Light weight electric WOT4

[Bruce Richards]

I have been following Timbo thread on his electric conversion to his WOT4 and also butting in with my plans to build a light weight electric WOT4. I think it is time I opened a thread of my own rather than filling up Timbos thread.

My plan is to build my WOT4 as light as I can which is not that light because I use too much glue and can't resist adding a little bit of extra "strength" here and there. I have just received the motor and ESC Turnigy 60A Plush ESC and Turnigy 42-60 500kv motor) and the model is just about finished apart from the covering. I weighed it with 6s 2p (4X3s1p 2200mah) lipos and all the rest of the gear and it looks like it will be about 5lb all up.

I bench ran the power set up with a 14X7 prop. I got 22v and 35A for a total of 770W. the motor was warm after a 20 second flat out burst. I also tried it on 3S lipo and got 23V 9.3A for  214W (not enough I think).

So on 6s I am getting 154W per pound(that will be plenty) I think I will try a smaller prop. I have a 12X6 but that may be too small.I do not want to use 4S or 5S becouse I have lots of 3S packs already and I do not want to buy new 4S or 5S packs.

Does anyone have any Idea of what weight will be added by covering with Solar Film?

Any comments on the power system and prop choice?

I am planning to fit the batteries through the bottom just behind the fire wall. Any suggestions on how to secure the Lipos and the hatch would be grateful received.

Thanks in advancefor your help

[Tom Foreman]

I fit all my LiPos with Velcro, although with your setup I would go for Velcro straps as well so you can velcro and strap them all together. I would stick with the 14x7 prop to start with, as long as your motor & ESC can take the power it will be more fun, and you can always throttle back. I over power most of my models if they can take it, just so I have that little bit of extra when I want it, rather than wish I had more power. That way I can fly on half throttle for general cruising, then go WOT for aerobatics and vertical manouvers

[Bruce Richards]

Thanks Tom I had planned to use Velcro straps its just working out what to strap them to. Given my battery hatch is in the bottom and the batteries slide in on the angle then push back I do not think there is room for a plate to strap them too. I guess i could attach the straps to the top of the fuselage which is made of thick balsa.

[Tim Mackey]

Hi Bruce - have you seen the web link to a "proper" electrification of a wot4 as approved by Mr Fossy himself

I am very surprised at the power figures you are getting. I have now trialled 3 motors and 5 different battery types with many different props ranging from 11 x 7 up to 13 x 6.5. It has flown best on a 13 x 6 powered by 8s LifePO4s on a 400 Turnigy motor.  I have not yet flown it on the 13 x 6.

The 3 motors tried are

1) A 400 kV 2) A 480 kV 3) A 919 kV

Taking the 480 Kv as the nearest to your 500 Kv my results when using 6s 3200 mahr Lipos were MUCH higher power than yours, yet mine is a slightly lower Kv motor. I got at WOT ( measured with the eagle tree logger and also an astro flight "whattmeter" )

12 x 6 prop - on load voltage 21V / Amps 43A / 903 watts

I have now just tried a new 6s A123 pack but havent yet logged the results. I will be posting the latest figure son my thread if you want to keep track. I think I will be settling for a 13 x 6.5 prop on the 6s A123s, and the 480 Kv motor, and with careful throttle management, I can also just about use the 8s Lifes....although the wattage in short WOT bursts was over 1 kW. I also have a replacement 640 Kv motor on its way - just for trials !

I can tell you it did not fly particularly well when I had it running at around 80 WpLb.

[Bruce Richards]

Timbo,

From what I have read the Turnigy 500kv motor is not that efficient, less than 70%. I am not sure whether this is relevant or not

[Tim Mackey]

Bruce... I had not heard that..... the ones I have are pretty good  ( not sure how "efficient" as such ) but lower efficiency would probably result in higher current consumption for the same output power and yours was way less than mine ?

[Bruce Richards]

So here it is

  

Yes I Know just another boaring Wot 4 But I am happy with the weight.

