Ecureuil AS 350, MSc 3 blade scale heli (+ video) - RC Groups
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Dec 02, 2006, 02:57 PM
0 Carbon fp? don't breed!
DarkHorse's Avatar

Ecureuil AS 350, MSc 3 blade scale heli (+ video)

Ecureuil AS 350 B-2 (3 blade rotor, 1:20 scale) aka Eurocopter A-Star, Squirrel

MS-900 Semiscale Kit

Bounce emails at
for helpful info and first class service.

Video posts:
- Indoor hover.
- Outdoor FF.
- Outdoor faster FF take2

Another detailed build thread with images. And see this thread.
And further paint info here.
Another Ms-Composit AS350 build, English translation, plus check out the really big scale Ecureuil AS350B1 with turbine .
Extra and repeat info at RCUniverse thread.

Manual.pdf drawings only.

Full scale Ecureuil AS-350B background information
Or go LARGE! with a Eurocopter Fennec AS550 Military Fiberglass Fuselage (600 Size)

Real crash footage plus 2 other AS-350s come to help: Rescue helicopter crashes off Rio's Copacabana beach
News Report1, News Report2 BBC


Well it's here and time to start fiddling
I think the building should go fine, just not sure how to do the body.
The 3rd image (HB-ZFA) is the colour scheme I want to use.
Anyone got any tips on how I create that effect convincingly?
Last edited by DarkHorse; Jan 01, 2013 at 04:42 PM. Reason: add links
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Dec 02, 2006, 03:09 PM
0 Carbon fp? don't breed!
DarkHorse's Avatar

3 Blades:

TE490 260 mm Glass Fibre grey blades, ~11g each and they are very skinny 20 mm cord width and more flexible under load, designed for multi blade usage. Here they are compared to MSC CF E489 12g, 255 mm 3mm thick, 26mm cord. Both have a 4 mm thick root mount for 2 mm bolt hole.
Last edited by DarkHorse; Feb 26, 2008 at 01:45 PM. Reason: bad link
Dec 02, 2006, 03:40 PM
Registered User
JustPlaneChris's Avatar
DH, that is going to be one very cool bird!

I'm looking forward to some video of this one for sure!

Dec 02, 2006, 03:55 PM
NYC's Finest
that helis looks really kool cant wait until you post some finished build pics.
Dec 02, 2006, 04:28 PM
Rotor madness!
Rodan's Avatar
Looking forward to the flight reports...

I was seriously considering this as my next heli, but I'm going to go with a TRex 450.

Then I might get another micro...if I don't decide to go BIG
Dec 02, 2006, 05:44 PM
Now Wren 1701
Wren1702's Avatar
I'll be watching this one. I had a very close friend who died piloting an air evac AS 350. I really would love to build one and paint it just like N350RM in his memory.

Looking forward to your build!
Dec 02, 2006, 06:16 PM
Now Wren 1701
Wren1702's Avatar
One more picture.
Dec 02, 2006, 06:25 PM
0 Carbon fp? don't breed!
DarkHorse's Avatar

Servo layout:

Wren1702, sorry about your friend.
I'll try and get this model flying sweet as soon as I can.

Some one might save time by following this layout. Hard to figure out what part of the frame your looking at when constructing. I went round a few times before I came to this. Stupid I guess . Rx and gyro will be on the back, far away from the ESC and motor.

The servo links to the swash will be at different lengths and with some varying angles but it won't be that far out of square geometry to make too much difference (I hope).
Dec 02, 2006, 08:25 PM
0 Carbon fp? don't breed!
DarkHorse's Avatar

Tail build:

I seem to have built the tail before taking any pics The long tail drive is 320 mm x 2 mm metal drive shaft including a 15 mm x 3 mm brass collar sleeve (ID 2 mm) factory fitted at one end for the main drive conical to push fit onto (large plastic 14T/3 mm ID conical pinion). The ali tail boom uses three 6 mm OD bearings in plastic cups to fit the ~6.5 mm ID of the 300 mm x 7 mm OD ali boom.
Note that the 2 6x2mm bearings with 3 mm IDs both go in the tail gear box chassis. Other wise the tail is basically off the X-3D but spins the other way on the otehr side of the boom (up side down). Follow the instructions...

