Topic: No speed with my Sibart Shark

Hi once again guys. I took my Sebart Shark out for its madden flight on sunday it flew lovely but there was no guts in it. it was so slow,no stall turns or loops or anything else It took so long to get any height. Can anyone help me with this.
It has a Hacker motor A30-14L, 60 amp speed controller, 2500 3s battery and a  apc prop 14x7e  All this is what's recommended for this model

HELP!!

the stick on the left controls throttle, push it forwards a bit

more helpful than that, make sure the speedo is maxing out, should be a light come on or something when it's full RPM
is the battery charged??

What make is the lipo, how old is it? Is the Throttle ATV set at 100%? daft question i know, but i know someone who had a slow pylon model for a practice day last year and it turned out that the ATV was only at 60%  lol

Was the battery chilled by the weather? Is the ESC set to fully "hard" on the timing? Is the battery knackered? Was it put off by the sanctimoneous baying of the pig-ignorant hoards complaining about bankers' bonuses?

PDR

Was it put off by the sanctimoneous baying of the pig-ignorant hoards complaining about bankers' bonuses?
PDR

pete, don't attract their attention - "Occupy Barkston" is something we don't want to provoke (except if it's by BMFA Members around August Bank Holiday!)

the stick on the left controls throttle, push it forwards a bit

 

Was the battery chilled by the weather?

It was certainly cold on Sunday afternoon and Dave hadn't done anything to keep his batteries warm - that was the first thing I thought of too.  But I would have thought the performance would have improved as the battery warmed up when flying...

Dave,  when you've got some heatshrink tubing on your wattmeter connectors, connect up the meter and post the readings you get at full throttle.  Obviously with the plane suitably restrained!  And if you have a tachometer see what revs you're getting.  That should give some clue as to what is going on.  As you know I wasn't too keen to mess around on Sunday with cold fingers and uninsulated connectors risking shorting out your battery!

Hi John, I have put heat shrink on all the connectors now. I've charged the batteries up and taken the readings for you at full throttle.
AMPS 28.72
Volts 10.3
WATTS starts at 340 then drop to approximately 240 within 30 seconds.
Thanks for the help mate.

   

That's interesting. My Sebart Katana 30E with exactly the same setup pulls 500w+ (& I think it feels slow). The only minor difference is that I'm using it with a 2200 3s 20c Turnigy and a 14x8 Turnigy ultra light wooden prop. Tried it with a 3300 3s 30c and it gave exactly the same reading.

Either prop it more or less as Mole Hunter suggests or try it on 4s with the current prop.

Hmm,  not so sure...  The motor is rated at 35A maximum,  so at just under 29A you're not that far short of the max for the motor.  And prop and battery are as recommended - so that's all consistent.  If you went for a 4S LiPo you'd need a smaller prop to keep the current below the limit for the motor.

In your test today Dave,  did the motor feel like it had more power than on Sunday?  If so then maybe the problem was the battery being cold and/or not fully charged?

Currently it is pulling just under 29 amps for 30 seconds initially, this then falls to about 24 amps.

ecalc suggests that the motor with that prop would take about 23amps on a full battery and assuming that roughly the other amp is running the tx and servos, that would concur pretty closely with the steady state running. eCalc then suggests that with 4s that on a full battery there would be a current of about 35.5 amps after the initial 30 seconds or so. While I don't usually trust calculators it did seem to be working out pretty well for this combination.

However having read another source on this motor it turns out that the burst rating is 35A and 23A is the continuous rating. So apologies, follow John P's advice I seem to have boobed, you are already just about on the correct limit with 3s.

How much does your shark weigh?
Does the video on the Sussex Model centre web site help you at all http://www.sussex-model-centre.co.uk/shopexd.asp?id=27314
They seem to be suggesting a 14x7 APC

The batteries belong to my son but he hasn't  used them for well over a year and has never charged them since.They were new when he brought them and according to him have not had much use. Before using them I had them in my pocket with my hand around them. Maybe new batteries would be in order.

Thanks guys.

