DarkHorse

Taken some time but here it is:


...MS-Ecureuil-AS350-FF.wmv 30Mb 3.5 mins 50fps WMV format

Heliko

WOW![X(]
Pretty heli and some pretty flying too!

Is she really as smooth as she looks?

DarkHorse

> Is she really as smooth as she looks?
Thanks, yes pretty much once you reduce any vibes, though this did take a while to fine tune after the initial build (not for beginers). Once understanding the heli better and giving myself a chance to settle in to the slightly different handling characteristics, the heli is fun to fly. Note that I still have a slight low frequency main rotor vibe causing the gyro in HH to malfunction (small wag/shimmy), luckily the standard rate mode works fine, producing the smooth sweeping tail movements you want in a scale model.

In the video there is a mild breeze, also you can see the occasions where I miss judged the collective input, normally when coming out of FF in to hover, with the rotor falling into dirty air. All micro heli's suffer from this to some degree but the 3 blades setup without any flybar dampening does have a tendency to continue to pitch backward more during transitions from FF to hover. Kind of weird at first but with a few clicks of forward trim, with correct +15mm CofG it soon becomes manageable. The cyclic can feel like a flying dinner plate at low rpms that sharpens up at higher rpms, the video is some where in the middle of the usable rpm range.

The setup is stock except for 2 extra bearings in the tail drive. There is more detail info on links from my web site.
Still need to test the top speed handling and when I get brave enough I plan to video some mild acro, loops and stuff

BarracudaHockey

My Feedback: (11)

Thats called "settling with power" and even the real ones do it.

Nice job, looks good!

DarkHorse

Yes that's right, also known as 'ring vortex state'.
My slow to medium flying style seems prone to this effect,
if you belt around a bit faster I find it less of a problem.

Heliko

I would think it's just the loss of translational lift that's causing it to drop. In 'settling with power' the heli already has to be in a descent for it to occur.

DarkHorse

Yes, in decent the vortex state is a more serious and extreme condition, plus the heli already has some downward velocity.

In the video I was using extra collective added to compensate the loss of transitional lift effect but as the heli is slowing from FF to stop in hover (quite a common occurrence) it seems just perfect for creating the kind of downward moving air for the heli to fall into. To avoid continuing to hit the ground I estimate adding an extra +50% power as there isn't always time to move off again avoiding the vortex condition. The earlier you get on the power the better, any delay once you start loosing altitude requires far more power to recover. My little old low power FPs used to just crash into the ground all the time before I understood the problem (a guy on RCG enlightened me). For a reasonable micro CP this normally looks ugly though not a problem with the great power to weight ratios we have available. For a full scale heli without such reserve power available it could mean imminent disaster if the pilot doesn't take alternative action to fly out of the deadly vortex state, as adding a only a little extra power makes the situation worse and a crash inevitable near the ground.

Your probably aware of this already but it might benefit other flyer's out there. I get this on all my micro's, I'm just dumb enough to keep doing the same mistake time and again LOL

Heliko

I noticed when hovering I get settling with power too. I'm still a newbie pilot so I'm not on your level, but if I do a slow descent without foward airspeed the heli will sink. If I remember right the way out is some forward cyclic. You had the right idea though. In your vid you had a couple nice approaches that ended with the heli in ground effect which gives the heli alot more hovering power. It's just so cool they now have scale helis in mini/micro size. The one I'm really waiting for is an MD500D with a scale 5 blade head. That would be really cool.

ewolow

You can get an MD500D fuse for a T-Rex mechanic. I have one sitting at home waiting for me to get around to building it. I have seen 5 blade rotor heads too, expensive little beasts.

archiebald

Very nice!!

I remember having a "discussion" with some idiot on one of these boards last year who claimed that "ring vortex state" cannot occur in a model heli.

Happens all the time to me when pootling about, especially in slow forward flight with a tail wind. It used to worry me, but now I find it fascinating.

Heliko

I know you can get MD500 fuselages. In fact Darth makes one, but about the scale head, was this for a micro size heli like the AS350 or a larger one? I've seen the head for larger scale helis. It was even on an episode of Mythbusters.

Bxcar32

I had read earlier in this post about the discussion of Vortex Ring State (VRS) and Settling with Power. There are multiple forces acting on a rotor system at any given stage of flight. Vortex Ring State and Settling with Power will only be addressed here.

All helicopter types, regardless of size and RRPM (N/R) are susceptible to VRS. When you enter VRS you may not necessarily be settling with power. VRS and Settling with power happen under the following conditions: Low forward airspeed, high rates of descent and minimal power applied. High GW increases both your power requirement and descent rate and decreases your available power and your ability to affect a recovery. Since you have to be descending (in steep approaches or vertical descents), with low forward airspeed to encounter these phenomena, forward flight through Effective Translational Lift (ETL) which is above approximately 40 KIAS and in ground effect hovering does not apply. The main difference between the two is that if in VRS and power inputs alone arrest the descent, then you have not entered Settling with Power. If in VRS and power inputs can not arrest, but increases the descent rate, you have entered settling with power.

