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« on: April 11, 2011, 10:50:14 AM »
aXedge
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Hi, recently the trainer that I was learning on (Boomerang 40) crashed.

As a result of the impact, the nose-landing gear got ripped off pulling out along with it a portion of the Firewall.
The portion of the firewall where the engine is mounted is intact, only the lower portion where the nose-wheel was attached has been damaged.

I wanted to seek advice on the best way to repair the a/c?
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« Reply #1 on: April 11, 2011, 11:47:14 AM »
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A photo showing the damage would be a great help to give advice
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« Reply #2 on: April 11, 2011, 04:22:34 PM »
AEROVISHWA
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i use this technique only if the portion where the engine is mounted is in perfect condition and the fire wall is perfectly intact in the fuse...
and the portion is not smashed into pieces

1> remove the nose wheel assay (just 4 screws)
2> check if the broken part fits perfectly inside the intact part
3> mix some arildite ( regular, fast setting does not help)
4> put some on the joint........ stick the two pieces and blow some hot air even stick the part of the fuse ( by a hot air gun or hairdrier )
5> don't use cyano ( it will spoil the arildite and if only used it will not give strength)
6> finally when it dries put some supporting gussets or plates( as u feel) it will be as good as new

if in-case u think of changing the entire firewall get the original out carefully and take the measurements and build one out of a 5mm or 6mm ply available locally

any asssistance needed can give me a call ..... or post here
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« Reply #3 on: April 11, 2011, 04:33:59 PM »
avijit17basu
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the model should certainly be repairable.
R/c vish's idea is good.
Be sure you show the model to an experienced flyer to accertain that the engine thrust line is okay.
also be sure to remove the engine and get all the oil off before aralditing it back together.
I WOULD measure out the firewall,  make another one with 4-6mm ply, accurately drill holes for the engine mount,throttle cable and nosewheel cable and sandwich it onto the front side of the original firewall. and coat the whole wood with araldite to fuel proof it.
regards
avijit
« Last Edit: April 11, 2011, 06:56:15 PM by avijit17basu » Logged
 

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« Reply #4 on: April 11, 2011, 05:06:17 PM »
AEROVISHWA
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that too is a nice idea..... avijit  Salute Salute

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« Reply #5 on: April 11, 2011, 07:00:01 PM »
avijit17basu
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1 hour of flying time takes 3-4 hour manhours of hanger work at home.
i wonder how much of maintenance time goes into real civilian and military aircraft per hour of flying time.
Maybe one of our professional pilots augustinev  could enlighten us.
regards,
Avijit
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« Reply #6 on: April 12, 2011, 08:31:56 AM »
aXedge
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Hi everyone,

    Thanks for your inputs.
    Just to help make the situation more lucid, I am attaching the pictures of the firewall section:
1. The original nose-wheel section which was ripped-out:

2. How the original nose-wheel section was fitting in the firewall:

FirewallRepair-OriginalNosewheelMount.jpg
Re: Repairing a Firewall
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« Reply #7 on: April 12, 2011, 08:38:47 AM »
aXedge
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I am trying to repair the firewall in the following manner:
1. created a new section (4mm ply) for the nose-wheel mount.
2. created an additional back-plate kind of thing that I plan to epoxy with both the original firewall and the new nose-wheel mount. This back-plate is also made of the same 4mm ply as the nose-wheel mount.
3. just to be safe I have ensured that 2 of the engine mount bolts pass through the back-plate as well (drilled holes and aligned with the engine mount for this).

Please let me know your views on this arrangement.

Attached are the pictures to show this:


FirewallRepair-New&OldNoseWheelMounts.jpg
Re: Repairing a Firewall
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« Reply #8 on: April 12, 2011, 08:49:30 AM »
aXedge
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The issues that I am facing are as follows:
1. The original firewall has become unstuck from the bulk-head at one side.
        - I assume that to keep the thrust line aligned, I need to ensure that the original firewall is stuck exactly at the same alignment before I can start to add the nose-wheel section. Correct? Also could you please let me know how I can ensure that the thrust-line is correctly aligned?

2. The nose-wheel section that has come out has not broken out in symmetric fashion, so while on one side I can fit it into the groove that was meant for the original firewall, on the other side it can only be epoxied to the portion of the original firewall. (This is one of the main reasons why I thought of adding the back-plate section).

