Futura SE Turbine, different belt-gearing available?

[Danyboy]

Hello, dear enthusiasts!

As noted in a different thread, I am a real happy owner of a FuturaSE-mechanic, which is powered by a Wren54 Turbine.

My problem is, that the gearing is nowhere near optimum:
I have to de-rate the engine to around 110'000 to achieve a headspeed of 1450RPM, a very nice setting if you ask me, crisp but not yet murder-style...
Problem is though, due to the low RPM, that the engine does not seem to be agile enough to compensate quick enough for load changes: In steeper turns, I loose quite some headspeed followed by almost an overspeed in the straight-flight between the turns...
If I go to the (currently set) Maximum of 140'000RPM, I'm somewhere above 1700RPM. Together with the 800mm blades, that's way too high for my taste...
Installation is original and consists of a 325mm-belt, a 22t- and a 42t belt gear.

So what I'm looking for, is a source for different belt-wheels, drop-in replacements for different gearing would be my wish, since I do neither have the installations nor the will to start manufacturing and modifying... ;)
If I can change the gearing, I'd rather go to 150'000RPM to get something between 1450RPM on the rotor than go anywhere below 140'000 to prevent overspeed...

Anyone knowing if there's a supplier?
I'd be happy for every information!

Cheers,

Daniel

[Andy4124]

I used to have a Futura se powered by .70 size and upgraded to .90 size. I seem to remember i managed to get parts from Robbe to change gear ratio. Skyline Models in High Wycombe England should be able to help. They helped me back then!!!! Although it was a few years ago....

The other thing i thought.. What is you FADEC accel and Deccel set to. It sounds like the engine may be tweeked to stop underspeed and overspeed.

[heliman53]

Danyboy, sounds like you are on the right track however I have found that if you limit max rpm toabout 137000-140000 you will have plenty of power and you get better fuel milage as well as less bearing wear. Just a thought, if you gera for those numbers I think you will have a good combo. Craig B

[Sparkhead]

Hi Daniel,

I had mine setup with a 21 tooth clutchbell and a 48 tooth rear pulley but this was with a Jetcat SPH5 so I don't know what the different output rpm's are between that and a Wren.

You can get the 2 different rear pulleys 42t and 48t and you can get the clutchbells from 21t throught to 27t and then a 36t so you should be able to get what you need.

[Danyboy]

Mick,

I already asked Robbe in Europe and haven't gotten an answer so far...

Could you please give me a source, name, linke, whatev' that I can trace?

I expect gear-box output of 12'700RPM at 140'000RPM of Turbine...
What's the figure for JetCat?

Andy, thanks a lot, I'm already eagerly looking forward to an answer from them...! :)
I agree I could tune the FADEC, but I don't see much sense in fine-tuning there, when the gear-ratio does not match at all... The higher the turbine-RPM, the quicker the RPM response to fuel-flow-changes, therefore the more agile it gets, and therefore the FADEC has an easier job to control...
I also admit: I'm a helluvalazy SOB... Too lazy to tune it in now and then redo it when I've gotten the correct gears... ;)

Craig, thanks for the pep-talk! :) Yeah, I already know now that I have power to spend... I have 6kW packed in a 8,5kg-Heli... I know of another model with a 3kW JetCat in a 13kg-Scale-Fuselage, and already that one flies quite ok... :)
Now if only I could get the RPM-control/response to where I want it, I'm cool... :)

Folks, thanks a lot for your support!

Cheers,

Daniel

[Peter Wales]

If you need 1450 rpm and have 12,700 you need a reduction ratio of 8.75:1

There isn't a combination of pulleys which will give you exactly that, but, I dont think you will get 12,700 rpm. As you increase the turbine rpm you increase the power disproportionally and I think you'll get more than 12,700

Here is a pdf of all of the combinations you can get with Robbe pulleys and belts.

http://data.robbe-online.net/robbe_pdf_en/S4112.pdf

You will certainly end up with a 48 tooth pulley, I use a 22 tooth clutch on my SPH5 powered Cuatro and run 1650 rpm on the head maximum

[Danyboy]

Hello Peter!

