olnico

Dear all.

I would like to give you some update on the latest research about fuel systems for the new generation engines.
We are slowly going further beyond the concept of high flow systems to ultra high flow system.

The reason for this is that our engines are getting bigger, with the current LTMA-1 regulations allowing up to 75 lb static thrust and LTMA-2 up to 90 lb static thrust, capped to the aircraft wet weight plus 5 lbs.
Although people are not allowed to use more than this thrust, we do provide precise thrust-to-RPM graphs that allow the modeller to down-rate the engine to comply with regulations and supply a proof for it.
These engines, even de-rated, can use very high peak flow. This is because the latest ECU and fuel pumps are fast and over sized, which means that they are able to supply very high peak flow when the acceleration condition dictates it.
In this case ( large de-rated engine on fast acceleration ), maximum cavitation vacuum could be reached on high flow systems and create a momentary condition for a single burst of kerosene bubbles that could generate a flame out condition.

I also found out that for the latest generation product ( JB-220, B-300F ) that do not normally require de-rating, fuel restrictions could occur over time in bends when Tygons harden or with slime/ dust accumulation ( from the vent line ).
I recently serviced a flying target that had all new Tygon lines, cleaned up air traps but was showing poor results on the vacuum gauge. The engine was still performing OK, thanks to our professional Ultra High Flow system but was getting on the edge of cavitation point. After scratching my head for a long time, I inspected the inside of the fuel vent fitting. I found out that remains of fuel + oil had evaporated, leaving a greasy deposit that had trapped lots of thin sand dust, almost clogging the vent! this was extremely difficult to detect, as hidden in the aluminum fitting and we only got along with it because of the flow capacity of the system downstream the clunk and dual vent system ( redundancy ).

So, because of all of these points I have decided to bring to the market redundant/ Ultra High Flow fuel systems.
Redundancy comes with the new Ultra High Flow fuel stopper system that I introduced recently here.

http://www.ultimate-jets.net/collect...stopper-system

That system is unique in many ways ( CAD, CAM, 3D print process... ), but most importantly in that it allows the modeller to use dual vent AND dual clunk systems with dual UAT!
That can be used on twin engine or single engine models!
Of course, no ECU system is capable to drive dual pump systems as of now, so a Y fitting has to be placed just before the pump.
This product is labelled UHF because it can be used to setup a redundant parallel system ( like the one I am designing on the Mibo A-10 ) or it can use 1/4" ID Ultra large Tygon tube ( 6.4 mm ID ). 1/4" lines are now the norm for us on 400 and 500 N engines and I have setup a few B-300F with these lines as well with complete satisfaction.

The other new product is a Ultra High Flow fuel clunk that is being released to the market now.
This one is labelled UHF because it is designed with an ID of 5.0 mm ( 0.3 mm higher than the 3/16" Tygon line ).

http://www.ultimate-jets.net/collect...uhf-fuel-clunk

Make no mistake. This is not just another clunk. I spent a full year designing and fine tuning this component. The reason why I did this is because I believe it is one of the most important item of the fuel system and very often the weak link in the chain.



Here is the description of the though process that went into it:

ID: 5 mm


This is very important. The internal diameter of the clunk is slightly bigger that the diameter of the XL 3/16" Tygon tubing ( 4.8 mm ). This forces the tube to expand further before the fuel enters it and reduces entry turbulence, thus risks of cavitation. This is the largest ID available on the market.

Barb OD:: 8.92 mm


The large barb makes a very good clamping effect for added safety. I found out that only one barb makes the best sealing against fluid leak. However there is less grabbing effect. Thus the following feature. This is the largest barb on the market.

Safety wire zone length: 12 mm


The cylindrical section after the barb is large and enables multiple safety wiring. This extra length also makes it much easier for the safety wire operator and allows the use of thicker wire. This is the longest safety wire zone available on a clunk.

Body max diameter: 15 mm

This makes the clunk compatible with the standard fuel stoppers available on the market ( Dubro, BVM ). It is a good size to pass the clunk through the stopper hole, even if not perfectly clean line it is often the case on kevlar tanks and allows to pass two of these easily in the UHF stopper..


