Electric motor for hang glider

I have been trying to do some calculations of how much battery power
would be needed to keep a hang glider flying level. With some help I
arrived at about 1 or 2 kW (a few horse power) for a typical hang
glider with 10:1 glide ratio and 180 pound (80 kg) pilot. As a
comparison, gasoline engines for hang gliders are 10 kW and give 1 - 2
m/s climb for half an hour on 4 litres of fuel.

I am unable to find electric versions of those powered harnesses being
sold. Looking around for battery prices I found this site:
http://www.hobby-lobby.com/flightpower.htm . The last battery on the
page is 22.2 V, 7.4 Ah = 164 kWh. I thought it may be interesting to
see how they would hold up when powering a human aircraft.

Each battery weighs 500 grams so with 10 batteries it would be a 5 kg
pack. The cost would be $500 * 10 batteries = $5000. Electric motor
with propeller and harness may weigh 10 or 15 kg on top of that, I am
unsure and would like to know figures. I have tried to find out but am
unsure of some of the terminology for electric engines. Also I do not
know if you can just attach a propeller to any old electric engine.

So it appears from my very rough calculations that you can achieve
around 3 kW for half an hour of flight, for $5000 and 5 kg of
batteries. Is this an unrealistic base line for me to use, before
adding the weight of battery heat insulation and other things?

"Legend Length" wrote

I have been trying to do some calculations of how much battery power
would be needed to keep a hang glider flying level. With some help I
arrived at about 1 or 2 kW (a few horse power) for a typical hang
glider with 10:1 glide ratio and 180 pound (80 kg) pilot. As a
comparison, gasoline engines for hang gliders are 10 kW and give 1 - 2
m/s climb for half an hour on 4 litres of fuel.

I am unable to find electric versions of those powered harnesses being
sold. Looking around for battery prices I found this site:
http://www.hobby-lobby.com/flightpower.htm . The last battery on the
page is 22.2 V, 7.4 Ah = 164 kWh. I thought it may be interesting to
see how they would hold up when powering a human aircraft.

First, let me say that you may be able to find a deal on bulk quantities of
this type of cell, that are not already packaged into the packs being sold.

Next, I suggest that you do careful research about the brand and discharge
rates.

The electric RC community has nothing positive about that brand of cell.
Lots of premature failures. Plus, the discharge rate of anything above C-15
will kill the batteries quickly.

You also need to consider the charging of that many batteries. The cost
will be a significant amount of your budget, as these batteries will catch
fire if not charged carefully with an appropriate charger.
--
Jim in NC

In article ,
Morgans wrote:

| I have been trying to do some calculations of how much battery power
| would be needed to keep a hang glider flying level. With some help I
| arrived at about 1 or 2 kW (a few horse power)

That seems awfully low. Having that much power on a 6 lb R/C plane
isn't uncommon at all, and you're talking about something much larger.

| The electric RC community has nothing positive about that brand of cell.
| Lots of premature failures. Plus, the discharge rate of anything above C-15
| will kill the batteries quickly.

If he's talking about keeping it up for 30 minutes, that's only a 2C
discharge rate -- most R/C batteries can handle that with little
trouble.

A 15C dishcarge rate = only 4 minutes of power. And yes, it's hard on
the batteries.

LiPos are generally only good for about 500 charge/discharge cycles,
and that's if they're not pushed too hard -- perhaps 1/2 of their
rated dicharge rate with plenty of cooling.

| You also need to consider the charging of that many batteries. The cost
| will be a significant amount of your budget, as these batteries will catch
| fire if not charged carefully with an appropriate charger.

Also, if you have lots of LiPo cells in series, they need to be kept
balanced which gets complicated too.

Personally, if you've never done anything like this, I'd suggest
getting started with a larger electric R/C plane -- 60 sized or so,
perhaps even larger, and get used to taking care of the batteries and
motor for that.

There's a program modelers use called motocalc
(http://www.motocalc.comt) that will, given information on your plane
and it's electric power system, calculate what sort of performance you
can expect, or given certain performance requirements determine what
equipment you need to attain it. It's made for models, but I see no
reason why it wouldn't work for something ... larger, especially since
you'll probably be using gear intended for R/C use for this endeavor
anyways.

--
Doug McLaren,
The victor belongs to the spoils. --F. Scott Fitzgerald

John Moody did something similar with the Solar Riser. IIRC, it was powered by a Hughes helicopter battery and a 3 hp electric motor. He also had a panel on the top wing to charge the battery. He could get a 3-4 minute flight after leaving it in the sun for 4 hours or so, though the thing had a climb rate of approximately .00000569 fpm.

I've considered doing something similar. I know that there is at least one electric motorglider available now, from what I've heard it will climb to 8500' on a single charge. With a lithium-ion polymer battery and a brushless motor, it should be possible to rig something up for under a fortune - and the components are getting cheaper every day. Electric power has pretty much surpassed gas for small r/c planes already.

Legend Length wrote:

snip

I am unable to find electric versions of those powered harnesses being
sold. Looking around for battery prices I found this site:
http://www.hobby-lobby.com/flightpower.htm . The last battery on the
page is 22.2 V, 7.4 Ah = 164 kWh. I thought it may be interesting to
see how they would hold up when powering a human aircraft.

snip

So it appears from my very rough calculations that you can achieve
around 3 kW for half an hour of flight, for $5000 and 5 kg of
batteries. Is this an unrealistic base line for me to use, before
adding the weight of battery heat insulation and other things?


