Tettra/FP.20

For all you guys out there considering a Tettra "Bubbless" tank to use with your Brett Buck FP.20 set-up: go for it. There's probably only one other person on Earth who might do it, and you know who you are, Dan.
I've been using this tank for a year and a half with an FP.25/Macs muffler and it has proved to be completely consistent and reliable. Last week I re-powered the plane with an FP.20. There's a bit less power than the .25, but the speed regulation is significantly better.
The FP.20 with it's stock (.267 id) venturi does not draw fuel as well as the FP.25 with a .248 venturi. Consequently, as the tank emptied I would get 5 or 6 ultra-lean, saggy, laps before the engine quit. I cured this by hooking up muffler pressure. Now the engine run is steady from start to finish with 1/4 lap of lean before shutdown.
I recommend the Tettra/FP.20 combination to anyone adventurous enough to try it. It has the advantage of being light weight and immune to vibration in addition to being completely consistent and reliable, as I said before.
Derek Moran

Thanks for the info, I really did not know what
a Tettra tank was so I looked it up and found some
info as listed below. I swiped this off the Darrol Cady Website.
http://www.darrolcady.com/Tettra_Tanks/tettra_tanks.html
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.
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The Tettra Bubbless tank has been the standard fuel supply for many years. The Formula One racers started using them in the early 90's. From there they went to Quickies and then to Q40. Bubbless tanks are found in most all of the racing airplanes today.
Bubbless tanks have the advantage of supplying a constant fuel supply to a racing engine with no chance of an air bubble or fuel foaming. The tank has a hard outer shell that is rigid. Inside of that is a latex bladder that collapses as the fuel is used from the tank. The pressure is between the hard outer shell and the soft bladder.
The Tettra tank in the picture is ready to wrap and install in a racer. Notice that there is only one outlet for the fuel and a pressure tap at the bottom. Taped to the bottom of the tank is a tongue depressor. It is there to keep the tank from moving too far ahead and collapsing or damaging the fuel lines against the firewall.

Good Lord! Unpredictability is one of the tools in my bag and here Derek has me completely figured out. This cannot be a good thing.

Yes, of course I have used Tettra tanks, in both 4- and 3-ounce sizes, on my ARF Flite Streak/20FP combinations. However, I had less than sterling results. Stupid, stupid, **stoopid** mistake, in a rush I grabbed a fuel filter known to be suspect, plugged it in, proved once again how highly durable are the 20FPs.

As I had a whole stack of various tanks to fiddle with, off came the Tettra tanks, on went Du-Bro SS-4s.

I have a defense, even if some will reject it out of hand: A good bit of the idea behind Brett's initial thinking, and a point of view I have since adopted, is that not only do we have access to a superior *system* in the 20FP tune-up as proven and then freely supplied by Brett, there is opportunity to assemble this killer setup from off-the-shelf components.

There's more to the story, now that tempers have calmed somewhat I will address it fully in the next day or so, but it should be obvious there is a crying need for a system approach which is not only highly effective, demonstrates the type of power delivery so sought after by our top fliers, **and** can be put together in a weekend without ordering any trick parts at all by mail.

Thus my current emphasis on using bottom-feeder tanks, plumbing just like the instructions, piping muffler pressure to them and flying. As mentioned before, both Pylon RST-4s and Du-Bro SS-4s are mounted to the inboard side of fuselage, and I have taken to liking them installed with narrow side of tank against the fuselage. Yeah, they work fine either way, but are slightly easier to mount on my models and with existing bracketry, plus plumbing is a little easier, a bit more reliable.

As the Tettra tanks, while readily available from Central Hobbies, do require mail-order sourcing, and are not at all cheap, I have been holding them in abeyance for the time when a lot more of us are on the same page in this 400-inch profile/20FP adventure.

Derek, tell me about the fuel pickup you are using. I know of guys running a length of silicone tubing which has cuts along its length, but I just terminate the hard tubing with a short piece of silicone to protect bladder from hard edges of tube. Tubing is installed such that it bends toward outboard side of tank, ending at about the mid-point of tank.

Also, as I am mounting Tettra tanks inboard, they are situated such that pressure inlet faces "up," simplifying the plumbing a little.

For those just reading along, do notice please, Derek's comment that the 20FP supplies less power than the 25FP, **speed regulation is significantly better."** Here's a guy who gets it, folks.

Just last night I was talking with a new friend and he's been though the 20FP discussions, proposes using a Super Combat Streak in Classic but with a 25FP. No, no!! If you're gonna sign on to the program, don't adulterate it by "going for more power."

Incidentally, several years ago I built a pretty nice Combat Streak (barenekd plans) for my 25FP. Nothing more than a fun sport model. Fitted it with a 20FP two weeks ago, can't wait to give it a try. Yep, may even fly it in Classic, just depends upon how much fun it is.

Oh, and thanks to jaco for the accurate description of Tettra tanks, the primary application and the picture.

Dan

P.S. Phil, I have not forgotten your request for sage advice, your whining about a shakey profile. The Tettra tanks might be worth trying. Or, as you are not known for spending money any too freely, DesignMan has had plenty of good input when it comes to "balloon" tanks.

>it should be obvious there is a crying need for a system
>approach which is not only highly effective, demonstrates
>the type of power delivery so sought after by our top
>fliers, **and** can be put together in a weekend without
>ordering any trick parts at all by mail.

I figure any yo-yo can get a good engine setup if you want to spend $500. I think it was worthwhile to consider how to do something 90% as good for $50.

