Arising Star Power Issue

[Simon UK]

I really didn't want to go down the lipo route Timbo, I would rather get myself a decent A123 setup, and know i have a couple of solid years of use rather than the lord knows how many charges i would get from budget Lipo's. £100+ pound lipo's are unjustifiable to me im afraid.

 

I am having to put 260 grams of useless wieght near the front to get cog, so i have wieght to play with. Also fitting a different UC and making it a tail dragger would give me more ground clearance up front for a bigger prop.

 

Would you be able to suggest a setup for 5-6 cell A123, maybe sourcing the parts from Giant Cod or HK?

 

It would be a great help honestly.

 

As to wether i'm happy or not with my 5s pack, tbh i do not have anything to compare it against, except my old I.C setup. And i would prefer rubber band power to getting covered in glow fuel again.

[Simon UK]

I did read somewhere about ESC efficiency, and maybe my setup could be losing some voltage through my El cheapo ESC?

[flytilbroke]

Propeller ground clearance with a tail dragger of this nature, is only ground clearance when the tail is on the ground. It does not stay that way as the tail lifts before take-off. If you have sufficient thrust/speed you may be able to hold the tail down. That is perhaps at odds with Simon's plans?

 

Taller undercart might be a way forward? Seen it work on a couple of models.

[Tim Mackey]

Whenever I have an issue with a component, and have eliminated all the obviuos points, such as battery charge level and ESC timings etc, then I find the only real way to track down the issue is by substitution.

However, maybe you dont have other ESCs and batteries etc to do that?

The ESC can certainly make a difference to motor performance, but Its unlikely that this is the cause of the batteries sagging. Of course, your wattmeter could be lying, and I have heard from an "expert" that these meters vary tremendously in their readouts from one make to another...something I am attempting to put to real world testing soon, when I can get enough different ones on the test bench.

£100 lipos ? - Blimey you are behind the times arent you

A stonking great 4000m/a  5s 3rd generation pack - chargeable in 15 minutes - is available these days for the paltry sum of just £45

from Rob at GC

These superb 20 /25C packs can hold up to 3.5V per cell under heavy loads of almost 80Amps. This would whack your input voltage up to 17V+ and then the Watts @ 40  would be almost 700. Assuming your charger can deliver the goods, these can be re-charged in the same amount of time as A123 cells, so again, extra packs are not really needed.

Food for thought ??

Edited By Timbo - Administrator on 20/12/2009 12:14:20

[Tim Mackey]

Otherwise, you are looking at increasing the series count of your A123s. The problem I keep mentioning here, is the capacity. A123s are only 2300m/ahr - and even allowing for the fact that they can deliver all of it and run quite "flat" without harm, its still not a lot of flying time when you need 40A plus current.

Having just done some quick mental figures, I reckon your 900 Kv motor ( which is luckily actually rated at about 750 watts ) on a 5s Lipo with a 12" prop would probably be about on the mark. Revs will be higher than Ideal, but then, that motor is not ideal for the model is it.

You may need to reduce the pitch of the prop to keep the watts under control, which means less flying speed, but, again, all down to trying to make the best of the wrong motor really.

Alternatively, how about a nice large capacity 4S lipo, which may allow you to use the higher pitch prop, albeit on higher current?

Edited By Timbo - Administrator on 20/12/2009 12:23:17

[Simon UK]

This is my first foray into what i call serious electric power (.40+ size aircraft), i only have to hand the equipment that i am using. I do however have this on the way

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6231

bought for my Hangar 9 80" wing span Cub (please tell me it will work!), i am also planning on a Turnigy 60A plush esc when they get back into stock.

 

Well tbh i was wanting to stick exclusively to A123's for me they have a couple of major advantages. One pack needed per plane, wont explode and burn my house down, will last longer than a lipo pack before needing replaced. The negative of a 5 minute flight IMO was worth the trade.

 

BUT i am starting to appreciate Lipo's are getting to decent prices (GC and HK only btw), and they do have much higher mah.

