Great Planes Siren Hotliner ARF Review - Page 118 - RC Groups
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Nov 14, 2012, 08:36 AM
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Hi guys,
About the only thing that I can see as a change, is mine came with a F/G firewall, all I can say otyer than that is the finish quality is very high.
And BJ, in relation to the bec, yes it is a switching bec. I checked it out today and yes it does put out a bit of noise, I wrapped the out put lead 12 turns around a circular magnet and that has quientned it down to the point where my test servos are putting out more noise, however I have to order a couple of things from hobby king, I think I may order a analog bec, just for peace of mind, though I would be mounting at a good 10cm from the Rx.
Also can someone tell me exactly what would happen on the siren with 4s gearox and the ammo motor I am running if I puta 12x8 instead of a 13x8 onit?
Espirit sent me the wrong prop, I will be ordering another one, but if I can get away with it for the moment, it would help, and I dont yet have a watt meter to test with, hence I would love some advice.
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Nov 14, 2012, 09:12 AM
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N2UMK's Avatar
Neale - the ammo 28-45-3600 is rated for 40A continuous; 70A burst. Gearbox is rated for 675W(?). My CC 75A ice lite logged 68A max @ about 1050W using a 12x8 CF Falcon folder. My Skylipo 3300mah/40C is new. I'm only holding full trhottle for a max of 10 seconds. Mostly 5 to 8 sec. Bigger props will draw more but it is a function of the battery capacity and C-rating.
My recommnedation is to try it.
Last edited by N2UMK; Nov 15, 2012 at 01:59 PM. Reason: corrected motor #
Nov 14, 2012, 09:23 AM
The wheels touch down FIRST??
BJ64's Avatar
Sdstick - HK seem to be making in-roads to creatiing hot/warmliners at an affordable price - composite using glass and CF (see mention of the 'Geronimo' a few pages back - as this is a Siren thread, I won't go into any more detail than that).

I don't profess to know the history of the Siren, but I'd dare say a few things would have changed since the first 2004 model.

Correct me if I'm wrong, but Carbon Fibre was an elite and extremely expensive commodity back in 2004 - F1 cars would have been using it, but I'm not sure the first Sirens would have had the CF underbelly.

For what it is and the price, the Siren is one sweet flier. Love mine to death. Still makes me go sweaty when setting up for a fast, low, motor-off pass. Simply love that sound.

As an introduction to hotlining, it's a great plane. But, as you said (and I said way on back), it's more of a fast warmliner than a true hotliner. Then again, you're getting a taste for hotlining with a flying Siren for about half the price for just a basic airframe when compared to an Alex Enigma.

A Siren with a fully composite slippery airfoil would be the next evolution I'd like to see

But that would probably push the price up - and into a range where for one or two hundred $ more you'd be in genuine HOTliner territory.

From what I've seen, bought, built and flown lately, I think glass/CF fuzes with balsa sheeted foam-core wings are the compromise between price and performance. As soon as you start talking moulded wings, the price seems to jump a fair bit...

Nov 14, 2012, 09:30 AM
The wheels touch down FIRST??
BJ64's Avatar
Originally Posted by N2UMK
Neale - the ammo 28-24-3600 is rated for 40A continuous; 70A burst. Gearbox is rated for 675W(?). My CC 75A ice lite logged 68A max @ about 1050W using a 12x8 CF Falcon folder. My Skylipo 3300mah/40C is new. I'm only holding full trhottle for a max of 10 seconds. Mostly 5 to 8 sec. Bigger props will draw more but it is a function of the battery capacity and C-rating.
My recommnedation is to try it.
Yep - try it, by all means.

But you don't have to run it WOT (but you know you're going to ).

My advice (from having smoked my SK3548) is DON'T. LoL

Get it set up just right, fly it - and resist the temptation to open the taps all the way.

Remember rule #1 - don't let the magic smoke come out. It never seems to want to go back in

Nov 14, 2012, 05:03 PM
Registered User
Hi guys,
I am just a learner when it comes to electric.
But if a smaller prop will not cause any other problems, (allowing over rev, or whatever else I am not aware of) as I understand the only thing it could do is cause less amp draw resulting in less thrust, am I correct with this?
I f I am correct, and I will wait for an answer to that!
The only outcome will be lower performance, and I am guessing that the drop in performance will not be so extreme as to make the plane harder to handle, or kill the flight performance to a really sad level, I hope I am rite, I will probably find out by flying, than before I get a watt meter on it!
I will try it!
PS I am assuming that the smaller prop will draw less amps!!
Nov 14, 2012, 05:34 PM
Registered User
Hi again guys
I am just going thru my heli stuff, seeing if I have ball links and so on. And I was thinking about the 12x8 prop sent instead of the13x8 prop, assuming all else being equal, the power draw would drop, but then the plane was recomended to have a max power of 500 watts, I am sure the drop in power is not going to be anywhere 50% or more, so I would assume the siren should fly bloody fine on a 12x8, hope i'm rite!!
Nov 14, 2012, 06:16 PM
The wheels touch down FIRST??
BJ64's Avatar
A 12x8 should fly fine, Neal. Even a 12x6.

