Need Some Repair Advice

[aeajr]

I fly a HobbyZone Aerobird.

Yesterday a sudden gust from the rear flipped the tail up, at 15 feet, sending it into a high speed lawn dart dive into the ground. The pusher motor displaced into the body pulling the motor mount with it and distorting the body somewhat. It pulled the screws through, and popped off the prop. Here are some photos.

http://www.shutterfly.com/osi.jsp?i=67b0de21b33bad5a05ac

If you have any experience in repairing these type of planes I would appreciate some tips:

Types of glues to use on the polyethylene body
Ways to reinforce the motor area
Tips on reshaping the distorted area

Any other tips

I could buy a new fuselage for $49, but I want to try an fix this one first if I can, for the challenge, if nothing else.

If you have repaired a Firebird XL, Fighterbird, e-gull, T-Hawk or similar plane, you may have some good advice. I would love to hear it. [:)]

[Spaaro]

aeajr

Have never used one of those planes but looks like standard, injection molded plastic(polyethylene, styrene, etc.)-toy grade. Not to demean your plane comparing it to "toy"; actually it could be a very easy material to work with, if you are resourceful and imaginative.

To regain some of the original contours, you could take an exacto or hobby blade and carefully slice into the plastic at the molded seams in the deformed areas and along curves. Do this in increments a centimeter wide or so. Several of these in a line around the perimeters of crushed areas could relieve stresses and permit you to bend or twist the weakened plastic back towards its original contours.
You could then use an epoxy/micro-ballons slurry or even grind up 1-litre pop bottle with a power tool/rasp file and mix this into the epoxy to create a matrix to fill the cracks and deformities.
Finally sand to shape. You would have to be judicious and experiment first, as weight could build up quickly.
If so, then thin your remolding out w/sand paper & Dremel & apply carbon fibre tows in a mesh inside the structure to return strength where it has been weakened.

A picture is worth a thousand words;
imagine one of those Fiddler's Green paper planes---highly detailed, cut&fold-insert-tab models that combine origami with glue & scissors work. Now imagine all the little fold tabs and slotted edges these things tend to have to assume a complex shape like a curved Spitfire's nose or wing fillet. Your plane is the same way in its damaged state.
Now imagine smoothing out the paper angles and seams of the paper model by wadding paper machiere into these gaps & edges, then sanding it smooth when it dries for a finish more like a plastic model kit... that is what I'm trying to suggest if you want to salvage the body.

If you're creative enough, you could creat a male mold out of cardboard, clay or wood(in the shape of the damaged section), then melt/mold a 1-litre bottle over this w/a heat gun. Reinforce with a layer or two of the plastic or epoxy & glass fibre(I even use Tyvek envelopes & dryer sheets here) and just splice it in in place of the whole damaged nacelle(motor pod) area of your plane. I'd try and get access to a digital scale or even several consecutive trips to the supermarket check-out scale to weigh the damaged fuselage sections to keep track of weight gain in your rebuild.

Depending on how arts&craftsy you are with wood or plastic(I like paper & cardsboard)you could do alot. Be bold and try to save that $49 bucks for some other plane-ware.

Cheers

[aeajr]

After some experimentation, I have begun to rebuild.

1) After removing all the guts, I let the plane sit over night. Some of the original shape returned.

2) using a hairdryer, I heated and did a little more shaping

3) After experimentation, I found that Liquid Nails Perfect Glue #2 will bond metal to the polyethylene with reasonable strength if I sand the poly first. So I did that and put the inner motor mount back in, but this time I glued it in. This is the part that punched through the side of the body as shown on the damage side view.

http://www.shutterfly.com/osi.jsp?i=67b0de21b33b90084578

4 ) I will come up with some kind of "washer plate" for the outer part of the rear of the motor area that is larger than the original. I will screw through this into the motor, as was originally done. I may glue this in place as well to try to form more of a bonded whole.

5) Then I will reset the motor in place and attach it.

6) finally I plan to put some kind of a support behind the motor to help take the stress should the motor decide to try and move forward again.

Overall, I expect I will add 1/2 to 2/3 oz to this 17 oz. plane. Hopefully I will get the right thrustline and we will be all set. Wish me luck.