Shouldn't a fully charged 3S lipo show more than 10.3 volts? i'm not sure on the KV of your motor, but at that vltage it's probably a few thousand RPM down at 10volts

A fully charged 3s lipo should show around 12.4 volts, if it's only showing 10.3 it's not a lot of good!

A fully charged 3s lipo should show around 12.4 volts, if it's only showing 10.3 it's not a lot of good!

But he was talking about voltage under load

Sorry, didn't read enough - in that case it's reasonably ok.

Sorry, didn't read enough - in that case it's reasonably ok.

I wouldn't be too quick to apologise, because you're probably correct, a fully charged 3S battery should hold at more than 10v initially.

I would have thought the voltage was a bit down at those amps, I would have thought that a battery running at just over 10c should be able to hold more than 10.3v. Also if the ESC cut off is set high ( 10.3v is only >3.4v per cell) then it may be holding back the amps to keep the volts above the minimum setting. Maybe a better or warmer battery would be able to hold a higher voltage and hence higher amps.

I was flying round with an old 2200 mah 3s battery in a telemetry equipped model, started off holding 11.1v and 8 amps, but once the volts dropped down to 10.1 volts you could see the amps still dropping off even though it was at full throttle, showing the ESC was cutting back to protect the battery. On some highish (15c) amp application I have I've found it's best to bring the batteries indoors for several hours before going flying.

Hi guys, thanks so much for your input on this subject. I have been out and brought a new battery today. I'm going to charge the old batteries as well and try them all on Sunday. Maybe I cocked up charging them. I'll let you know how I get on Sunday night. Thanks once again guys.

Cheers Dave........

The shark (despite it's looks) is not a fast aircraft. It reminds me of the Junior 60 when flying into wind.

Don't get me wrong, it's a very nice intermediate trainer and loops and rolls with enough power. But, it will never be a speed machine.

800KV on a 7 inch pitch prop and 3S isn't going to be enough for loops.

Edit:- a 138g motor should take a lot more than 30A fo a long time. Try a higher pitched prop. You only have 50MPH max on a 7" pitch (which isn't a lot). Try 14*9.

Hi Dogshome, Thanks for your reply to my blog.I have flown a junior 60 and is much faster than my shark. If you look in youtube at the sharks they are doing loops, rolls and stall turns and mine won't do any of this. Once it's off the ground you have to keep going round in circles to get any height. It does no aerobatics what so ever.
Thanks Dave.....

That's not right! Even at 250W it should be doing better than that. You did remove the box before flight     

Your motor calcs look right. 800KV is a bit low on a 7" pitch prop though. Try more load and pitch.


Incidentally, what is the static pull like on the ground? Does it pull strongly on the floor?

S**t didn't know you had to remove the box. LOL I have made a few alteration since the last flight Iv'e added a battery this time maybe this will make a different. I will be flying it on Sunday so we will see how it goes. I'll let you know mate......

Dave.......

I will be flying it on Sunday so we will see how it goes. I'll let you know mate......

I drove past the Downs at about 12:30 today.  The gate across the entrance was still shut - obviously the road hadn't been cleared,  and probably still hasn't.  I assume you weren't there,  I didn't see anybody at the strip and I certainly wasn't going to lug all my gear up there through the snow!

 We was thinking about going but Steve bottled out so I stayed in and polish my Sebart Shark.Hope to see you next week John.

Dave......

I've just been looking at a 4s setup for my Katana:

http://www.hobbyking.com/hobbyking/store/__18164__Turnigy_Aerodrive_SK3_3542_800kv_Brushless_Outrunner_Motor.html

http://www.hobbyking.com/hobbyking/store/__18463__Birdie_60A_Brushless_ESC_Opto_.html

http://www.hobbyking.com/hobbyking/store/__9948__ZIPPY_Flightmax_2650mAh_4S1P_40C.html

Wot4dave did you look at the Sussex Model Centre link I posted earlier. At the beginning they detail the set up and it is the same set up you are using but using a 14x7 prop. If the new fully charged battery fails to give you what you want that might be the way to go and use a bit of throttle management.

Hi TSR, yes I read it and it was interesting thank you. I have brought a new battery to try. I'll let you know after the weekend.Thanks for you interest mate.

Dave...