Thank you very much for the link!

Incidently, about 5mins before I saw it, I received mail from robbe in germany, containing as well that datasheet...

To be honest, I'm no more sure about the gear-box-speed...
Actually, I feel quite lost, especially since I might have some early production series gearbox...
Actual calculation - assuming stock gearing 1:9.29 on the heli-side - would mean, that with a measured headspeed of 1480 (at neutral collective) I'd have 13'750RPM on the gearbox...
Which is only able to deliver 14'500RPM at full turbine speed according to website?
Which would be with the trusted roar of 160'000RPM instead of the lousy whistling 100'000RPM I have dialled-in at the moment?
Calculating down the measured headspeed of 1780RPM with stock-gearing at 140'000RPM of turbine, I must have had 16'540RPM on the gearbox...

*scratchinghead*
Shouldn't that thing explode with such numbers...?
;) :glasses2:

So for the moment, I'll follow the motto printed on the US-dollars bills:
In Sara we trust... :)
Though one thing's for sure: I need bigger number for reduction, and there's only two more available: 9.73 and 11.1.

Cheers,

Daniel

[Peter Wales]

My recommendation is simply to change the 42 tooth pulley to a 48 and leave the clutch bell as it is. I think the Wren and the SPH5 will produce similar results and my SPH5 runs very nicely with that combination.

I have a David Owens conversion under way in England and it uses a 23 tooth clutch, but I will make sure I have a 22 tooth pulley on hand as well when I get back to that.

The gearbox output shaft is designed to emulate a 60 or 90 glow motor so the designed rpm will be around the 15000 mark. When this system was first designed it was in a Futura with a 60 motor and 680mm blades. Turning 1750 rpm on the head was not a problem.

Fortunately blade design has kept up with turbines and I am very happy doing silly things with my turbine Cuatro turning 1650 on the head using NHP 800mm Razors. I have had it running at 2200 rpm, briefly, but nothing blew up!!! :badair:

[Sara]

Daniel,

Your engine has the original SPS gearbox from Simon Peckham - I remember when Adrian bought it. Peter Wales also bought a SPS Wren at about that time, with the same gearbox, so he has experience with a very similar engine to yours.

Sara Parish
Wren Turbines

[Danyboy]

Sara,
Now *that's* a word of confidence...! :)

I will definitely go for the 48-wheel.

IF I can fit it in the heli...

I have some doubts that it will drop straight in, there might be some machining needed on the frame, but only arrival of parts will tell.

I ordered the 21-bell as well (now that's a rhyme... :) ), as well as the longer belt, just to make sure...

I do not yet have any expirience about the power increase and therefore whether the rotor-RPM really increases linear in relation to engine-RPM or if the rotor will climb a bit higher due to increased flow and efficiency.

And another, quite personal reason:
I do like the 1450 headspeed I have now, simple as that. :)
Combined with the 8,5kg of takeoff-weight, it packs quite some power without the screaming sound of the blades I had with the original headspeed, while still maintaining that crisp control that I'm used from the smaller electrics...

As said, only delivery will tell on the right choice and its mechanical possibility...

Peter,
Can you please tell me the feeling of constant-headspeed you have?
When flying somewhat sporty eights, in high-collective turns, toward the end of the turn, does it bog? When levelling for the short straight part, does it overshoot? Much? Little? Not at all?
Just trying to somehow increase my pre-joy... ;)
I'm so excited I'm almost shaking... :)

Cheers,

Daniel

[Peter Wales]

The SPH5 headspeed does not vary! I dont fly 3D hard enough to make it change but I would think a roll would cause a change as you go through zero to negative pitch. I had someone watching it at 1650 and it stayed exactly where is was set. I have tried flips, sideways loops and pie dish maneuvers and its constant.

