slick121985

My Feedback: (3)

Hello all,

I'd like to know if anyone else has measured the static thrust of their turbine and come away with a dissapointing result? I just recently tested the static thrust of a well reguarded turbine from a very well known engine manufacture, and on a 60 degree day here in Virginia, even turning 2K RPM faster than stock, registered 3 pounds less thrust than advertised. I feel ripped off. Should engines be up to par before before there shipped out? Should engines that fall below advertised values be sold at a discounted rate? I'm intrested in others experiences, and opinions. Thanks, Greg Murphy



P.S. Notice the profound lack of an engine or manufacture's name in this post. I'm intrested in results on specific Engine's, but please, no engine/manufacturer bashing. Thank you, and Merry Christmas to all.

pilott34

I had the same problem, and yes I felt ripped off. But hey, they dont put a pink case around them for no reason

slick121985

My Feedback: (3)

How down on power was it? Greg

pilott28

My Feedback: (27)

Can you describe how you measured the thrust? Was it on a calibrated dyno-like device?

slick121985

My Feedback: (3)

Admitedly just a primitive scale, but it was accurate enough to observe changes on the order of a pound in aircraft. Graduated in pounds, and tested installed (open air mounting) with aircraft sitting on the gear on smooth level ground, Greg

rhklenke

My Feedback: (24)

Greg,

What kind of airplane was it, i.e., did it have a tail pipe?

Bob

pilott28

My Feedback: (27)

Thanks for the response. When you say open air, I assume you mean an external mount with no pipe. I would think the other key factor to consider in this test setup would be downthrust. I would suspect if the engine is in a model like the Kingcat where there is a significant downthrust, it would tend to register lower on the scale than an engine that is horizontally aligned.

If you are seriously concerned, you might want to talk to the manufacturer and possibly send the engine back to them for testing. Could be some other problem that they can address that is costing thrust.

JONATHAN G

sorry to here you feel riped off if you buy a jet central turbine they do more than quoted thrust, i have been flying them for two years and have most off the range and the back up service you get is second to none plus now you get a lifetime warranty you cannot go wrong i went to the gtba comp and a jet central rhino was put on the test rig and at 117 rpm it pushed 17.6kg off pure thrust and the comp is open to all turbine manufacturers and home builders a like there is no BS because they all use the same rig and all the information is loged for all to see if all turbine manufacturers went to the comp we would all get a true data off the turbines we spend are hard earned cash on best regards jetman.

jason

My Feedback: (1)

I have also been doing some static tests lately. I have found that some engines are not producing what they quote. I have also found that a engine in a bypass is way down on static but in the air it's fine. For instance a P70 in my Bandit Arf is just about doing 14lb static but in the air it's not a 14lb motor pushing it around. I also checked a AMT mercury which we knew for a fact what the static thrust was on a bench, but when fitted in a Flash it was about 2lb down.

If you are feeling really bad about getting ripped off on the thrust side of it, I really would not recommend you testing the fuel consumption!I did that once and..[:@]


Jason

Miniflyer

Hi guys

turbine thrust itself is dependent on many factors. Mainly there is ambient temperature and air pressure (=elevation). With a turbine running on a low pressure, hot day at 6000ft ASL you can expect SEVERE thrust losses compared to the same turbine running at sea level on a cool day. Most manufacturers will specify their thrust ratings at ISO....
Apart from that: most manufacturers have a "spread" which is pretty wide. Some will produce high thrust ratings while other (identical) turbines produce less. This is due to the tollerances in parts....you might get a good one, or you might have bad luck and grab a bad one. You can always send it back and request improvement, as well as a test protocol under what conditions the thrust was measured.

Aother thing is static and dynamic thrust. Adding a pipe will cause losses of some sort. The static thust can be increased, though, by allowing more venturi air into the pipe. You can gain up to about 10% by this. However, this slows your exhaust drastically....high end performance is decreased a whole lot (effective thrust is dependent on the difference in velocity of exhaust air and
aircraft velocity....the higher the exhaust velocity, the more thrust will remain at higher airframe speeds). If you are looking for better high end performance then scoot the pipe closer to the turbine. Temps will rise a bit, and static thrust will drop, but on the top end you will be scooting along a lot better. A bypass will also help this effect a bit.

Best regards
Hank

Gary Arthur

My Feedback: (29)

Slick...I feel your pain.....Some manufacturers ensure their engines put out the stated thrust as a minimum before they advertise, others do not....

digitech

My Feedback: (10)

ok and now for the "real " testing.
i rather fly then talking
i flew a Flash with a Wren SS
it had unlimited Vertical.
what does that tell us?.
als the fuel consumption was full throttle and had 8+ minutes on 2.3 liters.
and that was IRL and not theoretic..

