RobinLeblond

Hello all !

I’m just curious about whyis IV bag or other flexible fuel tank are forbidden in turbine jet?

Thanks !

rcjets_63

My Feedback: (4)

It is my recollection that there was concern, should the model crash, that the bags would burst or be punctured resulting in a large loss of fuel containment and an increased probability of fire. Hard tanks (either plastic molded tanks such as typically used in gas/glow models) or molded fiberglass/Kevlar tanks are believed to be more impact resistant.

Regards,

Jim

RobinLeblond

Thanks Jim, What if the bag in enclosed in a solid and sealed container, are they now allowed?
(I'm asking because they have a great bubble risk reduction.)

rcjets_63

My Feedback: (4)

I would think that completely enclosing the bag in a hardened casing would be fine. At that point, the casing is really the tank and the bag is essentially an internal diaphragm.

Jim

RobinLeblond

Yes, tha's exactly what I mean (an internal diaphragm) ! Thanks Jim.

sysiek

My Feedback: (176)

Personally I think the IV bags are much stronger than the fiberglass or cevlal fuel tanks the IV bags are tested to free drop from 25m do concrete flor try to do the with the cevlar fuel tank ,I did use the IV bags for my racing gasoline boats and the much more resistant to shacking and harsh then other fuel tanks ,I think the biggest inconvinance is to hold them in one place so the don't travel inn side the jet.

Like2fly!

Are turbine tanks typically pressurised?

drac1

My Feedback: (4)

I use the Tettra bladder tank for my YS pattern engines. YS's are susceptible to stopping if air bubbles get to the engine and I have never had a issue using them. I think for a jet the same type would work great.
Like2fly, as the engines use a fuel pump, I'm pretty sure there is no need to pressurise the tank.

Jetmodeler

Answer from the day, IV bags were being utilized in early jets as fuel tanks by simply laying them inside the fuselage, unsupported, free floating, with the turbine right behind them. These scary setups only last 2-3 years but something had to be done.
Jim

2walla

My Feedback: (10)

If installed properly, i think you are correct that they are probably better and stronger.

RCFlyerDan

My Feedback: (54)

It is because here in the USA, it is in our AMA Safety Code under turbines, Regulation 510-A #8, plasma bags are NOT allow. Thus, no insurance! Don't care what you do in Canada or other parts of the World.

SAFETY REGULATIONS FOR MODEL AIRCRAFT
POWERED BY GAS TURBINES
Approved by the AMA Executive Council (EC)
on April 27, 1996,
at the Board of Directors meeting
amended by EC on April 9, 2011
… (noted in bold)
It’s the flyers responsibility to comply and the CD’s responsibility to enforce these regulations!
All items apply to all configurations unless otherwise stated!
EFFECTIVE April 9, 2011
Airframe Requirements
1. The model may be equipped with production engine(s); kit built engine(s), built in compliance with
AMA
Regulations for Assembly and Operations of a Kit Built Turbine Engine for RC and CL Models
; or nonproduction
engine(s), built in compliance with
AMA Rules for Design, Construction, and Operation of
Non-Production Gas Turbine Engines for RC and CL Models
.
2. AMA retains the right to exclude any engine, (individual or type), which is believed to exhibit a safety
concern.
3. For Turbojets and Turbofans single engine static thrust
 shall not exceed 45 pounds; multiple engine static
thrust
 shall not exceed 50 pounds combined.
4. For RC fixed wing aircraft: The maximum velocity will be 200 mph.
For rotary wing aircraft: The output power of the turbine shall be governed such that the rotor head speed
does not exceed the manufacturer’s recommended RPM for any rotor head com
ponent.
For control line aircraft the gross weight limit is 20 pounds. The maximum aircraft velocity allowed is
100 mph.
5.
It is recommended that multiple engines equipped with propane start be segregated or
partitioned to prevent
cross-ignition of exhaust gases.
6. For RC fixed wing aircraft: With the exception of hand-launched aircraft which have no undercarriage
and with a flight weight under 7.5 pounds wet, the model shall be able to come to a controlled stop on
command with the engine at idle on a level hard surface.
For rotary wing aircraft: The rotor head must be disengagable from the power source and remain
stationary either from the use of a throttle kill mechanism or a clutch system.
7. Fuels are limited to kerosene
, diesel and/or propane unless approved in writing by AMA.
8.

Manufacturer’s rating
Academy of Model Aeronautics
5161 East Memorial Drive
Muncie, Indiana 47302
(765) 287-1256
– Business
(765) 289-4248
– Fax
(800) 435-9262
– Membership Services
http://www.modelaircraft.org
Copyright © 1996
110409 Turbine Safety Regs.doc Page 2 of 4
The fuel tanks shall be of rigid construction with consideration given to burst and puncture resistance.
Plasma bag fuel tanks are not allowed. Consideration shall be given that non-metallic fuel lines may not
be able to contact hot parts of the engine as installed. The fuel system shall have two fuel shut-off
provisions, one of which is manual and the other one must be remotely operated. An ECU operated shut
down is compliant as a remote shut-off if it closes with loss of power.

