Have I enough power?

[Nigel R]

449.0Wp is the peak power used in the system as a whole, i.e. 449 watts.

27.55Ap is the peak current draw, in amps. That tallies perfectly with the 450W peak power on a 4 cell pack.

However neither of those match up to a 14x7 doing 8100rpm, which is very odd. The 14x7 at 8100 needs almost double the power your meter is showing. I would say 450W is roughly equal to a .25 two stroke.

Just checking - it was connected between lipo and ESC?

And, did you hold it at full throttle for very long?

[Piers Bowlan]

Here is my 2p worth! You need a bigger prop;- 15x8 or bigger or alternatively 5s or 6s battery.

4s is nominally 3.7v X 4 = 14.8v, as I am sure you know, and allowing for the voltage drop under load, call it 14v. 14v X 37.5A= 525A and if the motor is (optimistically) 85% efficient it will give you 446.25 Watts at the propeller. aka not very much . Your Watt meter was giving you 449W at the propeller, which is pretty close to my 'back of the envelope' figures. It probably explains why the motor is getting barely warm.

Personally I wouldn't compare IC RPMs with electric flight RPMs as from my experience and to make a broad generalisation, I would expect a bigger prop and lower RPM in my electric models compared with IC although it does depend on the motor Kv and a few other things.

I will now get my head below the parapet!

[Ronos]

Hi Nigel, yeah it was connected in-line and it was running at full throttle for the time it took me to write down the results.

[Andrew Calcutt]

Still reckon you need six cells,1000 watts and 50 amps,personally I would want closer to 1500 watts.

[Mike Blandford]

Something not quite right with those readings. You show 37.5A, but only 27.55A peak.
At 16V, and 37.5A you should have 600W.

Also with 16V in, I would expect the motor back emf to be between 13V and 14V. With a 580kv motor, 13V would be around 7500 RPM and 14V would be around 8100 RPM. Possibly the 16VM is a maximum value.

Mike

[Ronos]

I appreciate all your input, and please don't take this the wrong way but, if i new what you were all taking about i might know what am looking for and know what all these numbers mean on this wattmeter. So going by the general census the top and bottom of it is, Go 6 Cell.

[Ronos]

Fully charged battery at idle 16.74v, Ap 0.62. RPM at full throttle 8250. After 2mins at full throttle it reads.

Vm 15.09

Ah 1.555

Ap 37.61

Wp 609.2

Wh 24.2

worse,better,or get a 6 cell.

[Phil Green]

Ronos, please dont take this the wrong way but I would seriously suggest you put that 4.5kg scale model away for a while and get some electrics experience with a small sport model. 1000 to 1500 watts is an awful lot of power, its way, way above the average Sunday flyer's bag and if you are as inexperienced in this particular field as you say then personally I think you have a serious challenge of safety to yourself and to your clubmates. We appreciate that you're very experienced with large IC powered warbirds but electrics are different, and one-and-a-half kilowatts of electric is very very different. There are safety practises and throttle protocols that you've never had to even consider up to now - glows dont start themselves like electrics can and 1500 watts will take your your fingers off with ease, and it wont stop at that. I know you dont want to hear this but my suggestion is to gain some electrics experience with something more modest. Familiarise yourself not only with volts, amps and power, charging schedules, balancing, and more - but mostly the essential safety procedures of flying a large electric.

Thats my 2p anyway

All the best

Phil

[Nigel R]

deleted, as you'd already re-run

Edited By Nigel R on 30/01/2020 16:20:41

[Alan Gorham_]

At the risk of sounding sarcastic I was going to suggest finding the Wattmeter instructions and reading those, but Phil has been a bit more diplomatic.

If you are not sure what you are trying to achieve here and can't understand the advice being given, then it won't do you any harm to do a bit of background reading.

Possibly work your way through these useful documents on the 4-max site to start with:

useful info

[Ronos]

Posted by Phil Green on 30/01/2020 16:15:35:

Ronos, please dont take this the wrong way but I would seriously suggest you put that 4.5kg scale model away for a while and get some electrics experience with a small sport model. 1000 to 1500 watts is an awful lot of power, its way, way above the average Sunday flyer's bag and if you are as inexperienced in this particular field as you say then personally I think you have a serious challenge of safety to yourself and to your clubmates. We appreciate that you're very experienced with large IC powered warbirds but electrics are different, and one-and-a-half kilowatts of electric is very very different. There are safety practises and throttle protocols that you've never had to even consider up to now - glows dont start themselves like electrics can and 1500 watts will take your your fingers off with ease, and it wont stop at that. I know you dont want to hear this but my suggestion is to gain some electrics experience with something more modest. Familiarise yourself not only with volts, amps and power, charging schedules, balancing, and more - but mostly the essential safety procedures of flying a large electric.

Thats my 2p anyway

All the best

Phil

Thanks Phil and no offence taken. I started of with electric foamies for example Hobbyking B17 on 5200Mah 3s, FMS BF109 on a 4s 3200mAh and a Eflite Spitfire 1400mm on a 3s 2200mAh, but these are plug and play no matching up to do. The motor and ESC for this VQ Hurricane is the one recommended by Hobby Plastics, so I assume its the correct set up, just figuring out what the best battery would be. I understand about the safety aspect between IC and Electric and have always used the throttle cut in both cases. I just fancied going electric on this size warbird and had a 4s lying about and just wanted to know if it was capable to do the job before forking out x number of ££ on the wrong size lipo.

cheers Ron

[Nigel R]

"Vm 15.09

Ah 1.555

Ap 37.61

Wp 609.2

Wh 24.2"

OK, now we're cooking on gas, well, nearly.

