FxRES May 2023 2m F3L/F5L Monthly Duration Challenge

[Richard Newsham]

PuRES V2: F3: 6th May:  3mins 54secs 
Please note the borrowed bungee diameter is unknown so not sure if you wish to include this time.

I maidened my PuRES V2 this morning, Sat 6th May 2023 from Harden Moor near Keighley.  I am a member of KADMAC (Keighley and district model aircraft club).  The flying site is on a moor south of Keighley.  There is a triangular strip cut into it.  No slopes within the immediate vicinity.
The bungee cord is borrowed, old, with dimensions unknown but is 10m long. Attached is new, 31lb breaking strength, monofilament line of 50m length.  The bungee was rejoined twice after the weak parts were found.  New bungee cord of 6mm dia and 4mm internal diameter is on order from Ebay.
The two hand launch tests flights went very well. The first a simple chuck that flew straight and level down the strip requiring the spoiler to stunt further progress.  The second firmer hand launch saw one turn and land.  Spoiler to elevator curve mix trimmed to suit.
Without further a do I rolled out the bungee.  No point in putting the launch event off.  Not flat calm but a breeze.  Wouldn't have said it was above 5mph. About 25 steps back so a bit of tension on the line but not too much (trying to remember the feeling I last used a bungee when I was about 15 year old).  I can always add more steps back if required on the next flights.
"Launching......" and up she went.  The rattle of the pennant/piece of material and before I knew it it was time to part company with the bungee.  Not quite a ping but away she went. What a relief.  And down she came steady as anything.  A turn here and a turn there and a landing.  That'll do nicely.  Followed by 9 of the same with one catching a little bit of a thermal for a few seconds.  The 'just one more flight' did get the better of me and something I'll have to watch if I'm to keep in favor with the wife.  The PuRES lives to see another day which was my intention.  Now where are those damn thermals, the fun begins........

Any advice about the graph presentation is appreciated.  Especially the null time from switch on to connecting to the bungee.

[StraightEdge]

Well done Richard - and welcome here!

Re the graph, just play around with the Aerobtec graphing software until you're familiar with it.  At the top left are several little icon boxes which enable you to trim the start and end of the graph, etc.  You won't mess up your data until you're ready to save it.

Re the PuRES, a lovely machine for the job!

Jon

 

[Paul Wellacott]

Purito F5  -  6/5/23  -  time claimed 7:54 minutes.   Dishforth, North Yorkshire

Well, that was a day, looked like it was going to be a washout, but put the Purito in anyway. Soon realised that there might be the potential for lift, so we moved from the power line to the silent flight area.

3 of us were flying, and we soon discovered that it was a strange day, it looked like there should be lift, but could we find it? nope!

Andy was flying his 4m F5J, high launches 150/200m were a bit better, but it was a struggle from 60m. In the end I had 32 launches, the majority were straight into sink, but good practice for spot landings.

This flight was the best I could manage, the wind was quite strong and I baled out when I thought it'd be too difficult to get back upwind, at least its a score for the month. roll on some better weather!

[Andy Shutt]

Eli RES - Towton Battlefield - Yorkshire - 07 May 2023 - 21 minutes and 32 seconds.

8 launches into dead air, 3 to 4 minutes flight time and then managed to find lift in front of a dark looking cloud, managed to get follow the lift until the model was well down wind and I had to bring it back, as I did I felt the cold air come through, managed 21 minutes and 32 seconds so quite please with that after a day at Dishforth Airfield with only 4 to 5 minute flights all day.

 

[AnthonyB]

F5RES, cRESt – 7/5 23 – Time 28:30 – Clitheroe Lancs.

Had a few flights and decided to charge the battery rather than change it. Hoping that the conditions would change over 30mins. As I got to the car, the Eli (fellow pilot's) was circling upwards, so I launched to get just under him and cut motor. We both went up, until we didn't. We separated and he found some more good air, so I joined him just in time.

