Century Bell 47

[GyroAl]

Originally Posted by Globs

Nice flying there GyroAl, good to see the front of a heli as well as the back
Proper autos too - what pitch do you have set for the long auto part of that?

......

You can get much less smoky fuels and lean out (with a temperature gauge) to make smoke almost a thing of the past with nitro, My CF tail snake seems to work out well too, with roughed up CF ends and sockets it's very strong and seems to work well !

Thank you Globs, I have always loved how this heli flies (sometimes I cheat and even fly aerobatics with it).

As for the autos, I use a -5 on the bottom and a +9 on the top. As I also fly 3D, I always set my helis to hover at 3/4 stick. I do not like using more then +9 at the top, as I find if I set more then that at the top, it does not help much, because the drag above that setting, will bleed off any remaining rotor speed immediately. Most landings result in the stick to be just a tad below the hover stick point. I also find the FunKey 600 blades make for a relatively inexpensive blade that works a treat for sport and scale flight and they also auto very well.

I agree about the availability of fuels and settings that result in less smoke. I used to keep two fuels - 30% nitro/22% oil for 3D, and 15%nitro/18% oil for scale. WIth the 15/18 on the nitro scale helis, the smoke trail was easy to get rid of. But the 2 fuel storage etc. efforts became too tedious, so I now set all my nitro helis to use the 30% high oil. Unfortunately it means a smoke trail with them. Fortunately I have other scale helis on electric power (eg.see the A109/Swift videos on that same youtube site) and looking to do an H-500 with a Predator or Radikal gasser mechanics.

I also use a C/F rod-in-sleeve tail control rod system on the Bell 47 and other scale helis I have built. They are K&S of Japan items and I have found them to be very good for these applications.

Anyway, it is a treat watching your servo control system innovations here. Good show!!

[Globs]

Originally Posted by Donnie D

I bought 2 Hyperon 3S, 4200mAh, 35C batts I'm gonna connect together in series for 6S. I don't know how well they will work for this because I figured it out the way I figured everything else about this build, I guessed. Got my fingers crossed though. You think they will be OK?
Have you been able to test your pinion yet?

Donnie D

Looking at 600E and Swift power budgets I think that you need a max of a 20C cell at that capacity, in fact running 5Ah I think 15C would be fine.

For instance a (600E) 7min flight using 2.8Ah left a cool battery of 3.7Ah/20C capacity.
Avg. current draw (for 7 minutes) = 2.8 * 60/7 = 24A.
In fact all my computations put 25A as a top average figure drawn, so it is probably close.
Thus the 'C' drawn is 24/3.7 = 6.49. At 20C this is a C rating overhead of 20/6.49 = 3.1.

So if you pull 25A out of a 5Ah pack you'll be pulling 25/5 = 5C, so with a overhead of 3 that gives you a 15C battery - I.e. buy a 5Ah/15C 6s pack.

If you really do pull 25A from your pack you get 25C/4.2 = 6C, given you have a 35C rating and you need an absolute max of 20C I think your cells should be very under-stressed, and last for 60 * 4.2/25 = 10 minutes.

If you go flybarless later (you save 14% apparently) you should have a near 12 minute flight.

Not flight tested the pinion yet, runs up well though.
Mine is a 19T pinion on an 1100rpm/V motor on 6s, you are running a 6s pack with 26T for what rpm/V motor?

[Globs]

Originally Posted by GyroAl

As for the autos, I use a -5 on the bottom and a +9 on the top.

Thanks for that and the explanation - I'll set mine up for that then.
I'll check out the vids too - what battery and flight time do you have on the swift and what is its weight?

Originally Posted by GyroAl

I also use a C/F rod-in-sleeve tail control rod system on the Bell 47 and other scale helis I have built. They are K&S of Japan items and I have found them to be very good for these applications.

Wow - I thought I was a pioneer, good to see it has a wider adoption! Mine is looking good and very strong (I put on a metal solder end (roughed up) and a drop of CA, then a single crimp in the middle of the gripped bit.

Originally Posted by GyroAl

Anyway, it is a treat watching your servo control system innovations here. Good show!!