However, as I am a scale guy, I would never admit that :D

I have never managed to bog either the Wren or SPH5, they both have way too much power, although, in my case, both were set at maximum rpm on the turbine so they had planty of room to move into power if they need it.

The only thing I am still having a hard time over is the contantly varying turbine note as it keeps the headspeed constant. I am used to the HP5 and the PJW LE having a constant turbine note and to hear it varying is a little unnerving, but I am getting used to it

[Danyboy]

Peter,

Thanks a lot!

That is really reassuring!

Boy, I start getting really excited... :)

Will report back as soon I have the new gearing installed... :)

Cheers,

Daniel

[Sparkhead]

Hi Daniel,

Sorry about the late reply but this is what I had with my setup which was originally using the same frames as you have.

S4591 21t clutchbell
S4652 48t pulley
S4112 390mm belt.

These are all genuine Robbe parts ans RCMarket should be able to get you all of those.

I found the belt tension to be perfect with this combination so I don't know how you will go with bigger clutchbells. The belt tension on these setups is reasonably important, so don't get the belt to tight.

I'm no expert on turbines but I think that the lower gearing the better as the second stage would be spinning faster which would make it easier to keep a constant rotor rpm. With the above combination I could get up to around 1700 rpm on the head and the power was very smooth.

[Danyboy]

Mick,

I COULD KISS YOU FOR THAT!!!

But since I live here and you live there, I'll delegate this duty to your wife/girlfriend/lover... ;)

I have already placed an order for those three things with robbe germany, all in stock and express-delivery...

I was quite unsure though about the belt-tension, so I ordered the 290mm and already started to construct some kind of device which would act as belt-tensioner, should it be too long: If it's too long, you can add tension by an additional spring-loaded wheel, but if it's too short, you can't stretch it...

You're saying that 48t-wheel fits in the frame?
That's really reassuring, I had some doubts there as well and started to prepare myself to make some mechanical adjustments to the frame...

Oh man, I'm really looking forward to next weekend... :)

Thanks a lot for your help guys!
I'm *sooo* excited...
I hope I can get anything done next week at work since my mind might wander off all the time... ;)

Sincerely, wishing you all a nice weekend,

Daniel

[Sparkhead]

Hi Daniel,

No the belt tension will be perfect with the 390mm belt. The only problem you might have is getting the clutchbell nut undone. I had to split my turbine in 2 to get to the big nut so I could put a socket on it. I couldn't hold the fan tight enough to undo the clutchbell nut. The Wren might have a different setup where you can get a spanner on somewhere else. I'll try and get a photo on here for you to show you the belt setup.

[Sparkhead]

Heres a picture of the belt setup with the 48t rear pulley, 21t clutchbell and the 390mm belt. Don't take any notice of the different top frames these were changed over after I originally had the same frames as you have. The bearing rail and the lower frame structure remains the same.

[Danyboy]

Yeah, Baby...!

Change completed and SATIS! :)

As mentioned and recommended by Mick, I went for the 21t/48t/290mm combination, belt tension really is sweet!

Though I am still not at my beloved 140'000RPMt for 1480RPMhs, but when adding full pitch..
Ooh boy...
When before, I could hear her spooling down, now it's really steady...

Bad thing is: I'm grounded... :(

Reason being a tiny air-bubble that seemed to have made the "veni-vidi-velcro"-move and remained in one of the connectors, the valve or even the pump.
I did a ground-run for TX- and RPM-adjustment and had the expected flameout, and though everything was fine.
So off I went for a quickstop with fuel and gas.
After 2mins of hovering and zoom-climbing, just when I wanted to go to forward-flight, I had flameout in about 3m height and subsequently my premiere in autorotation...
All appears fine except the landing-skids, which appear to have absorbed most of the shock.

I'll be experimenting with headspeeds, but for that, I need to experiment with some kind of RPM-logger, to check inflight.


Therefor:
For the purpose of inflight-RPM-Datalogging, can anyone recommend one system or the other?

Cheers,

Daniel

[Danyboy]

Well guys...