 

I am using a couple of Lipo's in smaller aircraft and i am happy with the performance.

 

Maybe Timbo as you are knowlegable about these thing's you could tell me how long on average your lipo's tend to last before needing replaced?

 

I can see why the I.C guy's stay away from lecky by the way it's a steep learning curve, unless your buying flight packs (at rip-off prices)

[Tim Mackey]

First off, my lipo packs last anywhere between 20 cycles, and over 100 - too many variables to give an average....use /abuse, storage temp and level, quality of packs etc.

I agree that the A123s have some advantages, but these are dwindling since the introduction of good 5C chargeable lipo - but of course - the jury is still out on the longevity of these packs so don't ask.

I have around 100+ various packs in my garage, summer and winter, old and new, and none of them have exploded and burnt my house down  - there are simply far too many ignorant,  inflammatory and non factual scare stories about lipo batteries. I will not go down that well trodden road, but rather leave it for the silly people who think its useful or entertaining to post videos of exploding batteries on U tube.

 

Stick with your A123s in this model by all means..... but I still think you will need at least 1 x more series cell, and for a 6lb trainer, I also think 2P would be better, Ho hum.

Incidentally Danny Fenton and Chris Bott use a lot of A123 cells, and I believe their formula is something like one cell per pound of AUW.

 

As to your imminent arrival  - it should do fine on your 80" Cub - PROVIDING you select the right size prop ( large ) and battery configuration ( not too high V ) to get the power you want at a proper flying / pitch speed. This brings me back to the point I made earlier...your 900Kv motor on a 12 " prop with 6s cells will be noisy and high revving....just like an IC ....but without the gunge

[Stephen Grigg]

Go on Simon buy a Lipo you know you want to,although reading your thread you dont.Im surprised about the weight thing I suppose its due to it originally being IC,.Why have you become fed up with I.C.

[Simon UK]

Thanks Timbo for the advice, with a bit of surgery i could make another pack fit in the Trainer.

 

What do you think of 5s2p on a prop 1" bigger or same diameter but higher pitch say 13x10 cut down to 12x10. Do you think this would provide slightly more power.

 

Good news also on the Cub, the ground clearance should be better than my trainer so i would think a 14 or 15 inch prop would fit comfortably.

I would be looking to use the batteries from my trainer, (really just my experimental plane) so i would be wanting again to run 5s2p on it. I have the Original information from Hangar 9 that states they recommend the E-Flite power 46 and 4 cell lipo. So i guess what i'm asking is this, is the motor i linked as capable as the power 46 on the same cells?

 

I will get there in the end!

 

You stated something earlier that i have wondered about, and that is the accuracy of the Watts-Up meter. I think it cost me about £30(ish) and it gives a lot of info for that money, i doubt it is 100% accurate myself, but it does take the guess work away for me. I would love for the Magazine to one day do some testing and a round up of these meters though, that would be very helpful to us non educated types

 

Could i also ask one more question Timbo, what sort of battery do you use at the field for recharging? Is it a Leisure Battery and if so have you ever drained it at the field?

 

[Tim Mackey]

12 x 10 would certainly increase power.

Use the 15" on the Cub.

The motor you have linked to will be as powerful or more so, than the eflite 46 - providing the prop is right for the 5s cells.

Watch this spcae for a review of wattmeters

I use a leisure battery - they are far more tolerant of deep dischrge.

No.

[Simon UK]

Posted by Stephen Grigg on 20/12/2009 14:23:38:

Go on Simon buy a Lipo you know you want to,although reading your thread you dont.Im surprised about the weight thing I suppose its due to it originally being IC,.Why have you become fed up with I.C.

 

 

 

I.C well i wont completely bore you with a very long post, but i will tell you this. I have spent a good few minutes between flight's with a rag taking oil of my plane. I have spent 10 minutes plus at the end of every session cleaning up the plane to make it look semi respectible.

