1c flying?

[Simon Chaddock]

With the rain lashing down outside and my 55% wing nearing completion I started to think of what I might try next.

 

In my own case LiPo and brushless gave a significant improvement in both performance and duration, and lightweight construction took that even further.

 

So aiming just to keep something like the original level of performance (mildly aerobatic?) and avoided building a high performance sailplane, just how much flight time (as distinct from full power duration) is possible? 30 minutes, 45 or even an hour?

My aim is to have a simple plane that I know can safely stay up rather longer than I am likely to want to fly.

 

[ken anderson.]

my example simon-the j perkins pretty with a small brushless motor in and 2200 lipo will stay up for an hour for sure--but boredom normally set's in....

 

         ken anderson...........

[Tim Mackey]

Thats a tricky one Simon as there are so many variables...the temperature, the weather ( wind speed etc ) you flying style on the day, etc etc.

A little spreadsheet I knocked up years ago to log bench testing data of new models / installations  uses a factor of +30% of duration calculated from WOT settings.

For example, if at WOT my model is pulling say 20A ( airborne estimate ) and the battery is a 2A version, than flying flat out will last 6 minutes.

( 60 / 10 = 6 ) .... where 60 is the minutes in an hour and 10 is the "C" rate that the battery is being pushed at  ( 20 / 2 = 10 ).

My spreadsheet then adds 30% to the result, so I would expect on average to achieve flight times of around 8 minutes. In practivce this seems to work quite accurately, but do remeber the factors I mentioned earlier...and of course, over time, as the battery ages, times reduce further. I never actually fly to LVC anyway, preferring instead to set my timer conservatively. Of course, if you are talking of non powered models, then the normal current consumption of the radio gear alone is the key figure in calculating duration.

 

Edited By Timbo - Moderator on 28/08/2009 12:01:06

[Tom Foreman]

For a laugh some clever guys over in the states mananged to fly for a couple of days, several pilots flying in shifts, using electric gliders, equiped with large capacity batteries and solar panels. I think they stopped flying due to pilot fatigue rather than the models giving up on them, plus they might have been using FPV as well so they could search out optimum lift and altitude rather than being restricted by eye sight, also useful for the night flying bits where one would assume there is very little lift about

 

Will try and dig out a link to prove I'm not making this up

 

Tom

[Tom Foreman]

Here you go 48h duration

 

Tom

[Simon Chaddock]

Tom

Yes an amazing achievement but with 13lbs of batteries, solar cells, auto pilot and GPS its not quite what I would call a simple (or in any way cheap) sort of model.

Remember the MacCready Helios? A true flying wing!

I believe it eventually crashed into the sea taking a million dollars of solar panels with it!

Timbo

With a combination of aerodynamics and lght weight construction I was hoping for rather better than a 30% increase in WOT duration. Being realistic to get anwhere near an hour I think you would a flight time of atleast 5 times the WOT duration.

Ken

The Pretty certainly looks the part but in the RCM&E review of Feb this year Nigel Hawes suggests that a 2250 3s LiPo will give 25 minutes climb and glide, which is still very creditable.

 

I will have to see what I can do.

[Simon Chaddock]

Just a few quick calculations using the Wing Dragon as a starting point.

 

The original weighed 23 ounces. Using my light weight depron structures I believe I can make an aerodynamic equvalent, less batteries, for 12 ounces.

So with the same thrust I should get the same sort of performance (mildly aerobatic) with upto 11 ounces of batteries.

 

My experiments so far suggest that a small brush less with a 2s LiPo gives about the same thrust as the original 8 cell NiMh and 480 brushed motor.

 

With careful throttle managemnt the original 1000mAh NiMh gave just about 10 minutes flight time.

Within my 11 ounce battery limit a 2s Lipo of 5000mAh or more could be installed and coupled with the higher efficiency of a brushless motor, 1 hour begins to look possible.

 

But its just numbers at the moment.

Edited By Simon Chaddock on 29/08/2009 22:41:52

[Simon Chaddock]

A few more calculations.

The 2812 brushless on a 2s LiPo and 7x6 prop takes 15 amps WOT so with the 5000mAh battery I have on order that's just 3C - very gentle indeed.

 

With an all up weight of 19 ounces my "endurance" Wing Dragon will still be a couple of ounces less than standard.

 

One hour flights?

We shall see.