[aeajr]

I fly an Aerobird, which is the top of the line in the Firebird Series from HobbyZone. From what I read, all the planes in the series are fun. I have also had great experience with the HobbyZone support folks. So read this as a happy flyer who wants to make these fun planes even better.

There is one weakness in the series that is easily fixed. The motor mount is weak. A hard hit into the ground or a tree can shift the motor, or disloge it completely, as it did on mine. But, with a small modification, this weakenss can be corrected and you can enjoy lots of fun flights with these "birds" Read my post and see what you can do to prevent this from happening to your "bird".

There are also other planes that have similar bodies. Planes like the e-gull, the vector and the t-hawk, just to name a few. They may benefit from this modification as well.

What Happened?

Last week my Aerobird took a good shot in a hard, nose first, landing causing the motor to break free of its mounting and shift forward inside the plane. I have since learned that this is not uncommon. Also, while mine was dramatic, if it is only a small displacement, you might not notice it, but the motor can get out of the proper thrust line causing the plane to fly to one side or the other.

After some experimentation and excellent advice from other threads, I have begun to rebuild the Aerobird and repair the damage done by the forward shifted motor. There is a link to photos below.

What some other people have done:

Several people created some kind of plate to put behind the motor, inside the body. This can work, but I think this is difficult to do correctly and may require you to dismantle the plane. I think it could also reduce cooling air flow within the plane.

Others replaced the little oval metal piece "washer" that sits below the prop and holds the motor. They replaced it with a larger plate made of plywood or metal so that it covered the whole motor mount area. This would prevent a pull through and reduce the likelihood of the motor shifting left or right. This is easy and will provide reinforcement, but I don't think it is enough.


Here is what I did.

I drilled two holes on either side of the body, right behind the motor and put a nylon tie wrap there. This holds the body tight to the motor AND blocks the motor from shifting backward. I did this as part of my repair, but you can do it now, before a repair is needed.

The holes are 1/2" apart, centered on the motor. I used an 8" tie wrap, but a 4-6" wrap would probably be better as they are a little less bulky. You want the tie wrap to either sit against the motor or sit barely behind it so that, under stress, the wrap stops the motor from shifting which will either distort the motor mount area or pull it through all together.

Here are pictures of the damage I incurred and the repair.
http://www.shutterfly.com/osi.jsp?i=67b0de21b33864ea2534

(A tip on viewing the photos. Select view pictures. It takes you to a slide show. In the upper right is a stop button. The photos will flip on their own if you don't stop them.)

The photos show a yellow tie wrap, but that was just for pictures. I cut this out and replaced it with an orange one that looks much better on the plane. I got the wraps from Home Depot, but Radio Shack has orange tie wraps as well.

After putting this tie wrap in place, there was no longer a need to put any kind of bracing plate by the prop area. This tie wrap really holds the motor solidly AND prevents it from moving forward.

Recommendation to all Firebird, Firebird XL, Fighterbird and Aerobird flyers and those with similar fuselage planes:

I love the Aerobird and think the whole "bird" series is fine. However a weak motor mount exists in all the planes. I would recommend this modification be done on ALL new "birds" BEFORE the motor mount is challenged and repairs have to be done. If the motor shifts far enough, it will hit the control board and wipe out all of the electronics. If it only shifts a little, the plane flies badly, commonly to the left or right and can't be trimmed properly.

You can do the drilling and insertion of the tie wrap without having to take the guts out of the plane. Just be careful to limit how far the drill bit goes inside the plane. There is enough room to do this, just be careful.

When you put the tie wrap in, make sure it slips UNDER the noise suppression components that are soldered between the motor terminals. You can see them in the photo. A 4-6" tie wrap is not as wide as the 8" wrap I used, so it will fit more easily with less displacement of the components, however I believe that it will be strong enough to get the job done.

Don't over tighten the tie wrap. Just make it snug, don't distort the body of the plane. If you are skilled and have some very long nose pliers, you can probably hide the square head of the tie wrap inside the plane so it looks better.

I plan to send a note to the manufacturer and advise that this should be done at the factory. Don't get me wrong, I like these planes, but they have a weak motor mount. This will take care of the problem before it becomes a problem.

I hope you find this post and the photos useful. Thanks to everyone for their advice and tips.

Don't wait, do this mod now on your Firebird, XL, Fighterbird or your Aerobird. Do it now, before you need it and you will have a much longer, happier relationship with your "bird".