Two saturdays ago i was helping a fiend start his Prangsters Irvine 46 because the prangster is basically made of floppy foam, i was holding it at waist height. Due to a previous crash the fuel tank had a hole in it, i was covered in glow fuel and not happy. It wasn't his fault of course but no the less it made an allready strained relationship with I.C snap!

Also on saturday past i was up at the club to test my Lecky setup and see if she would fly (she = sexist i know), my buddy had a plane with him fitted with a .90 FS, the glow plug had died and as he hadn't brought a spare so had his day.

Lastly, i have literally laughed at the site of 5 planes in the pits all struggling to start there engines, whilst the one or two Lecky members at my club  have had a flight and are in the club house (Hut) having a cuppa. I want to be one of the cuppa guys

I could droan on forever but i will leave it there.

Edited By Simon UK on 20/12/2009 14:43:04

[Andy Gates]

Timbo

 

I am wondering if Simon may be better adopting a smaller diameter prop with a higher relative pitch.

 

With a 15 ft take off he is obviously not short of thrust but is short on pitch speed.

 

Maybe a 11x9 would be better, 11" giving slightly less thrust and a little more pitch giving a better flight speed.

I would guess the power would be similar to his current (excuse the pun) readings.

 

Your thoughts?

 

Simon

 

This exercise you are going through is the reason I use one of the many estimation software packages available. Try one and run the figures through it.

Providing you use the readings as an estimate, then to do comparisons like you are costs nothing and can be very profitable.

[Stephen Grigg]

I put a couple of leccies in the car today but Ive got my batteries confused so havent bothered to go,I know what you mean I struggled to get 1 of my Ic,s going on Thursday and when it started it covered my colleague with fuel,oh we laughed,well I did

[Stephen Grigg]

Ans of course you can warm your hands on the battery

[Simon UK]

Super news Timbo on my choice of motor for my Cub, that was a main concern tbh. I am also glad to hear about the Leisure battery, how high AH is yours by the way? I see different sizes available but would like to keep it affordable, would the 110AH be ok do you think?.

 

Andy could you elaborate on the "Estimation software packages", name of software, and ease of use? And thanks for the tip's btw

 

Stephen had'nt thought of hand warmers, but at this time of the year, i reckon i could make the I.C guys at my club jealous using lipo hand warmers - lol

 

On a last note about I.C, how come guy's that use Real (sarcasm intended) engines allways have to roll their eye's when i tell them i'm going Lecky!

 

 

Edited By Simon UK on 20/12/2009 15:10:25

[Andy Gates]

Last question answered first Simon.

 

"Because they do not understand it!"

 

By estimation software packages I mean stuff like MotoCalc which has a free trial period. www.motocalc.com

 

There are others but that is the one I use.

Like most things it takes a while to get used to what it will do and how it does it, but it does save the cost of keep buying components.

[Andy Gates]

I have run some figures through MC which shows your set up should work fine for 3 minute flights.

Dropping to an 11 x 7 prop will drop the current slightly but will give you a 10% increase in flight times .......... to 3 1/2 minutes. It will also help you in flight speed, but as Timbo says your set up seems to be under performing.

 

Maybe your batteries need some more bedding in.

[Simon UK]

Well as they are supposedly good for 1000+ charges i dont mind cycling them a few more times to see if it makes a difference. On another note during my first test flight i was definetly airbourne for more than 3 minutes, more like 5 ish, and when it was landed a power was applied it would have still had enough juice for another Rog.

 

Will look into the Motocalc Andy thanks for the advice 

[Andy Gates]

Time I gave you is for a full throttle flight.

 

On the second RoG, my reply would be I doubt it.

Although it may have accelerated away at the start, the power would drop off quite quickly and you would be in the position of not enough speed or height and a crash would be the result.

 

Most of us have been there,  don't not try it.

Its like taking off with too weak mixture on an IC engine which I am sure you know all about!

[Tim Mackey]

Sorry for the delay....email notifications stopped working for some reason.

