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HelicopterTurbine Helicopters › Two-stage turbine Vs Single-stage turbine ?
12-28-2009 10:48 PM  7 years agoPost 1
iandavidson99

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Ipswich, England

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Hi All,

I'm sure this must have been covered before so apologies for asking, but I wonder if someone could please help out...

The advantages a two-stage turbine provides over a single-stage unit in terms of vastly greater efficiency, as well as mechanically decoupling the rotor shaft from engine seem very apparent, yet new single-stage turbines are still being sold and integrated into model helicopters, so what advantage does a single-stage turbine provide which I’m not aware of?

Cheers,

Ian

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12-29-2009 12:16 PM  7 years agoPost 2
Jack Martin

rrApprentice

AKA HeliJack, Washougal, WA

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Availability.
Gearing (some)
Belts (some)
Size of package (shorter)

Advantage? I think it is all choice, price, fit.

Remember our Veterans.

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12-29-2009 12:30 PM  7 years agoPost 3
iandavidson99

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Ipswich, England

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Thank you Jack - that's great!

Cheers,

Ian

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01-17-2010 05:48 AM  7 years agoPost 4
kogibankole

rrKey Veteran

albuquerque/ibadan

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Okay; this is what I understand about the 2:

Single stage turbine - gets its power off of the compressor wheel, while still making huge thrust out the back. The thrust has to be diverted unless it will move theli. These helis have to have bigger fuel tanks and they also have shorter run times compared to the 2 nd stage turbine. They are very inefficient.

2nd stage turbine works basically by attaching a pretty nice ducted fan with many blades to the back of a turbine and have the thrust spin the blades. Gear the fan down to a reasonable rpm and you have massive torque. The exhaust basically just had all its energy drained so it doesnt have a lot of thrust anymore; and cant push the heli around as much. It is more expensive than sinagle stage, but more efficient and a must for someone yet to purchase one.

I think a mix of the 2 would be good. Use the mechanical energy off the turbine wheel to spin the tail blades, and the thrust from the exhaust to spin the main blades. Or maybe its not even possible thermodynamically !

if im not blade bogging youll find me pack puffing

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01-17-2010 08:25 AM  7 years agoPost 5
Darkstar1966

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Monaco

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Actually that is incorrect, a single stage turbine that you talk about actually has a takeoff on the main shaft, the examples of this are Pahl and Jaka. Pahl has a geared section at the very front of the turbine where the normal "nut" that locks the compressor to the mainshaft. Jaka has a gear section cut into the main shaft behind the diffussor, it then has a couple of step down shafts that are mounted to the back of the diffussor and then the output comes off the front as well.
Both Pahl and Jaka have very little residual thrust as they are power turbines and therefore the turbine wheel is designed for this rather than thrust. This is achieved by different angles for the turbine blades therefore they develop power not thrust and little residual thrust. Additionally they are more efficient as they have no throttle, they are designed specifically to run at the exact same rpm at all times so therefore the flow dynamics can be designed much easier.
When the gear train requires more torque the EGT just goes up and down depending on the load. Therefore you fly completely on pitch alone and no throttle curves are required,
Second stage turbines, aka Jetcat, Wren use the thrust from the turbine wheel to spin a sencond turbine wheel therefore have basically the same exit thrust as any "jet" class turbine based on their main turbine wheel dia. They are not efficent in any way as you have losses in the exhaust stream and also all the additional weight required to step the rpm down is normally by a planetary GB or other complicated gearing that is basically behind the hot section and therefore requires more plumbing for lubrication.
The weight is more and the efficientcy is less, in terms of fuel consumption they are basically the same and if anything as you are pumping more fuel to lubricate the geared section you have slightly higher consumption in the second stage systems.

Regards,

Gregory

"Anything that screws its way into the sky flies according to unnatural principals."

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01-17-2010 12:45 PM  7 years agoPost 6
kogibankole

rrKey Veteran

albuquerque/ibadan

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Hi Gregory,
Thanks for your inputs. The compressor wheel and the shaft you speak of are connected right? So we are talking about the same thing.

Also im pretty sure that the 2nd stage turbine is more efficient than the 1st stage and I have heard this from different mechanics and even read it online. You might be right about it. Im interested in this now.

