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Oct 27, 2020, 05:12 PM
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Dirty Dee's Avatar

I need a bungee launcher


Well, I was unsuccessful with my maiden trying to toss the model myself. I grasped the tail and give a few practice movements, and it felt like I can make a successful toss. This is similar to how I have tossed my 750mm FMS BF-109 and my 50mm U-2R successfully, so I thought it would work here too.

The first toss was too shallow, nose popped off, and fuselage dug into the grass. I reinstalled the nose, re-secured the battery and give it a second try. Second try was also unsuccessful, shallow, and caught a wing and damaged the airframe. I stripped a servo and I need to reprint a section of the airframe where the spars go in.

Any recommendations to a bungee setup?
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Oct 27, 2020, 05:37 PM
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Quote:
Originally Posted by Dirty Dee
Well, I was unsuccessful with my maiden trying to toss the model myself. I grasped the tail and give a few practice movements, and it felt like I can make a successful toss. This is similar to how I have tossed my 750mm FMS BF-109 and my 50mm U-2R successfully, so I thought it would work here too.

The first toss was too shallow, nose popped off, and fuselage dug into the grass. I reinstalled the nose, re-secured the battery and give it a second try. Second try was also unsuccessful, shallow, and caught a wing and damaged the airframe. I stripped a servo and I need to reprint a section of the airframe where the spars go in.

Any recommendations to a bungee setup?
I was wondering how to launch this on my own and one way I thought off is to paint it in one of the sqn colours that used the Blue Steel missile and model the missile as this would probably make a good grip for single handed launch.
Whether I do it or not is another thing as my father was a armourer in the RAF and was stationed with 44sqn Vulcans which didn't use the Blue Steel so I am thinking of other ways.
Simon.https://i.pinimg.com/originals/15/01...21a3b9d431.jpg
Oct 27, 2020, 06:34 PM
Mk9
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Sorry to hear that Dee - you are a fair bit heavier than ours with not much extra static thrust so I can see that launching would be marginal. Could you have been worrying about being too nose high and so launch too shallow? There are 3 handlanches on video with MrWaz and it does get a pretty hefty chuck each time, and honestly, without an assistant, I could see it being 50:50.

I have no idea about Bungee's I'm afraid - I might try mine off the dolly we designed for the Buccanneer (based on Ken's design actually!). Bungee's put such a massive load on the model that if they aren't designed for it, I reckon a dolly would be easier. Depending on your field.

I'm really gutted as I was so hoping yours would go well
Oct 27, 2020, 06:38 PM
Mk9
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Quote:
Originally Posted by kenelder
I've been playing with thickness to get better prints. I'm seeing that with my PLA+ .4mm wall thickness is a bit thin and flexible. I've tried 2 walls at .26mm and now a single wall of .5mm. I've measured the thickness of finished parts with a digital caliper. It seems my 2 wall at .26mm makes better parts but they are heavier. Can anyone measure their actual wall thickness and report back? thanks!!
These planes do end up with quite flexible and thin skins - almost like 1/32 balsa sheet in terms of being fragile. But the monocoque nature of the designs, with some internal structure - and the fact that the CA to PLA bond is stronger than PLA to PLA strength - makes them viable.

Ours is around 0.6mm extruded, but hard to measure really accurately. A club mate whose printer is sorted definitely ended up lighter than ours - and more of the steeper angles on his didn't have enough plastic to bridge completely with a single perimeter, so I'd say we are likely over-extruded. If you are doing the 2 servo version, with the FMS fan on 3S and a light powerful battery, I'm sure 5-10% overweight on the print would be OK, but as Dee has found - getting a heavy EDF airframe into the air with marginal static thrust is not easy. No one has yet managed to fly the 4 servo version, it's completely untested still.

In my view, printed weight is a better indication of extrusion than wall thickness, but there are good guides to setting up your printer to extrude correctly and I really recommend people follow them. We didn't, back in 2018 and we chased our tails for a while. There are so many variables involved, it's extremely unlikely to 'luck in' with a perfect set from the outset. Although I understand printers are always improving and it's getting easier.