3. The weight of the back-plate section. I am not sure if this is something very critical. So I request you to also help me in this regards. If the weight is an issue, I was thinking of reducing this by drilling holes in the back-plate section. These holes would be well clear (> 5mm) of the edges of the section as well as any holes I had drilled for the engine mount bolts or the nose-wheel mount screws.

there .... long mail, and I hope I have explained things clearly enough.

Now I look forward to your good advice  SaluteBow.

TIA
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« Reply #9 on: April 12, 2011, 01:55:06 PM »
AEROVISHWA
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i will suggest you to fix the orignal broken part first in the orignal position  and not make a new one....

( given the procedure above...)

make another firewall and drill holes w.r.t the orig one..... and epoxy it behind the original one.... if u are thinking about the strength........ don't worry .... it will have enormous strength ...unless u cyano and spoil it....

do not replace it.... with new one all the parameters will change.... instead stick the broken in the best possible way..... or u epoxy the new made complete firewall and then put this into place....  Salute Salute
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« Reply #10 on: April 12, 2011, 09:55:24 PM »
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Just stick everything back together like a jigsaw puzzle with adequate epoxy (make sure all the parts being put pack align properly) let the whole thing dry up, and for added strength, glue with epoxy a 3mm ply plate covering the entire firewall portion from rear. Even if you do it from front it wont matter much except that you will have difficulty in finding the orginal holes.
If you still want to keep to original engine and fuse clearance, in case the additional ply plate is mounted at front, you will have to shift your engine back by the thickness of ply.
The weight of the ply plate or the 3 mm difference in engine postioning would be almost un-noticeable on a high wing trainer of this size    
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« Reply #11 on: April 13, 2011, 11:01:05 AM »
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I thank everyone for their valuable inputs  Bow.

As I understand, what everyone has advised is to try to reuse as much of the original firewall as possible.

However, the portion of the firewall which was ripped out (the where the nose-wheel housing was attached) looks to be in bad shape. I mean the ply has become splintered and the various layers of the ply seem to be loose.

So if I epoxy this section back to the original firewall, would it have the required strength?

It was because of this doubt that I had started to build a replacement of this section.

Please note that the portion of the firewall on which the engine mount is attached is fine and I only intend to replace the section where the nose-wheel housing was attached.

once again TIA  Salute
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« Reply #12 on: April 13, 2011, 11:09:48 AM »
avijit17basu
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gluing the whole thing together as accurtely as possible is th get the alighnment correct. The 3-4 mm ply back plateis for the strength. if the engine is slightly mis alligned, it can be set right be fixing a few thin metal washers beteen the engine munt and firewall.
regards,
Avijit
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« Reply #13 on: April 13, 2011, 03:07:16 PM »
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Real life and mil aircraft philosophy is completely different and not required for RC, however what i did once for a friend is (I have never crashed a Nitro Gas or a heli, knock on wood ) we sawed off the nose behind the smashed firewall and put a dove tail joint on the balsa to the original length with an another balsa piece and attached a new firewall, this arrangement ensured neat , well aligned nose and CG was not out too. Dove tail joint is easy to make Fir Tree has better stress resistance due pull (In fact it becomes stronger than a unbroken piece), Easiest though is Lapped Scarf Joint. whichever suits you you can use to join the balsa. you need Dremel , drawing , sanding and a lot of patience, don't be in a tearing hurry. For joints See image below.  Bottom line is, no offense meant to anyone, i personally don't like this Jig Saw thing. Building a new nose is what i suggest.

DovetailJoint.jpg
Re: Repairing a Firewall
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« Last Edit: April 13, 2011, 03:18:00 PM by augustinev » Logged

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« Reply #14 on: April 17, 2011, 06:45:45 PM »
aXedge
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Hi everyone,

    Thanks for all your inputs  Bow.
    So I managed to fly her this weekend, although I was a little anxious about the nose-weight & thrust-line.
    But in the end she flew fine, no nose dipping, but she does seem to have a tendency to roll to the right.
    Not sure if that is an issue with the thrust-line, or just the fact that I was using a new Radio (thus all new trim settings).

    Once again, thanks for all your inputs  Salute.

Cheers,
a
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