FxRES September 2024 2m F3L/F5L Monthly Duration Challenge

[martynk]

 

FxRES Monthly Postal Rules

This is a “for fun” challenge for UK based pilots. Anyone may enter with:

1. a bungee-launched F3L specification glider using the reduced length Hi-Start. The reduced length Hi-Start bungee has a maximum of 10m of 6/4mm surgical tubing and 50m of static line (minimum 30lb breaking strain). Lighter/smaller/shorter bungee rubber may be used.

OR

2. an Electric motor launched F5L specification glider fitted with an Altitude Limiter set to 60m and a maximum motor run time of 20 seconds.

Object: Fly your F3L or F5L glider for as long as possible from a flat field. Each monthly challenge will commence on the 1st day of the Calendar month and  the person who's time is unbeaten at the end of the Calendar Month 'wins' and a new challenge will start. The annual challenge league will end on the 31st December of each year. A new annual challenge league will then commence on the 1st of January.

Rules:

Models must comply with the Model Specification rules for F3L or F5L as appropriate.

You may self-time your own flights

Flight times begin when the tow-line falls from the tow-hook  for F3L or in the case of a F5L glider when the motor stops.

The model must land in the launch field or (if there is no field boundary) within 150m of the launch position for times to count. There is no landing bonus.

If you are using a bungee launch (for this event or any other), then the launch line MUST be secured using a corkscrew dog tether or similar bungee stake to minimise the risk of injury caused by a loose stake.

Scores must be submitted on the relevant monthly postal event posting on the FxRES forum at www.barcs.co.uk/forums/   

Scoring flights must be submitted within 24 hours of the flight taking place.

A flight log graph from the Altitude limiter should also be submitted if entering with a F5-RES glider.

All scoring flights must start with a hand release from Ground Level with (if applicable), the motor running.

No flight information telemetry permitted except for Received signal strength and Receiver battery status.

Submitted scores will be amalgamated into an annual league. Points will be awarded as follows:  1st -25 points, 2nd - 22points, 3rd - 20 points, 4th to 22nd, 19 to 1 point respectively.

You may enter as many times as you wish using as many different models as you wish, but only your longest duration flight will count towards the league position. Separate entries (best flight in each) will be recorded for those who fly both F3L and F5L.

Please enter your best/latest monthly scores below in the following format...

ON THE FIRST LINE OF YOUR POST

Model Name : Class (F3L or F5L) : Date of flight : Time Claimed

Any text or commentary or images please add afterwards.  Thanks  

[AnthonyB]

cREst : F5L : 4:35.

This is a day late, but it takes FOR EVER to process video.

Yes it is rubbish. It was done just before sunset. It was also done in a breeze from the South East, which has a very slight down hill component.

However 4:35 (275sec) from 60m launch is like 7:38 from 100m.

These gliders are meant to do 6mins from 90 / 100m launch – job done !

The whole area is covered in grass, except where they have just removed silage from – my test field. How dumb are cows wanting to be in there ?

Sometimes it is good to video a flight. Perfect to show how a thermal affects the flight path – superb teaching aid.

What is needed is a tiny camera that you can fasten on the nose. They do not exist (at a reasonable price).

This one weighs 30g and must act like a big air-brake. Never used in the year I have had it.

https://www.youtube.com/watch?v=_Wi79j1_xdY

[martynk]

Thanks Anthony.. Nice scenery, you are lucky to have that on your doorstep..

 

     

[Carl]

Magic 2 SL : F5L : 07/09/2024 : 7 mins 1 sec

After 2 days of solid rain, today was grey and cloudy but no rain or wind. Even though it was cold and soggy this morning I took the opportunity to test out my Magic 2 SL after repairing the damage caused from spearing into the ground last month.

So happy the performance of this glider is in a different league to my Resco. I was consistently achieving 3 to 4 minute flights in the cold, damp conditions - something the Resco would not have achieved.

So for this flight of 7 min 1 sec, I launched straight into a light thermal and I could tell it was climbing, so tried to hang onto it for as long as possible. Unsurprisingly the thermal fizzled out, but the descent was very slow.

I'm so impressed with the Magic 2 SL. The rudder has good authority, and turning in tight circles is so smooth and easy. The other thing I like, is that I'm getting a little zoom without a stall when the motor cuts. It's almost like a DLG as it levels out. 

I'm glad I got out this morning because the outlook is back to wet and windy from tomorrow (Sunday) onwards again - pretty much the whole of the coming week.

Carl

 

[martynk]

7/9/24 F5L MH2e 05:55 

Managed to get out yesterday. Light drift from the NW drifting me out over the no fly zone towards an industrial area. Lift was very patchy and very weak. Several 3 minute plus flights but only one half decent attempt.