Taper: 30 degree



I found this to be the optimal angle to grab fuel in most tanks corners. It also keeps the tip of the clunk heavy enough so that it always faces down.

Taper edge: 0.3 mm



This is an important feature as a thin edge reduces pickup turbulence and together with the proper taper angle, will allow you to suck the last drop of fuel from your tank. The edge is continuous with no notch that tend to suck air bubble. The minimum edge thickness is a function of the material strength used and machining technique. By using high density brass and ceramic insert cutters, we can achieve this ultra-thin wall while keeping strength at the tip.
This is the thinnest edge available on the market.


Material:



The HF clunk is machined from high density 360 brass alloy. This is very durable, does not degrade in kerosene/ diesel/ alcohol and offers excellent cutting and finish with ceramic tools. Tensile strength is 17 000 PSI. Our alloy is ASTM B16 certified and quality traced.
Weight 40 grs/ 1.4 oz:



Allows for a very high driving force that will bend stiffer large diameter Tygons that have aged.

A super large version that just fits the UHF stopper as single and with an ID or 1/4" will be coming on the catalog very soon.

olnico

As always with fuel systems, the whole supply follows the chain rule. The system is only as good as the weakest link. This is why it is so important to pay close attention to all the components in the system, make then easily serviceable and with a very clean routing.

One of the essential point about clean routing is the use of proper clips. I designed designed some PYCABS clip for this to let you place the fuel line and remove it easily but most importantly, these using our unique PYCABS material that is 100% CA gel compatible!
This makes installing the clips on the fuselage walls a matter of seconds and offer super strong bonding capability ( the glue always stays put on the PYCABS side when removing a clip ). Thy are sized to offer easy clipping of the line, yet allows it to slide and does not pinch it!

http://www.ultimate-jets.net/collect...e-pycabs-clips

olnico

I also believe that we are the only ones on the market to offer 3/16" as well as 1/4" products that are designed to work together.

Tygon tubing:
http://www.ultimate-jets.net/collect...on-fuel-tubing

Ultra flexible Viton tubing:
http://www.ultimate-jets.net/collect...on-fuel-tubing

Brass tubes:
http://www.ultimate-jets.net/collect...hf-brass-tubes

olnico

Also, I see more an more people being victims of the communicating vessels law with the modern air traps.

Here is the description of the phenomenon as described in the new Ultra high Flow article to be released in my blog very soon.

"On the latest designs, capillary drag is very law, allowing the fluid to travel between the air trap and the tank. This is especially true with the larger air traps I designed a few years ago that feature large plated paper filters.
Plated paper is great in that it offers very little resistance to fluid travel, thus reducing risks of cavitation. However it also allows the fluid to escape from the air trap and the filter, thus allowing air to enter.
This would happen if the level of the pickup line is placed somehow at the level of lower that the top of the fuel filter unit when the tank is empty.
This can happen in case of rotation of cylinder type air traps, or if the model is place on its side for storage or transport.


In the case shown above, air has entered the filter section and will enter the pump at some point. Even if the air is purged, micro bubbles can stick to the membrane and enter the pump. It the case above, after purging the air, a thorough high flow test while tapping on the air trap will be required to remove these bubbles."

FenderBean

Oli you have an extreme talent of taking something very simple and making it sound very sophisticated LOL I cant keep up with you, nice stuff you make and I completely agree. Even with my short time in jets I have learned that having a proper fuel setup will save you tons of hassle and possibly flame outs. (knock on wood)

olnico

Lol.

Unfortunately fluid mechanics is nothing like simple, but I am trying to keep things that way.
I could talk about correlation between fluid dynamic viscosity and internal shear at molecular level leading to the cavitation process, but that's no the point.
I prefer to offer simple and coherent solutions as seen in the fuel hardware section of my web site.

Also not that I have updated the technical article on my blog with practical solutions and recommendations.

I added 3 chapters there;

Ch 5. Avoiding restrictions
Ch 6. Fuel pump considerations
Ch 7. Servicing considerations

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

olnico

I have just updated the blog with the latest version of the " Fuel system for RC jets" technical article.

