More advice on Wot 4 motor?

[Peter Beeney]

Cliff - I hope you soon get back on track here. I’m afraid I can’t really comment on the Wot 4, oddly enough it’s one that our learner pilots have not chosen, so I’ve not had any contact. I don’t think at the moment anyone is flying it locally.

Probably a good idea to hang fire for a moment, if I get really tempted by something I always wait for about a week, just to see if I will still be as keen. Often I’ve got a different perspective by then.

Looking back at your original post, you mentioned the 4 cell pack and the increased watts up to around the 700 mark. I’d say this 700 watt level is toward where you’ve got to go with your 4, otherwise you might always consider that it’s a bit underpowered?

With regard to a biplane, a Panic is certainly an aerobatic model but it is a bit universal. Surely there must be some plans around that could be made to a ‘stand off quite a way away’ type of scale? Such as a Stearman Kadet, or Yellow Peril as I believe it was known, the student pilots must have given that a bit of stick occasionally. There were many other Stearman variants too, and there’s at least one with a 600hp lump in the front flying at air-shows. There’s also the Waco Taperwing, another famous aerobatic bipe, that’s Waco, pronounced Wah-co, an acronym for the Weaver Aircraft Company. How about the Beech Staggerwing? Or maybe a Curtiss Jenny, perhaps in it’s time one of the most flamboyant barnstorming planes of them all? I fancy an Avro 504, built to your own spec. it could be very spritely indeed, but would also look the part when flown in a scale like manner. Also have a little read about Prince Constantin Cantacuzene and his legendary exploits in a Bucker Bu 133 Jungmeister, and see if you can follow that. There is also the Jungmann, built specially to be very lightweight, which was still current in Aerobatic Championship Competitions until the 1970’s. And I just have to mention the Great Lakes biplanes, one of the most enduring pictures for me of all time that I can remember.
Or twins perhaps, the de Havilland D.H. 84 Dragon I’ve always really fancied, rather than the D.H. 89 Dragon Rapide! Then there’s the Vickers Vimy, a bomber, or the Short Scylla, an airliner with 29 seats and 4 milling machines between the wings, rather like the Handley Page H.P. 42. A colleague scratch built a small foam H.P. 42. I’ve got a photo in my computer backup file somewhere, if I can ever get it back!
Going the other way, how about considering the Stits Sky Baby, the full size, at 7 ft 2 inches span it zipped along at 200 mph! There is also the Whing Ding, an ultralight biplane that the pilot sat on, rather than in. Plus there is also the two seat fully aerobatic Sorrell Hiperbipe.

All mouthwatering stuff, and there are one or two more obvious ones that I’ve left out. I often punt my friends Tiger around, it’s 120 FS powered, which is always very willing indeed. Perhaps a little bit too much sometimes, but it can go, a bit like a sports hack, if you want to, and the power makes it pretty impressive, but I think in some respects it’s also safer to fly, it means there is total control at all times.

A replacement for the Super 60 might be a Bleriot monoplane. We have one at the patch, it’s very simple, and it really does look the part. I/c, of course, but it would convert to electric in a trice!

Hope you come to some satisfactory conclusions re the Wot……

PB

[Clifford Stone]

Posted by Steve Hargreaves - Moderator on 03/08/2012 15:17:19:

Clifford I think you are getting a bit too hung up on theory here.....worrying about this kv & that kv & different props & pitches. All good fun for the determined tinkerer but really not necessary for a successfully flying model

The watts per lb rule is a tried & tested method.....what is the AUW of the model ready to fly? Multiply it by 100 for Sport performance, 150 for good vertical performance & 200 if you are a hooligan....this gives you the total power in watts you need. Use a prop around 6" pitch & a motor with a kv around 11-1200 for 3S & around 850-900 for 4S. Divide the watts by 10 (3s) or 13 (4S) & this will tell you how much current is likely to be drawn & hence the size of the ESC. Divide this current by the capacity of the battery in amps & this will tell you how hard you are pushing the battery...if its getting on for 20 consider fitting a larger battery.....

Check the results with a wattmeter........& maybe tweak the prop size slightly either way to get the performance you want.

Fly & enjoy....