WrenTurbines

Some of you may be aware that the issue of accurate thrust and fuel consumption figures has been a concern of ours for quite a while now. We have independent tests (GTBA, magazines) showing figures for our engines which confirm our advertised figures. However, we are aware that some of our competitors over-estimate thrust and under-estimate fuel consumption and so we took our evidence for this to the UK Trading Standards, who control advertising claims, and registered a complaint.
Their response was that they could not do anything about it as there is no controlling body or international standards for miniature jet engines, so effectively companies can claim what they like and if they claim "It performed like this on our test equipment" there is nothing anyone can do about it. There are accepted rules and tests for things like miles-per-gallon claims in car adverts because the car industry has regulatory bodies who make the rules and do the tests. The miniature jet industry does not have any national or international organisations with these powers.

As we see it, this situation gives problems for both customers and manufacturers. For the customer, there is an uncertainty as to whether advertised figures are correct. For the manufacturers there is the problem that a competitor can make their engine appear more efficient and persuade the customers that they are getting a better engine when it is, in fact, an inferior product.

There doesn't appear to be much we can do about this situation, except to make people aware of it. It's very difficult for us as a manufacturer to do very much, as it could be seen as bashing the competition. We really need the fliers to take the initiative. Any ideas?

Sara Parish
Wren Turbines

Big Tony

Sara so what are you saying then ??

rcdriver22

My Feedback: (1)

The GTBA efficiency tests are held on a 'like for like' basis as posted in another thread today. Its happens fairly regularly when viewing the tests say in RCJI by Tom Wilkinson that manufacturers figures are often seen as optimistic. In contrast the GTBA winner figures are found as stated. (well done Sara's team)

Paul

Gary Arthur

My Feedback: (29)

I put a poll on to see if people feel their engine meet the thrust/fuel economy claims of manuafacturer's.

Miniflyer

That you're a wren dealer?

All jokes aside, i think Sara really has a point. The problem is finding an institution with which all manufacturers are willing to cooperate (also those who are knowingly cheating their numbers). The GTBA is a great point for reference, it's just nothing that has any influence on ads....
Also, a "test engine" can be selected so that it will accually produce great figures, whilst many of the production engines come not so close to these values....
Because of the "small" number of turbines sold compared to cars, i guess there is just no large economical interest in getting law enforcement on this subject...it remains in the hands of customers to see wether their product of choice is superior or not, or if they have reason to send it back to be re-worked to specs or given a refund....

Doctor J.

Sara,
AMT USA is and has always been willing to test the quality and reliability of our product with that of any other engine out there in our thrust class. I am glad to see you bring up the point of inflated performance numbers. I like to see how engines perform in the planes and I can tell you that this is what is important. Do two 18LB thrust engines perform the same in the same application? No! Do they deliver their power the same? No! The proof is in how they perform.

John Ligons
AMT USA, LLC.

Robrow

Here are the GTBA results, all engines were run in free air 'like for like' apart from Mark's g-booster which was installed in his fantastic huge F104 fitted with a Kramer modellbau static thrust augmenting pipe.

It was great to see more of the manufacturers entering engines this year and hopefully the numbers will go on and increase for next year but as Sara rightly says this has to be consumer lead.

Rob.

jescardin

My Feedback: (1)

Rob:

Regarding that chart, the engines are spooled up to full power just from start during the test?. I ask for knowing if the consuption is at full throttle or at mixed powers. If at mixed powers I suppose you have timed periods for different settings or do you really produce integrated figures of max. thrusts (thrust versus time) and then calculate fuel efficiency from total consuption regarded to the integrated max. thrust?.

If not done so, anybody may take a short bust of full power for a top thrust reading and then keep the turbine at a lower setting for getting low consumption figures. I would much like an aclaration so I may test my engines as per GBTA standars and compare with figures from that well respected association.

Best Regards from Spain,

Jesus Cardin

rjbob

My Feedback: (8)

I was working on the assumption that a calibrated fuel flow meter is used for measurements at any given power setting. No need to time or average anything.

Woketman

My Feedback: (6)

That's the way I thought I remember reading about their test methods once. The person demoing the engine can choose any throttle setting for the test, but it must remain at that setting for the entire test period. Obviously, if you want to show how efficient your turbine is, you would run it at the throttle setting that you believe yields the highest efficiency.

Woketman

My Feedback: (6)

And you do have to time it. You need to know the exact amount of fuel burned in a known period of time.

rjbob

My Feedback: (8)

A calibrated fuel totalizer can programmed to give an ounce/minute reading to eliminate timing. Of course the reading shouldn't be taken until the engine has stabilized at the given power setting.

Robrow

Jesus, there are 2 trophies to be won, one for best fuel efficiency and the other for best thrust/weight ratio. Engines have to be run at the same rpm for 2 mins minimum, so once the engine is settled at the selected rpm and the operator is happy the run is timed with measurements of fuel used and thrust taken.

If a particular engine has it's max efficiency point less than max thrust then 2 runs would be required at the appropriate rpm points.

Hope thats clearer.

Rob.