My X8 launcher

[Coyote]

Lol I will do, I think Paul and Stu will be praying for rain so they can join me for it at the weekend though for the launchers maiden so many video will be recording :)

[Coyote]

How do you mean Flyn ?

If you don't get a good launch the second thing the plane will hit after the ground could be the triangular metal handle of your bungee stake (ground anchor) as the x8 will pulled directly toward it!

I nearly (& I'm taking nat's whisker) hit mine on one of my 1st launches, with the zed when I launch I hold 1/3-1/2 up elevator & it gets off every time without fail, as long as I have the bungee tension right.

Ah ha ! Got you, very good point, I will do this :)

[MarkLincs]

watching with interest as I need a way to launch my x8 as well :)

[Coyote]

After reading what Flyn and Zeeflyboy said I think it might be wise to start at 12kg and work down in load after all

[Flyn]

Just hold a bit of up on launch to prevent a X8 & ground anchor meeting, a little more up for lower wind speeds, wouldn't hold more than half thou - might be too much at near stall speeds.

[Coyote]

Roger dodger :)

[skyscraper]

After reading what Flyn and Zeeflyboy said I think it might be wise to start at 12kg and work down in load after all

from my previous calculations
http://www.fpvhub.com/index.php/topic,6556.15.html

with a mass of plane of 3.2 Kg
takeoff speed of  8 m.s-1  (18 m.p.h)
launch ramp length of 2m
angle of 5 degrees

should need an average force of 55 N  ( 5.5 kgf). (With a long bungee thats about the same as the initial stretch force)

so if the above values are about right and your scales show 5.5 kg + of force it should go OK!

All the above assumes no wind and not much friction against the rails. Obviously any wind helps so you dont need as much stretch!

regards
Andy

[Coyote]

5.5kg does seem to be way too low tbh, the load would instantly drop right off after release. Only when I got to around 7kg did I think there was at least a decent amount of energy stored, 9kg I figured was plenty.

But Ill keep trying lower and lower until it still launches but starts to struggle or takes more distance than I`m happy with to get up. Ill let you know what value that is ( if testing gets that far ) and see if it helps any with your calculations

[skyscraper]

5.5kg does seem to be way too low tbh, the load would instantly drop right off after release. Only when I got to around 7kg did I think there was at least a decent amount of energy stored, 9kg I figured was plenty.

But Ill keep trying lower and lower until it still launches but starts to struggle or takes more distance than I`m happy with to get up. Ill let you know what value that is ( if testing gets that far ) and see if it helps any with your calculations

It would be useful to know if the calcs do stand up, then they could be generally useful (might even do a Java App if I get around to it!), though they are currently based on the values I have guessed.

Do you know the minimum takeoff speed of the X8?
And also how long is the takeoff run on the launcher?

regards
Andy

[Coyote]

I dont know the minimum speed ( yet :) )

The launcher ramp is 1.65m

[skyscraper]

I dont know the minimum speed ( yet :) )

The launcher ramp is 1.65m

Changing the launcher length to 1.65 m in the calculation, then the required force goes up to 65 N, which means 6.5 kg + on the scales, so sounds like your instinct of 7 kg is pretty much bang on!

regards
Andy

[FPVSteve]

and 12kg is almost double the required pull...... ;D birds gonna fly! ;D

[Skipper Billy]

Some real world info that might be useful.

Depending on the amount of stiction - these figures are with the foam wing touching the rails.

12kg of pull = good launch
9kg of pull = passable but bordering stall speed off the ramp if there is little wind
anything less = short walk of shame

With carbon fibre tape under wings where rails touch and a waft of furniture polish on the rails -

12kg = great launch
9kg = good launch
7kg = passable
anything less = short walk of shame

These are all from a 1.8 metre ramp with 2 x 10m x 10mm lengths of bungee side by side. 10 degree ramp angle.

This is with 9kg of pull - no stiction reduction and a fair headwind.

https://www.youtube.com/watch?v=RTf_qWHf-jc&feature=plcp

[Coyote]

Ok, I finally did it :)

Here are the first 3 launches attempted, I love this launcher !!!!!

bungee

Point to address though I think is less of an angle on the tow hook to help with an earlier release, apart from that pretty happy.

The chute worked to pull the ring off, but I think a chute that isnt open from the start would increase speed and work better

[FPVSteve]

Result!