Thread: 500 Blackhawk
View Single Post
Old 09-20-2020, 04:55 AM   #5 (permalink)
Registered Users
Posts: 4,228

Join Date: Apr 2008

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 ?

Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )
Andy01 is offline        Reply With Quote