Cheers!
I think if I remade the top servo tray (which I may - it's not difficult and just unscrews) then I'd move the elevator servo back to the same level as the aileron (centered) servo, it's the best location given canopy overhang and bolt access. The aileron servo position is perfect.

I'm now puzzling over the best way to mount the canopy, the battery will be the seat I think.

[Donnie D]

Thanks,
If I can get 10 min flights, I'll be happy. I'm usually a nervous wreck by then anyway.
My motor is a Scorpion 4035 series 630 motor. I have an 18T, 20T, 22T and a 25T pinion ordered. I'll see which one works best.
Got my fingers crossed.
Donnie D

By the way, I'm really enjoying your stuff on clearing the cockpit area. I may even be able to do mine later now. I noticed you only use one aileron servo.

[Globs]

Cheers Donnie - it looks much better with a clear cockpit, probably because most of the front is clear canopy

After more thoughts about the seat battery I ordered a 6s 5000mAh 20C Turnigy today, plus a UBEC and a 6s battery monitor. I use monitors now so I can land as my leisure at the end of the battery.

Did the top canopy back/shroud too - photos later. Still figuring out the floor!

I may also paint the legs and supports - I'm looking at the full size pictures to get all detail from and I haven't seen a yellow with black supports and silver skids. I'll keep the silver skids though I think! Everything else on the frame may need a bit of silver humbrol on it to get the general tone. Any ideas where to get a scale 6 cylinder turbo charged Lycoming?

Your motor is 630rpm/V, so to get the same gearing as me (same as Bell Bloke) the following applies:

6s * 1100 * 19 = 6s * 630 * DT
DT = (6 * 1100 * 19) / (6 * 630) = 33T (33 tooth pinion)

If however you hop up to 9s (3 x 3s batteries) you need
DT = (6 * 1100 * 19) / (9 * 630) = 22T

and I'd estimate a 50% longer flight time with 50% more batteries
Alternately your lower gearing might be better on 6s than mine and allow a more efficient flight at full motor speed, ESCs work better like that.

[Donnie D]

6s * 1100 * 19 = 6s * 630 * DT
DT = (6 * 1100 * 19) / (6 * 630) = 33T (33 tooth pinion)



Where the heck would I find a 33T pinion with the correct tooth size and pitch?

Donnie D

[Globs]

Originally Posted by Donnie D

6s * 1100 * 19 = 6s * 630 * DT
DT = (6 * 1100 * 19) / (6 * 630) = 33T (33 tooth pinion)



Where the heck would I find a 33T pinion with the correct tooth size and pitch?

Donnie D

It's just a consequence of your 630rpm/V motor, Bell Bloke used a 1050rpm/V with 20T so I used a 1100 with 19T.
As I said you may be fine with that motor, just use it higher up the throttle curve.

The original clutch had 26 teeth I think. I tried working out the drive ration but failed:

Counter gear (driven by pinion) = 55T
Counter-gear pinion = 13T or 14T
Main gear - no idea ????

Can you count your main gear teeth (internal)?

[Globs]

I decided a needed a fixed main panel, so this is it:



Actually part of a side panel from a Textronix 545b - the curved bit at the top. I found some hole punches too so I used them where the seat back will cover it.



This is the dummy battery - same size, shape and weight:


I need to trim a little but it will fit quite well and balance too. I did find a major issue with the century kit however - check this out:



That vertical yellow bar to the left should not be there at all - instead an angled bar (that I'm holding) should. It looks 10x better with that bar, so yes - Im changing that too

Vs:

[Donnie D]

quote: Can you count your main gear teeth (internal)?


I think (not easy to do) I counted 60 teeth on the inside rim of the main gear.

Donnie D

[Globs]

Ok so we have:

Counter gear (driven by pinion) = 55T
Counter-gear pinion = 13T or 14T
Main gear - 60T
Pinion = P

so for 1500rpm headspeed (assuming a 14T pinion) we have a counter-shaft speed of 1500 * 60 / 14 = 6,429rpm.

That gives a counter gear speed of 55 * 6429 = 353571 teeth/min.
So your 630rpm/V motor at 22.2V = 13,986 rpm

so 353571 / 13986 = 25T motor pinion.

So for you to get a 1500rpm rotor speed on a 6s battery you need to be running flat out with a 25T pinion. (Assuming my maths is correct!).