>
>>it should be obvious there is a crying need for a system
>>approach which is not only highly effective, demonstrates
>>the type of power delivery so sought after by our top
>>fliers, **and** can be put together in a weekend without
>>ordering any trick parts at all by mail.
>
> I figure any yo-yo can get a good engine setup if you
>want to spend $500. I think it was worthwhile to consider
>how to do something 90% as good for $50.
>
>
> Brett

I would change only the tense: I think it *is* worthwhile to consider
how to do something 90% as good for $50.

If only I had had the good sense to take much more seriously the District 10 column, March/April 1999 Stunt News. Was it really five years ago? Sigh...

LAST EDITED ON Apr-14-04 AT 11:59 PM (CDT)
 
Dan,
My tank is plumbed "racing style" with only the fuel pickup penetrating the bladder. I did not install the "Fuel Charge" and "Air Ejector" vents recommended by Tettra. The fuel pickup is exactly as illustrated in the instructions. I chose the hole in the stopper that biases the pickup slightly outboard (the "C" hole), but otherwise did not add any bends. Since there is no air in the bladder and the bladder collapses toward the pickup, bending the pickup outboard is unnecessary. I did not slice nor did I dice the silicone pickup extension. In my opinion, it is nearly impossible for the collapsing bladder to block the pickup.
As I said in my opening post, I added muffler pressure only to cure a sloppy shutdown- which it does beautifully. The muffler pressure is run directly to the pressure inlet of the tank. Except for the ID of the stock muffler pressure fitting, there are no other restrictors or check valves.
FWIW, I use a Jett fuel filter in the feed line and OS spring tube clamps on all connections except on the inlet side of the filter. This is where I break the line to fill the tank.
Again, my experience with this tank has been completely positive. It has always enabled my engines to run consistently and reliably. I have no problems with the fueling procedure, in fact I enjoy it.
Oh, one more thing. I found the joint where the muffler halves meet leaks. I sealed this with a tiny bit of hi temp silicone. I reasoned that if this muffler is acting as a quarter wave pipe, then any leaks would destroy the resonance. Might be worth checking on your mufflers.
Ion,
I posed the same questions about the longevity of the bladder to Darrol Cady when I tried to buy spares. He told me he'd never heard of a bladder failure other than from careless puncture during assembly. He doesn't carry spare bladders, but I bought a couple spare tanks just in case.
Tettra (and Jett) bladder tanks should work fine with larger displacement engines. Go ahead and try one.
Derek

Derek, I've been "addicted" to Dubro SS-4 tanks for some years.

I adapt them for uniflow and use muffler pressure, and ampng all the "culprits" for the engine trobles I've ever had (very few, BTW) the only innocent party has been the tank.

Here at Rio we call glow plugs "the butler" (if you know about mystery crime stories, the butler is always the first suspect).

I've had troubles with fuel, with the consequencesofmy own stupidity (like "forgeting) to tighten the engine head, dirt in the NVA, bue never ever since I started using them clunk dubros clunk I had no tank trouble.

Plastic tanks usually won't develop a leak after a crash, unlike brass tanks.

The only drawback I experienced was the threaded part that "squeezes" the rubber plug goin' bad.

I solved that by using a 4/40 screw with a blind nut.

About those Tettra tanks, are they also good for bigger engines?

How long does the "bladder" last?

Have you been using them for long, and did they ever let you down?

I might get curious and try one...

Ion (curiosity killed the cat...) Muniz

If you want to fly at a sporting pace with your flight streak and fuel pickup is the problem, a five or even 4 0z. medicine bottle and a shortened fast combat bladder with probably two onces of fuel will always get you a consitant run.I am training my son and dauter in combat( which is the intended event for the flight streak)and recieved a pile of well flown slow combat models for which they could bounce.
The easest way to get consitant engine runs is with a bladder....
The hard tanks that were required are expensive are damaged easily and the neadles can be interesting. I'll try to attach the picture and I'm sure you could make it cleaner for your sporting pleasure.
Get your bladders from Phil Cartier at the corehouse.3or 4 should last a whole season almost,maybe more..

Derek,

You and I are setting up the Tettra tanks nearly identically. I know the instructions say to add tubes which I find to be extra and not required, in fact I reviewed the instructions last night, assuming there might be some interest in these excellent tanks.

For those who do not yet know exactly what we are talking about, the bladder is relaxed, is always relaxed unless the tank is over-filled. These *are not* Combat-style bladders, instead they are suction tanks, albeit in an unusual configuration.

(Ah, a hand is raised. Yes, we already know Jim Walker did something very similar many years ago. Thank you. Sit down.)

The single tube setup is preferred, as one really must evacuate the tank of all air prior to filling and the best way I have found is to first pull a light vacuum with a syringe, clamp line with hemostat. Fill tank with fuel only. Go fly. In the case of a tank recently flown, and using a 20FP, fill 5-ounce syringe with 3 ounces (or less) of fuel, break feed line at filter, hook up syringe, with syringe vertical pull light vacuum, fill tank.

The extra tubes and stuff shown above merely complicate the proceedings, along with giving more places for leaks.

When used with muffler pressure, residue from the muffler builds up in the tank. Not a big deal, especially with a small-bore motor. Suck the stuff out with a syringe fitted to pressure fitting which is integral to tank.

The Tettra tanks have been overlooked by many in the CL Stunt community, and while I do not propose them as a universal solution to all tank-related issues, in some applications they are easily the best and most reliable tanks around.

Further, the Red Menace (Svetlana) was discovered during the '89 Nationals to be using a relaxed-bag fuel tank, claimed (I think) that a great many Soviet Stunt fliers did so as well. During one of my trips we even discovered the exact size balloons required and I bought a bunch for approximately 19/32 of a U.S. penny. Unfortunately, they were worth exactly what I spent, even when back home...

Ye GADS! Someone has stolen my Avitar!

Oh, BTW, welcome Emil ...

Andy "Swordsman18" Tomasch