It did not matter what you did, nothing would scoop you up. You would go up and then it fizzled. In the end we decided that the NW breeze was coming from the surrounding hills and being on the west bank of the Ribble (they were swimming in it !) it was all downhill breeze. The field we were flying in has a slight slope down to the river, so that was against us. We also decided that the ground was really wet and it was little bursts of water vapour that were rising. Full flight.........

In the end I managed 90m. On the last part, I was really fighting to get up, all six mins, but all I could do was maintain height.

Finally the landing, showing 28:30.

[AnthonyB]

Transparent Oralight - white becomes grey at 150m and the (so called) orange becomes cloud grey at 100m.

So you get to see a few bits of red. 

Now - cover the model in glow red and glow green - boy, can you see that.

Ah, the price we pay for a bit of weight saving.

[andyharrold]

3 hours ago, Andy Shutt said:

Eli RES - Towton Battlefield - Yorkshire - 07 May 2023 - 21 minutes and 32 seconds.

8 launches into dead air, 3 to 4 minutes flight time and then managed to find lift in front of a dark looking cloud, managed to get follow the lift until the model was well down wind and I had to bring it back, as I did I felt the cold air come through, managed 21 minutes and 32 seconds so quite please with that after a day at Dishforth Airfield with only 4 to 5 minute flights all day.

 

Nice thermal.

 

[Hydeflyer]

15 hours ago, Andy Shutt said:

Eli RES - Towton Battlefield - Yorkshire - 07 May 2023 - 21 minutes and 32 seconds.

8 launches into dead air, 3 to 4 minutes flight time and then managed to find lift in front of a dark looking cloud, managed to get follow the lift until the model was well down wind and I had to bring it back, as I did I felt the cold air come through, managed 21 minutes and 32 seconds so quite please with that after a day at Dishforth Airfield with only 4 to 5 minute flights all day.

 

Nice model Andy.. Good to see another Eli on the score sheet. I've had problems with the power train on mine. Using 2S I was only just getting to 60m in 20 secs so moved up to 3s and burnt out the wiring yesterday on the first flight! Think my 20A cheapo ESC wasn't up to 3S.

[AnthonyB]

Sorry about bandwidth, but that batteries going flat thing caused an itch in my brain, which I have to scratch.

Yesterdays flight (28:30) was unusual, because I was going to charge the battery after about 4 runs to 60m.

From the RC Electronics data stored, the voltage was 7.61v (when connected).

It fell to 7.44v at the end of the motor run. The motor draws a little over 10A static, so we can say a little under 10A with an off peak battery – 10A x 7.44v = 74W. It is probably at about 75% efficiency (poor) at the prop and so about 53 – 55W. The climb was less than 45deg because I was just aiming to reach fellow's model. It could actually have been <50W.

The climb was 4.22m/sec so it was a very reasonable rate. That's 15sec to 60m.

The battery is a Turnigy 450-2S and 25-50C. So really you should limit the output to 12.5A (0.5 x 25). This is a lowish C battery (light) compared to (say) 80C discharge batteries, which would be heavier.

After the motor run the voltage rose to 8v, I assume because the 10A discharge warmed it up a little.

Then I flew for 28mins and right at the end the voltage was 7.32v.

Hence it went down from 7.61v to 7.32v after 28mins and a motor run.

Subtract a drop from the motor and the whole Rx + servos (Yes – all 4 servos) for 28mins did very little to the battery. I have NEVER had a problem with battery on glide – Hence the itch.

There is something going on here which I am not doing.......

Only 2S and not 3S.

No telemetry.

No BEC / Sbec.

Something is using far more power than I do ?

From a power point of view a 300-3S has (should) EXACTLY the same energy as my 450-2S.

**On a good day for a long flight there cannot be much wind. It simply cannot work. But on a calm(ish) day you just want to get up to 60m (90 in F5L) and 50W to the prop is more than enough. On a windy day (at a comp) it could be an advantage to rocket off 200m – NOT HERE. On a windy day you want a heavier model. Great – add a 3cell larger battery and a larger motor – Perfect.