That's 4lb 15.5 oz all up with 6s 4900mah lipos 500Kv motor and 14X7 prop. Not sure how well this power set up will work in practice so a higher Kv motor on order for use with 3S setup and 11X7 or 12X6 prop.

Wing structure

Just need to add a few screws to the engine mount an elastic band and pin to secure the aerial and film over the undercarriage. Should come out at just over 5lb on 6S.

I will let you know how it flys when the wind drops.

[Tim Mackey]

looks great, and I reckon it will fly very well on that setup as it is. Nice one

[Bruce Richards]

The only issue I have with the way it has turned out is that I need to take the wings off to fit/change the batteries. I was planning to have them right up front but the motor was much heaver than I expected which meant to get the CofG right the batteries need to be on the CofG. I can't see how to have a door in the bottom because the U/C is in the way and I can't compromise the strength of that area.

O I will just fly it and stop farting about.

[Tim Mackey]

[Bruce Richards]

Well it flew yesterday and was totally ballistic on 14X7 prop and almost uncontrollable. Three other problems compounded the situation:

1. not enough aileron movement. Which meant full  left and right stick to get it to respond. Could have tried the rudder but didn't think of it until now.

 2.very gusty wind. Which meant continuous control input was required to keep it anywhere near flying straight.

3. I think there was a tad of unplanned upthrust on the motor.

So all together I did a single takeoff go round and land with a huge sigh of relief to get it on the ground with out damage and me shaking in my boots.

So I have now fixed the aileron throws and the up thrust. I have also changed to a 12X6 prop. I have also changed to 6s1p instead of 6s2p Lipos which should make it just under a pound lighter. AUW now 4lb 50z.

Now when the wind is fixed I will have another go and report back.

[Tim Mackey]

I think you will find the 12 x 6 prop a tad small - let us know after you try her - well done by the way

[Bruce Richards]

Timbo,

I really appreciate your input thanks.

On the 12 X 6 it pulls 28A static on a fresh charge at 23V 644W and theoretically 12880 RPM. How will I tell if the prop is too small? Will it just struggle to take off and be reluctant to climb?

Do you think I need more pitch or diameter or both?

[Tim Mackey]

No I am sure she fly...but I just like my wottys to have a bit more grunt - IMO you will need more diameter as I think it may be weak in the climb on a 12" - besides...part of the adavantage of electric power is spinning larger props more slowly ( always more efficient ) and keeping the revs down keeps the noise down.

However as ALWAYS....test flying it is the only way to tell what works best for you / your style / model

[Bruce Richards]

Yes it is noisy at WOT. I guess limiting myself to 3s or 6S has its drawbacks

[Bruce Richards]

Well I took the Lecy Woty out for some evening aviation and flew it for the second time with modifications listed in post above, totally different beast from last time. The wind was gusty but not strong and it flew a treat. Took off no trouble on half throttle. Only 1 or 2 clicks of up elevator trim for level flight. No trouble with the vertical climb it just went up and up and did not want to stop. Rolls fast and loops are lazy and slow if you want or fast and furious if you prefer. I can really feel the lightness compared to other WOT4s I have flown. It makes a good glider power on and gain some height close the throttle and glide around for a while and bring it in for a nice floaty dead stick landing. I had 2 flights one of about 2 minutes and one of about 5. The lipos are on charge so I will report back on how much charge they took. I can then get some idea of duration.

[Tim Mackey]

Excellent stuff there Bruce - was that on the 12" prop too?

[Bruce Richards]

Yes Timbo 12 X 6 and 6S1p. I think the light weight helps a great deal with the vertical performance. I will fly it again today to double check the performance. Just to make sure its not just rose tinted specks brought on by excitement of flying a new model.

Thanks for replying I am beginning t think no one but you is interested in my WOT4 trials and tribulations.

[Tim Mackey]

Yes I am sure you are correct - "add lightness" was never more relevant in our sport than with electric flight.