Tons of hands-on advice and techniques as well as a large table with fuel hardware compatibility with engines by thrust class.

http://www.ultimate-jets.net/blogs/f...considerations

jason

My Feedback: (1)

I could not agree more...

ravill

My Feedback: (11)

Oli,

One of the things that I shy away from with fuel clunks is, having only one flat end where the fuel gets drawn from.

As our fuel systems are under significant vacuum, considerable G forces and in varying geometries in the sky (aerobatics, etc...), these are some conditions that can cause a clunk to be "sucked" to the back, side, bottom or top and cause a flame out.

I was having that situation in my ultra bandit when it was new. Every time I pulled into a vertical with full throttle, I would have a flame out. I was using BV's clunk (rolled, but flat edge at the pick up) and my fuel tank line was just long enough (and my head tank flat enough) that under those loads, the clunk was sticking itself to the back.

I cut the intank line a 1/4 " shorter and cut grooves onto the tip.

That said, I now have a completely new clunk and fuel system. Just something that makes me think about the clunks I pick.

mr_matt

My Feedback: (10)

Has anyone seen a measurable drop in full power pump voltage when switching to these very large diameter fuel fittings?

Nice BVM drawing, makes me want to buy another BV kit just to get back to these quality drawings, plans and manuals.

http://www.bvmjets.com/images/K7300-32_34.pdf

olnico

You won't see a drop in pump power/ pump voltage at any thrust setting as the non digital ECU control the pump by voltage.
For digital/ brushless pump it is a different story.

olnico

A big thank you to all the customers who purchased the new UHF articles just after our market introduction.
This is very heart warming and motivates me to carry on with my research and development of new products.
I am doing my best to send a personal email to all of you as fast as I can and offer you a special deal as early adopters.
Just bear with me for a few days as I have a huge rush of orders.
Thanks again

olnico

I have published an article in the "fuel systems for jets" blog on the two methods used for plumbing tanks:

Traditional semi rigid high flow tank plumbing

This method is used to avoid reverse bending the line that could get stuck at the front of the tank.
Our UHF fuel stopper is used to accept 3/16' ID or 1/4" ID fuel lines.
Our UHF fuel clunk is used in 3/16" or 1/4" ID size.

In this example, I am using a transparent sports bottle just for the purpose of showing the line behaviour. DO NOT use such a bottle in any flying model!

1. Measure the length of your tank from the stopper to the end wall. Substract 1/2" or 10 mm.



2. Cut two sections of 3 " o four ultra flexible Viton tubing. They will be used to connect the stopper tube to the long brass tube, to the clunk. Cut a section of brass tube in the measured length minus 2".

3. Insert the Viton lines on both ends of the tube by 1". Spray the tube with Zip Kicker before inserting. This will ensure that the line is lubed along the tube and slides properly. Zip Kicker has no silicon and does not contaminate kerosene ( higher risks of fuel stick clogging ).



4. Insert the fuel clunk on the line. The clunk has an aggressive barb and will require more pushing than the tube.

5. Safety wire all connections as per chapter 1.1.2 above.







The example below shows how the clunk line used to be made with a smaller clunk and stiff tygon tubing. this type of setup doesn't bend much and hardens with time till it becomes completely stiff.



Note that with this setup, the clunk will never be at the front of the tank. This means that on long dives, the pickup line will suck air. This is acceptable if you put your engine to idle in your dives. However hardcore aerobatics pilots should not use this setup as it will put most air traps to their limits.

Here is the seating of the clunk in the tank in the horizontal position:



In the vertical nose up position:



It is imperative to verify that the clunk stays 1/2" away from the wall. Otherwise there would be a risk of sucking the clunk flat against the wall and immediately starve the engine.



The vertical nose down position:



In this position, the clunk will feed air to the air trap. At this point the air trap will play its role and provide buffer fuel to the engine. If you like to keep your engine running full power in the dive, then we'd recommend that you use the next setup.