Thats pretty much all there is to it....

You are right Steve, I have alowed my old pylon polishing instincts to get involved . . . 'down boy'.

However, because I know what the Wot 4 is capable of its got me a little frustrated? . . . plus ovecourse my 20 year o;d rough edges are not coming off quick enough! . . . as well as trying to get my dyslexic head around technicality that I have neaver been good at.

The 'watts per lb' rule helps a lot, the model weights 4lbs, so I have enough power to fly as a sports model . . . but thats not enough!!! I want true vertical performance, an E-Power 3548, 930kv is on order, I will swap the ESC from 50a to 60a, of may be the 85a? . . . do the watt test again. I get the idea now, the more amps draw, the less flying time, arive at a compromise.

I need a couple of extra 14.8v batteries.

The first thing is to fly the 'Wot 4' on 3 cells with the two props that I think are right for the curent set up, I especialy want to experiance the 11.5x4?

Depending on the results, depends on where I go from here. Thanks all for your help and patience, still some dumb questions to come I have no doubt?

CJS

[Clifford Stone]

Hi Peter, feeling a little better today, afraid I can be a bit down, black dog moments, but that another story. You have covered my wish list comprehensively. I had a Panic for a long time with an HB 61/Perry carb, big, fine pitch prop, ticked over faultlessly at 5-600rpm, what a combination with the Panic. There were a group of us in my club, they used to line up to fly 'my Panic', a 'tiger in pussy cat' disguise . . . however, as you say a bit bland to look at.>>

I had a semi scale Bucker Joungman, the most amazing aerobat . . . perhaps it had something to do with moving the CG back and back to the point of almost unflyable, then come forward half an inch . . . happy memories . . . The best biplane (satisfying to fly) I ever owned was a 48" Aeromaster, sort of puts me in mind of the Great Lakes to see it in flight, all it needed was a radial cowl and round off the fin . . . Merco 61 powered, big, fine pitch wood prop, yep Merco 61, that long ago, 4 strokes were not thought of, she lasted about 5 years, radio failure/interference did for here in the end.>>

Waco, Beech Craft, Jenny, Avro, you have named a flying circus . . . I will persevere with the situation as my previous post indicates . . . ?????>>

CJS>>

[Clifford Stone]

The E-Power 2826 kv930 arived this morning, took a bit of thought to get it in to the same mounting holes etc., but It was done in the end. Runs very smooth as sugested by PatMc . . . Prop driver/shaft adaptor has no knurling on the driving face, it dont grip the prop to well . . . I had one from the other motor that fitted.

I tried a 3 cell battery first, no real joy, needs 14.8v!

First up on a new 4s battery, that has only had two charges:

All APC props.

13x4 , 37a - 550watts - 4.5lbs - 10,250rpm

12x6, 40a - 580watts - 4.6lbs - 9,600rpm

11x 7, 36a - 520watts - 3.75lb - 9,680rpm

11x5.5, 30a - 433watts - 3.75lb - 10,000rpm

10x7, 29a - 480watts - 2.8lb - 10,000

These are the significant props I tried, I did the 11x4 again as the battery was getting tiered by this time showing 14.61v

2nd reading: 13x4, 32a - 457watts - 9,500.

I'm still a bit puzzelled with the 'watt' figures, they will be something in the regon of +10% up in flight, so the 13x4 and 11x7 look promising, I ike the 12x6 but those amps are going to cut the flying time, if only they did a '12x5e'?

The 10x7 might be a compromise of power over flying time, its loosing out on static trust, small prop disc is ineficient? The important things are, I dont think the 50a ESC will be compromised . . . or would you put the 60a one in just for a little extra safty margin?

The props now need testing in flight, which one gives the performance I like against a good flight time?

CJS

[Steve Hargreaves - Moderator]

Cliff, I'm not sure why you're puzzled by the watts figure...Watts is simply the SI unit of power & for DC electrical power is simply the current multiplied by the voltage.....also I'm not sure that you are right about the figures being +10% in flight.....in flight the prop takes less effort to turn it so the current (& hence the watts) is likely to decrease rather than increase.....

