacement to commercial UAT's" rather than having or not having a UAT/header.

On that I would feel having a header is still more reliable, as "empty" should still be a full header where as a turbine will majority of times stop before it fully empty's a conventional tank.
The landing weight of a full UAT is not an issue either as you will not empty a single tank setup in flight and will have a minimum of about 4-8ozs left anyway after each flight for the fear of a flame out.

There is no reason why a single tank with a good clunk should not be used and one of our guys P80 boomerang has been like that with nearlly 200 flights and no issues, but he does still always land with sufficent fuel in the tank.

I never could understand or see the need for all these fancy commercial bubble bags and traps, but like the idea of a header more as a reserve than anything else and gaurantees the pickup to the turbine to be fully in fuel at all times.

John

What brand/type of paper filter do you use

Sandor

Thanks for your input, the UAT that I have does not have a bag in it, just a paper fillter on the end of the solid brass rod suspended in the middle of the tank, what I have done is run a full tank of fuel through my turbine using the Orbit clunk and was amazed at how much fuel it took out of the tank, even when the fuel level had dropped below the top of the clunk the fuel still come out of the tank without any bubbles in the line, the residue fuel left was just that which was beyond the end of the clunk. I can see the use of them with multiple tanks, but with a single tank it looks to me from my own observations that if you use a good clunk which I think the Orbil felt and membrane one is and you have a good installation a UAT is not essential, by the way I am using one of your tanks with the Orbit clunk also bought from you.

I think its a bit like power boxes/match boxes those that use them say they are essential and in a multiple servo large jet they have there place, but in something like the Elan sports jet???

Mike

Xairflyer

If you want to land with a reserve of fuel in your tank you can fly for a little less time or get a bigger tank, I don't feel you need the complication of three more connections in your fuel line just for that.

One thing that was mentioned in RCJI when they tested the Graupner G Booster was how tollerant it was to air in the fuel line, this they put down to the Kero start or at least it was a contributing factor, this I have found to also be true of Kero start JetCats, even it there is a bubble in the start line my JetCat seems to ignor it and still go through its start sequance without problems, perhaps this is one of the reasons why I am not getting a problem without a UAT.

Mike

My Wren SS was shipped with a felt clunk as part of the "kit" and it was recommended to be used without a UAT.

I have also found this engine very tolerant to bubbles in the fuel line. I recently landed and found the aircraft lacking power to taxi back. When I checked the UAT was only 1/2 full and the main tank was dry. There were some bubbles in the line but the engine was still runnning. Did a normal shutdown and reduced my flight timer a little....

well be carefull
large engines wil run on large bubbles without problems or "foam" fuel as i call it
BUT dont try it with a small engine with a small fuel consumption they will flame out on you 5 times as fast then a lets say 120-160 engine

Sandor

Godd advice, the proportion of fuel too air would be far more critical with a smaller turbine, I have to admit I have only tried this on my JetCat 120SX the P80SE I will try once I get my winter hack ready.

Mike

No problem

about the Orbit clunck when did you purchase it?
i dont have them anymore.
if you bought anything from us it should be a Felt clunck Large (elan tank)
and yes they can work fine without a UAT.

I think I bought the Clunk about last December or thereabouts, you correct of course the Elan tank did have a felt clunk in it which I took out and replaced with the Orbit.

Mike

The orbit clunk seems to work well for a season or two and then seems to clog up. Been using the O.S. felt filter for over 5 years now, high quality stuff,over 500+ flights on different airframes, comes in 2 sizes, the small one fits into dubro,sullivan type tanks and the bigger one fits into the UAT type bottles.

Chaitanya.

I have used felt filters in all of my petrol engined airframes in the past with good results, but they do not have a membrane around them to hold fuel around the felt when the level drops, I have noticed that when the fuel level gets low in the petrol engined airframes the engine will start to play up, but does not give up, by using an Orbit clunk this does not happen so it must give a more consistant fuel flow at low levels, this is what made me use one on my turbine, I will keep experimenting and extending the flight envelope to see what happens.

Mike

do a Search here on Orbit cluncks you see the pro,s and con,s

Sandor

Did the search and it seems that most who where getting problems with the Orbit Clunk where using over a 120 size turbine, perhaps that was just a case of the Orbit clunk not being able to supply enough fuel for these, it seems strange that air is able to enter the feed pipe when the clunk is fully immersed in fuel, I would not have thought that the fuel itself had enough air in it to cause this and my thoughts are that the air is entering at the front of the tank through the joint at the cap, what do you think?

Mike