Newer full flexible high flow tank plumbing method

This method was not recommended previously as there were no proper heavy clunks and flexible enough lines to avoid reverse bending the pickup. It would eventually get stuck at the front of the tank, resulting in a fixed pickup point ( flameout at the end of the flight guaranteed ). Additionally most plastic lines ( including Tygons ) would harden with time and render this scenario more likely.
However our new specific UHF clunk is heavy weight while compatible with regular fuel stopper diameters and allows for a super flexible Viton line to never get stuck in a reverse bend scenario. It is also optimally designed to avoid pinching the thin wall Viton line. Additionally the super high quality Viton tubes that we use are completely unaffected by immersion in kerosene or diesel and will never harden. The weight of the clunk was carefully chosen and tested so that the Viton line would never kink when it is driven in the corners while keeping high line flexibility ( thin walls ).

This plumbing technique is in fact very simple:
Our UHF fuel stopper is used to accept 3/16' ID or 1/4" ID fuel lines.
Our UHF cross drilled fuel clunk is used in 3/16" or 1/4" ID size.
A long section of ultra flexible 3/16 " or 1/4" ID Viton tubing is used to connect the stopper tube to the clunk. The length should be so that the clunk is just 1/2" short of the tank end wall.



When you are done with the plumbing, dry test the tank. Just turn it in all positions. you should hear the heavy clunk fall on the tank wall every time. The heavy weight of the clunk and fluidity of the line/ setup should be obvious. Safety wiring is essential here as the clunk is constantly falling and pulling on the Viton line...
Note that with large tanks of 8" diameter or more, the fuel clunk line can reverse itself into the tanks, which is acceptable. Just make sure that the tank does not have any blobs of glue that could block the clunk in position.



Also note that in this case, a cross slotted clunk is necessary to avoid having it sucked flat against a wall and completely blocking the system. This would not happen on the previous semi rigid scenario if setup as described.

Note that I have published a full tutorial on how to safety wire fuel lines here:

http://www.ultimate-jets.net/blogs/fuel-system-for-jets-considerations

Edgar Perez

My Feedback: (13)

Thanks for taking the time to publish!

olnico

Rav, we have a cross slotted version of our HF and UHF clunks for flexible pickup line configurations ( see post above ). For the exact reason you mention here!

Viper1GJ

My Feedback: (20)

Oli,

For 200-300N turbine fuel systems do you prefer the 1/4" tygon tubing from the main tanks to the air trip or the clear 8mm "hard" tubing from the main tank to the air trap? I have been told that the negative pressure could "suck in" the softer tygon tubing and cause a restriction. Any data either way?

Thanks,
Gary

olnico

Good question. We had to check this 5 years ago when we started using the B-300F in our UAVs. The level of vacuum at which the 1/4" Tygon would collapse was far beyond the bubbling point of the fuel. If I remember well, the 1/4" tygon was collapsing at 750 mb of vacuum and the thinner and softer 1/4" Viton at 700 mb of vacuum.
Kerosene starts bubbling at 600 mb of vacuum.
I will try to dig in my archives to find the test reports.

Viper1GJ

My Feedback: (20)

Oli,

For my question above I was really thinking about the 3/16" ID Tygon pictured below not the 1/4" ID tubing. I want to know if the 3/16" Tygon is OK from main tank to air trap without worry of collapse when using my K210 or B300F. It is much easier to work with than the clear 8mm tubing.






For the larger 1/4" ID Tygon, I have never seen a clunk, any tank fittings, or air traps with 1/4" ID fittings. What are you using for the UAV ops and are these fittings, air traps, and tanks available for the B300F for normal RC jet use?

Thanks for taking the time to post the all the info on the fuel blog. I learned a lot from reading your work.

Gary

Viper1GJ

My Feedback: (20)

Oli,

Ok, after studying the UJ website I see that the UHF stopper set and UHF clunk takes care of the tank side for 1/4" ID tubing but what about an air trap that has the UHF fittings?

Also how do you connect the pump to the air trap fitting since the pump nipples are smaller than the UHF fittings?

Thanks
Gary

olnico

3/16" ID is almost impossible to collapse under vacuum. Only a professional vacuum pump for composite bagging can achieve this.
1/4" ID is also very difficult to collapse as it requires 800 mb of vacuum to achieve so.