Oh and I forgot to mention that 2nd stage turbines are based on how the full scale operate.

if im not blade bogging youll find me pack puffing

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01-17-2010 01:11 PM  7 years agoPost 7
Darkstar1966

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Monaco

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Yes you are correct, the simple point you seem to be missing is that model turbines do not have mutliple stage compressors and turbine wheels hence there inefficency. Each section of the compressor is designed for the mass flow of that stage, the exact same for the output end and the turbine wheels. Hence all energy is converted and little residual thrust.
Jaka's don't stip gears been using them for over 10 years and never had an issue, this is in models and various other systems (APU's and UAV's)and I think my current count is about 30 of them and again never had a single issue.
Have you ever striped any gears with a Jaka, would be interesting to know as you have stated you have one. You have mentioned this in your PM and I see no logic to PM me your thoughts, hence these points are being answered via a forum.
Only takes a minute to go through the forums to see the ongoing issues with JC and Wren and they are mainly used en mass due to there lower cost. Also the complexity of running gas takeoff is perfect in the real world but then again in the model side it is not hence the issues.
You also stated that JC strip belts and point is actually correct as it is a poor design to use belts in any form of turbine conponents, especially the drive train. Something you do not see in the real world again.
Do you actually know what the weight of a Jaka LE is or any Jaka model? You have indicated that your other turbines (JC and Wren) are 1.5kg lighter than a Jaka, so maybe you should actually determine the weight of a Jaka before you make such statements as it would seem you have the lightest turbines manufactured......period.

Regards,

Gregory

"Anything that screws its way into the sky flies according to unnatural principals."

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01-17-2010 02:45 PM  7 years agoPost 8
windy62

rrApprentice

USA

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Only takes a minute to go through the forums to see the ongoing issues with JC and Wren and they are mainly used en mass due to there lower cost. Also the complexity of running gas takeoff is perfect in the real world but then again in the model side it is not hence the issues.
Maybe I'm in the wrong forums, but would it be possible to point out where those problems are being discussed? Since it only takes a minute...

I am SERIOUSLY considering Turbine Power for my next AP ship and really do not want to add more trouble if it's not worth it.

windy62

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01-17-2010 05:30 PM  7 years agoPost 9
PETER ROB

rrElite Veteran

Devon UK

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It only takes a minute

Actually it takes less than a minute
Go to search and type, Wren, then search RR
Go to search and type, Jetcat then search RR
You will find all the posts on either turbine
Peter R

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01-17-2010 05:58 PM  7 years agoPost 10
Darkstar1966

rrNovice

Monaco

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Better to spend the money on a stabilised image system and solid downlinks for the AP work. Some say that the turbines are best for it due to less vibration yet the whole point for AP is playload and duration, with a good gas engine you will have the duration and will save a lot of weight on fuel which can then be used for superior image systems and high quality downlinks.

Regards,

Gregory

"Anything that screws its way into the sky flies according to unnatural principals."

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01-17-2010 09:36 PM  7 years agoPost 11
windy62

rrApprentice

USA

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Ok,

https://rc.runryder.com/helicopter/...?highlight=Wren

This one sounds pretty positive...

https://rc.runryder.com/helicopter/...?highlight=Wren

This one appears to have been some settings in the ECU that needed adjusting..Not sure how that makes Wren an inferior product.....

https://rc.runryder.com/helicopter/...?highlight=Wren

This one is positive about Wren, not so happy about the predator kit he recieved...

https://rc.runryder.com/helicopter/...?highlight=Wren

No problems noted here....

https://rc.runryder.com/helicopter/...?highlight=Wren

None here either...

https://rc.runryder.com/helicopter/...?highlight=Wren

Some more ECU adjusting....

https://rc.runryder.com/helicopter/...?highlight=Wren

Now here was a starter problem, solved by adjusting some ECU parameters...

I looked back over 5 pages of searching "Wren", and found NONE of what you speak...BTW it took more than a minute...

Let's try Jetcat...

Well over the same 5 pages, I found complaints about service, but those that HAD Jetcat turbines seemed pleased with them.

Checking over 5 pages of Jakadofsky saw many similar posts, good talk, a few for sale, but all in all, those that had them seemed very happy.

I suspect that "Darkstar" (Gregory) has some connection to Jaka or possibly some axe to grind.

Obviously this statement,
Only takes a minute to go through the forums to see the ongoing issues with JC and Wren and they are mainly used en mass due to there lower cost.
Has proven false, so I'm not sure how that looks to Jaka as a spokeperson falsely accusing other manufacturers....But it looks to me like bad business....

windy62

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01-18-2010 07:38 AM  7 years agoPost 12
Darkstar1966

rrNovice

Monaco

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I have had turbines over the years from almost every manufacturer and I also made my own designs, therefore my comments are made from experience not allegiance. I'm sure you know best so good luck with it.