In theory I get a max headspeed of 22.2 * 1100 * (19/55) * (14/60) = 1968rpm.
At this stage I'd consider another 3s battery (assuming your ESC/BEC can take 9s, or getting a new motor..

[Globs]

This heli is 1.23m long, as opposed to 9.62m, giving a scale of 1:7.82, so I suppose it's a large 1/8th scale.

So a 6' pilot should be 1.8 / 7.82 = 23cm tall or 9.2".

[RAV50]

I use 5S/3700 and 5S/4300 packs on my Swift16/A109. I run the head a 1700 head speed, with 550mm FK blades.

I run 6 minute flights on the 3700's and put back 3000mah or so after 6 minutes and 3500 or so in the 4300 packs after 7 minutes.

It weighs 7lbs 7oz. ready to fly with the 3700's

My Eagle Tree readings show an average wattage draw of between 520 and 530 with amperage averaging between 29 and 30 at an average 17.8V (these 3700mah packs are over 3 years old and all have over 120 charges on them now).

The same power system is in another Swift 16. It is set-up for 3D and uses 6S/4500 packs at a much higher head speed of 2150. It is also a lot lighter at only 5lbs 14oz, but because of the higher head speed, it consumes a lot more power - 770 to 780 watts average!!!

I have found that everything being equal, the best way to get longer flights is to lower the head speed. I get well over 8 minute flights if I set for a head speed of 1550. But then it is not as aerobatic, and sometimes I like throwing in some aerobatics. so I now turn it up at 1700.

When the A109 is cranked down to the 1550 area it will only consume 420 watts as an average.

[GyroAl]

I have run my Swift A109 on 4S packs, 5S packs and 6S packs. I am using the 1110 kv 600+ motor and the smallest pinion I have is the 9T one. I also like running as high an ESC throttle setting as possible to keep it all running as efficiently as possible. Consequently, I find the 6S packs results in a little too high a head speed for this power system at the lower head speeds I like for scale flying.

The models weight has varied from the lower 7 lb area with the smaller 4S packs I have used to the higher end of the 7 lb area with some of the bigger 6S packs.

I also find that the head speed, has a lot to do with the resultant flight times. At the lower head speeds, a 4S/5000 pack gave some pretty good flight times. But I also found that my preferred packs are the 5S 4000 to 5000mah packs for this scale application.

There are three Swift A109 video's on this youtube address, Chuck's is on 4S packs, mine is on 5S packs and Randy's is on 6S packs...all fly very well.

http://www.youtube.com/PreddyGS

Looking at your calculations for your Bell 47, if you get it in the weight area of my nitro Bell 47 of about 8.4 lbs. and gear for a 2500 head speed your power consumption would probably be in the area of 600 to 650 watts.

[Globs]

Hi GyroAl,

Your 1550rpm a109 figures all tie up well, 3Ah for 8 minutes = 3 * 60/8 = 22.5A, which on a 5s at 18.5V gives 416W, and you say 420 Watts.
Amazing what difference headspeed makes!!

Not sure of the relative weights, but if I draw 450W at 1500rpm on the 600 stock woodies then I'll be using 450/22.2 = 20.3A, giving a 5Ah runtime of 14.8 minutes, which sounds good.

If I decide to go for a smaller pinion to up ESC efficiency on 6s, I need a pinion of:

353571 / (22.2 * 1100) = 14.4 or 15T. To give a little headroom perhaps 16T, giving a max headspeed of:

22.2 * 1100 * (16T/55) * (14/60) = 1643 rpm

so if my ESC gets hot I'll go for that, although it is an 80A esc switching c.20A so I'd be surprised. I could do with testing different ESC timings on different current draws, I'm just not sure how to measure that. Maybe use a bit of bell wire in series and measure the voltage across at lift off?

[Cletus]

You do nice work Dude! .....nice project. I'm keenly following this thread.
I am thinking Raptor 90 mechanics in my Kavan Bell Jet Ranger fuse for my next project.
BTW A Tektronix 545A was my shop workhorse up to a couple of years ago

[GyroAl]

Originally Posted by Globs

Not sure of the relative weights, but if I draw 450W at 1500rpm on the 600 stock woodies then I'll be using 450/22.2 = 20.3A, giving a 5Ah runtime of 14.8 minutes, which sounds good.