If you're starting out, you don't really want the thing to go like a bat of of hell - give yourself some time to learn its characteristics at a slightly slower speed. That prop should have plenty of grunt - particularly if you're running 4S.

What was the kV of your motor again?

If it's in the 800-1000kV range, the 12x8 is in the ballpark. Much higher than 1000kV, I'd be looking at propping down to 11x6, maybe even 10x6 if you're around 1400kV,

If you're using a gearbox, don't forget to divide down by the gear ratio.

For example, 1000kV on 4S = 1000 (revs per volt) x 4 (number of cells) x 3.7 (nominal volts per cell), so:

1000 x 4 x 3.7 = 14,800 theoritcal :"no load" RPM at 3.7v per cell.

You'll find that as soon as the system is under the load of the spinning prop, the actual RPM will go down. And with fresh LiPo running 4.2v per cell, it will go up. So, as a ballpark figure, that setup should spin somwhere around the 14-15,000 RPM mark.

My HET 600-43 1100kV should theoretically spin to a similar RPM, but in reality it really drops off with the bigger prop on it.

If you recall the figures I posted the other day running 4S on the HET running the 14x9, 13x6.5 and 11x7 props, I got:

14x9 - 65A, 950W, 2.5kg thrust, 6750 rpm
13x6.5 - 45A, 550W, 2.25kg thrust, 8300 rpm
11x7 - 35A, 450W, 1.5kg thrust, 9500 rpm

You can see the actual measured Amps drop off and the actual measured RPM increase as the props get smaller. And it's not just the diameter of the prop to take into consideration, but also the pitch (as you probably know anyways).

So you can maybe use those above figures as a rough guidline.

If you're using a reduction gearbox on your unit, don't forget to divide the final theoretical result by the gear ratio e.g. 3500kV on 4S with a 3.5:1 reduction:

(3500 x 4 x 3.7) / 3.5 = 14,800 RPM

Hope this helps...


PS - running a reduction gearbox actually multiplies the available torque - but I think I've filled your head with enough crap for now LoL
Last edited by BJ64; Nov 14, 2012 at 06:35 PM.
Nov 14, 2012, 07:27 PM
Registered User
Thanks for that post BJ, those figures make me feel better, and I think all will be fine.
And your rite a lower power set up for me to start with!
Any, ANY plane car or whatever takes time to "learn" anyway.
I am off to jay-car on the way to work to grab a plug for the aileron servo's,so as to pput them both on one plug, make it a lot easier to change batts etc.
Because I have to spread my budget over the year, and I am (wife) limited to how much I can spend at a time.
So in that light, and I am trying to move aloong with the siren, my TT325 has decided to cough up it's three HS 65 MG's for the siren, I will replace them in the new year, so now to choose and order a esc and batts, I think thats all I need. I would like the H/K super brain 100 amp for $90 however the non logging 100 amp esc with an external bec just released by H/K at $48 may have to do the job.
At least I know the servos are good, with low hours on them, I just dont know if the H/K MG servos are a good idea or not.
Nov 14, 2012, 07:29 PM
Registered User
Is it better to run this bird with a gearbox as opposed to a direct drive? Where are these gearboxes being bought from?
Nov 14, 2012, 07:42 PM
Registered User
G'day yellow colorado.
It is morre for the room running an inrunner instead of an outrunner.+ wieght
The box is a great planes 4.2:1 unit rated for 675 watts, but will take more if treated nicely 40 dollars plus postage. seem to stand up fine
Nov 14, 2012, 09:26 PM
Registered User
N2UMK's Avatar

370W/lb is stupid power!

My Siren with the 3300mah, 4S lipo weighs 2.7lbs; @1000W that's 370W/lb! That is stupid power! However I like it!
Nov 14, 2012, 10:39 PM
The wheels touch down FIRST??
BJ64's Avatar

If you're trying to save your pennies but still want some form of inbuilt ESC Data Logging, check out the specs on the HK DLux line of ESCs:

100A is about 10 bucks more (ca $37). You'd need to buy the 'programming box' as well, but they're only around $10, and you only need to buy one once to cover all the DLux Speedies.

Might be another option worth considering...

Nov 15, 2012, 08:56 AM
Registered User
Hi guy's
I'm not trying to save pennies BJ,It's a lack of pennies!!
I would like some data logging for sure, I did not see that this had data logging, for the price plus $10 for programming box, I like it.
I was looking at an esc with external bec, but the data logging has sold me, I will order tomorrow.
And that, other than some new batts is about it.
Dropped into jay-car today and picked up a mini molex 6 pin, so I will start to set the wing up tomorrow and do both ends of the aileron plugs, and that will be the start of the build, must extract servo's from heli in morning!
Very much looking forward to this build, only thing that will slow me up will be esc and batts.
Never mind I will have it up by chrissy.
Nov 15, 2012, 02:01 PM
Registered User
N2UMK's Avatar
Post#1757 motor # is wrong; should be 28-45-3600; sorry, hope no one got confused. I corrected it today.
Does anyone know the # of poles in this motor?
I guessed 4 poles but not sure.
The rpms on the data logger come out about right with 4 poles.
Nov 15, 2012, 05:50 PM
Registered User
Hi Pat ,
I believe it is 2 Pole

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