Just want to let you guys know, if it saves only one more pilot the trouble I went through, I'm happy...

I think it is safe to say: Problems solved...

Since my last postings, I had lots of nasty flame-outs.

First I thought I had them fixed by venting thoroughly (all in all 3 tanks) the fuel system.

Went well for 3 to 4 flights.

Back at my usual field, doing wing-overs, getting into the groove, climbing real high, have the tail turn, readjust a little, coming down, shut down. Lucky me it was in the most favourable position and speed to autorate, the spectators thought - after those wingovers - that I just wanted to show off...

Fixed this, done that, mainly suspected the fuel-tube just at the fuel-tank, where a Festo-elbow was pushed onto pure brass.
My last autorotation was during my military service on the airfield of our UAV's, all went well, just until a buzz-by, where - in level and steady flight - there was flame-out. Autorotation was ok, again I had lots of speed and sufficient height, but the farmers had just cut the grass, and one skid set down of the remainings of a grass-bush, the other skid went a bit lower onto pure soil, which was enough to tilt the rotor enough to catch the laying hay and - Wufff... On her side she went. First official crash with rebuild. That was when I grounded her until *really* fixed.

So I really went after that fuel-line and had a friend of mine manufacture a little elbow which I soldered onto the tube, threading a straight coupling at a 90°-angle.

On two flights no flame-out but *still* not satisfied or convinced.

And then it struck me hard... I charged all three batteries and three days later, I took the heli out on the field. FADEC wouldn't initialise. I really was stumped. Took the charger to check voltage: Big fat zero. I had the battery disconnected after charging, so no uncontrolled discharge over those two days. I did know, that the battery was supposed to be 1400mAh in capacity but only took 1000mAh on charge. Well, if the battery's breathing out its last breaths, no wonder I had troubles... And all of a sudden, all fell in line very nicely... Problems with non-consistent starts, problems to keep the RPM stable after starting, problems that FADEC-parameters do not really and greatly affect engine performance as they're described to.
During start was the highest load, so voltage must have dropped quite low, so the FADEC had to increase the fuel-pump power significantly, to keep the engine within its RPM-schedule for starting. After switching to run-mode, the battery was unloaded since only power to the fuel-pump had to be delivered, which let the voltage recover. Which increases fuel-pump-power, so the RPM went up, and the FADEC had to correct down, unloading the battery further, and so forth. The RPM went from set 45'000 up to where the clutch was fully engaged and set back to normal value after pretty exactly 3,5mins.
As I further suspect, fuel-schedule upon RPM-deceleration is not only lowered to the new value, but is being lowered below that momentarily for a quick engine-response. If the battery was weak, than the fuel-pump-power might have fallen below any permissable limit (which was not detectable by the FADEC, since RPM were revving down as they should) and might have even stopped for a short moment.

I have now a nice, shiny new battery in front, and - whoa...
Every start is like each other, everytime successfull without priming and external gas and stuff. I'm really starting to appreciate the wording "trouble-free"...
Inflight, the turbine's acc- and deceleration sound way more sharp and guess what: No more flame-out since over 30 flights... :)
Though I have to admit, I did not do any crazy stuff yet, mostly hovering manoeuvers and some slow forward flight, still having the fear of flame-out hovering in the back of my head, I hope that'll come back with time...

Now don't read me wrong here or get a wrong picture! I'm not one that's lazy on preventive maintenance, saving those 40 bucks for a new bat (and risking the heli for it), and coming from the F5B-corner, I *do* know my ways around batteries, handling them with equipment you'd normally find in a lab rather than a workbench... ;) I was aware that this pack had to be replaced sooner or later (both RX-packs were already replaced as one cell started to show signs of age, try that with a normal charger... ;) ), but I would've never guessed that a worn pack would have such a big influence...

Consensus:
Whenever you have several strange behaviours, check your battery thoroughly. When in doubt, replace it.

I'm really looking forward to an interesting winter as my starting-gas-pre-heater will prove valuable... :)

Cheers,

Daniel