We do carry a full line of fittings and a complete solution for either 3/16" or 1/4" systems.
1/4" fitting equipped air traps do not exist yet but we are working with Tom Cook to offer this to the market very soon.

The B-300F new pump offers a 6 mm OD push-on fitting. If you use a 6 mm brass tube in there, you can then hook up a 1/4" Tygon tube to it with a little section of 7 mm tube as a barb ( 1/4" is 6.35 mm ).

olnico

I found these pictures and added them to the blog as well:

1/4" Viton line under 700 mb of vacuum:



1/4" Tygon line under 800 mb of vacuum:

olnico

One of the very interesting property of the mega 1/4" clunk associated with the super flexible 1/4" viton line is its ability to bend and stay in the fuel a lot more than traditional semi flexible lines.
The weight of this clunk is chosen so that it never drives the line hard enough to pinch it. Additionally, the cross slotted version is perfect for flat wall tanks as it will never get sucked against them.

Viper1GJ

My Feedback: (20)

Oli,

Is there an operational advantage when running the B300F to using 1/4" ID tubing rather than 3/16" ID tubing.

My setup in the 1/5 F-16 will be two saddle tanks feeding a center header tank which feeds the air trap. How would you set this system up and what size hardware do you recommend from your experience with the B300F? My B300F fuel pump has the 6mm nipples.

I am ready to start acquiring fuel system hardware so I would appreciate your advice.

Thanks,
Gary

marc s

Guys, I have been making a CAT-U (Ultra 450cc) product for these larger turbines for 3+ years now, no doubt as Oli mentioned others will follow but the CAT-U has been used on many B300's, P300's, Big block AMT's and military targets and drones for many years so if you want a "UAT" for these 300N+ turbines I have them already available.

They are made to order but the parts to assemble are in stock.

The barbs are 5mm ID with 7.5mm OD. The picture below is the original version, V2 now has black FR4 end caps, chrome barbs and a black ABS mounting plate.

If you want info just PM or email.

marcs

olnico

The most important factor when running a jet engine is to offer a fuel buffer quantity of 30 seconds flow at full thrust and a proper clunk system that is able to minimize air pickup.
This is true for all engines but is an enhanced requirement for large engines like the B-300F.

The 30 seconds requirement equals to an air trap capacity of 500 cc/ 17 fl.oz
I highly recommend using the Extra Large JMP air trap for these types of engines.
This air trap has been designed from ground up for for UAV applications and has demonstrated superior strength and resistance to cracking, as well as very high flow capability.
We are coming out with a version of this air trap that offers true 1/4" barbs ( 6.4 mm ID ) up to the pump.
http://www.ultimate-jets.net/products/jmp-air-trap

With a system like this one, you can have a complete supply chain in 1/4" up to the pump.

On the clunk side of things, it is extremely important to be able to feed the system with as little air as possible.
For this purpose, I strongly recommend using ultra flexible Viton tubes with an all flexible clunk line. However, this type of setup is trickier than a semi-rigid line.

. First of all, the clunk will be able to go everywhere in the tank and it is essential to ensure that it cannot get stuck in a corner. Also, safety wiring must be dome properly to avoid catching the twists.
. Then the clunk weight must be sufficient to drive it in all directions ( overcome the stiffness of the line )
. The clunk weight must not be too heavy neither or the Viton line could pinch
. The suction drag of the vent system must be low so that the tank does not get into much vacuum ( the 1/4 " Viton line collapses at 600 mb of vacuum )

I recommend a vent system that uses the same fuel line diameter ( 1/4" or 3/16" ) as the pickup line and a careful fastening of the line up to the vent.
I have seen vent lines pinching because they were left floating in the fuselage.
I have designed a specific clip for the fuel lines that is using our PYCABS material, which is meant to be glued with CA gel.

https://ultimate-jets.myshopify.com/...ucts/351995881

For the vent itself, I designed a fitting that is suitable for 3/16" or 1/4" ID lines:
http://www.ultimate-jets.net/collect...vent-fitting-1