 

Only as a rough example (as previously). I take a full 8v to power everything from a 450 battery – That's (let's say) 1A at 8v = 8W. The question becomes (a) If you take 1A at 12v out of a 300 battery, what power are you actually using ?

If it takes 8W to power the system and you have reduced the voltage to 5v, then you would need 1.6A to be back at 8W.

So I would take 1A out of a 450 battery and the user of a 300-3S would use 1.6A out of their 300 battery. (BEC)

Then (b) if you are also transmitting from the Rx, then that figure could hit 2A. That is 2 from 300 as against 1 from 450.......... That's 150 against 450.

Or just for glide THREE times more duration.

 

Then I could be a fair way off, because if the 12v could be converted to 5v at 100% efficiency, then the power drain would only be (for 8W) 0.66A from the battery. They can NEVER be 100% efficient, so the efficiency is the question.

 

I'm OK, so that's that. If you are wondering how bad your system is, you will need a good sized 5ohm resistor as a load and an ammeter / watt meter to measure the power out of the battery and then into the load, to see how bad it is.

[StraightEdge]

4 hours ago, Hydeflyer said:

Nice model Andy.. Good to see another Eli on the score sheet. I've had problems with the power train on mine. Using 2S I was only just getting to 60m in 20 secs so moved up to 3s and burnt out the wiring yesterday on the first flight! Think my 20A cheapo ESC wasn't up to 3S.

Sorry to hear that, what was the full power-train?  Did you not step down a size or two in prop?

In both my Eli (still just at the pre-covering stage) and in my Medina I'm using the HyperFlight 28A BLHELI-32 which is pretty 'cheap' and very light.  In bench tests the current draw never went above 12.5A (Hacker A10-7L geared with 13x8) or 15A (Hyperflight 1806 with 6x4), both running off 3s.

[Andy Shutt]

1 hour ago, StraightEdge said:

Sorry to hear that, what was the full power-train?  Did you not step down a size or two in prop?

In both my Eli (still just at the pre-covering stage) and in my Medina I'm using the HyperFlight 28A BLHELI-32 which is pretty 'cheap' and very light.  In bench tests the current draw never went above 12.5A (Hacker A10-7L geared with 13x8) or 15A (Hyperflight 1806 with 6x4), both running off 3s.

My Eli has a Hacker A10 geared motor in it, easily reaches 60m in about 10 seconds so I have the ability to push the model out.

[AnthonyB]

I'm not writing this to be contrarian or awkward or anything – Just trying to help.

 

The hacker A10-7L is a tiny little 21mm diameter 20g motor 2200kv and the spec is.....

Their figures not mine.

The 7 part is the number of winds (7) to a given weight of wire.

They also do an A10-13L and that has 13 winds for the same weight of copper.

It is thinner wire, but more winds so the kv is lower and its ability to pass current is far lower, because it is thin wire. But more torque and so the kv is only 1300 (almost half). You can also use a higher voltage with these.

The spec for this being..........

Then they take the A10-7L and put a gearbox on it, otherwise it would be on tiny inefficient props. It doubles the weight, but it is worth it because it can turn larger more efficient props (I love geared motors).

The spec being......

That's great and you believe the retailer.

However they also do the same with the A10-13L – Remember, the far lower kv one.

The spec for that is ….......

And you believe the retailer about that too ?

The problem here is that the 7L and the 13L are exactly the same when geared.

You don't have to be a rocket scientist to work that out !

So the final part is that we started with a 50W motor (for 15sec) – stuck a gearbox on it and suddenly it will handle DOUBLE power. That is scientific progress if ever I saw it !

How many time have I read that their motor blew ?

Please don't let me influence you – I may be jealous because at 70W I can only climb at 5.38m/sec (11sec to 60m) and I'm using a far heavier motor (29g).

[mikef]

37 minutes ago, AnthonyB said:

The problem here is that the 7L and the 13L are exactly the same when geared.

