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Eflite Viper too heavy

Old 02-23-2021, 01:55 PM
  #1  
jangodog
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Default Eflite Viper too heavy

Hi. I had great pleasure of my Viper until lately when i can't make it takeoff anymore. If it's because of the extra weight i added in form of a centerburner, seperate bec, and a plastic triangle in the tunnel for the wires and heavier trailing link landing gear i don't know. I'll post some clips and photos so you can see what i'm talking about. I don't feel the thrust is as powerful as it use to be. Would an upgrade of esc and motor get the extra power and maybe som better batteries with higher C rating do the trick? I'm close to buying the Avanti S high performance instead. Thoughts?

Videos
https://imgur.com/a/jFFIpn4


://ihttps://imgur.com/rVwcjCGmgur.https://imgur.com/rVwcjCGcom/rVwcjCG
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Old 02-23-2021, 03:19 PM
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Do you have a watt meter? EDFs are amp hungry and batteries lose the ability to deliver high amps long before they lose capacity. I have batteries that where once good in EDFs but are now only good for prop planes. I get one maybe two seasons on my high C rating batteries before they are no longer good enough for EDF use.

Buy or borrow a good battery (or parallel a couple batteries) and measure the amp draw on your EDF and compare that to the batteries that no longer fly your jet before you give up on the plane.
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Old 02-23-2021, 04:09 PM
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How much weight did all that add? They are not that heavy to begin with so every little bit you add makes a big difference
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Old 02-23-2021, 04:22 PM
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Well a watt meter seems like a good idea. I'll try it later. About weight i haven't calculated it but a guess is somewhere around 100-120gram at the most. So maybe new high rated 70-100C lipos could work?
Any suggestions on lipos not to heavy 4-5000mah 6S ? Prefer European websites because of the costums fee
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Old 02-23-2021, 04:26 PM
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not a European site but my favorite batteries are the Potenzas from Flex innovations. I have some 6s 5000 40c's that I have been using for about 4 years now and they perform great still Flown them in my Prometheus, GP Reactor, Sebart Angel S, and others. Love the way they perform.

https://www.flexinnovations.com/prod...ics/batteries/
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Old 02-23-2021, 07:28 PM
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So i don't necessarily need 70-100C lipos for the Viper? What about the esc 70amp stock in the Viper would a bigger esc like 80 or 100 amp be better?

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Old 02-23-2021, 09:21 PM
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Need to know how many watts amps you are pulling. The higher C rating the better. but that doesn't always mean you need it.

If you are not pulling over 70 amps putting a bigger ESC will not produce any more power.
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Old 02-24-2021, 09:40 AM
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Originally Posted by firemanbill View Post
Need to know how many watts amps you are pulling. The higher C rating the better. but that doesn't always mean you need it.

If you are not pulling over 70 amps putting a bigger ESC will not produce any more power.
Iíll connect my HK wattmeter later today. C rating how is this visuel on the wattmeter?
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Old 02-24-2021, 10:22 AM
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C rating is not shown on meter ...

What you need to know is :

AMPS at full throttle
VOLTS at full throttle shown on the meter
WATTS on meter at full throttle.

We know you have 6S but not what mAh and C rating they are. Lets assume you have a 6S 4000mAh and 30C ..... - in theory you could pull 120A out of that battery - but in reality - because of wire gauge etc. - the real max would be about 70 - 80A. IMHO a battery of that rating would have a relatively short life regardless of theory.

Those batterys you see with quoted high C ratings of more than 60 ... I am not a believer that they actually can deliver such high rates ... you just have to look at the wire leads connected and imagine such ampage going through them !
ESC's either work or not. They have little effect on power through them except as throttle. The ESC will not restrict power max as long as the ESC is rated for such load. If not rated for it - then it will overheat and cut out or burn out.

Last test is to remove all your additional stuff - revert back to factory ... weigh the model ... then weigh separately your parts .... arrive at total figure.
Now with digital scale - stand model on its nose on the scale - read of weight ... note that down. Then open throttle full and read the total weight and Thrust ... deduct first figure from second - gives you static thrust ...
You should aim for ideally a difference of 60% or more ... ie - if model weighs 1000gr ready to fly with battery etc. - then with thrust at max - you want at least 1600gr. TYhe more you can get - the better. Some models with large wing areas such as Vulcans etc. can get away with 45 - 50% thrust ratio ... but models such as T45 .. Viper etc. really should go for 60% or more.

