Will this turn in a 1 hour flight ?

[ChrisP]

OK - This is the next project : I want to fly for an hour. There's a bit of thermal assistance at our field in summer, but nothing to brag about. So I'm not assuming too much help from that side.

I have ordered an FVK Prima. I pick it up at Sinsheim from the FVK stand this week. They are kindly doing one for me with a V-tail : http://www.fvk.de/Englisch/Prima.html

Here's the numbers :

Bare model 330gms
AXI 2212/34 72gms including prop
2 off 3s1500 Lipolys (3 cells @ total 3000 mAh capacity) 216gms
R/C 65gms
Odds & ends 65 gms
AUW 748 gms

Wing Loading 9.45 ozs/sq ft @ 402 sq ins (net)
10x5 folder

So what's the chance of it turning in a 1 hour flight ?

Or am I going to have to rob a bank and buy a third Lipoly ?

[Sparky Paul]

You want the motor to run for an hour?
Or climb-glide.. then go for 8! :)
Find a good slope...

[Ollie]

If you want to fly at a low and constant altitude at about 1/3 throttle then I think you will be able to fly for an hour. With this strategy you might select a smaller motor to operate at a higher efficiency with a higher throttle setting.

I think you can save a little weight, a little money and increase battery capacity a little by using only three 3270 Mah cells if they fit in the fuselage.

If you want to climb at full throttle and glide, I think you can do about an hour without lift if the prop folds and the plane is low drag. With this strategy, much depends on how well the model is trimmed in climb as well as in glide. It won't take much in the way of thermal lift to put you well over the one hour mark.

With a good slope and wind, you can do an hour and land with an almost fully charged battery.

Paul says it much more succinctly than I do.

[Sparky Paul]

I was checking some flight notes on the e2TeeVee, it went 26 minutes on only 2 climbs, on 8x1400 nicads. Maybe 3 minutes total motor-on time.
Some of the thermals around here are wider than the plane's visibiltiy permits using! :)
Going up isn't an option, it's unavoidable!
Getting back is the problem!

[Dick Huang]

ChrisP,
Indeed you can fly for one hour. I used my Prima data (actual measured) and changed to 2S2P Tp 1320 cells and got a motor run time of 28:32 0r 28.53 minutes. The total duration = (Vc/Vs+1)*motor run time. For the case listed : Duration=(289/103+1)*28.53=108.59 min or 1.81 hours. You will need to fly it in several climb and glide segments to keep the model in sight. Here is the data.
Dick Huang:)

[Dick Huang]

ChrisP.
I am sending the data on my Prmia. Keep the weight down!
Dick Huang:)

[ChrisP]

As always guys - incredibly helpful.

I really do want to fly the hour at my club field, not on slope.

The whole thing was kicked off by the Wingo seaplane that flew 100 kms in just over 2 hours over Lake Constance in the summer. Kind of got my attention !

My Topic 400 has a bog standard Jamara 480 with 8x600's and will easily turn 18 minutes on a good day. So crude extrapolation suggested that the Prima would have a good chance of cracking the hour.

All the stuff is ordered, so I'm basically committed to the equipment. I'll report back in summer when it's warmer ! :)

[ChrisP]

My buddy Harald and I were down at Sinsheim yesterday. I picked up my V-Tail Prima from FVK.

Two thumbs up to FVK for putting this 'special' together for me at NO EXTRA COST :D :D :D

[opualuan]

how about some pics of the v-tail?

I've flown the prima on MM extreme 6:1 12.5x8, etec 2400 2s2p (1200 cells). easily to fly on flatland for an hour. 130 watts. motocalc predicted ~50 minutes at lowest throttle setting.

I'm now moving to TP 2200 3s with typhoon 15 13wind outrunner, 12.5x8, 250 watts. motocalc is predicting over two hours on the lowest throttle setting. I'm expecting at least 1.5hr runtime.

[ChrisP]

Originally posted by opualuan
how about some pics of the v-tail?
Et voila :

[ChrisP]

.........and in company with the world's one and only (according to FVK) non-aileron Mini Prima for comparison :

[BEC]

Should be doable......

I almost casually did over an hour with my Astro 010-powered Mountain Models Dandy last spring in Chilliwack BC. (16T in GWS 3.75:1 gearbox, APC 10x7SF, 3s Etec 1200s). This hour included rocketing to altitude, spinning back down, floating around, loops, rolls, some touch and goes, and more......

FYI the Dandy has about as much wing as your sailplane but it weighs about 2/3 as much (all up weight less than 13 ounces).

Using the same prop my AXi 2212/34s deliver twice the input power (too much for ETec 1200s) but I don't know if they're really more efficient than the Astro 010 in the 20-30W or less power range where you'd want to run it for a long flight.

[ChrisP]

The Axi 2212/34 has still not turned up. Actually I'm getting a bit nervous about it fitting in the model.

The spinner diameter on the Prima is 29mm. I cut out a sillhouette of the motor in cardboard and it was squeaky tight. The problem with outrunners, of course, is the wires coming out of the front of the motor.

I'll wait until the motor turns up. If it doesn't fit I guess I have the following options :

1. Install motor further rearwards and use a short extension shaft through a ball bearing in the bulkhead.

2. Install the motor 'backwards' to get the wires to the rear using one of those prop shaft adapter things.

3. Cut the nose shorter, install a new bulkhead and use a bigger spinnner.

4. Buy a geared Hacker or similar.

Hmmmmmm..........