On a side note about hovering characteristics:
If you find your helicopter descending in a hover, its caused by a shift in the airflow your rotor system is operating in by either wind changes or your own rotor wash. If you’re hovering in ground effect you’ll notice that even in a no wind day you’re helicopter will still require pilot input to maintain the hover. However, if you have a head wind while in a hover and the wind dies, you will see the helicopter loose some altitude. This might give the effect of VRS as someone stated earlier. I suspect that in an In Ground Effect (IGE) hover, if your helicopters altitude fluctuates that is more a function of rotor wash.

My intent here was to help specify the differences between VRS and Settling with Power. It was hard to tell if the helicopter in the video had entered VRS or was more a function of steep approach and power application techniques.

Nice helicopter and some really good scale flying.

DarkHorse

Good additional background info, thanks.

Heliko

Hooker good info, but it's a little off. I borrowed these definitions from Wikipedia instead of writing it myself as a shortcut. I'm feeling lazy, but the definitions are accurate.

Settling With Power- also known as Vortex Ring State, is a hazardous condition encountered in helicopter flight. It occurs when the helicopter has three things occurring; a rate of descent greater than 300 feet per minute, an airspeed slower than Effective Translational Lift, and the helicopter is using more than 20% of its available power.

When these three conditions are met, a second set of vortices, similar to the rotor tip vortices, are formed in the center of the helicopter rotor system, resulting in a loss of lift. Trying to raise collective to reduce the rate of descent only increases the size of these vortices, and therefore increases the rate of descent.

Settling with power is especially hazardous because the three conditions that cause it are most commonly encountered while on steep approaches, and low to the ground. Failure to recognize settling with power quickly can often result in the aircraft settling all the way down into the ground.

Corrective action for Settling with Power is to lower collective slightly, apply forward cyclic to build airspeed and "blow away" the vortices, and once airspeed is regained apply power and climb back to altitude.

The effects of settling with power are similar to vortex ring state. A standard procedure exists to correct both conditions.

Vortex Ring State- A helicopter typically induces a vortex ring state by descending into its own downwash. This requires low airspeed and a moderate rate of descent with power applied, and can lead to an undesirable phase of flight known as settling with power. This condition can be corrected by lowering the collective, which controls the pitch angle of the rotor blade, slightly pitching nose down, and establishing forward flight. The aircraft will fly into "clean air", and will be able to regain lift.

Lastly I'll quickly explain some characteristics of ICE and OGE hovering. The reason IGE hovering requires more cylic input is partially due to ground turbulence. The reason it's still difficult to maintain a smooth hover even in an open flat area is when the heli is hovering close to the ground (about 1 to 1-1/2 times the main rotor's diameter) the air get's compressed. It can't get out of the way fast enough. This is a combination of the high speed of the downdraft created from the main rotor as well as the friction between the air molecules and the friction between the air and ground.

The important thing to know about both "settling with power" and "VRS" is how to get out of it. Lower collective and increase foward airspeed. Although on RC models that have alot more power than there full scale counterparts and fly much closer to the ground increasing foward airspeed would probably be my first action.

Think of it this way. It's like the heli is on a large spring made of compressed air. As long as the heli is stable and level the force is the same throughout the rotor, but with any cyclic input the trapped compressed air tries to escape from the highpoint of the rotor disc. This gives the heli a "jumpy" or "squirrelly" feel. When hovering OGE the heli is too high for the air to compress between the rotor and the ground. It diffuses before it gets there. The upside of IGE for real helis is it requires less power to hover than OGE.

DarkHorse

Ecureuil Faster FF video (in the right threadthis time)

Yep it's still in one piece so here's another one :



...MS-Ecureuil-AS350-Take2-FasterFF.wmv 38Mb 3.8 mins 50fps WMV format

Shuttle RG

What kit is that, what mechanics? Did I miss it somewhere?

Thanks

DarkHorse

Hi, the heli is a micro with a 3 blade 56cm rotor diameter made by MScomposit (from Europe and USA MS-900 Semiscale Kit) and shares a few similarities with the MS Hornet X-3D.

Ecureuil AS 350 B-2 aka Eurocopter A-Star, Squirrel

More build info and links on my site at http://dhrc.rchomepage.com/

c550

My Feedback: (16)

Coll Astar. I would really like to get one. How much of a jump would it be to move up to that from a blade cx? Also how hard would it be to change the model from the large forawd door configuration to the sliding rear door configuration(thats what I fly and I would want to model that version)?

Thanks for your help.

Regards,

Dave

DarkHorse

The MScomposite site does advise that it is 'intended for advanced pilots' and you should really be familiar with setting up of a micro CP and computer Tx programming etc. Also I would say being fairly confident at sport flying around and understand a little bit about heli physics and how your setup decisions impact upon the heli's handling (in the squirrelly micro world). Definitely not for learning any new moves, crashing is not an option with scale heli's, money and time relative I guess. Micro's are toughest to master.