OK - wheels on ground .... check that wheels do not twist or bind when weight on ground and start to roll. Its not unusual for wheels to feel ok when spun by hand ... but on ground 'lean' to one side and bind.
What angle does model sit on the ground ? is it more nose down since change of legs ? Is it too nose up causing drag ?
Are the wheels too small or too heavy ?
Are the main wheels toed in or out too much causing them to scrub instead of turn easily ?

Final : If the model flew out of box OK ... then its better to REMOVE gear or clean up than to add gear ...
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Old 02-24-2021, 01:54 PM
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I must agree with Solentlife.
For a specific airframe the power to fly is directly proportional to its weight. Add 10% more weight and you need 10% more power. If the extra weight creates more drag then you need more power still.
In modifying or improving a plane unless it has substantial excess power to start with it is easy to get to a point where flying, particularly the take off, becomes marginal.
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Old 02-24-2021, 02:39 PM
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Hi. Well i hate to admit your right. But jesus, all the time i spent during winter is now useless. My lipos are from 30-45 to 60C 3300mah. It flew perfect out of the box. Should had weight the plane before and after. I'll post a little video showing my watt meter connected.
Thank's for now.

https://imgur.com/w8BZOhU
r.com/a/DWLayly.com/w8BZOhU
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Old 02-24-2021, 02:40 PM
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So adding better motor and bigger esc could work?
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Old 02-24-2021, 03:46 PM
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jangodog
More power could indeed be an answer but first you really need to be sure if it is simply the battery that is loosing performance. If it is the battery adding a more powerful motor will make very little difference.
EDFs work their batteries hard so they do tend to degrade and any weight you have added will only make the effect of the loss worse.
Perhaps the simplest would be to buy a new battery and see if that at least allows it to take off.

You may still have to decide if the changes you have made are essential to you and accept any penalty in performance. If they are for appearance it may be better to do without.
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Old 02-24-2021, 04:01 PM
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I get your point. But the lipos for the Viper has only been used very little, max 20 cycles. But members of my club recommend lipos with bigger C rating more power?
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Old 02-24-2021, 08:11 PM
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Originally Posted by jangodog View Post
Hi. Well i hate to admit your right. But jesus, all the time i spent during winter is now useless. My lipos are from 30-45 to 60C 3300mah. It flew perfect out of the box. Should had weight the plane before and after. I'll post a little video showing my watt meter connected.
Thank's for now.

https://imgur.com/w8BZOhU
r.com/a/DWLayly.com/w8BZOhU
You say 30-45 to 60C ..... are they Nanotech's by any chance ?

Technically a 30C 3300mAh battery should be able to supply 99Amps ..... 30 x 3300/1000 .....
In reality it would be fair to guess about 45 - 50A is good to go....

You say the model flew well out of box ... I know we all dabble in modifying models - but as you say it flew perfect.

As suggested by Q .... get a new battery and check thrust with it - then compare test with old battery .... it may just be a simple case of tired batterys.

?? Did the model take off before with the modifications you made and later fail ? Or did it fail first take-off with modifications ?
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Old 02-24-2021, 09:35 PM
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No Nanotechs. Got 3 Blue Turnigy 3300mah 6S 60C heavyduties 2x3600mah 30C Blue Turnigy and one Gens ace 3300mah 45C. As mentioned all 5 6S lipos are used very little so doubt there "burned" out already. I haven't got it airborne with the new "twin" main gear and the centerburner yet. It just ran across the field without taking off. Never charge the lipos more then 1C so i take good care of my lipos. Would a 2150KV motor give me the extra punch?
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Old 02-24-2021, 09:41 PM
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It just ran across the field without taking off.


This is a grass field ?

I haven't got it airborne with the new "twin" main gear and the centerburner yet.
So you changed from single wheel to twin wheel mains ? So you doubled the wheel drag on the ground ?

Sorry to be blunt - but if you are on grass field and you fitted twin wheels ... IMHO - you are asking a lot !
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Old 02-24-2021, 09:59 PM
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A higher C rating does not deliver more power unless the amps being taken are causing a significant voltage drop in the battery..
According to your video the voltage was 22.5 V at the full power of 50 A. That is an average of 3.75 volts in each cell which not bad at all being just above the nominal LiPo cell voltage of 3.7V.

