500 Blackhawk

[Thtasher]

To all the scale gurus out there
Just looking for some advice please for a Trex ESP in a Blackhawk fuse with a 4 blade head.
I was originally going to use a Hyperion 1000Kv & YEP80 with a 162main/14T pinion so looking at 1800 headspeed but I subsequently got a good deal on a Kontronik Jive 100 but later realized that the optimum setting for Kontronik Jives is only 60-65%(in mode 4)thus to obtain a 1800RPM = a 24T pinion!
Would I be better off with
(a)Hyperion 1000Kv / YEP80 (100% Throttle ) 14T = 1800RPM or
(b) MX1600Kv (stock)/Kontronik(60% Throttle) 14T =1800RPM ?
Any advice is greatly appreciated.

[Medic33]

Originally Posted by Thtasher

Any advice is greatly appreciated.

I'm not going to give you a fish... I'm going to teach you to fish...

Generally, scale helicopters are happiest between 80-100 watts/lb power loading - on a 2 blade head. For comparison, full on 3D machines are often in the realm of 300+ W/lb. For more comparison, their full size couterparts are often much, much lower. In your case - the full size UH-60 weighs 23500lbs (MTOW) and has 2 x 1410 KW engines - which works out to 120W/lb.

So, what the heck does this have to do with pinon and motor Kv? They're the last thing to think about - because they are actually the easiest to alter.

You need to know first of all (approximately) what your machine will weigh at takeoff. For a 500 size fuse, it wouldn't be far off to estimate 10lbs, I'm guessing. Easily more. But for the sake of argument, we'll say 10lbs takeoff weight. So, at 120W/Lb, you'll need at least a 1200 W (continuous!!!, not peak) motor. But wait - that's for a 2 blade head... You're using 4 blades. Rule of thumb (that I've heard, there are other thoughts) is to add 25% for each extra blade. So we actually may need to have 180W/lb, so now we're looking for a 1800 W motor.

Motors are most effcient running near to 100%. So are ESCs. So we need to guesti-mate our desired headspeed. My 600 class Bell 412 flies very happily at 1650rpm (2 blade head). My 600 class Mi-24 at 1280rpm (5 blade head). Flying scale, we don't need high head speed. Running multi, even less. But there's no hard rule. It's what feels right. Because we don't know what our final headspeed will be - you want a gearing / Kv solution that allows your ESC to be running around 90% or so.

Lastly... (yes, there is an end to this)... How many cells are you going to run? Higher cell count = higher voltage = lower amp draw = more effciency. Great! Unfortunately, higher cell count = more weight & higher cost.

I hope that helps - and doesn't frighten you!

ed

[Medic33]

And to give you two examples:

Mi-24
600mm 5x head (triple tail)
AUW: 16lbs
Motor: 2650W (Scorpion HKIII 4035-330Kv)
12S power / 1280 rpm / 18A in hover
Power Load: 165W/Lb (66W/lb 2 blade equivalent)

Bell 412
600mm x 2 head (std. tail)
AUW: 12Lbs
Motor: 900W (Neu 1907 1Y)
6S power / 1650 rpm / 25-30A in hover
Power Load: 75W/lb
(this helicopter is under-powered)

[heliscalefreak]

Originally Posted by Thtasher

... with a 4 blade head.
I was originally going to use a Hyperion 1000Kv & YEP80 with a 162main/14T pinion so looking at 1800 headspeed but I subsequently got a good deal on a Kontronik Jive 100 but later realized that the optimum setting for Kontronik Jives is only 60-65%(in mode 4)thus to obtain a 1800RPM = a 24T pinion!
Would I be better off with
(a)Hyperion 1000Kv / YEP80 (100% Throttle ) 14T = 1800RPM or
(b) MX1600Kv (stock)/Kontronik(60% Throttle) 14T =1800RPM ?
Any advice is greatly appreciated.

I use 1300KV motor, 6s, 12T 162T, YEP 60A @75-90% (freewheel active) on 500 4 bladed head in my 500 scale helis.
You need low headspeed with this head. I dont know about your calculation but 1800rpm is right.

Sikorsky HH-60J Jayhawk RC scale 500 helicopter (5 min 0 sec)

500 size MD500E Four blades main rotor (4 min 33 sec)

[Andy01]

I am going to chime in here.


I disagree with Medic about power because I think his numbers are too high (or he flies a LOT more aggressively than most scale flyers). I have;


2 blade 500 size UH-1N - 1700rpm, ±60W/lb

4 blade 600 size Seahawk - 1350rpm, ±55W/lb

2 blade 700 size Vario Long Ranger - 1350rpm, ±50W/lb

4 blade 820 size EC-145 - 1050rpm, ±52W/lb


Over at ScaleRChelis forum, the general view is that scale helis flown in a fairly gentle scale manner run around 50W/lb for a 2 blade and around 50-60W/lb for a 4 blade (it is not 25% more per blade) - this pretty matches my experience with my 4 helis. Note that the power numbers are for gentle FF - generally hovering uses around 15-20% more power.