SECRET AGENT

My Feedback: (18)

I guess then by the rules, you can stil have a plasma bag as long as it is encased in a tank made of rigid construction. Not sure if that would be of any great benefit, but by the rules seems to be ok.

schroedm

My Feedback: (1)

2. AMA retains the right to exclude any engine, (individual or type), which is believed to exhibit a safety
concern.
3. For Turbojets and Turbofans single engine static thrust
 shall not exceed 45 pounds; multiple engine static
thrust
 shall not exceed 50 pounds combined.

So does this mean a large percentage of guys in the US are flying uninsured??? I guess this has been update?? What are the rules now?

drac1

My Feedback: (4)

The benefit of a bladder tank is you get no air bubbles. This may mean that there would be no need to use a air trap??

Bladder tanks are available for IC and I have been thinking for quite awhile that they would be perfect for turbines. I'm surprised there isn't a commercially available one suitable for turbines.

George

My Feedback: (57)

Under the Large Model Airplane Program there are exceptions.

All AMA turbine regulation (AMA website document 510-A) shall be followed in the LMA
Turbine Class, unless otherwise specified in this appendix.
The maximum thrust for the LTMA-1 class is 75 pounds.
The maximum thrust for the LTMA-2 class is 90 pounds.

schroedm

My Feedback: (1)

Thanks George.

Does that mean every model running a 200/210/220 turbine (>45kbs) has to go through this large model program??

George

My Feedback: (57)

Not necessarily, it is solely dependent on weight.

1. Large Model Airplanes (LMA) are classified as follows:

LMA-1 are all non-turbine powered model airplanes weighing 55 pounds (25 kilograms) to 77.2 pounds (35 kilograms), with fuel, ready to fly.
LTMA-1 are turbine-powered model airplanes weighing 55 pounds (25 kilogram) to 77.2 pounds (35 kilograms), with fuel, ready to fly.
LMA-2 are all non-turbine powered model airplanes weighing 77.3 pounds (35 kilogram) to 125 pounds (56.7 kilogram) with fuel, ready to fly.
LTMA-2 are turbine-powered model airplanes weighing 77.3 pounds (35 kilogram) to 100 pounds (45.4 kilogram) with fuel, ready to fly.

Regarding any planes that do not fall under the LMA Program AND have the engines you mentioned, the remedy is to simply "turn down" max RPM.


With that said, we've slid off topic slightly, but should be able to come back to fuel bags/tanks now.

Art ARRO

My Feedback: (5)

Hi Robin,
The plasma bag fuel cells were disallowed shortly after the introduction of liquid fueled model turbines due to a rash of crash-induced fires. Previous turbines used propane fuel in a sturdy steel container, resembling a large thermos jug. It was theorized that the plasma bags would rupture or tear on crash impact from any sharp edges found within the model fuselage. These bags were simply filled to capacity and literally stuffed into any free space within the fuselage. Molded fibrglass/aramid/plastic fuel tanks were deemed to be more resistant to tearing/rupturing but usually split at thier seamlines during a crash.
Turbine shutdown, even a few seconds before crash impact, greatly reduces the probability of fire since the primary ignition source is eliminated. Fires can still occur from secondary sources such as batteries shorting or cooking off.
As for the maximum allowable thrust under AMA turbine rules, this is 45 lbs for a single or 50 lbs combined for multiple turbines-excluding Large Turbine Model Aircraft (LTMA) where the limits are 75 lbs and 90 lbs respectively, As George stated in Post 17, tubines models weighing less than 55 lbs (wet) must have their maximum thrust reduced to comply with the 45 lb single or 50 lb combined AMA limit. The pilot would have to document the "turn down" to these values using manufacturers data, but in reality I've never witnessed this at any AMA sanctioned event or chartered club field.
Rgds,
Art ARRO, AMA Leader Member, Contest Director/ Fixed Wing Turbine Waiver # 2570.

schroedm

My Feedback: (1)

"tubines models weighing less than 55 lbs (wet) must have their maximum thrust reduced to comply with the 45 lb single or 50 lb combined AMA limit. The pilot would have to document the "turn down" to these values using manufacturers data,"

Interesting how the rules don't really keep up with the new technologies! With everyone on the forums (rightly) hammering the safety/insurance/cover peg till it bends lately, it seems odd that the combination of 55lb wet with >45lbs thrust (pretty common nowadays) is probably being broken at most events.

As for the plasma bags, I reckon if they were installed correctly they'd be stronger than a kevlar tank. Who here would drop a full kevalr fuel tank from 20m and expect it to stay in one piece??

George

My Feedback: (57)

I don't think the rules will be reviewed or changed unless the JPO pushes the issue. At least that seems to be the case in the past from what I remember.

schroedm

My Feedback: (1)

But until then aren't people technically uninsured if found to be running >45lbs in a (up to) 55lb model? One for JPO/AMA to deal with I guess. I just find it odd that the US are sticklers for rules/litigation/safety etc yet ignore this elephant in the room ;-)

George

My Feedback: (57)

Technically!

schroedm

My Feedback: (1)

Oh! LOL

George

My Feedback: (57)

I think for the most part, people have been responsible, and there hasn't been a negative impact by the few infractions. If that were to change, then maybe...

I run a 180, so no problems!

George

My Feedback: (57)

I would think there are just too many plane-specific tanks for this to be profitable, but perhaps some of the generic (square, rectangular or round) tanks with internal bladders would be potentially viable.