If I may be so bold I think there is an important piece missing from your electric knowledge here Cliff....you need to understand that an electric motor is essentially a fixed speed device in that it will always try & turn at the speed dictated by its design (the kv figure) & the voltage applied....it will never "over-rev" in the way that an ic motor will.....if the motor has a kv of 1000 & we apply 10 volts it will never ever ever do more than 10,000 rpm...even if we run it at full throttle with no propellor....(in actual fact it will run slightly slower than 10,000 rpm as it needs a little "slip" to generate enough torque to overcome the motors' inherent losses but don't worry about that bit!!!!) Similarly if we put a large propellor on then this will be a large load for the motor to turn.....however it will still try & reach its design speed & to do this will draw more & more current until it reaches that speed or melts in the attempt.....(again not totally correct but close enough to be going on with...)

This is why the propellor in electric flight is so crucial as it determines the power produced by the motor......you say the E-power motor was no good on 3S.....this is because you didn't have a big enough prop on it...if you'd gone up to a 15 or 16" prop then I guarantee you the current & the watts would have increased & you would have had a perfectly flyable model......assuming you have enough prop clearance.....

I hope I've explained it in a way that helps your understanding.....

[Clifford Stone]

Yep Steve, I hear what you say, you are so right about my lack of electrical knowledge, that vertical learning curve again . . . Yes the rev counter is showing the speed to be fairly constant regardless of prop . . . So concentrate on watt meter, I have 7" of safe clearance on the W4, ie, center of shaft to ground with fuz level, 8", I supose I could swing 15", at a pinch?

A 13x4 gave me 24a - 274watts and a 12x8 30a - 340w.

I have a 13x6.5, I have not tried this in any guise, I will look at the 14" props at Slough Models? They certainly keep APC props that I have not seen elswere.

Puzzelment over watts? I sort of see it as a measure of porwer, 'watts per pound rule'?

Any sugestions as to where I might look in props to get the best from 11.1v 3s? Props are cheaper than 4s, 14.8v, 2800-3000mah!

How significant is the static thrust Steve, that 13x4 has suprised me, on the second reading I did not show ST, it was 4.19lbs.

CJS

Edited By Clifford Stone on 04/08/2012 18:52:46

Edited By Clifford Stone on 04/08/2012 18:54:55

[PatMc]

Clifford, the static thrust is virtually meaningless in anything but hover. As soon as the model moves forward it reduces.

[Peter Beeney]

Steve, - with all the greatest of respects, but I’m afraid I’ve never quite been able understand this line of reasoning. I’ve read other commentators that also say that if the load is increased the current will increase until the design speed is reached, I’m not sure that is entirely correct, in my view the motor speed is proportional to the load, and so the current will thus be proportional to the speed. The speed being the number of revolutions per minute. I’m firmly of the opinion that these are interlinked, if you change one, the others will change. As with other electrical devices, I think that motors will always obey the fundamental electrical principles.

I believe that I’ve already said in a previous post in this thread that I consider there is one ‘best load/speed point’, and I still think this to be true. As with i/c engines, anything just either side of this will be close, but the further away you get from this the worse the situation will become, in the case of overloading an electric motor the current will increase, together with the heat dissipated; but in my opinion the revolutions will not increase, rather that they will proportionally decrease.

Sorry about this, just another view point. But it may be worth considering…

PB

[Clifford Stone]

Posted by PatMc on 04/08/2012 19:37:28:

Clifford, the static thrust is virtually meaningless in anything but hover. As soon as the model moves forward it reduces.

??? I know we are dealing with electric motors hear, which I am strugling to get my head around . . . but, statick thrust is converted into forward motion, relevent to prop, model weight, streamlining etc., untill the two equal out to a 'terminal speed' . . . I have had many a pylon victory because of the work I did on static thrust before hand.

I may not be the sharpest knife in the draw, but from a practical point of view, thrust is critical to any aircraft, the convertion of a rotary action into forward motion. The theorist will be able to predict the speed factor. I'm not that bright so have always don it in real time, as a practical measured demonstration of fact, spring ballance infomation and flying performance against a stop watch.

However, in an arobatic terms thats 'upwards or a positive manuvers' . . .