Had to fly back early which was a bit of a bummer. You can see where I started the return journey.

 

[martynk]

Updated table:

     

 

     

[Carl]

Magic 2 SL : F5L : 13/09/2024 : 13 mins 54 secs

After several days of wind and rain, today was a gorgeous, calm, sunny day in North Devon. The time I'm claiming was my first flight (I'll tell you what happened next shortly). I've already said this previously, but the Magic 2 SL is an incredible glider. The way I was able to use the light thermal was magical. The best bit was when dozens of Swallows or Swifts (I don't which they were) swarmed in to feed on the bugs in the thermal I was using. Absolutely lovely.

Now onto my second flight. I identified the thermal with my streamer, so launched into the breeze and circled round whilst climbing. But the glider under power started on a very slight downward trajectory and I didn't have any up elevator control! I was very close to tall trees, so I cut the power immediately and thankfully the glider didn't continue to dive, but slowed down and I regained control of the elevator. You can see this in the Altis graph below. Things got back under control at about 43 metres. I went straight into the thermal and enjoyed a very nice climb up to approx 370 metres, during which I was flying with buzzards sharing the same thermal. Now the thermal was drifting away, so the glider was not only high but quite some distance down wind. So my decision was to come out of the thermal and fly back towards me. But to come out required a little bit of a dive. This is where it went wrong again. I could see the glider was moving at great speed and I had no control again. It was diving, and diving fast. I couldn't pull it out of the dive! Does the motor work? I powered it for a moment (this can be seen on the Altis graph) and I could hear it, so it wasn't signal loss. I tried rudder, to see it I could spiral it - nothing. It kept going down, down, down!

So what went wrong? I think it's because I'm using spring-pull on the rudder and elevator. I noticed last month when this happened, that the rudder was flapping violently when the glider got into a similar dive. I could see it that time as the glider was close enough. 

Going back to my launch, I control the climb with a little stick input on the elevator, so it doesn't climb too steeply. This glider is fast, and I think at speed the spring just wasn't pushing the elevator up against the airflow across the tailplane. Therefore I had no up elevator control until after I cut the motor and the glider slowed down. I think the same is happening, when trying to get the glider out of a thermal - I dive a little and it gathers speed to a point I no longer have any up elevator control.

What's the solution? I'm going to dispense with spring-pull and install pushrods instead.

I really thought the glider couldn't survive this a second time, especially as it came down quite some distance from me. Well it did! Somehow it missed all the trees, a swamp that is dangerous, the estuary, and a few big, fancy multimillion houses. Look at the picture - again it speared straight into the ground with a little bit of damage on the middle wing panel. The right wing tip simply separated from the centre panel. It's less damage than the first time. It took me almost an hour to find it - I was almost about to give up and spotted in a neighbouring field. My transmitter was very helpful in finding it as it reported "RS Signal Critical," "RS Signal Low." So when it was reported as Low I new I wasn't too far away, and even closer as there were periods where I was getting normal signal strength, so no warnings being reported. I just can't believe my luck! Looks like an easy repair again, but I will install pushrods. I won't get away with it a third time.

Carl

 

[Richard Newsham]

Wow.... 

[cirrusRC]

What servo are you using on your elevator?  What guage wire are you using on your elevator and how long is spring?

Must surely be either spring or servo or something is flexing under load.   On a day like today, pull spring setup should easily cope.

The elevator looks quite large.  Looking at Martin o's build, I see he used pushrods.

I can only assume you're spring(s) are inadequate or servo too weak under load.

Edited September 13 by cirrusRC
Thought about it more

[martynk]

Is it pull up or pull down against the spring Carl?

[martynk]

Updated table.  Get that model fixed Carl.. 

 

     

[cirrusRC]

I revised my response above. 

https://www.barcs.co.uk/applications/core/interface/file/attachment.php?id=32898&key=2d29085a447a9d5e84eb591b8fa4bef2

[cirrusRC]

I've only had one beer honest. Ok martins build actually used pull springs.  Sorry

[cirrusRC]

20 minutes ago, martynk said:

Is it pull up or pull down against the spring Carl?

Good point.  When I had flutter the model wanted to pitch up or pull off bungee early.   Spring was wanting to pull up elevator.

[Carl]

In answer to a few of questions:

Pull up or pull down? - the elevator is pull down/spring up (rudder is pull left/spring right)

Servos used? - Kingmax CLS0511H metal geared - similar performance to Bluebird BMS-101DMG but the Kingmax centres much better than the Bluebirds (I've had to chuck about 50% of Bluebirds for terrible centring)

Spring strength? - pretty strong - when the tailfin and tailplane are off the glider the control surfaces spring right back - so the elevator springs all the way back to the tailplane surface and the rudder springs all the way back to the fin quite strongly with a tap.