Regards,

Gregory

"Anything that screws its way into the sky flies according to unnatural principals."

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01-18-2010 09:14 AM  7 years agoPost 13
WIRLYBIRD

rrVeteran

CAPE TOWN / SOUTH AFRICA.

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Well it seems every now and then the same old squabble comes up! I have the same two Jet Cat single stage turbines in two NH90's 30 pound hellis , and in four years , I don't have any issues with them what so ever. IMHO it's very much how one uses the turbine + model of their choice , I fly mine in a very scale manner , and collective usage is very gentle , there for I think less stressful on the belts. What I'm saying here is , that there are hard drivers , hence the same goes for helli pilots , and in the club I belong to they only replace parts after a crash!!!!
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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01-18-2010 09:23 AM  7 years agoPost 14
Bhavik

rrApprentice

London

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I have the jetcat SPH5 in a cuatro and am very pleased with both the engine AND the Jetcat service, Max of Jetcat and Dave Wiltshire from Motors and Rotors (UK dealer) are both great guys to deal with.
The Jetcat is also very user friendly to setup, no messing about with ECU numbers etc.

This statement is based soley on my experience and NOT Hearsay.

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01-18-2010 10:01 AM  7 years agoPost 15
WIRLYBIRD

rrVeteran

CAPE TOWN / SOUTH AFRICA.

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Although I've had nothing for repair , when the kero start first came out my one turbine from Graupner didn't have the required clearance between the combustion chamber and the casing , and there for the kero start would not fit. I sent an E-mail to Jet Cat who asked me to return the turbine , and an up to date combustion chamber would would be fitted at no charge. Now to me that is good service , how ever , I decided not to fix what isn't broken , and is still purring along like a baby.
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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01-19-2010 03:52 AM  7 years agoPost 16
windy62

rrApprentice

USA

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Gregory I'm sure your experince is vast, however your statements made here are still false..

In my search, as you suggested, I found a whole lot of people very happy with their Wren or Jetcat engine, single stage or 2 stage, so what does that mean for your experience?

It means to me that your experience is questionable, or meant to be derogatory to those manufacturers who have sold many engines to many happy owners.

I'm sure Jakadofsky engines are very nice, but I am turned off by the tone of your comments.

Just tell me why jakadofskys are better without telling me about "their" supposed problems....Tell me why I should spend almost 3 times as much for an engine with fewer possible uses in pod and boom or scale applications?

windy62

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01-19-2010 07:43 AM  7 years agoPost 17
PETER ROB

rrElite Veteran

Devon UK

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so what advantage does a single-stage turbine provide which I’m not aware of?

Ian, In very simple terms, a set of mechanics, included in the price,
With the 2 stage, you will have to buy some thing to support your turbine/gearbox, there are a few conversion kits out there priced at around £500.00
Peter R

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01-19-2010 07:50 AM  7 years agoPost 18
PETER ROB

rrElite Veteran

Devon UK

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windy62,Back off, after reading some of your post's, all you seem to want is an argument
Gregory's preference is Jakadofsky, mine is JetCat,others prefer Wren,Its there choice,
Some of us are fortunate to have experiences with a lot of different turbine combinations, and are therefore able to make a comparison, then an informed judgement as to what suits them best
Peter R

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01-19-2010 10:55 AM  7 years agoPost 19
Vinci

rrNovice

South of France

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Interesting thread, however it is well documented that 2 stage turbine engines develop more power and are more efficient than single stage units. I find this also to be true also in the model world, which is unsurprising. My advice to the man with the cameraship is to go for 2 stage power because you will need it. Wren Jetcat and now Phal do 2 stage engines.

Life is Richness

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03-19-2010 05:52 AM  7 years agoPost 20
andyman_sf

rrApprentice

San Francisco, CA - USA

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Its possible that many companies do 2nd stage because Jak has the patent for a reliable and efficient 1st stage and has decided not to license it to others.

Anyway I prefer jako myself and I have no proof of which is better. I can see owning a 2nd stage turbine from any manufacturer but I don't see myself ever buying anything with belts on a turbine.

With that said the only way to see which is more efficient is for someone to do some controlled experiments and provide proof. Till that happens talking about turbine efficiencies of model helis is just hearsay.

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