If I decide to go for a smaller pinion to up ESC efficiency on 6s, I need a pinion of:

353571 / (22.2 * 1100) = 14.4 or 15T. To give a little headroom perhaps 16T, giving a max headspeed of:

22.2 * 1100 * (16T/55) * (14/60) = 1643 rpm

so if my ESC gets hot I'll go for that, although it is an 80A esc switching c.20A so I'd be surprised. I could do with testing different ESC timings on different current draws, I'm just not sure how to measure that. Maybe use a bit of bell wire in series and measure the voltage across at lift off?

With any of my electrics, or those for customers, I always try to select a motor with a KV and a pinion which will allow a gear ratio that will result in the rotor speed I desire while using as close to a 100% throttle ESC setting on the ESC. I have found that using higher voltage packs and using lower KV motors and/or lower pinion teeth result in the lowest amperage requirement. This of course results in longer flights for the same MAH. That is why I prefer to talk in watts instead of just volts or just amps, as watts is a consideration of both (Watts = Volts x Amps).

So if a heli weighs 7.5 lbs and uses 420 watts to turn 520mm blades at 1500, then I can use a 4S (14.8V) pack and the amperage draw would be 420/14.8 = 28amps, a 5S (18.5V) pack would work out to 22.7A and a 6S (22.2V) pack would be 18.9 Amps. So all things being equal, if I only want to push my packs to 85% capacity for long life, then a 5000mah (5 Ah) 4S pack would deliver a battery friendly 9 minute flight. On the other hand, I would only need a 3150 mah (3.15 Ah) 6S pack for the same 9 minute flight. An interesting side note, is that if you use the same C rating cells from the same manufatcurer, you will find the 4S/5000 pack will be close to the same weight as their 6S/3100 packs.

Note that in your calculations, you are assuming a 100% efficiency of the said power system. I have found that one is more accurate, if he uses a 90% efficiency constant in such calculations. So your 1643 calculation would be more like 1643 x 0.9 = 1478.

[Globs]

That's interesting GyroAl, thanks for that. Do you run a model shop then?

I found this link too: http://dhrc.rchomepage.com/calc.htm

that has a calculator on it. I also understand what you say about efficiency, so if I have a theoretical headspeed of 1968rpm (with my 19T pinion) at 85% efficiency I'd get 1673, which actually isn't that far away from 1500. Perhaps Bell Bloke was onto something with his ratio (which I copied), I'd just need to go to 17T to get a max of 1497rpm.

I suppose a battery is measured by energy/mass, or Watt-hours / kg of which I'd expect lipos to be reasonably consistent. At higher voltage (lower current) the wires, fets etc will be for efficient too.

So if Donnie goes to 9s power with a 20T pinion he'd going to have a real headspeed of 1513rpm at full throttle - which sounds ideal, or with a 22T he'll have almost exactly the same headspeed as me.

So Donnie - if I were you I'd order another 3s pack and use your 22T pinion and you should be fine (or at least where Bell Bloke and I am).

[Donnie D]

Thanks guys,

I've got 4 pinions coming, 18, 20 , 22 and 25T. I may go with a differant motor and use the 18T. That way I can stay with the two 3S in series. I've gor two Hyperon 3S, 4200 mAh 35c. Maybe a Scorpion 4025/1100 or something.

Donnie D

[Globs]

I've modified the frame now to take out the incorrect verticals and add in a strut. I used copper one the LHS and spare material to fill in the missing bit from the silencer outlet, and the other RHS I used two spare material bits joined by a 3mm rod and solder.

The frame is brazed interestingly - my new joins are soldered. The new struts however just join with flattened ends and 3mm holes onto the existing bolts and actually strengthen the existing structure.

I've added a dummy air-filter(?) as on the full size for the last photo, where the original Century rod was.

[Donnie D]

Cool. I don't have the extra truss like pieces on the sides, but I think I'll order them when I finish the build. Looking forward to seeing how the aileron function works with the one servo.
So which pinion are you going to use, 17T or 19T?

Donnie D