609 watts is still a ways under what I'd expect for that prop/rpm.

[Nigel R]

If you have a bigger prop I'd say test that.

15x8 would be my next port of call.

Or, 5s / 6s lipo, but start with a 13x6 and work up toward 1000W or so.

 

"5200Mah 3s"

If you have two or more of these, you can always run a pair in series to figure out a good prop for a single 6s lipo.

 

 

Edited By Nigel R on 30/01/2020 16:36:31

[Alan Gorham_]

I'd still love to know why you have to add 40 oz of weight to get it to balance...

[Alan Gorham_]

Having now visited Hobby Plastics website and looked at the page for this model it looks like the recommended power pack does not come with a propeller, nor does the website seem to recommend a prop. The specs for the motor recommend props from 14 x 6 to 17 x 10 so I am guessing that you have chosen a prop at the lower end of the range. I'd buy a 17 x 10, 17 x 8, 16 x 10 and try those props with the wattmeter fitted to make sure I wasn't exceeding the max current for the motor or ESC and see what that takes the RPM and wattage up to.

[Ronos]

I have 15x8 ic prop somewhere I'll put that on and see what it comes up with also I'll put two 3s 5200mAh together, same set up as the B17. Thanks all I'll post the results , my heads done in.)

[Alan Gorham_]

I don't think an 8" prop will give you enough pitch speed on 4s. It might be great on 6s however, providing your motor current isn't too high.

[PatMc]

Unfortunately the max current isn't given in the motor spec & the power quoted doesn't say with what voltage.

Rule of thumb to stay within the safe max current whilst & getting max power is aprox : rpm = applied volts x kv x .8

If the rpm is much below the motor is overloaded, if rpm much above the motors not working hard enough.

As far as the weight's concerned 4.5kg means the wing loading is around 42oz/sq ft. Not looking good for a model with a wing area of under 4 sq ft.  

IMO the model needs to gain 2 cells & lose about 3lbs. 

Edited By PatMc on 30/01/2020 17:53:29

[Alan Gorham_]

HobbyKing's Propdrive 5050 580 kV motor has a max current of 90A, so although that's not a guarantee of anything it is at least a guide.

[Piers Bowlan]

Looking at the spec on the Hobby Plastics website with a KV of 580 this is a 5s to 6s motor so running it on 4s you will need a huge prop to get some decent power out of it (maybe 17 X 10). This may not work too well as your landing gear may not be long enough!?

I found this rather scrappy video on You Tube where someone tests a similar motor:- a Hobbyking NTM 5050/580kv motor. He ran it on 6s (22v) and fitted a 15x7 propeller. It pulled 65A and produced 1443Watts. So the 14X7 prop you have been using may be perfect when used with a 6s LiPo. 1443 Watts may be more than you actually need!

Edited By Piers Bowlan on 30/01/2020 18:09:14

[Alan Gorham_]

And bear in mind the OP said he's put 40 (count them) ounces of noseweight in then perhaps a 6S pack is a no-brainer.

[Mike Blandford]

Just read both a manual and a listing for the VQ Hurricane. The listing says 4S, 5000mAh and the manual says 14x8~15x8 for the propeller. It does say weight 3.3-3.6kg, so something seems to be wrong if 40oz of lead is needed for balance. CG is shown as 3.3-3.5 inches (85-90mm) back from the leading edge.

The manual does say some nose weight is needed, but 1.15kg seems too much.

Mike

[Ronos]

Yeah ,40oz that what it took to get the CoG. To get that down will be to get the battery forward as much as possible, with a bit of modification on the fire wall, cutting out the middle for the battery. I had to open the inside bulk head to get the 4s in so to get a 6s in it's going to be major surgery. Going to see what I get with these two 3s together, if it works then that's the answer or is it??.

[Ronos]

Thanks Piers, I can see what I need to achieve, or along them lines anyway. Once again THANKS everyone for all your input, it's a learning curve and your never to old to learn👍👍👍

Edited By Ronos on 30/01/2020 20:03:52

[Piers Bowlan]

I maybe now about to eat my words!

I see on the Hobby Plastics website that a Saito FA62B is the recommended IC engine for the VQ Hurricane, and this is claimed to produce .95 PS. That equates roughly to about 750 Watts. I also see that the model RTF weigh is 6.5lbs, so 800W - 900W should be enough as a ball park. So with a 4s battery at 14.8v, 60Amps should produce around 900W. The question is, what size of propeller will draw 60 Amps? Your 14 X 7 is only drawing 37Amps so it needs to be bigger.

The problem with using a 6s LiPo is that the weight and wing loading will increase. That doesn't solve the problem of the c of g. Have you found any VQ Hurricane electric conversions online? Could the c of g position be wrong and is moving the battery forward, beneath the motor, impossible? Adding 40oz of weight to the nose does not seem like a recipe for success.