Great Planes Siren Hotliner ARF Review - Page 17 - RC Groups
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Nov 27, 2007, 09:28 AM
YardGoat lives with mama
I dry fit 2 3s2100 TP lipos right ontop of each other and it fit perfect. Any larger and it would not have fit. I know that does not answer your question, but should provide a visual.
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Nov 27, 2007, 09:32 AM
'FPV'er...not a "LOS'er
Vantasstic's Avatar
My Impulse 3S 3200mAh packs fit my fuse, but, if I recall right, it was a tight fit, but they did fit.
Nov 27, 2007, 01:35 PM
Morning Light Mountain
badbill's Avatar
I was running the two 2100's with one in front of the other, with one as far forward as it would go. Balance worked out great.

Bill Davenport
AMA 28141
Nov 27, 2007, 03:14 PM
Registered User
I think 205g for the motor is good, the motor I've used has only 165g, so I need a lot of additional dead weight to reach the correct CG.

About the battery: it depends on the size, I think the maximum width that will easily fit is about 40 mm.
I use also a 40mm spinner, it has a carbonlike finish, so it looks great with the carbon from the fuselage.

Originally Posted by panzerd18
That 40mm looks great!

Would a 205 gram (7.3 oz) motor be good for balancing?

Are you guys running with a three cell or four cell lipo?

Also if I buy a 4200mah 3S lipo would it fit in the battery compartment or is it really cramped? What was the largest battery size you fitted and is it better to go for a lower mah battery to keep the weight down?
Last edited by fwolf15; Feb 03, 2008 at 12:02 PM.
Nov 28, 2007, 01:37 AM
Registered User
panzerd18's Avatar
I have ordered two hyperionCX 2500mah 3S lipos. I'm thinking I might have enough room for both. I could use one but someone said the battery won't last that long as its rated continious is 45 amps and the WOT amps is 35amps if my calculations are correct.
Nov 28, 2007, 07:41 AM
Upside down Miss Jane....
Stuntman's Avatar
Panzer, trust me - one 2500 pack will give you 3minutes + of motor on time at that current, and that will give you plenty of flying time. You are only going to be climbing for 10 to 15seconds at a time.

I am flying a little hotliner that draws 40amps on 3S 2500 cells. Its climbs vertically and gives me plenty of flying time. In fact this afternoon I had a 15 minute flight of mixed thermalling, speed runs and aerobatics.
Dec 01, 2007, 03:14 AM
Registered User
panzerd18's Avatar
How would JR331 micro servos in the wing go and a JR371 Submicro in the tail? I heard people are just getting HS81 servos all round?
Dec 01, 2007, 06:42 AM
Registered User
Andy W's Avatar
As stated in my review, I have Hitec HS-56 on ailerons and a HS-55 on elevator. No problem with those, but I'd probably use 65's all around if I did it today..
Dec 03, 2007, 01:11 PM
Peter Mar's Avatar

Siren Lite

Stats of my 2nd Siren should help some of you trying to figure out power systems and servos etc,

Powered by $25 UH/HC HXT 35-36C

TP W30A Brushless Speed Controller $13

Esprit sourced Turbo 38mm AL spinner pictured above by rcplanefubar.

Grapupner 12x6 folder, pulls 33A HOC

Batteries = 2 packs, in line, CSRC 3s1p 2000 mah 8c or 10c (155g-160g per pack), making it a 3s2p system. The now puffy packs are about 80mm x 34mm x 25-28mm thick depending upon puffiness of the individual packs (25-30 cycles on them, 8c packs are puffy the 10c are ok).

Servos HS-65HB all around.

Rx = Old reliable FMA Fortress 8 DC

*** CG = 80mm from leading edge!!!! ***

This second bird came with much more wrinkled covering and the stab did not fit level. It seems the QAQC is getting poorer. Overall it is still worth the street price.

I wanted this bird to be lighter than my first one so I could improve its thermalling ability.

The way far back CG is accomplished with everything moved as far forward as possible. The cheapie drive system works like a charm. It does not climb nearly as fast or steep as my previous geared setup (reported earlier in this thread). Once again, I don't care about that. It takes 20 seconds to get to climb and dive height (150m) and about 40 seconds to get to serious thermal hunting height. With two packs on board I can climb til the cows come home.

The wires on the outrunner rub against the case. I have yet to butcher the fuse to let the wires hang out so to speak.

The real treat is the glide. With a rearward cg of about 80mm and the low AUW, the Siren can be a nice floater in calm conditions (no not like a sailplane with a 5 oz/sq ft loading). It can actually thermal very well in winds greater than 15 kph (10 mph). I have flown it in 30-40kph winds (just trim for faster glide to prevent stalling due to turbulence). Under those conditions it lands at slow ground speeds without spoilers. However, it does get bounced around dangerously.