Note that drawing 50A from a 3300 mAh battery is 50/3300 x 1000 =15.5 C so it is not actually working a 30-45C battery particularly hard at all.
I am sorry to say but the lack of a take off does still tend to point to the changes you made rather than an issue with the battery or motor performance..
What is the current weight of your Viper? .
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Old 02-24-2021, 10:36 PM
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mmmmm watching the video ... I assume that the battery in use was not fully charged ? I respect Q's knowledge and he is so correct about higher C rating not giving more power if original is suitable rating. But 22.5V total (3.75V per cell) voltage if the battery was full charged for the test - indicates a larger voltage drop than I would expect. A full charged battery of 30C and 3600mAh - I would expect to show about 23.7V (3.95V per cell) and slowly drop back as power is used ...

mmmm the first video showing the take-off run ... you veered off into the longer grass after quite a short run .. so TBH - I would have been surprised to see it fly ... if you had managed to stay on the runway - you may have got airborne.

BUT I am still thinking the change of wheels .. addition of material in the air duct ... and possible extra weight at back end all adds up to no flight - along with the going off the runway.

The out of box Viper is well known to be a good flyer and with reasonable power to weight .....
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Old 02-24-2021, 10:59 PM
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Yea, i know what you all mean. I f... up my Viper Didn't know that twin wheels would be a problem. The weight i'll get later. The lipo stuff is something i haven't learned about yet. I'll called it the night, friends
Thank's for now.
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Old 02-25-2021, 04:43 AM
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Originally Posted by jangodog View Post
Yea, i know what you all mean. I f... up my Viper Didn't know that twin wheels would be a problem. The weight i'll get later. The lipo stuff is something i haven't learned about yet. I'll called it the night, friends
Thank's for now.

Here is a tip on Lipo's, I learned.
hook up a wattmeter to monitor the battery voltage and current
1st you will see the unloaded voltage just off the charger.
2nd put a little load on the system like just a touch of throttle, I call this the running voltage at a low current.
3rd advance throttle while watching the voltage, if you see a drop equal to 0.3 volts times the number of cells. ( 6s x 0.3 = 1.8 volt drop)

This is the max that that particular battery can put out without losing power.
As a lipo ages the internal resistance slowly goes up. This is what drops the voltage. a new high C rated battery has very low internal resistance ( IR ) a low C battery has a higher IR.

I have had what was an unused battery fail in midair when I needed more power, I landed a Senior Telemaster 96" wingspan in a tree.
The batteries just would NOT put out what I needed.
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Old 02-25-2021, 02:33 PM
  #22  
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Well i did another wattmeter test today. Seems like there is plenty of thrust.

https://imgur.com/kaFWgY2
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Old 02-25-2021, 04:24 PM
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Originally Posted by jangodog View Post
Well i did another wattmeter test today. Seems like there is plenty of thrust.

https://imgur.com/kaFWgY2
You have plenty of Power .... thrust cannot be measured on a Wattmeter. Thrust is measured on a digital weighing scale ..... example :


Testing my T45 ......

I'm still a bit concerned about the voltage drop you are getting ...

I would put the model back to its original if you can - then try a flight ... if it flies - then you know its one or more of the modifications you made.

Its normally better to only do one modification - test fly ... if successful - then next modification ... test ... etc.
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Old 02-25-2021, 07:02 PM
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Hi. Yes i ment power not trust I know about the weight scale ting with the plane nose down Will do it later. Hate to strip it and donít have the stock landing gear anymore. The Centerburner and bec inside the tunnel iíd like to keep. I could remove one of the two wheels on the mains?
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Old 02-27-2021, 12:11 AM
  #25  
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jangodog
My own guess is that none of the changes you have made would be expected to stop it flying, although each would degrade performance a bit, but all together might be different.
I would imagine the centre burner unit is heavier that the motor cowl it replaces and iit is not as aerodynamic as the motor cone. In addition its lead is directly in the fan airflow.
The twin wheel undercarriage will almost certainly be heavier and will also add a bit of drag both extended or retracted..
The added triangle cowling looks ok unless it is in the narrowest part of the duct in which case it could be restricting the fan airflow.
The extra 'decoration' on the tail pipe will have added some weight and more importantly it is right at the back so could have effected the CofG.

The Viper is described as having an 'adequate' performance rather than being a 'rocket ship' so it is possible it doesn't take that much to have a significant effect.
Just my two penn’orth.
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