To make a flying airframe using a 3D printer, is not easy. To make one that flies well and repeatedly, even harder. But a logical approach will allow anyone with a bit of persistence to succeed. It's not a quick, or cheap way to make an RC plane though, which is why many people get frustrated and give up.
Last edited by Mk9; Oct 27, 2020 at 07:16 PM.
Oct 27, 2020, 07:01 PM
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Its a bummer, but nothing a roll of filament cant replace ( and my electronic spares collection)

The tosses I tried for ~30-40 degree inclination, but when I released it, it was closer to 10-15 degrees. I think another contributing factor was that it was just above freezing today, so I was wearing a bulky coat which may have restricted the chuck a bit.

I double checked my slicer settings, and I realized I have been printing with the default Prusa Slic3R of 0.45mm extrusion. I suspect that I can shave ~12% of my airframe weight if I re-do it with a true 0.4mm extrusion.

My field can support a dolly (850ft runway, I am spoiled) so I may re-purpose the one I have for my U-2. I have also seen some bungee setups that have a long pull/low force that might work out otherwise.
Oct 27, 2020, 08:29 PM
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In my case there is a big difference in flex between 0.4mm and 0.5mm. Only a couple grams more in weight though. Will be interesting to see my total printed weight. Sounds like we should stick to the 2 servo version though.

Did anyone consider a switch on the trans to give a little up trim for launching?
Oct 27, 2020, 08:33 PM
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Forgot to mention: I've been known to glue nylon on the bottom of the fuse and wing tips and skid launch edfs.....nylon wire ties work as do thin clear plastic fins. Of course I also do wing tip launches too- but not sure if a printed plane can take a wing tip launch.
Oct 28, 2020, 06:13 AM
Mk9
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Quote:
Originally Posted by kenelder
Forgot to mention: I've been known to glue nylon on the bottom of the fuse and wing tips and skid launch edfs.....nylon wire ties work as do thin clear plastic fins. Of course I also do wing tip launches too- but not sure if a printed plane can take a wing tip launch.
I think a wing tip launch (discus?) will result in the wing detaching, the magnets aren't that strong
Certainly, needs some reflex, and trimming in some up to allow that to be flicked out on a switch is not a bad idea - I always find the 'get the hand back to the stick quickly' is guaranteed to result in some pretty hefty over controlling in those first few seconds. A switch would be a quick, measured way to retrim and would be a way this mode 2 right handed pilot could apply elevator with the left hand.
Oct 28, 2020, 06:17 AM
Mk9
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Quote:
Originally Posted by Dirty Dee
Its a bummer, but nothing a roll of filament cant replace ( and my electronic spares collection)

The tosses I tried for ~30-40 degree inclination, but when I released it, it was closer to 10-15 degrees. I think another contributing factor was that it was just above freezing today, so I was wearing a bulky coat which may have restricted the chuck a bit.

I double checked my slicer settings, and I realized I have been printing with the default Prusa Slic3R of 0.45mm extrusion. I suspect that I can shave ~12% of my airframe weight if I re-do it with a true 0.4mm extrusion.

My field can support a dolly (850ft runway, I am spoiled) so I may re-purpose the one I have for my U-2. I have also seen some bungee setups that have a long pull/low force that might work out otherwise.
Just above freezing?! Yikes, brrr. Do you warm your lipos first? THat would drop some C if not.
I can see the problem with Bungee being there's no easy wing spar attachment, AND the wings might want to stay put on the runway...I'll have to get mine finished and try it on the dolly. Your field looks awesome if its the one the U2 footage shows.
Oct 28, 2020, 06:44 AM
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Quote:
Originally Posted by Dirty Dee
Well, I was unsuccessful with my maiden trying to toss the model myself. I grasped the tail and give a few practice movements, and it felt like I can make a successful toss. This is similar to how I have tossed my 750mm FMS BF-109 and my 50mm U-2R successfully, so I thought it would work here too.