Unfortunately the bird I did ( oo err missus ) was an Ex slimer, and carried about 3 hundredweight of 'orrible smelly oily fuel soaked ply and balsa. Repairs by the previous owner had also contibuted heavily towards the profits of epeoxy resin suppliers, and there is only so much that could be realistically done to shave any weight. I have just about completed other projects which had interrupted my conversion, and later today the final rig chosen should be completed and ready for some test flights, complete with further eagle tree data. It used to fly on a 52 2T engine with an 11 X 7 ( but obviously much higher revs than I would like on the leccy setup ).

I have settled on the 480Kv KMS motor as the other flavour I was going to trial has been returned as faulty, and as a result BRC are no longer stocking them, so I have taken a refund instead of replacement.

As I have 2 quite different batteries ( 'twas all part of the experimentation ) that I intend to use in it, I will probably use a 13 x 6.5E prop as a compromise between the 2 packs. It does mean slightly more current consumption than I would like whilst using the 8S softpak Lifes, but I shall use careful throttle management to limit the power. The motor and ESC are rated above the figures....but the batteries I am dubious about, and at the moment I cannot recommend them to people. Interestingly, I see that these are no longer showing on BRC website either!

However after a few flights and some bedding in, we'll see. These static current figures will of course be somewhat lower in flight - eagle tree will confirm.

On these softpack 8s - peak figures are 55A / 1200 Watts ( yikes! ) / 9550RPM ( cells rated to 60A max )

On the 6s A123s its 37A / 686 W / 8640 RPM....so should still be reasonable performance, and after all, its meant to be the trainer for the missus !

[Bruce Richards]

Sounds good Timbo I look forward to seeing the results from your flight tests. 

It was very gusty at my patch today nearly didn't bother to unpack the car! But we (my son and I) got our chairs and all our gear out and convince our selves that we should fly. We had a great day with some mishaps. As for the Elecy WOTy : I set my timer for 10 Min's and took off. Landed back after 10 Min's of mixed flying. Plenty of go left in the Lipos I think they were showing 3.8V per cell. By the end of the flight the vertical climb was distinctly less impressive than on fresh packs.

 I am very pleased with the duration and I think other club members that have seen it fly have been surprised how well it goes. 

My son was flying his ASP .52 2T powered WOT4 that I built him for Christmas and it was an interesting comparison. I think his was faster but  he tends to use far more WOT than I do.

AS ever thanks for your comments and support.

[Jon]

All great stuff... cant wait to start on the Acro WOT...

Great reading chaps...jon

[Bruce Richards]

I flew the Wot 4 on a 13X7 prop (cut down and rebalanced 14X7) it flew very well with more authority in the climb than with the 12X6. It did not appear to affect duration even though it is pulling 33A WOT. The packs I used are still more than half full.

[Bruce Richards]

 I have added some decoration to the top of the wing helps to see which way up it is. I think it looks quite fetching for a simple scheme. I always have trouble deciding on colour schemes and patterns.

 I have also started making a cowl because some of my fellow club members say it would look better with a cowl. I am not sure what do you think?

[Derek Hammond]

personally i always think they look better with a cowl. i just never get around to fitting them!

I notice you have your esc mounted internally - i was intending to do the same but was concerned when i saw Timbo had arranged outside seating for his - does it run warm?

I did a few tests on mine tonight and found the voltage from the A123's i'm using drops to 17v on load so am only acheiving 540 watts max on a 14x7 which is a bit less than i was hoping for but i am happy that it will fly like a seagull rather than a penguin

[Tim Mackey]

Nah inside should be fine - all my leccy models have internal ESCs - the Wotty is not really classed as a "proper model" currently ( dreadful pun intended ) it was / is purely an experimental ship, and the ESC got stuck outside only 'cos it was the easy option at the time .

However, do note that all my ESCs are usually rated at around 20% more than they actually get used at.