Jump to content
Ben

Robbe ASW17 fuselage strengthening advice

Recommended Posts

Ben

Hi guys, 

My next project is well underway, refurbing an old ASW17 by Robbe, and I'm looking for any wisdom on strengthening the fuselage to avoid any nasty surprises in the future.  

This model has Robbe Plura fuselage which (in)famously get brittle over time. I bought this model back in the late 90s and it's noticeably brittle and I would imagine a bumpy landing would result in failure. 

I've read a few threads on the net about glassing these fuzes, but I'm wondering if anyone has any advice on old, brittle, plastic fuselages. For example, will epoxy/glass adhere to the surface, how far down the fuz should I go, what weight of cloth etc. From experience the greatest forces on a fuselage are just behind the wing, but I've never had to reinforce a fuz before so I'm a total noob at it. 

Here is a pic looking towards the tail from the canopy area. I've already removed the old wood reinforcements so I can get access. 

Thanks in advance 👍

Ben

IMG_1881.JPG

Share this post


Link to post
Share on other sites
pete beadle

Hi Ben

Oh dear!

These Plura fuselages were always susceptible to UV degradation

The "cladding" idea raises the overall weight substantially and doesn't reduce the degradation effects by much.....easier to paint the shell with an "exterior"/weatherproof paint, brushed or sprayed....alternatively advertise too see if someone out there in "BARCSland" has a glass one.....

Good luck

Regards

Pete

BARCS1702

  • Like 1

Share this post


Link to post
Share on other sites
Ben

Humm, thanks for the reply Pete, it's seems ok-ish where it maters right now and there is no damage to the structural areas, but around the tail area it is clearly degraded and snaps easily where it's thin. I don't want to 'test' it too much right now though in case it gives!  

Share this post


Link to post
Share on other sites
isoaritfirst

You could put a few full formers down the fuselage. 
they can be very light ply. Their design such that they hold the fuselage shape more than add strength in themselves. 
By stopping the fuselage I sliding in a bump it will impart a lot of strength without adding weight. 

Share this post


Link to post
Share on other sites
pete beadle

Hi Mike

Great idea for strengthening fuselages with negligible weight gain but, does it work with Plura fuselages?

As I remember from my Henkel/Supergloy days, builders were warned that you will/would never get an acceptable bond on items moulded from Plura  without using a very specialist adhesive that actually melted the skin and penetrate the surface finish .....the skin had a  "soapy" feel.

I was told, at the time, that the only 100% effective bond was a mechanical fix using screws or bolts. However, the holes drilled in the mouldings would probably seriously reduce their strength.......as I understand it, that was why Plura as a moulded material never really caught on at the time:( 

I may be wrong, I often am, but I'm fairly sure about this........wish my memory would work better on Sunday mornings!:yes:

Regards

Pete

BARCS1702 

Share this post


Link to post
Share on other sites
oipigface
2 hours ago, pete beadle said:

As I remember from my Henkel/Supergloy days, builders were warned that you will/would never get an acceptable bond on items moulded from Plura  without using a very specialist adhesive that actually melted the skin and penetrate the surface finish .....the skin had a  "soapy" feel.

There’s a discussion on rcgroups that ends with the adoption of Goop as an adhesive. The person who started the thread didn’t think to go back after he’d tried it to say whether or not it was successful. Does epoxy not work? Thread is at https://www.rcgroups.com/forums/showthread.php?1269-Repairing-Plura-(plastic)-Fuses.

  • Like 1

Share this post


Link to post
Share on other sites
satinet

I don't think epoxy sticks well to polyester resin which some things are laid up with. Or were perhaps.

Breaking behind the wing seat is a common break on all models.

As Mike says you probably want to put in anti crush formers. I'm not sure fully glassing the outside or inside of the fuse is a goer.

 

There's a few threads on different forums talking about stablit express as the glue.  There is also a thread on here talking about it.