IMO if you are drawing anywhere near 180W/lb with a 4 blade scale heli there is either something wrong or your are flying it very hard.


I would be quite surprised if almost any 500 sized motor was underpowered for a scale heli because most of them are designed for some form of 3D or sport flying, so the power number can almost be ignored - focus on the kV number to get it right.


My little UH-1N flew on around 350W in FF scale flying - yes it only 2 blades but nowhere close to the rated power of most 500 sized motors. Generally I look at my maximum power draw in normal flight, and double it (for an unplanned evasive move) to get the most likely maximum ever power draw.


So, to OP;


IMO 1800rpm is probably a bit fast for a 4 blade 500 unless you are planning to fly it quite aggressively - I would have suggested around 1600-1650mm. Note that at the slower headspeeds you may need larger tail blades (even with 4 tail blades) to maintain decent authority.


My little UH-1N flies well at 1700rpm and I use (from memory) a pair of 95mm tail blades.


As for which motor & ESC - it probably doesn't matter as long as you calculate it correctly.


I generally use;


RPM = kV x 0.9 x (# of cells x 3.7V) x pinion teeth / main gear teeth to get a headspeed at 100% throttle towards the end of the flight. The "0.9" factor is an efficiency factor because no electrical system is 100% efficient



So, for your "standard" scenario (assuming a 6s battery);


RPM = 1000kV x 0.9 x (6 x 3.7V) x 14T / 162T = 1726rpm at 100% throttle.


This means that you may reach your desired 1800rpm at the start of the flight with a fresh battery (and no governor), but that will drop quite quickly.


I generally try to run my Castle ESCs around 95% governor speed (no lower than 90% if at all possible), so I would take the 1726rpm and multiply by 0.95 to a governor speed of 1640rpm.


But you will not be able to govern much faster than this with a 1000kV motor and 14T pinion. If you do want to run 1800rpm you will need a 16T pinion.


I had thought (but I have never owned one) that YEP ESCs were active freewheeling like Kontroniks so you could govern them to much less than the 90-95% that Castle ESCs (and most others) like.



As regards the Kontronik ESC, I have zero experience with them, so I cannot comment on how important the 60-65% is ?


Colin

[heliscalefreak]

I have lots of helis so I try to get the cheaper solution , and although I respect the quality of more expensive gear sometimes I cannot afford it (for the lots of helis I have).
But yes, YEP freewheel is having no probs running at 75%.

BTW, the Jayhawk as it is too tail heavy it flies with two 5000mah in parallel. Still 60a ESC is more than enough.
It needs a bit more headspeed than the MD500 not to lift but to fly well and not being and feeling heavy in the air.

[Medic33]

Just in response to Colin; my numbers came from Peter Wales, and while they might be on the higher end, they include a significant “Oh, Crap!” factor.

Spending a bit more on a more powerful motor is a much better deal than seeing your scale ship auger in!

And I probably fly less aggressively than most scale pilots... Having the power there doesn’t mean I use it.

[Andy01]

Originally Posted by Medic33

Just in response to Colin; my numbers came from Peter Wales, and while they might be on the higher end, they include a significant “Oh, Crap!” factor.

Spending a bit more on a more powerful motor is a much better deal than seeing your scale ship auger in!

And I probably fly less aggressively than most scale pilots... Having the power there doesn’t mean I use it.

Fair enough. I think we just work it out differently and get to a similar answer.


My numbers (based on many in the scalehelis forum) are lower and based on actual logged realistic in-flight power, and I then suggest an actual motor power number that is around double the realistic number to deal with the unexpected (as quoted from my post below).


I would certainly never suggest to anyone to buy a motor (if it is even possible since most are 3D-biased motors) that is only good for the baseline conservative scale flying.

Originally Posted by Andy01

I am going to chime in here.

Generally I look at my maximum power draw in normal flight, and double it (for an unplanned evasive move) to get the most likely maximum ever power draw.

Colin

Anyway, I think it may be academic since the OP doesn't appear to have been back to comment or further discuss the answers and advice given in this thread - gotta love that


Colin

[Medic33]

Originally Posted by Andy01

Anyway, I think it may be academic since the OP doesn't appear to have been back to comment or further discuss the answers and advice given in this thread - gotta love that

Well, at least it’s here for someone else to discover, saves the creation of another new thread

ed