2.5m span motor glider electric conversion

[Ryan]

Hi all

 

I have a aviomodelli ariane 5 motor glider with a wingspan of about 2.5m and weighing 3.5kg that is currently running a magnum gp 40 engine turning a 10*6 prop.

 

I have just moved and the area I m in now doesn't allow glo flying and it has to be electric. Now I have read loads on electric motors and it is still all magic to me.

 

Can someone maybe suggest a cheap electric alternative to me - motor, esc and 2 or 3 bladed prop. I did look at the BRC A2814-8T 1000Kv 300W motor but I dont think it will be powerful enough.

 

I have 4 3s1p lipo batterys that I would like to retain so if the motor can run on 3s1p packs that would be helpful.

[Tom Wright 2]

HI Ryan It sounds like there's lots of ground to cover here ,first of all take your time to fully understand all the information coming your way,are you familiar with all aspects of lipo batteries ,and charging?

[Ryan]

I have read and read and read about battery's, charging rates, battery's in series and parallel....its just the motors that are getting me. I have been looking for over two weeks for an equivalent motor to a .40

[Tim Mackey]

One simple and somewhat rough and ready method is to double and add zero so that

your 40 becomes 80, and then becomes 800 ( Watts ). So an 800 watt motor should do ya - but of course you then need to decide on the kv value.

Large slowish prop required? = Low kv.

Fast sporty model with smaller high pitched prop? = high kv.

[Tim Mackey]

3s battery for 800 watts of power means WOT high current of 76A - too much really, so either settle for less power ( its only a glider after all ) or use 4s battery.

[Tom Wright 2]

Thanks for picking this one up Tim,Sorry Ryan i did not come back to your reply,had to go out.

 

Ryan do have the wing loading in oz / per / sq ft?

Edited By tom wright 2 on 14/02/2011 22:19:38

[Tom Wright 2]

Ryan You could check out hobby king and giant cod for your motor ,but brc do have a good range at reasonable prices. a 500 to 600 watt motor with a 60amp esc and 4cell batt should do the job,a kv of 500 to 1000 should keep a good folding prop within max rated rpm. Unless designed for the job over powered gliders can be a hand full.

Try a prop that gives about 400watts read out on the watt meter and take it from there.

Of course you can use a larger motor as the power output depends on the prop used.

Edited By tom wright 2 on 14/02/2011 22:53:49

[Andy Harris]

FS91-II gives 1.6HP or just under 1.2kW.

 

I use Hyperion motors in my Panics which are propped to draw just under 1.1kW.

 

I've got a faster climb rate than any other IC powered Panic in the club. There is one running a 70 IC that I cannot catch in a straight line. Most Panics are running 90's.

 

I know I can peak the Hyperions at 1.8kW so using Timbo's rule of thumb I could have a double ballistic Panic.

 

However I need to be easy on the throttle to get 7 minutes of airtime. This is easy when practicing. It is not easy in the heat of a streamer cutting event. I've invested in a 4000-6S but oddly this gives a poorer performance than the 3000-6S and similar flight times.

 

I've read some notes stating that it is quite tricky to realize the full power output of IC, mostly because they have to have the right prop and spin it in the sweet spot RPM.

 

Was Timbo's rule for 2S or 4S ?

[Ryan]

I think it is 48.5oz/sqft but that is probably way off.

 

The weight is 3.5 kgs

Wingspan: 2.92m

Tip chord: 14cm

Root Chord:26cm

 

I would like to use a 3 blade prop and Just waiting to find out which motor so I can order the prop. The prop I am going for is a vario prop so I can fine tune the ptich.

[Tom Wright 2]

Hi Ryan the wing loading looks to be nearer 19 oz per sq ft, are you looking for a hot ship performance? and do you have a watt meter?

100w per LB will be on the hot side,55 to 65w more average for a powered glider ,with that wing loading,

Edited By tom wright 2 on 15/02/2011 14:23:24

[Tim Mackey]

You stated the weight is 3.5 kgs - is that fully fitted with battery et al?