Area's of concern:

Straighten the long steel drive shaft. Normally find the long drive shaft needs some bending into shape. This is very important, roll on a good flat table with the 3 mm brass sleeve off the edge. Very carefully locate any curves or the shaft will buzz when spun at 12k rpm. The problem is difficult to get at and fix once assembled, so get it right first or it will mess up your gyro (wag city). You could always get an alternative 15 mm x 3 mm sleeve (2 mm ID) on to a 320 mm x 2 mm CF rod, I think it would not vibrate in the same way as CF is much lower in mass.

After building several X-3D tails I found this one off build defect. The brass tail sleeve was too large and couldn't get the bearings to fit onto. I had use a 20 mm M2 nut and bolt to hold the sleeve and spin it in a dremel tool (or small drill) so I could narrow the area just before the thread started. It could have been a slight burr from the thread finish, I'm not sure. Tricky, as you want a tight fit to avoid tail slop but if you force a stuck bearing, they can break apart as you separate the centre ring from the outer ring (happened once in the past). No spare bearings in the kit so you would have to wait for and order etc.

Check the tail rotor hub for hole symmetry. I've seen offsets before that mess up the tail and vibrate. OK this time.

Carefully teeter totter balance the very light tail blades. Less the a 10x10 mm square of thin sticky tape placed in the dead centre of the blade corrects any imbalance. At 10K to 12K rpm it matters.

The plastic tail yoke (cross member bridge from pitch slider to blade grips) never screws the brass pitch slider sleeve in square for me, I quite often get this problem. Without the bearings attached, had to use a quick heat up the brass sleeve from a soldering iron to soften the plastic and reseat so that the brass sleeve sits square in the plastic yoke. Or else you get uneven tail blade pitch (tracking) issues.
Last edited by DarkHorse; Dec 02, 2006 at 08:33 PM.
Dec 03, 2006, 08:11 AM
0 Carbon fp? don't breed!
DarkHorse's Avatar


3 blade main rotor
70T main gear
14T conical on motor, 3 mm ID
14T conical to tail, 3 mm ID (tail RPM is 1:1 with motor RPM)

EM300/34 estimates:
(1100 rpm/v * 11.1v) / (70T/14T) = 02442 main rotor rpm on stock recomended EM300/34 motor
(1100 rpm/v * 11.1v) / (14T/14T) = 12210 tail rotor rpm on stock recomended EM300/34 motor

I'm using a similar EM350/20 (2212/20 12A 1150 rpm/v 57g) motor instead of the EM300/34
(2208/20 7A 1100 rpm/v 45g)
. I think the larger motor will come in useful for a plane one day may be. A bit concerned about driving the larger motor with an MS-116 8A brushless controller when it could peak at 16A with the EM350/20. So I better run shallow pitch and throttle curves, which will also drag my efficiency down a bit also.

Fresh 3x1320mAh value estimates.
EM350/20 estimates:
(1150 rpm/v * 11.1v) / (70T/14T) = 02553 main rotor rpm on EM350/20 motor
(1150 rpm/v * 11.1v) / (14T/14T) = 12765 tail rotor rpm on EM350/20 motor

Plastic conical pinions are press fitted. Could cause trouble if you get it wrong. I don't have a vice or press. So on the floor I placed the motor bell firmly up against a wall, then I took a heavy weight (1kg) with a flat edge to ram squarely into the pinion, pushing it onto the shaft. Using little regular nudges until the pinion sits flush with the mounting plate. I found that it was 1 mm to deep and carefully lodged a pair of small nose pliers behind the pinion and without damaging the motor housing or axel bearing, levered a screw driver to move the pinion 1 mm. In the picture below you can see the 1 mm mesh mismatch I have now fixed.

The tail pinion is easier to fit (less friction). I chose to do it last after the tail gear box was assembled. A little more difficult but with the bearing supporting the tail drive shaft it shouldn't bend under load. I take a flat head screw driver and place it flat across the back of the tail gear, strike carefully down onto the horizontal screw driver with the boom and pinion held vertical on the floor. It looks like your going to damage the rear bevel gear but I haven't had a problem in years on the Hornet. That's the same way I would replace the main tail drive front conical if it was damaged in a crash (cut the old one off), without disassembling the tail gear box.