Two things:
1. that would be 164 wh not kwh it would be .(point)164 kwh.
that times ten would give you1.64 kwh or 3.28 kw for a half hour so your
3kwh figure was ok.
2. you really need to research how the battery holds up to deep discharges
and how well the recover. also how many cycles can they handle? $5000 is a
lot for a battery pack and if in only last 10 or 20 charge cycles you'll
need to win the lottery to be able to fly it! ;-)
I personally am not familiar with that battery so can help you much there
John

UltraJohn wrote:
Legend Length wrote:

snip

I am unable to find electric versions of those powered harnesses being
sold.

John,

I've never seen an electric harness either. The only power harness I'm
familiar with for use with an HG is the Misquito. There are a few more
options if you want to consider a nano-trike, and even more if you want
to go PG. I'd use the performance of the existing machines as a
baseline for the performance of your design.

A few other things to think about...

What type of HG wing are you trying to power, and what type of harness
are you modifying? Will they accept a power-unit ?

Will your hook-in weight with the proposed power-harness be within the
weight range of your wing? What will the effect of power be on your
control range?

Will the purpose of the power unit be to take off and climb out, or
just as a sustainer between widely spread thermals?

Why electric and not gasoline? Site restrictions? Noise? Objections
from other HG pilots?

Harry "yep, I can fall that far" Frey

After a little more research I found batteries are aroud $300 / kg,
giving about 150 Wh / kg. This seems to be for quite a few different
brands so I would imagine that is a reasonable baseline price. This
doesn't take into account chargers or controllers for the power source.

What type of HG wing are you trying to power, and what type of harness
are you modifying? Will they accept a power-unit ?

Sorry I was a bit unlcear in my initial post. I am not actually in the
process of building this, just throwing it out as a hypothetical (at
the moment).

The HG wing would just be a typical one for these calculations. Same
with harness weight. Modifying a harness to add an engine on the back
would be an issue, i agree.

Will the purpose of the power unit be to take off and climb out, or
just as a sustainer between widely spread thermals?

Just for self-launch..

Why electric and not gasoline? Site restrictions? Noise? Objections
from other HG pilots?

Yes noise is an issue. I also feel 'solid-state' type machines like
electric engines are more reliable than petrol, due to only a single
moving part. It would also mean the fuel source could be spread out in
some interesting ways over the aircraft.

So to restate some of the calculations using the new values:

One kg of batteries will give you 150 W for an hour of use. Keeping a
250 pound hang glider fly level needs about 2000 W. You could fly
level for about 5 mins with 1 kg of battery for $300. Each kg would
give you an extra 5 mins of level time.

Don't batteries seem appealing these days with those numbers?
Especially for small engines like hang glider ones as you only need
them for a short amount of time, ie. to get equivalent height of a
cliff launch but from your paddock.

I do not want to spool the fun here, but ... whichs formulas did you
use to get those figures? I used some basic formulas and totally get
other figures. OK, I assume a bad efficienty of the prop and took it
for safety at 50%. I get for 10,5 glide ratio, 1300 N total weight, 16
m2 surface, climb rate of 2m/s --- needed power of about 10 kW!

I used some rough formulas found in a book which tells the basic
calculations rather very easy. So ... my estimate might be a bit rough.
But the difference between your estimate and mine is soo large that I
fear that one of us is ... euh ... wrong.

Ok, I am not a engineer. But I wanted to follow this item because it
interests me TOTALLY! If we would succeed in making a possible kit for
hanggliders we would at last have a way to get airborne at soaring
height with a system that is more reliable and less annoying for the
surroundings. AT LAST a way to counter those endless complaints that
get small airfields closed by orders from communities. And ... at last
a way to get airborne without the need for a entire club and the need
for a official airstrip.

Please, guys, continue this search for a electrical powered hangglider.
I keep following it.

nestofdragons wrote:
I do not want to spool the fun here, but ... whichs formulas did you
use to get those figures?

They were from he
http://www.ornithopter.org/forum/sho...98&postcount=3 .
Even though the question asked on that page was regarding flapped
flight the answer was given in general terms of energy needed. It
ignored the 80% engine efficiency and the propeller efficiency which I
thought was also 80%.

I used some basic formulas and totally get
other figures. OK, I assume a bad efficienty of the prop and took it
for safety at 50%. I get for 10,5 glide ratio, 1300 N total weight, 16
m2 surface, climb rate of 2m/s --- needed power of about 10 kW!

Those are the approximate figures that were used for the calculations.
I should have doubled (approximately) the final result to allow for
engine & propeller. So I would guesstimate 3 kW for level flight. For
climbing at 2 m/s I think the power needed would need to be doubled
again to 6 or 7 kW.

So perhaps a more accurate cost calculation would be:

7000 W needed

= 45 kg of batteries at 150 kWh per kg

= 0.75 kg for each 1 minute of flight

= $250 for each minute of flight, at about a kilo per minute

$2500 for ten minutes seems a bit steep so I can understand why
manufacturers might not be making these yet. The gasoline engines for
hang gliders (including harness) are around $5000 total. A harness by
iteself is $500 - $1000. An Electric engine + prop is around $500 -
$1000.

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Focus group started on this topic.
All are invited.