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Plywood Fin Repair

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davdue

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Had a hard landing when the main failed and stuck in airframe. I was thinking of sanding of the paint and fiberglassing the sides of the fin. The tube is quantum so I can't do tip to tip. What do y'all think?

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Handeman

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I would use wood glue in the joint, wrap with plastic sheet and clamp for a day or so. Then put a layer of 6 oz. or so glass on each side.

BTW, why can't you do TTP with Quantum tubing? just rough it up like you would as glass tube.
 

MaxQ

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I have a PML Quantum Leap ..when the kit came in (local vendor) it was Quantum tube.
I wanted phenolic, but kept the kit anyway, thinking I would replace it.

Never got around to ordering phenolic airframe.
I recently did the T to T on the Quantum tube and the rather flimsy G10 fins.

After I posted a picture or two...the Wildman himself chimed in...told me not to fly it extreme cold temps...it would delaminate.


Its in primer now.
Seems pretty solid to me.

Ql 2.jpg
 
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markkoelsch

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Sorry to say this, but you have two choices in my estimation.

One- get that fin out, remove filets, and replace the fin.

Two- throw it in the trash.
 

davdue

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I would use wood glue in the joint, wrap with plastic sheet and clamp for a day or so. Then put a layer of 6 oz. or so glass on each side.

BTW, why can't you do TTP with Quantum tubing? just rough it up like you would as glass tube.
Per PML website they say not to fiberglass Quantum tube

I was thinking epoxy on the fin first not wood glue. This is a 7.5# rocket that flies on 54mm J/K motors. It was L2 cert rocket. It won't take an L so won't ever see one.
 
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MaxQ

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Per PML website they say not to fiberglass Quantum tube
REALLY?
I'd wish they highlighted that information where you could see it easier.
I had this kit sitting around for fifteen years and I never saw that on their website...I did see a lot of stuff warning that Q tube was NOT for high stress flights, and to use the phenolic glassed for those kind of flights.


If PML does NOT want anyone to put fiberglass on Q tube they sure don't put that warning where it is easily read.
To the contrary, they even extoll the virtues of Q tube taking epoxies well.
Eventually maybe this will be proven one way or another, or qualified to some extent by folks that have actually done it and had good or bad results.

Anyway, thanks for the post Dave...I went back to their website to check again.


Quantum Airframes:
The Quantum Tube (QT), is made from a special blended polymer that is extremely durable and easy to use. You will find this new
material easy to work with and very forgiving. Most hobby type epoxies and paints will readily adhere to this material as well. The
Quantum Tube can be squeezed, dropped, or even thrown and will not suffer any damage as can sometimes occur to cardboard or
phenolic tube. The Quantum Tubes are molded in medium gray and have a glass smooth finish. The Quantum Tube does have one
thing missing, the spiral groove! You will appreciate the fact that you no longer have to fill and sand the airframes to achieve the
perfect finish. All PML rocket kits 2.1" dia. through 3.9" dia. come standard with Quantum Tube airframes.
Our larger kits use our kraft phenolic airframes. They can be used as-is or can be wrapped with fiberglass for Level 3 type
launches. We can even glass wrap them for you! See our Airframe page for more details on all of our airframe choices.
https://publicmissiles.com/

PML QUANTUM TUBE!
The Quantum Tube (QT), is made from a special blended polymer that is extremely durable and easy to use. You will find this new material easy to work with and very forgiving. Most hobby type epoxies and paints will readily adhere to this material as well. The Quantum Tube can be squeezed, dropped, or even thrown and will not suffer any damage as can sometimes occur to cardboard or phenolic tube. The Quantum Tubes are molded in medium gray and have a glass smooth finish. The Quantum Tube does have one thing missing, the spiral groove! You will appreciate the fact that you no longer have to fill and sand the airframes to achieve the perfect finish.
All our kits in the 2.1”-3.9” diameter range (except Nimbus) now ship standard with Quantum Tubing. These kits are all available with phenolic airframes on request, though there may be a slight delay as they are considered a special order.
Some customers have thought that QT is a replacement for ‘glassed phenolic. This is not the case. Quantum Tubing is not intended for super-high-stress applications. It is intended as a replacement for standard phenolic for sport rockets. QT makes it easier and faster for flyers to achieve a nice finish, and to eliminate some of the problems of plain phenolic in high-impact situations like landing on rocks, cold-weather flying, etc. ‘Glass-wrapped phenolic is still the best product for high stress flights. See the FAQ Page on this site for more information.