110Ahr will be fine for the battery. As to the prop change, yes that may help, but still doesnt address the issue of the poor power figures. Dropping diameter and increasing pitch by the same amounts should result in the same overall load on the motor, but in practice I find diameter has more effect, so the smaller diameter may drop the watts even more

Perhaps that prop and the extra cell may work.... and of course how the model actually flies is often quite different on different props despite the meter readings...thats why I like to have a few props to experiment with. Any "spares" are eventually used on something later.

Edited By Timbo - Administrator on 20/12/2009 16:09:26

[Simon UK]

Well Andy if read back a page or so you will find a post about a test i tried, 3 minutes on full power then voltage dropped like a brick along with rpm. So the Motocalc software was spot on if it gave you 3 minutes.

 

Will pick up a few props of varying sizes, what about a 3 blader out of interest? Havent looked at them yet but they may be an option.

 

Andy your probably spot on with the, it would'nt have made another RoG statement, wish i had thrown the battery on the charge at the time just to see how much juice was left.

 

On a different note have any of you tried the Fusion Smart Guard on Life cells yet? Looks like it could be a handy gadget.

 

Hope your mail box is sorted now Timbo, your presence is required around here :P

will pick up a Leisure Battery in the new year, looks like it will be needed for Lecky Flight

Edited By Simon UK on 20/12/2009 17:45:17

[Andy Gates]

I have a Smart Guard but only use it on Lipos so I am not in a position to comment on the use of it with LiFe.

Again like MC, use it as a guide and not imediately after a flight.

The cells need to settle down first before an accurate reading can be obtained.

Once settled, the results pretty much agree with what my charger puts back into the packs.

[Simon UK]

Sorry to resurrect this thread again guys, but after much thought over Crimbo i have decided to buy myself a couple of Lipo's i reckon they will make my life easier reagarding getting my Arising Star to perform (yes Timbo you where right)

 

Couple of questions before i purchase 

 

Just to recap and save anyone having to read from the top of this thread my setups are

 

Arising Star

AUW 6.8lbs in order to get proper CoG

Motor fitted Turnigy Sk3548-900

Prop 12x8 apc-E can lose diameter but not gain (maybe gain an inch if i really had to)

 

H9 Piper Cub 80" span

AUW as above around 7lbs

Motor Turnigy 4260-500

Prop can go to atleast 13" diameter (should be able to go to 15" i hope)

 

 

Need to know wether to go 4s or 5s Lipo, ideally i would like the batteries to be useable in both planes, and i would like to buy two to start with to allow more flight time at the field.

 

Shelving the A123's for the time being, may suit my future project (Flair Magnatilla) i hope.

Lipo's will be either from GC or HK so if anyone see's some suitable for both planes that would help.

 

 

Edited By Simon UK on 31/12/2009 00:51:02

Edited By Simon UK on 31/12/2009 00:51:47

Edited By Simon UK on 31/12/2009 00:53:32

[Bruce Richards]

I think 5s would be too much for the 900 Kv motor in the trainer. Ideally  A high Mah 3s would suit this model but a 4s will probably be OK.I would say that the Cub should also be OK on 4s as long as you can fit a nice big prop.

[Tim Mackey]

I agree. However, we should stress that to get the power you will need for the 80" Cub, a 500Kv motor on 4s lipo will need a BIG prop like the 15" you mentioned - which is fine, cos its a big model and should have thrust rather than top speed for scale like flying.

The higher Kv motor in the trianer should be OK on a 12 or 13" prop, but as always, please use a meter to confirm WOT current is within tolerance of both motor and ESC

Your 7lb models @ the norm 100 watts per pound will need 700 watts.

From a 4s ( assume around 14v under load ) thats still 50A.... so quite high. Maybe I would try propping for a tad less power, say 80 watts per pound which is 560 Watts, therefore dropping the current to about 40A.

 

These are my current fav 4A  4s 20C Lipos of choice from Rob at GC

 

Those would be running at 10C only on discharge, and should give at least 6 - 8 minute flights with sensible use of the throttle

 

Great VFM @ £36 and 5C chargeable too if your charger can handle it.

Edited By Timbo - Administrator on 31/12/2009 15:47:04