Is this too powerful?

[Old John B]

All my modelling life I have been an IC man, but after many years have gone electric.but I am old and am baffled by science The chaps in the club are most helpful I have an albatross and the battery for it according to the instructions is

14.8 volt 2200mAh LiPo 25C

I have 14.8 volt 3300 mAh 3.3.

In simple terms, YES or NO, will it blow the thing up

My expert wont be there next week and I want to fly it if possible

Old JB

[Frank Skilbeck]

JB, no it's the same voltage just 3300 mah rather than 2200 mah, so it has 50% more capacity. Bit like changing out a 4 oz tank for a 6 oz tank.

It will be larger and heavier and hence will increase the wing loading and could affect the centre of gravity, but apart from that no issues.

[Piers Bowlan]

Like Frank says, just check the centre of gravity is still within limits as you don't want any surprises. You may also find that you have a little more power with a larger capacity battery despite the voltage being the same. However the higher wing loading may make the model fly a little faster and be less floaty. That can be an advantage in a breeze with better penetration and also less susceptible to turbulence too. On the other hand you may not notice the difference at all! (apart from a longer flight time perhaps) Have fun.

[Old John B]

Thank you very much, you have set my mind at rest now. Will probably bore you next week with a report on its flying. Once again thank you

Old JB

[Frank Skilbeck]

Posted by Old John B on 20/02/2019 16:01:03:

Thank you very much, you have set my mind at rest now. Will probably bore you next week with a report on its flying. Once again thank you

Old JB

Look forward to hearing how it went, sometimes on these lightweight models a bit of extra weight doesn't go amiss.

[Old John B]

RE the queery I had on lipos. To those who replied and gave me the answer thank you. I said I would report on its flying, (The Albatross.) .Went nicely but the weather has been so iffy I haven't flown it since. Looking forward to better days to come.

Old John B

[Old John B]

Further to my queery I had on lipos for the Albatross, Frank wondered how it went. Well the weather has been lovely and we have had lovely modeling winds (8-10mph) and sad to report I seem to have had the odd ball. One of the club' s top flyers tested it and even though we had to change the receiver, it was no great shakes. I have had a couple of flights with it and to me it does not have the get up and go that it should, in fact after three circuits on full power it seems to slow up a bit . I know that one would not expect it to dash about like a pylon racer but it did seem not to have anything in reserve for emergencies if you know what I mean, perhaps I am odd but I don't like flying planes about on full throttle all the time!!

Anyway I shall persevere, certainly looks the part. Perhaps it was because I didn't put the pilot in it, if the one supplied and the plane were real he'd have a hard job as his feet would not touch the pedals !!??

Old John B

[Shaun Walsh]

What was the exact spec of the battery you were using, particularly the C rating?

[Allan Bennett]

What condition was your battery in Old John? If you left it fully charged since the time of your first post in this thread, it may have deteriorated so much that, even though fully charged, its internal resistance is so high that it can't provide the required 'oomph' (i.e. amps and watts) to power the model.

As per the initial replies to you, with the same voltage and higher mAh capacity than originally recommended you should get the same or slightly more power.

[Shaun Walsh]

Posted by Allan Bennett on 28/04/2019 11:44:03:

As per the initial replies to you, with the same voltage and higher mAh capacity than originally recommended you should get the same or slightly more power.

Providing that the motor is not trying to draw more current than the battery can supply. For example a 3000 mAH battery rated at 15c might not perform particularly well if the motor is trying to draw more than 45 amps at WOT.

[Shaun Walsh]

Can someone at the club put a wattmeter on the model so you can see just how many amps the motor is pulling and compare that to the battery spec and the limits of the ESC? You might be able to determine the cause of the poor performance.

Also which albatross is it, the Dynam one?

Edited By Shaun Walsh on 28/04/2019 12:04:25

Edited By Shaun Walsh on 28/04/2019 12:04:45

[Frank Skilbeck]

Measuring the watts is a good idea, it maybe that you need to change the prop, more pitch perhaps, to draw more power from the motor.

Remember an electric motor will always try to turn at the same speed for a given voltage, and draw more amps as the load increases, so if the battery volts are holding up well under load then it maybe that you just need to make it work a little harder.

If you can post some details of the motor and prop I could run them through Ecalc and give some suggestions.

[Old John B]

Hi All, I'll run through the questions you have asked ,so here goes.

1) It is a Dynam Albatross, excellent kit nothing to complain about there.

2) Batteries are almost new and are balanced charged every time I go flying.

3) Turnigy 3.3 30 - 40 discharge 3300 mAh 4 cell battery used. (Battery reccomended 14.8V 2200mAh Li po 25C)

4) Motor size, BM3720A-KV600 Brushless Outrunner

5) Speed controller, 40A Brushless

6) Prop. 13 X6 Dynam (two supplied.)

I shall press on as there must be hundreds of these flying successfully. Don't forget , it might be the old stick on the end of the stick causing the problem ? I can hear someone saying, "More than likely."

Old J ohn B

[Keith Berriman]

Heres an option I read you have changed receiver did you reset the ESC to high low rev range ??. I had similar problem and that was my solution

[Shaun Walsh]

Another couple of thoughts

Has the Tx throttle been set to give the full 100% output at WOT?

Are the ESC settings correct, particularly the motor timing and calibrated to high/low throttle? I usually set timing to "Auto" but it may be necessary to change it to suite the motor.

The motor spec appears to be 42A continuous, 50A burst.

If you can connect it to a watt meter and check how much current is drawn you may be able to use a 13x7 or 13x8, you might need to change the ESC to a 50A or 60A , that should give you 580W continuous or 700W burst.

[Frank Skilbeck]

OK, running the motor.prop and battery through ecalc gives 24 amps, 330 watts on the 13 x 6, with a static thrust of 1.75kg and pitch speed of 40mph, as the model only weighs 1.6kg it should have enough umph to go vertical. Changing to a 13 x 7 prop would increase the amps to 26 amps and speed to 46 mph, 13 x 8, 29 amps and 52 mph. So room to experiment.

Also one other thing to note, on electric the rpm is fairly linear to the stick position, where as on IC often the last 30% of the throttle opening only gives a slight increase in rpm, so the lack of power maybe perception due to the different throttle response. Or maybe your IC models are all adequately powered

[PatMc]

Has the ESC been calibrated to suit the Tx ?

Not all ESC's need to be calibrated but a lot of popular ones do. It yours does it should be explained in the instructions. Only takes a couple of minutes & doesn't have to be repeated unless a different Tx is to be used.

[Nigel R]

Concur with above, check the ESC calibration to throttle stick movement as your first port of call.

A wattmeter is an almost essential investment for electric flight. Would suggest getting one, they are not too expensive. This will tell you if you are getting that 24A current (or close to) that Frank mentions.

A cheap servo checker can also be useful to check the ESC / motor combination - that would avoid having the TX/RX muddy the picture.

At 3lb weight and just over 3lb thrust it this thing should be fairly punchy! So something is amiss. Just need to track down what.