Chris P

[opualuan]

32mm litespinner just fits. 30mm RFM is just a bit too small.

typhoon micro 15-13 fits, you just need to tack-glue the wires to the fuse sides to make

[ChrisP]

Dick
I spent a lot of time analysing your numbers. The short Hacker is definitely the way to go. I'm thinking of ordering one tomorrow.

With Lipoly's it should be easy to fly for 1 hour.

[ChrisP]

The Prima had its third flight yesterday. 35 minutes in a thermal-less sky and still bags of power.

It was getting a bit dark and I had to finish the flight. The wing loading is so low that if I have to install a second 3s1500 to get the duration there will be no problem.

In any case the next step is to go for the hour with the single 3s1500 and then double up for the hour if I need to.

Chris P

[opualuan]

finally got the 10C TP 2100's set up on my prima... climb is not rocketship fast, but solidly vertical on this setup (typhoon 15-13). haven't weighed it yet, but it's still very light, no fun with wind. As far as duration, haven't tested it yet, only flown for a few minutes so far (tuning cg, radio installation,etc), but I'm pretty sure it will do at least an hour...

[vintage1]

Well I can easily do well over 1/2 hour witha criude sp 400 and LIPOS. A do7ble sized pack is no heavier than the nickles I used to use, so I'd say an hour is actually not a hard target to achieve with a low wing loading model.

[Ollie]

In level flight at a constant velocity with the plane trimmed for no load on the elevator, the thrust will be equal and opposite to drag and lift will be equal and opposite to weight. At an air speed of 23.8 FPS, the lift coefficient of the wing will be 0.8. The airfoil is not specified but a Cdp is assumed for 0.03. The Cdi is 0.2 for 10 AR. The Cdp of 0.004. The coefficient of total drag of 0.054. The ratio of lift to drag is equal to the ratio of the lift and drag coefficients. Therefore L/D = .8/.054. Since the weight is assumed to be 1.65 pounds the drag force is no more than 1.65/14.3 = 0.12 pounds. In one second the drag force acts through a distance of 23.8 feet. Power is feet times pounds divided by seconds. Therefore the power to move the model at 0.12 times 23.8 = 2.86 foot pounds per second. There are 550 foot pounds per second in a horsepower. Therefore, it takes 2.86/550 = 0.0052 horsepower. The propeller probably delivers that horsepower at an efficiency of about 70%. The shaft horsepower required to drive the propeller will be about 0.0052/.7=0.0074 horsepower. The motor will probably not be very efficient at this power level so I'm assuming an efficiency of 40% (it's probably closer to 60%). The power input to the motor will be less than 0.019 horsepower. There are 746 watts in a horsepower so the input to the motor will be less than 14.2 watts. The battery voltage is 11.1 volts so the current will be about 1.28 amperes.

Using to size the battery yields three, 1500 miliampere hour cells in a 3S1P configuration.

[ChrisP]

Hi Ollie
I appreciate your input.

Actually I it looks even more optimistic than that as after I changed to a geared Hacker rather than an outrunner I finished up with an AUW of 690 gms = 1.52 lbs.

I assume that the 4:1 gearing is driving the motor fast enough to achieve reasonable efficiency - an advantage over the outrunner - and I'm not operating it extensively in a cruise condition, more of a ca 30 degree climb and then glide. I am currently playing with the amount of 'down' mixed with 'throttle' to give me a reproduceable climb rate automatically as the model pitches up under power.

I chose the 10x6 prop size to be below the 10A constant current limit of the cells, so I am hopefully not significantly reducing capacity below the 1C discharge rate.

Actually your estimated 1.28A X the 70 minutes cruise your numbers suggest correlates well with my concept of flying 9A bursts for a total of 10 minutes and gliding for 50. Although we only have unpredictable thermal activity at our field, we find that the chance of catching one increases significantly with altitude. So it seemed to make sense to go for a burn & glide approach rather than mimsing around (an English expression !) at low altitude.

Cheers !

Chris P

[vintage1]

yes. Burn and glide also puts the motor in a more efficient regime. Unlike can motors which are typically at their best on about hlf throttle, thise hackers tend to be optimised for neareer full throttle operation.

Mimsing? As in 'all mimsy were the borogroves" ?

Beware the Jabberwock, my son....:D

[ChrisP]

And as in uffish thought he stood,
The Jabberwock, with eyes of flame,
Came whiffling through the tulgey wood,
And burbled as it came!

:)

[shaneyee]

And as in uffish thought he stood,
The Jabberwock, with eyes of flame,
Came whiffling through the tulgey wood,
And burbled as it came!

And you wonder why so many people have trouble with English....

Isn't it bad enough that pear, pair and pare all sound the same but are different and cough, dough, bough should sound the same but don't..... now you have to come up with that!

;-)

Shane

PS. Learning English by reading Lewis Carroll is like learning Physics by watching Dr Who!

[vintage1]

Better than learning Latin from 'Winnie Ille Pu'

"De Heffalumpi, semper disputandum est"

[ChrisP]

And you wonder why so many people have trouble with English....Download some Stanley Unwin to understand us Brits a bit better. The poor old devil died at 90 a couple of years back, but his spirit lives on :

http://www.bbc.co.uk/england/thinkofengland/unwin.shtml