Share this post


Link to post
Share on other sites
pete beadle

Hi Tom

Stabilit Express is also a Henkel/Supergloy product specifically made for bonding polyester products, it's actually produced from polyester by them. It's only drawback, for modelers anyway, was that it's not cheap!:yes:

It's not the right adhesive for Plura either, in fact, I don't know which other adhesive is. My understanding was that the surface skin had to be abraded heavily either mechanically or chemically before anything would bond to it......and the bond itself wouldn't be 100%.....that's why the nuts and bolts idea was floated

I can't imagine that Goop or Epoxy resins are any good either as they don't attack the Plura's skin to produce a surface that they would adhere to.....as I said before, a lot of people tried but I don't know any that succeeded:no:

Regards

Pete

BARCS1702

  • Like 1

Share this post


Link to post
Share on other sites
oipigface

Ben, Your way forward is clear: use the original fus as a plug to mould a new one!

  • Like 1

Share this post


Link to post
Share on other sites
Kyri

Is plura some sort of PP? if so then some of hot melt glue may work as it could melt the surface during the gluing. Someone must have had this problem before.

Share this post


Link to post
Share on other sites
oipigface

No one has mentioned fish tank silicone sealant yet. I use this for installing formers and other wooden parts into GF fuselages. I don’t know anything about this Plura stuff, though.

  • Like 1

Share this post


Link to post
Share on other sites
Ben

These are all great ideas guys, I really appreciate the input.

I had to hack away at the fuz today to fit a retract unit and it’s still very flexible in places so it might be ok - perhaps. 

Im still going to give one of the ideas mentioned a try to see if it can get some more strength in there. I’ll keep you posted 👍

Share this post


Link to post
Share on other sites
pete beadle

Hi Ben

Personally, I'd suggest leaving the fuselage "as is", repair it into flying condition, FLY IT, then see if it's worth doing lots of work to get the fuselage stronger

I assume you've bought it at a "bargin" price(?).....so, do as much as you have to to get it flying, THEN  make the decision:yes:

Good luck

BTW I'm suggesting this from bitter experience......I once bought myself an "unflown, still in the box" Veron Cobra, 117"  spent months straightening out all the faults  and finally flew it at Ivinghoe,it was a DOG! too heavy, needed ailerons (it was "designed" as an R/E when bought) I thought that wouldn't matter because it had LOADS of dihedral as standard......instead, the massive dihedral ruined the scale look, and taught me just how awful "Dutch rolling" was!:(

Others I met said theirs were "delightful" but I just didn't believe them.......

Regards

Pete

BARCS1702

  • Like 1

Share this post


Link to post
Share on other sites
Big Si

 I would give  polyester resin a go with some light cloth but give it a good sanding first to get a key

 polyester resin is very good on most things where epoxy wont work I use it when building the C32 pylon racers,its how we stick the tail plane and rudder on to the fuz .just have to wait till it goes to a gel and then use a stick to put it onto the fuz and hold the said parts on till its set and its dam hard to knock them off the fuz even after a good crash

So if I was to give anything a try it would be that after a good sanding to give it a key to grip to 🙂 

most car paint specialist's sell it still or Aeropoxy but that's not cheap but there is not much that will not stick to

You almost need to pre-make a tube to go down the fuz first then slide it down the fuz but would need to remove the wing bar tube first  to give you more room ( that would need a good sanding if you used  polyester resin first as well )

good luck

Si

  • Like 1

Share this post


Link to post
Share on other sites
Ben

Thanks again for the suggestions guys. It's really appreciated. 

Pete - actually the I bought the model new back in the 90s so it's got a fairly long history with me. After reading more online I think Robbe recommended the Stabilit back in the day, so I've bought some to try on the formers. 

Si - I'm going to give the polyester resin a crack with some light cloth and see how that stacks up. I'll report back! 

Thanks again guys, these ideas super appreciated 👍

Cheers

Ben

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.