Note that the 'one way' main gear is like the X-3D only the brass clutch sleeve sits top side.
Last edited by DarkHorse; Dec 21, 2006 at 03:47 AM.
Dec 03, 2006, 07:01 PM
0 Carbon fp? don't breed!
DarkHorse's Avatar

Tweak setup and First hops


The motor spins backwards compared to a standard Hornet due to the conical main drive reversing the required motor direction, so swap 2 wires.

Also the tail is on the other side of the boom, up right flight still pushes air left to right as with the Hornet (same clock wise main rotor, reversed tail rotor rotation) with the forward tail blade still rising up through any main rotor downwash.

A bit concerned as my Rx is glitching the servo's slightly, moved Rx to the bottom and rear...

Tip: use blade bolts with nuts! I tried to spool up with the blade bolts supplied, as the blades sit very loose it all got out of shape and started dancing. Lucky it was at very low rpm and got off the power but still managed a slight boom strike and tip over . Don't do that again. I replaced the stock bolts with longer M2 hex bolts (the same but longer, ~15 mm), covered them in thread lock and now use securing nuts to adjust blade tightness, to moderate friction as described in the instructions.

Initial spools: Got a bit of a tail buzz, not as smooth as my X-3D but that took a while to get to that stage, so far so good. Found a strange resonance (wiggle) with the landing gear above ~2400 rpm. I added a screw driver to each ski and it's flies smooth . I tried frame reinforcement, wasn't that...

Decided to paint the blade tips white and colour the tips fluorescent red, green and yellow. With safety glasses on and spooled up in my hand, I could just notice one blade (still quite invisible) riding slightly high. Locked the tracking in with a couple of link turns. Still got that wiggle...

Blade balance: 2 blades had good centre of gravity and the other was 3-5 mm out and heavier. So I added about 2 wraps of insulation tape to the other lighter blades, placing the tape about 30 mm from the tips. Then teeter totter each blade adding tape to the CofG point for good 3 blade balance. Takes a fair bit longer with three.
After all that balancing, it made no difference to the LG wiggle at higher RPM.

Ecureuil zero pitch rpm with 1150 rpm/v motor:
2235 rpm at 40% throttle
2431 rpm at 70% throttle
2604 rpm at 80% throttle

For some reason I was quite nervous lifting this heli off the deck. Anyway after a fair while ground testing and double thinking, checking all the angles... what's it going to be like with the swash directly linked to the blades?... Hey we are up!

Once dialled in some soft tame numbers the hover is very stable and stays put very well. I can keep it within a 6 inch drift with minimal effort. The cyclic is hard to test in a 10ft room. From what I can tell it feels pretty good, quite different to my other micro's and gives out a nice grown from the blades when jabbing the cyclic . No head damping on this heli, other than the slight give in the plastic blade grips (which are from the X-3D) and the custom flexible GF blade design. First flights where a bit scruffy on the tail, dialled the HH back to 60% and reducing the tail rotor vibes helped make the heli purr sweet (no wag! well almost). I've spent quite a bit of time fiddling and dialling though and tore the tail rotor down a few times. There isn't a tail fin to help damp down vibes like on the X-3D. Residual vibes effecting the gyro (wag speed increased with gain) came from main rotor blade imbalance and small tracking discrepancies.

AUW weight without body (+60g estimated) is 373g with 10g heavier motor. That's about the same as a stock X-3D (minus the 10g).
EM350/20 1150 rpm/v 57g
3xTP1320 prolite 85g
MS-044 HH gyro 13g
MS-116 ESC 12g
MS-027 35Mhz Rx 9g
Last edited by DarkHorse; Dec 21, 2006 at 07:15 AM.
Dec 06, 2006, 11:49 AM
0 Carbon fp? don't breed!
DarkHorse's Avatar

The Body Prototype

Here's some images. I'll try and add some detail later.

AUW without paint is 415g

Just noticed that my tail planes where up side down and back to front (I think).
Last edited by DarkHorse; Dec 21, 2006 at 03:56 AM.
Dec 06, 2006, 03:33 PM
NYC's Finest
damthat thing is coming out great!!!
Dec 06, 2006, 07:30 PM
Registered User
Do you use the pure windows parts (maybe, smoke transparent windows)?
Dec 06, 2006, 09:14 PM
Registered User
I really love the way my Ecureil flies - I didn't have a tough time dialing in the tail... just got lucky or maybe I'm just more willing to put up with vibes than everyone else!

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