<p>As I see it, there are two differences.</p>
<p>One is that the main tank is gradually emptied during a flight, so the air pocket can be quite large. The UAT is small and fed from the tank, so it's always full.</p>
<p>The other is that an UAT is not just a tank, it's a pressure accumulator. Inside the tank is a 'duck bill shaped sack' that can change volume. Presumably this is designed to handle surges in demand, or brief pauses in supply from the main tank.</p>
<p>I don't see any mechanism for removing air that reaches the UAT. Maybe it's such a small amount that it's not a problem. Maybe that's why the clunk/filter thing is fixed near the middle of the tank. It never needs to suck up that last bit of fuel (because this tank is always full) and you want to keep it away from a small air bubble that might form near the top.</p>
<p><a href="https://i.sstatic.net/NfN1M.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/NfN1M.png" alt="duck bill shaped sack" /></a></p>

CC BY-SA 4.0
2022-10-19T07:58:59.867Z
2022-10-19T07:58:59.867Z
Robin Bennett
<p>I am confused about what an Ultimate Air Trap is.<br />
I understand somewhat that its task is to remove the air bubbles in the fuel feed to an engine. But how does it work?<br />
How is it different from a normal RC Fuel tank? For example I am unable to see the difference between the following two. (The first is a normal fuel tank, the second one is a UAT.)</p>
<ol>
<li><a href="http://www.rchyderabad.com/plane-accessories/fuel-tanks/fuel-tank-for-rc-planes.html" rel="nofollow noreferrer">Fuel Tank</a></li>
</ol>
<p><a href="https://i.sstatic.net/6QwFy.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/6QwFy.png" alt="enter image description here" /></a></p>
<ol start="2">
<li>UAT</li>
</ol>
<p><a href="https://i.sstatic.net/HpRh3.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/HpRh3.png" alt="enter image description here" /></a></p>
<p>or <a href="https://pilot-rc.com/jet-uat-tank/" rel="nofollow noreferrer">this</a>:</p>
<p><a href="https://i.sstatic.net/mWsiT.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/mWsiT.png" alt="enter image description here" /></a></p>
<p>Internal Parts:</p>
<p><a href="https://i.sstatic.net/JcIlz.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/JcIlz.png" alt="enter image description here" /></a></p>
<p><strong>Other Questions:</strong></p>
<ol>
<li>Why is the tube to the rear end in the case of the fuel tank but only to the middle in the UAT? Also, is there a reason why is it hanging mid-air (not touching the wall)?</li>
<li>Is the white part in picture 4 a clunk or some kind of filter? I have read of Bubble trap in microfluidics is it a similar device?</li>
</ol>

<engine><fuel>
What is an Ultimate Air Trap (UAT)?
Atharva
# What is an Ultimate Air Trap (UAT)?

(Asked by: username_0 on 2022-10-08)

I am confused about what an Ultimate Air Trap is.  
I understand somewhat that its task is to remove the air bubbles in the fuel feed to an engine. But how does it work?  
How is it different from a normal RC Fuel tank? For example I am unable to see the difference between the following two. (The first is a normal fuel tank, the second one is a UAT.)

1. [Fuel Tank](http://www.rchyderabad.com/plane-accessories/fuel-tanks/fuel-tank-for-rc-planes.html)

[![enter image description here](https://i.sstatic.net/6QwFy.png)](https://i.sstatic.net/6QwFy.png)

2. UAT

[![enter image description here](https://i.sstatic.net/HpRh3.png)](https://i.sstatic.net/HpRh3.png)

or [this](https://pilot-rc.com/jet-uat-tank/):

[![enter image description here](https://i.sstatic.net/mWsiT.png)](https://i.sstatic.net/mWsiT.png)

Internal Parts:

[![enter image description here](https://i.sstatic.net/JcIlz.png)](https://i.sstatic.net/JcIlz.png)

**Other Questions:**

1. Why is the tube to the rear end in the case of the fuel tank but only to the middle in the UAT? Also, is there a reason why is it hanging mid-air (not touching the wall)?
2. Is the white part in picture 4 a clunk or some kind of filter? I have read of Bubble trap in microfluidics is it a similar device?

**Tags:** engine, fuel

---

## 1 answers

### Answer by username_1 on 2022-10-19. Score: 1

As I see it, there are two differences.

One is that the main tank is gradually emptied during a flight, so the air pocket can be quite large. The UAT is small and fed from the tank, so it's always full.

The other is that an UAT is not just a tank, it's a pressure accumulator. Inside the tank is a 'duck bill shaped sack' that can change volume. Presumably this is designed to handle surges in demand, or brief pauses in supply from the main tank.

I don't see any mechanism for removing air that reaches the UAT. Maybe it's such a small amount that it's not a problem. Maybe that's why the clunk/filter thing is fixed near the middle of the tank. It never needs to suck up that last bit of fuel (because this tank is always full) and you want to keep it away from a small air bubble that might form near the top.

[![duck bill shaped sack](https://i.sstatic.net/NfN1M.png)](https://i.sstatic.net/NfN1M.png)


---