Thankfully the damage was indeed less than the last time, and is already structurally repaired. I just need to recover the section of wing. I can't trust pull/spring anymore, so I'm already installing pushrods at present. This has been the largest glider I've used spring/pull on and these 2 events has put me off.

Thanks everyone for your input 

Carl

[Pete in Northiam]

Sorry to see that Carl! Flutter is a complicated bugger! The underlying causes are a combination of excess speed, the mass distribution of the fluttering part relative to the hinge line or twisting axis and lack of torsional rigidity. Wings will often flutter when their mass balance is behind the main spar. For hinged sufaces on full-sized aircraft you'll often see a part of the surface extending forward of the hinge to move the centre of mass ahead of the hinge exactly to reduce chances of flutter. Unfortunately spring--pull controls can meet many of the conditions For more try https://en.wikipedia.org/wiki/Aeroelasticity#Flutter

ps Only way I know to get safely out of strong lift is to fly away from it cross-wind - you'll soon find the downdraft outside the updraft without needing to dive.  I very nearly self-destructed a wing a couple of years ago by opening the spoiler at 900 feet but closed it quick enough to just shred the covering on one side before pulling out of the dive.

pps The sin on bungee launch is flying fast forwards instead of slower up. My RES Eagle is notorious for wing flutter if I don't pull enough up on release!

[Carl]

3 hours ago, Pete in Northiam said:

ps Only way I know to get safely out of strong lift is to fly away from it cross-wind - you'll soon find the downdraft outside the updraft without needing to dive. 

Thanks Pete for the information and especially the advice on getting out of a strong thermal safely. I'll certainly try that approach in future 

Carl

[AnthonyB]

ONCE (only) have I used a pull spring elevator.

It was the recommended method for the 2m kit I was building and it came with the parts etc.

All has / does work fine. It is for 2m F5J and so it has full crow braking.

Being who I am, I test models to the limit and so you need to know the VNE etc.

One day at the club I was challenged, among other things, to do a Vertical Eight (using the motor as well).

It all went well until I was pulling out of the bottom loop – and nothing.

I guessed what it was and flicked in Crow Brake – then the elevator worked.

I had dived out of strong thermals on full brake and never had a problem.

However the dive from the top of the top loop (using motor to get there, then switch off) to the bottom of the bottom loop is a big dive.

The BlueBird I use or the KingMax have a pull of over 1kg at 1cm. That's TWICE the weight of most F5L models.

When I switch the radio off, the servos instantly go to one end as the spring pulls over.......... That irritates me.

With the elevator on top of the boom, the string is always going to pull down elevator and the spring does the up elevator part.

The real question is (using a 1kg servo) how much power is giving up elevator.

The answer is (on mine, and the spring feels strong) 128g – well somewhere between 100 and 140g. It is not easy to hold a constant pressure and photograph.

So in this case there is TEN times more power to give down than there is for up.

Now, on all my models you will see carbon push rods (same material as the boom).

If you want to dive out of a thermal – do it inverted !

 

[Carl]

21 minutes ago, AnthonyB said:

If you want to dive out of a thermal – do it inverted !

 

Thanks Anthony for your analyse  It's funny you suggested coming out inverted, because in hindsight I thought if ever I get into a dive I can't pull out of, I'll do an inverted loop instead so at least I know the servo is pulling the elevator surface down. As long as I don't leave it too late, hopefully the wing will take it. But I have installed the pushrods that came with the kit, but using a lighter tube. I've left the springs in place for the time being.

Carl

[Will_A]

Purito : F5L : 16/09/2024 : 17 mins 7 secs

I've been away on hols in Greece, just got back to see Carl's second drama. Wow, that was unfotuntae, but also another lucky escape from having to put the pieces into a bag to avoid leaving litter! I do hope you get it sorted. I have used pull spring with no issues on my Medina, the recommended method, and those have quite large V-tails, so it can work. Also pull strings are standard on all DLGs as you probably know. But my Purito has carbon push rods and that's certainly a more secure way of doing it.

Anyway, I managed to nip out at lunch time today and there was some nice conditions, with a bit of wind, but no really big thermals, but quite consistent lift with not too much sink between. But enough to get this nice flight, before heading back to work again.

Oh & I took my Alula with me to Greece, and managed about 3 fun flights off various beaches.  All quite exciting, not knowing, if I was going to ditch it in the sea, get it caught in trees behind beach or knock someone off their sunbed! One place had amazing lift with cliffs either side of the beach and I could have stayed up for hours. Only trouble was trying to land it safely with no airbrakes on a very narrow, rocky beach.  Managed to ditch it into some soft bushes just behind. Phew! Just goes to show, even a little Alula can provide a lot of fun & packs down really small. Really recommend them for travelling.  Will