Electric Powered Bird of Time

[Alan Williams]

Hi all I am just finishing a Bird of Time glider and have installed a Hyperion Glider Motor.I have in my store of batteries a 7.4volt 3200 20c lipo.I have run the motor up via an astro flight watt meter.The reading at full throttle was 150 watts at 21.5 amps.The prop is a graupner folder 13x7.The weight of the model is 56 ounces.I feel this is on the borderline of sufficient power and probably need a bigger prop.I am a relative newcomer to e flight and would appreciate advice.Perhaps Timbo would oblige?Thanks in advance.Alan Williams.

[Former Member]

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[Alan Williams]

Thankyou,the motor is a hyperion brushless glider motor.The battery is 2 cell lipo the esc is 60 amps so should cope with more current.the motor is equivalent to a 20 ic engine

Thanks ,Alan Williams

[Former Member]

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[David Ashby - Moderator]

I've worked out about 42 watts per lb on the model Alan. Trouble with the watts per lb rule is that it doesn't take into account the physical proportions of the model. My Cularis was in the 50 watt/lb region and I though it wouldn't be enough but it flies great - I put this down to a big 2m wing generating lots of lift?

[Alan Williams]

Thanks for the replies.The motor is a hyperion 3025/10.815 revs per volt.The Robot Birds website states 12x6 on 3s lipo.I dont have 3s lipos but I do have 3 2s lipos.I will try it and see.The glider does have a three meter wingspan so it should fly on 150 watts? Thanks.Alan Williams.

[Erfolg]

I fly a 3m Sagitta type on 300w, altjhough it is a a good 16 oz heavier, from memory. Mainly nose weight and very strongly built (ex open class comp glider) to get CG right. I also have a 3m Algebra, with similar weight to power.

Although OK in the climb out, the climb is not rocket like. But once up there, beats my 2m jobs hands down, in the glide etc. If windy they really come into there own, penetrating vey effectively, yet thermalling with best of the light weights in dead calm.

 Motors areTyphoon 2912/10 vector and Tornado 3618/1200 both on 10*6 Graupner/Aeronauht on 3s.

My own view is that you need to load the motor up and supply the volts to get the power up on brushless. In a recent thread there is a tale of  woe, of one of my models that would not perform because I was attempting to use a 8 cell 2/3 Sanyo nicad (9.6v).

Just try and see what happens. If no joy consider more volts.

Erfolg

[Tim Mackey]

Hi Alan. If Davids calcs are correct then I think 40watts per lb is too low. With a powered glider you really want a good thrust / power to weight ratio....to get it up and flying, then you can turn the tap off and ...err....glide

One thing I should point out though is that if you use more volts the amps go UP, not DOWN, assuming the same motor and prop. Definately sounds like you need a bigger ( diameter probably ) prop, and 3s Lipo

[Former Member]

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[Tim Mackey]

Nope....given the same load ( EG prop and motor ) more volts equals more current - simple ohms law at work

( although other factors at play too )

[Alan Williams]

Thanks for the replies.I will try a bigger prop.If that proves unsatisfactory then a 3s lipo it is.Thanks again.Alan Williams.

[Tim Mackey]

Remember, the bigger prop  will drain the pack faster

[Alan Williams]

Thanks,yes but it is 3200mh pack.I will be satisfied with a couple of climbs to altitude.I hope it will stay up for a while with 9 feet of broad wing clarke 5.Thanks again.Alan Williams

[Erfolg]

Alan

If you can get it to climb then +20 minutes is pretty easy. Which at first is great, later it becomes a little boring.

The one thing that I have found, that with these bigger models, a really big heave is necessary, like throwing a javelin, but at the horizon. The prop needs help to get to flying speed.

With my 2m jobs you can almost just let go, and they will accelerate away, but that is at 100w per pound.

Erfolg

[Alan Williams]

Thanks for the advice.I am getting pretty frustrated with the weather here in Cumbria,its been blowing too hard to fly with any enjoyment for what seems like weeks.Alan Williams

[Erfolg]

Alan

Winds up tp about 10mph are great for these larger models, they cope well, whilst getting flying. Being clark Y probably less well than E205, etc.

My own models are flown regularly up to about 20-25mph but at these speeds your are essentially pointing into wind. Any lift has been and gone before you can recoginise or use it., so just looking for low sink location etc.

I live in Greysouthen nr. Cockermouth are you near? Although staying in Manchester at present.

Erfolg

[Alan Williams]

Thanks for the reply.I live on Walney Island which is connected by a bridge to Barrow-in-Furness.Member of Furness Model Aircraft Society.We fly off a field overlooking the Duddon estuary from a height of about 200feet.west facing slope good for gliders.Cheers,Alan Williams

[Reg Tyson]

Hi Alan,

I must live very close to you indeed. I am also on Walney.

I fly alone usually on the moors above Kirby, but other local spots as well, I am not in thelocal club but I do know their flying field location.

 I have a Flair Albatross glider, 100 inch wingspan and just lately converted to electric power.

It is heavier than standard at about 7lbs when using a 10 cell nimh pack. The wings were modified a while ago to be fully sheeted with balsa, 

that resists the tough heather on the moors better than film covering.

  To cut to the chase...... 10 cell nimh at 3,700 mAh and all up weight of 7 lbs and a total power of 300 Watts turning a 13 * 8Graupner folding prop.

The model launches easily on the flat,and climbs readily. It will go up at approaching 80 degrees... but not straight up, more like a series of steps

allowing it to level off a bit after climbing and then pointing it uo again.

 A 30 second motor run is enough to get it as high as I can see.

I have some lipo packs to test which will give 50 watts more power and save 1lb 3oz in weight. As you have noticed it has been pretty windy lately

so haven't tried them yet.

 I reckon if you can get 50W/lb then it is worth trying the model out. There is a nice slope at the western edge of the club field. That would be ideal to give it a

preliminary try when there is also a bit of wind to assist a test flight.

 Reg

  

  

[Alan Williams]

Thanks for that info.Bigger props ordered and should arrive Wed.14x8.The next size overlander have is 15x10 but I Think They will be too big.Cheers,Alan Williams