CJS

 

 

Edited By Clifford Stone on 05/08/2012 00:51:02

[Alan Cantwell]

so, after all this, and no, i havnt read any of it, i sleep ok, dont need help, what engine and prop are you fitting to the wot4?

[NigelH]

Steve beat me to it yesterday when he suggested that this was way out of hand. Far too complicated. Honestly.

Just go for about 100 watts / lb, on 3S to keep the weight down, and use a watt meter to help you fine tune the prop choice. If say, you'd like a bit more speed, drop an inch on the diameter and add an inch onto the pitch and re-measure and then fly. It's that simple.

Fly the model. That's what you bought it for

[Clifford Stone]

Posted by NigelH on 05/08/2012 10:24:11:

Steve beat me to it yesterday when he suggested that this was way out of hand. Far too complicated. Honestly.

Just go for about 100 watts / lb, on 3S to keep the weight down, and use a watt meter to help you fine tune the prop choice. If say, you'd like a bit more speed, drop an inch on the diameter and add an inch onto the pitch and re-measure and then fly. It's that simple.

Fly the model. That's what you bought it for

Yes Nigel, having slept on it, I have come to a similar conclusion, the head is going round and round, keep it simple, amps and watts, i cant deal with the maths, so go back to the original first advise, 'use a watt meter'. Which is why I burned out the last motor/ESC, I did not have a watt meter.

CJS

[PatMc]

Posted by Clifford Stone on 05/08/2012 00:49:17:

??? I know we are dealing with electric motors hear, which I am strugling to get my head around . . . but, statick thrust is converted into forward motion, relevent to prop, model weight, streamlining etc., untill the two equal out to a 'terminal speed' . . . I have had many a pylon victory because of the work I did on static thrust before hand.

I may not be the sharpest knife in the draw, but from a practical point of view, thrust is critical to any aircraft, the convertion of a rotary action into forward motion. The theorist will be able to predict the speed factor. I'm not that bright so have always don it in real time, as a practical measured demonstration of fact, spring ballance infomation and flying performance against a stop watch.

However, in an arobatic terms thats 'upwards or a positive manuvers' . . .

CJS

Edited By Clifford Stone on 05/08/2012 00:51:02

Thrust reduces from it's highest when static at the same time as drag increases until the two are equal which in level flight is when aircraft has reached it's highest forward speed. You can get an enormous amout of thrust from a very large low pitch prop which wouldn't be able to take an aircraft to flying speed but might be able to lift it verticaly. Prop size is about compromise between high enough thrust at low speed for initial acceleration & maintaining thrust to overcome drag at high speed. That's why Spitfires & Hurricanes etc had low pitch for take off & high pitch for the rest of the flight.

[Clifford Stone]

Thats about it Pat, I have sheets of infomation on the static prop test I have don . . . at the end of the day I see 'compromise' as the final word . . .

A 12x6 is the best on 4s/90kv motor @ 580w. 4.6lbs ST, but the 40a it draws, I would thought to have a big effect on flying time, even on a 3000amh battery? sadly I cant work that out The 11x7 is the compromise @ 520W, 3.75lb and 36a. The 10x7 comes up a lot in these posts and in conversation, 480w, 29a but only 2.18lb of ST? Its down to a pratical flying test?

On 3s I'm having trouble generating enough watts with the 900kv E-Power motor, a 12x8 the the best, giving 340w and 30a . . . I'm going to have a try with a 13x6.5 later.

The head is beginnig to spin . . . covering the same ground . . . ?

So to move on, I have the issue of three 3s 2200mah batteries, and one 4s 2650amh. One needs to invest in batteries? I think a couple of 3000mah 4s . . . the three cells even with the 1100kv motor just dont seem to meet the 100/150w per pound criteria.

Which brings me back to the manufacturer recomendation on the Wot 4, 3s battery, 2820/05 1100kv motor and an 11x5.5e APC. I have two static figures for this set up one was taken from a fresh chaged battery, the other, after a few mnuits use, they average out to 38a, 440w, sports fly/trainer performance, I realy want more of what the Wot 4 is capable of, therefore the rule of thumb, 150w per lb?