Looks like a mistake on the website ? - the three geared motors on their site show identical 'drive recommendations' as shown in your tables above.

[AnthonyB]

10 minutes ago, mikef said:

Looks like a mistake on the website ? - the three geared motors on their site show identical 'drive recommendations' as shown in your tables above.

So also the 9L-1700kv ?

So the next question is which is right.

Looking at the 1700kv @ 10.8v it would want to rev at (1700 x 10.8) 18360.

The 4472rpm and the 4604 would give ( x 4.4) 19,676 and 20250rpm at the motor, which has to be the 2200kv one.

It will take about 84W to turn a 13 x 8 prop at 4600 - That's 84W net !

They say 108W gross and I just can't see that being 77% efficient.

[mikef]

The -9 and -13 tables on the website were not correct.  Hacker sent me these new ones this morning and say that they will be corrected as soon as possible.  Stop press!  They have already corrected them!

Edited to reflect current (sorry…) situation.

[AnthonyB]

2 hours ago, mikef said:

The -9 and -13 tables on the website are not correct.  Hacker sent me these this morning and say that they will be corrected as soon as possible.  Stop press!  They have already corrected them!

 

My point was that you take a 20g,  21mm motor and it is meant to be good for 50W and then put a gearbox on it and it becomes a 118W motor. It seems like a good solution and so people "want" to believe it is true. 

The web site has had all that on for a long while and they never saw their mistake - wow !

All this is a smoke screen and we never get to the real problems.

A very light model will get to height on time with 50W (net) driving the prop (oversimplified) - BUT, one weighing 50% more will (duhh) require 50% more power. 

I said "net" - NOT  GROSS - By over propping or banging another cell on may look like more power (gross) it is NOT more power turning the prop. It is in fact all just warming up the motor - a lot.

I always aim for 80% efficient and settle for 75% on very light models - it is called a compromise.

So - not looking to be argumentative or fall out with people - just trying to throw a few facts about, rather than Urban Myth......... To help.

[mikef]

May I suggest that you contact Hacker directly if you have a problem with their figures.  I got an instant response when I pointed out the error you were confused by.

15 minutes ago, AnthonyB said:

My point was that you take a 20g,  21mm motor and it is meant to be good for 50W and then put a gearbox on it and it becomes a 118W motor.

But they add a gearbox and change 2 cells to 3.  Voltage up 50%, current draw up a similar amount, input power more than doubles.  I don't see an error there.  And now you can turn a larger, more efficient prop.  Maybe that's how they get the 77% efficiency you calculated and were surprised by.  And you say you aim for 70-80%.

This is an interesting conversation and I'm out of my depth - but it’s a bit off-topic - it would be great for you to get Hacker's explanation of their numbers and start another thread.  Please.

 

[AnthonyB]

1 hour ago, mikef said:

May I suggest that you contact Hacker directly if you have a problem with their figures.  I got an instant response when I pointed out the error you were confused by.

But they add a gearbox and change 2 cells to 3.  Voltage up 50%, current draw up a similar amount, input power more than doubles.  I don't see an error there.  And now you can turn a larger, more efficient prop.  Maybe that's how they get the 77% efficiency you calculated and were surprised by.  And you say you aim for 70-80%.

This is an interesting conversation and I'm out of my depth - but it’s a bit off-topic - it would be great for you to get Hacker's explanation of their numbers and start another thread.  Please.

 

It might be great to get Hacker's explanation - for you. I have no interest what so ever.

In this world it is probably best to just not bother trying to help. I will know in future not to.

[Graham Lorimer]

Anthony,

 

You say "By over propping or banging another cell on may look like more power (gross) it is NOT more power turning the prop. It is in fact all just warming up the motor - a lot."

What is the explanation that leads you to say that adding another cell, and therefore higher voltage, "it is NOT more power turning the prop."

 

I really would like to understand.

 

Graham

 

[mikef]

2 hours ago, Graham Lorimer said:

….   I really would like to understand.  ….

Me too.