The first toss was too shallow, nose popped off, and fuselage dug into the grass. I reinstalled the nose, re-secured the battery and give it a second try. Second try was also unsuccessful, shallow, and caught a wing and damaged the airframe. I stripped a servo and I need to reprint a section of the airframe where the spars go in.

Any recommendations to a bungee setup?
I have been thinking about this as I mostly fly on my own and one way I thought of is to paint the plane in the colours of one of the Sqn's that used the Blue Steel missile and to model it, glue it to the bottom and that looks like it could be a handy hand grip to chuck it.
My father worked as an armourer in 44 Sqn but they didn't use the Blue Steel so I am looking at other simple way to do this.
May have to make a small grip to hand launch it which wouldn't look to obvious.
Simon.

Post above of mine was posted last night but didn't see it this morning so I did another.
Last edited by SimonDR616; Oct 28, 2020 at 09:17 AM.
Oct 29, 2020, 08:09 AM
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Quote:
Originally Posted by SimonDR616
I have been thinking about this as I mostly fly on my own and one way I thought of is to paint the plane in the colours of one of the Sqn's that used the Blue Steel missile and to model it, glue it to the bottom and that looks like it could be a handy hand grip to chuck it.
My father worked as an armourer in 44 Sqn but they didn't use the Blue Steel so I am looking at other simple way to do this.
May have to make a small grip to hand launch it which wouldn't look to obvious.
Simon.
That's an interesting idea for launching, but might cause issues on landing.

I like the idea of skid take off. That's about the only way I can get my The World Models EDF wing in the air without a launch buddy.

Geoff
Oct 29, 2020, 08:20 AM
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Have it on a release button. Use it for takeoff, drop it before landing
Oct 29, 2020, 09:07 AM
Mk9
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I did put some thought into how you could have a releasable blue steel. With a rocket motor I got as far as remembering my only foray into Jetex which happily set fire to balsa airframes and balsa ignites at much lower temps that PLA softens!

It actually wouldn't be hard to redesign an alternative lower motor mount to take a hand launch grip. If printed in clear PLA it may not even be that noticeable. Or two finger depressions either side of the fan duct on that piece? What would work?

A fixed blue steel would probably survive grass landings, as long as the lower fin was either sacrificial, or from flexible filament. Cool pic, and that your Dad worked on them Simon.
Oct 29, 2020, 09:58 AM
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Quote:
Originally Posted by Mk9
I did put some thought into how you could have a releasable blue steel. With a rocket motor I got as far as remembering my only foray into Jetex which happily set fire to balsa airframes and balsa ignites at much lower temps that PLA softens!

It actually wouldn't be hard to redesign an alternative lower motor mount to take a hand launch grip. If printed in clear PLA it may not even be that noticeable. Or two finger depressions either side of the fan duct on that piece? What would work?

A fixed blue steel would probably survive grass landings, as long as the lower fin was either sacrificial, or from flexible filament. Cool pic, and that your Dad worked on them Simon.
That would be fun to see and as I believe the reel blue steel dropped down on a 100ft long lanyard connected to the nose and as the lanyard pulled on the nose it ignited the engines, although that would be quite hard to do on the model.
The two finger thing I am also looking at and may try that.
The holes would have to be inline with the screw holes so that you have the depth for those like me with big hands.
I will model something for this purpose and see if it looks like it may work.

It is cool my dad worked on Vulcans (he also worked on a Hunter Sqn in Singapore before joining the Marine Craft branch) although definitely not as cool as having a father who actually flew them

Also meant to add the lower fin is usually folder for take off as it extends to far down so it shouldn't be that much of a problem, or just model it without the lower fin. I would have printed the missile in flexible filament as it would take less damage than PLA, but granted a lot of pilots have a hard ground runway rather than grass which we have at our local club.
Last edited by SimonDR616; Oct 29, 2020 at 12:02 PM.
Oct 29, 2020, 10:29 AM
Registered User
Bigger with retracts lol?

How's the LW PLA nose in terms of durability? Really curious about this stuff.


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