Head spinning . . . CJS

Edited By Clifford Stone on 05/08/2012 13:25:01

[NigelH]

No, 150w/lb is for models that will fly on the prop as much as on the wing.

3000 4S packs are not light and, IMHO, that plane's already a brick. Make it heaver with larger batteries and you'll lose out performance wise and you'll no doubt be landing faster.

[Clifford Stone]

Posted by NigelH on 05/08/2012 14:12:02:

No, 150w/lb is for models that will fly on the prop as much as on the wing.

3000 4S packs are not light and, IMHO, that plane's already a brick. Make it heaver with larger batteries and you'll lose out performance wise and you'll no doubt be landing faster.

Brick it might be Nigel, however a 4s battery brings the CG to something like managable, but still back compared to the recomended 70mm, I'm closer to 80mm, it has flow a 100mm (250mm cord) but it was a handfull. I have to carry 80g lead slugs with 3s batteries to correct it. Time over again and hind sight, I would not have gone the Wot 4e 'woody' rout . . . learn the hard way. So its making the best of what I have for the time being. Silver lining . . . I think it is helping with the learning curve?

I did some re tests this morning, lots of pawing over the facts and figures . . . a couple of 4s batteries all be it cheap Hong Kong types, will sufice for the rest of the year. I think the prop options are 13x4, 11x7 and 10x7 all giving 480w to 550w and 29a to 37a, no strain in either deartment for the motor or electronics fitted according to spec.

Get out and do some flying, test the props, see which I prefer in performance terms?

Back to the flying brick . . . Landings are not to fast, a few ounces could have been saved in the weight department if they had 'built' tailpane, fin and rudder, rather than solid sheet, it would have solved the CG issue. I'm now considering my option for 2013, which have already been mentioned.

CJS

[PatMc]

Clifford, the HK cheapy batteries are as good as any around. I now only buy lipos from either HK or Giantcod(Shark) or a local part time trader who gets the same types.

[NigelH]

I agree that extra battery weight is better than ballast.

Someone who's building one of these told me today that the retailer was saying that another customer was flying one at 600 watts and was experiencing tail flutter. That's worth considering while you're flying.

The model looks good until you read the specs. It was me who started what's probably the main Wot 4 e balsa thread.

I've been getting my batteries from Hobby King for quite a long time and they've been pretty good for the money. I had to send one back with a dead cell. Be sure to check whatever you buy as soon as it arrives, just in case, regardless of the vendor.

[Clifford Stone]

Posted by NigelH on 05/08/2012 17:15:40:

I agree that extra battery weight is better than ballast.

Someone who's building one of these told me today that the retailer was saying that another customer was flying one at 600 watts and was experiencing tail flutter. That's worth considering while you're flying.

The model looks good until you read the specs. It was me who started what's probably the main Wot 4 e balsa thread.

I've been getting my batteries from Hobby King for quite a long time and they've been pretty good for the money. I had to send one back with a dead cell. Be sure to check whatever you buy as soon as it arrives, just in case, regardless of the vendor.

I recon thats where I might have been when I fried the motor/ESC, I'm not sure but looking at my figures??? I did not have the watt meter then, it arive the next day! . . . 11x5.5, 14.8v, kv1100, went like the wind and vertical just kept going. 'Holigan' is good ocasionaly, can be expensive though . . . call me 'Earl' . . .

Problem I see, speed is everything to some people, cars, motor bickes, models . . . ? No finess, I have been there, don that, grown up now. Smooth and easy, manage the throttle, point the nose up and she climbs effortlessly as the throttle is fed in smoothly, not *alls out like a scalded cat. Wot 4 is not a speed machine, its not the sleakest plane around, but put some 'vertical' grunt up front, gently tickle the throttle stick, nothing like it, beep breath . . . how many times do you see square manouvers at the field . . . ?

Any old how, I've ordered these to day: 1608486228848, not the cheapest, but they have a UK base, I have had stuff from then in the past, took about a week or so. Had a few things go astray from China/Hong Kong, got the money refunded but thats after 40 days and it costs a PP service charge!

Roll on tomorrow evening, Flying Club Bar-B-Q on the field, if the weather holds . . . ?

CJS