> How much of a jump would it be to move up to that from a blade cx?
Honestly I would say don't try it yet. Get a couple of micro CPs tamed and under your belt first.

> Change the model from the large forward door configuration to the sliding rear door configuration
Not sure about that. The body is easy to cut and you can get clear windows for them now but cutting away material may deform the overall shape and the interior frame if visible wouldn't look that great, well on mine any ways.

Follow the links on my home page for some good build threads and info.

JordanT

Are you using any additional gyro's on this heli. I have heard that using a gyro on the pitch axis can help control the pitching problem of the heli pitch up when transitioning from forward flight to a hover.

DarkHorse

Hi, no the setup is not using any extra gyro's on the cyclic. I suppose you could experiment but as you can see from the first outdoor slow FF video and the FasterFF video 'pitch up' effect(s) can be managed (of both types during transitions and from advacning/retreating blade lift differnces). Not too bad to fly, just slightly different. I once wrote: ... helped by a combination of some pre-emptive forward cyclic (with respect to any wind direction) and high angle tail stabilisers at moderate speed (30ΒΊ to 40ΒΊ). Plus setup CofG +10mm and some forward trim. More RPM would help, at the expense of flight times.
Generally flight is easier to command with the upper swash advance offset to straighten up the cyclic input orientation. Plus I run -45% expo for soft friendly cyclic stick centres.

Not sure how fast the heli is in the video... estimate stock ~2.3K rpm is fine for scale cruising 10 to 30mph (maybe more?), below 2.1K and the cyclic goes all mushy in a breeze... The thing is, the relatively low RPM and lack of automatic flybar damping does cause some 'pitch up' effect as forward flight speed increases (more info here)... Running 2.6K would give another 5mph to top FF speed (based upon my higher Kv motor setup and tip speed numbers).

Edit: I forgot to mention that I got brave enough and pulled a nice round medium sized loop a few days ago[8D]. In the video's I'm not stressing the collective (or cyclic) very much when using the 8A MS-116 with the 12A EM-350 1150 rpm/v motor. Only briefly hit full collective a couple of times in the video and never max'd out in FF. Full pitch swing available is set high around 12ΒΊ to 15ΒΊ when statically measured but I suspect the flexible GF blades may be twisting under load and reducing or delay the actual in flight pitch.

ewolow

I just ordered one of these kits. I've been looking at one for a while now and the price dropped enough to spur me into getting it (that and the wife factor gets reduced a bit). I was on your site trying to get to your build link but it's broken.


Any advice or issus that ran into that I should look for? I've been building models for about 25 years, helis for about 10. I'll most likely put in an AR7000, JR DS285 servos, and maybe my GY420 ( I may switch that into my T-Rex still undecided.) then it would be an Align RCE 500x.

Is there enough room to use an align 430xl brushless? I downloaded the instructions and it looked like a shorter motor in the illustration.

DarkHorse

> build link but it's broken.
Well worth checking out the build details. Try the link again and let me know what fails where, it seems ok to me so far...

I'm not sure about using the bigger components. The motor should be fine a bit longer but the base diameter is probably the limiting factor and must be a 3,175mm (1/8th inch) shaft diameter for the special conical drive pinions. Servo's should be about HS-55 sized micro servo's or you'll be cutting out bigger holes.

Then I'd recommend keeping the weight below 500g on a 560mm rotor span or the disk loading will become too high and manoeuvring could get sluggish. My 432g has a 1.75 kg/m^2 loading in hover, requiring just over 5 Amps to stay there. I feel if you push up to the T-rex sized stuff the economy of scale will have some negative side effects. Should be stable in hover though .

ewolow

I have the heli together and I'm waiting to finish the gloss coat. I have the mechanics together and just finished trimming it out. I used the stock motor as I noticed, just as you pointed out that the drive shaft on the motor is unique to the conical drive.

You are absolutely right about having to get used to the way it flies. I went thru an 800mah lipo trimming it and getting used to it. Mainly just tried keeping it in hover, tail was a bit touchy but overall flew well. I noticed that while I was flying in a confined space, the wash from the walls had more of an adverse affect on the heli more so than say my T-Rex would have. I also noticed the dirty air drop off you mentioned. It's not hard to fly, just different.

Hopefully it won't be as squirly once the fuse is on and I'll have to adjust the transmitter (dx7) a bit as it's almost too responsive.

I'll post some pics once I get the gloss coat done.

DarkHorse

> I'll post some pics once I get the gloss coat done.
Cool, looking forward to seeing them. The art work was a hurdle for me and was happy to use a simple spray colour scheme that looked passable as a heli.

Tuning the setup took me a while, initially some days I couldn't quite get to grips with all aspects of smooth manoeuvring and flight. I would be wrestling with the heli in a breeze looking kind of ugly with my no patients mate over my shoulder saying 'just ebay it man, get rid of it' but I'm glad I worked the setup through to what it is today, now he wants to buy it .