 

Wingspan: 2.92m

Tip chord: 14cm

Root Chord:26cm

 

Equals wing loading of = 19oz / sq ft

Its quite a large and heavy model really, so I think you need to be sticking with a decent amount of power. If the weight was with the IC engine, then expect to be a tad lighter with leccy, but not much. Lets guess at around 7lbs? For reasonable power to weight ratio go for 75 watts per pound, so therefore you need 525 watts, or rounding down a bit call it 500.

500Watts from your 3 cell battery will draw 47A but thats only at full power, and with a glider your unlikely to be WOToften.

Thats quite do-able. I suggest a decent size prop,turning slowish, so as I mentioned earlier, you need a 500 watt, low Kv motor thats happy swinging say a 12" prop.

Something like this maybe?

Use a 60A ESC, with BEC, and decent C rated 3s lipo battery of around 2200 mah or higher.

[Tom Wright 2]

Spot on Tim I have several of those motors , one is installed in a 3m 6lb glider ,12x6 two blade folding prop.Picking up on some of Ryan's comments i think he has got missile performance in mind, But i would continue to recommend the approach that we have suggested particularly if this is a first leccy project , Ryan has not yet confirmed that he has a watt meter,which i feel is absolutely essential for such projects.

[Ryan]

Hi tom I am not after missile performance with this aircraft just a nice gentle flyer. Its more endurance I am going for with this one. I have a homebuilt twin boom thats going to be my missile performance aircraft.

 

I don't have a watt meter at the moment but seeing the requirement for one I will be looking for a decent one and ordering it tonight.

[Tom Wright 2]

Hi Kevin The watt meter purchase is good news ,it will pay for its self very quickly,and take all the guess work out of all your EP projects,please don't hesitate to ask about any aspect of EP setups you are not sure of.

By the way i have a 5ft span own design twin boom ,its a joy to fly ,must get some photos done. Cheers TW2.

[Ryan]

Thanks for all the replies

 

If I have this correct would this setup work

 

Turnigy TR35-42D 1000KV( 15v*35A=525w-if I am correct)

45A ESC

12"Prop

 

would you recommend the use of a UBEC....

[PatMc]

I think a 3542/1000 might be a bit weedy for that model. I'm using one in my 1Kg Easyglider with 3s & an 11x6 folder.

However I'm using a 3548/ 900 in my 2.8Kg Magnattila. On 4s driving a fixed 12x6 it takes 31A for 464W . This power would probably give a good performance in your much cleaner airframe.

 

IMO an ESC with built in switched mode BEC is as good as a separate UBEC, the Hobbywing Pentium 40A - 60A for example give 5v 3A.

[Pete B]

I'd agree with PatMc about the 3542/1000 - I used one in my Aviomodelli Super Grone, described in this thread and it was fine for a 2.06kg/4lb 9oz model. The motor, with a 12 x 7 folding prop and a Zippy 3S1P 2200mah 20C, produced 412W at 37A, so it would be very marginal indeed for the Ariane.

 

I would aim for something between 500-600W output for this 3.5kg model.

 

Pete

[Ryan]

Right looking at it:

 

The above motor

2 turnigy 2650mah 3s1p battery packs(or would 2200mah 4s1p packs be better)

50Amp hobbyking esc with bec

2 bladed prop 12*6

 

The battery packs I will be using the now or was going to are 11.1v 1300mAH 26a 20c connected together to give me 2600mAH

 

I am looking for endurance and not speed.

[Tom Wright 2]

Ryan keep in mind you can fit a larger motor,to give any amount of power discussed within the various posts.you can then use the watt meter and various prop sizes,to set the best balance between economy and performance.

[Ryan]

thanks for all your help tom. I am going to order what I have posted and then at least I have a starting point. Like you say I can then play with prop sizes etc

[Tom Wright 2]

That sounds good Ryan ,sorry i called you Kevin a few posts back.For real economy you could build a glider with a lower wing loading,some of my 3 and 4m EP gliders return 1 to 2 hours air time ,on one 2.2a lipo.