*** Warning the 80mm CG may not work for you. ***
It is a full inch behind the recommended CG. So if you are new to the Siren or have a new one to maiden, I suggest you set the CG at least to 65mm-70mm as a start. Depending upon the decalage of your particular bird it may be too far back to be controllable. Now that I am accustomed to it (really touchy controls and easy to snap roll) I am confident in all aspects except for slooow flight. I fly very slowly only when I am way up there in calm conditions. There is a real danger of stalling with vicious snap rolling. Test this behaviour at 150m or higher as you'll need some diving space to get the speed up before you pull up. Otherwise you will get a second and third snap as you plow it in. Don't ask how I know...

Lastly, make sure the lipos are well anchored. A good hand launch may shift them back and at 80mm there is no CG margin left to play with. My packs are wedged in with copious wiring holding them forward. They do shift a bit and I can tell when they move back a few mm. Once again, if the CG shifts too far back you are toast right at the worse time (right after launch).

My first Siren core sampled due to Rx lockout:


Others in this thread have mentioned CGs as far back as 100mm. I have tried 100-110mm and would not recommend this to Siren newbies. I am only able to use these rearward CGs when flying in light to no wind and when I want to float around. Because of possible tolerance diffs between each batch, the decalage of your bird may not allow a CG that far back.

The best way to test this is to do the usual dive test. Then do the same dive test inverted! Then you will know if the CG is too far back. For me at 110mm the bird will pull out inverted and that tells me my CG is way too far back. However, this is also the float CG I use when I have one or two flights at sunset when the boundary layer has set up and the air is completely dead. That's about the only time the Siren looks like a floater. Of course it'll snap stall on a blink so be very careful with the amount of up elevator you feed for turns etc.
Last edited by Peter Mar; Apr 28, 2008 at 04:56 PM.
Dec 07, 2007, 04:01 PM
Registered User
panzerd18's Avatar
Peter my Siren came with very wrinkled covering as well! Thanks for the tips about the C of G.

I bought the Siren as my second plane, I can fly my .40 sized trainer really well. A guy I know said the Siren is too advanced for me, but I bought it on the knowledge that if you don't use too much throttle it just acts like a big glider. I'm upset because I spent all this money and now someone said I shouldn't fly it.
Dec 07, 2007, 05:46 PM
Upside down Miss Jane....
Stuntman's Avatar
Too advanced - what a crock. Just give it a go on the buddy cord first. So, what's different to your trainer.

No noise
No wheels
Launch method
You can restart the motor in flight
Will go where you point it - ie nowhere near the self righting characteristics of your trainer
Will want to pitch up when under power - this catches a lot of people trying e-gliders for the first time
Much more efficient airframe so it will pick up speed quickly

Anyway you have to make the leap sometime so I say whack it on the buddy cord first and get someone experienced to help you out until your comfortable flying it.
Dec 08, 2007, 08:14 AM
Registered User
Andy W's Avatar
Originally Posted by panzerd18
I'm upset because I spent all this money and now someone said I shouldn't fly it.
It's a big glider. If you point it at the ground, or put a lot of power into it, it will fly relatively fast, but if you fly it like a glider you won't have any trouble.
Dec 08, 2007, 10:42 AM
'FPV'er...not a "LOS'er
Vantasstic's Avatar
Ah...if it only had a rudder it'd make a decent glider...other than that it isn't difficult to fly. The hardest part is the likes to float in.
Dec 08, 2007, 11:27 AM
Registered User
Originally Posted by Vantasstic
Ah...if it only had a rudder it'd make a decent glider...other than that it isn't difficult to fly. The hardest part is the likes to float in.

I'm close to finishing mine up. Are you using flaperons and still getting an extended approach? I've seen various comments on the thread but no definite conclusions about the value or need of flaperons. Any comments would be appreciated.

Jim, KK1W
Dec 08, 2007, 04:26 PM
'FPV'er...not a "LOS'er
Vantasstic's Avatar
Well...I don't actually have my Siren anymore. It meet its demise during a landing approach when, A)Someone turned on their radio on my channel, B)Glitched. Either way the thin C/F fuse didn't survive the impact. I replaced my Siren with something else (FVK Bandit) and switch to 2.4G.

As for the flaperons, I don't think they're needed. Flaps will slow the plane down, but also create additional lift which can make the landing glide even longer. Spoilerons will do a better job of killing lift and getting the plane on the ground, but spoileons don't really slow it down much. I think you're just as well off keeping it simple and just fly it 'straight' works well in stock configuration. FWIW, I bashed additional ailerons on my inner wing panel. Through my Evo9 radio I could set them up to act as flaps, spoilers, or ailerons at the flip of a switch. I could also do crow/butterfly setups with it, but didn't get much experience in any of the configurations. For the price the Siren is a great value if you keep in mind the fuse isn't super durable.

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