https://publicmissiles.com/secure/components.asp?groupid=9

Finally....
When you go deeper into the website they have a FAQ page with a big list of PDFs you can start opening if you are interested.
Eventually, you can find this little gem - buried in there in the PDF titled "airframes". :facepalm:

However, there are some limitations with QT:
1. It comes only in 2.1, 2.5, 3.0 and 3.9” diameters
2. It is not intended for near-mach (transonic) or above-mach (supersonic) flights. (See our online FAQ for information on mach and near-mach flying)
3. It is not intended to be used as a base for fiberglassing, Kevlar, or other typical tube-strengthening methods.
4. It is not intended for use in minimum-diameter rockets (rockets where the airframe IS the motor mount; the motor casing touches the airframe directly) If your rocket does not fit any of the above special applications (and about 90% of most fliers’ rockets don’t), QT’s right for you
.
https://publicmissiles.com/PMLAirframesFAQ.pdf

That said...I notice they carefully state Q tube is "not intended" to be a base for FG or other tube strengthening methods, - but they don't outright say NOT to do it.
There were a lot of postings over the years here - and the other two Rocketry Forums (now defunct - Rocketry Online and Rocketry Planet) where folks said they FG on Quantum Tube - no problem.
One of them that advised it would be possible was/is a well known flier on all these Forums.

I know very cold temperatures have an effect on QT - I can detect shrinkage when fitting the parts together when they have been subjected to cold, and I've heard about the piston jamming in QT.
I'll be interested is seeing if QT contraction in cold weather begins to delaminate the FG layer I've put on.
If the QT subjected to cold temperatures sheds the epoxy of a FG layer, well, - I have to wonder if it would do the same to an epoxy fin filet or a glued on part on an airframe that wasn't fiber glassed. ?

Guess I'll find out if I made a big mistake...on the other hand I never planned on flying this Quantum Leap supersonic...it is going to be a fun flyer for my sunny Virginia climate. :)
 
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Steve Shannon

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Per PML website they say not to fiberglass Quantum tube

I was thinking epoxy on the fin first not wood glue. This is a 7.5# rocket that flies on 54mm J/K motors. It was L2 cert rocket. It won't take an L so won't ever see one.
No, they don't say not to fiberglass it. They say it's not intended to be fiberglassed.
3. It is not intended to be used as a base for fiberglassing, Kevlar, or other typical
tube-strengthening methods.
That's a slight difference, but it is a difference. With that said, QT's bond with epoxy, as far as I know, is purely mechanical and less intimate than with another substrate. And, QT does have a larger coefficient of thermal expansion than other substrate tubes like phenolic or kraft paper tubes. If a person uses an epoxy that cannot flex somewhat and fails to roughen the surface adequately, the stresses caused by thermal cycling could easily cause the epoxy/fiberglass matrix to pull free from the surface of the Quantum Tube.


Steve Shannon
 

MaxQ

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I would use wood glue in the joint, wrap with plastic sheet and clamp for a day or so. Then put a layer of 6 oz. or so glass on each side.

BTW, why can't you do TTP with Quantum tubing? just rough it up like you would as glass tube.
I know you have done fin repair...I've seen them at the field.

One way to be absolutely sure would be to pull the fin and replace the fin completely...but if that fin is through the wall and seated on the motor mount, I wouldn't do it.
I think you would have to tear the hell out of this thing and probably end up doing more damage just to do that.

Appears to me there is enough of the fin remaining to work with.

I think there is even enough fin root in the second picture that you could do the repair with a new replacement section of fin - w/o overlapping FG onto the BT, just the remaining fin root.
Would be the easiest way...IMHO
 

Coop

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I'd lean toward removing that fin entirely, cutting a new one, and attaching, but, hey... your rocket.

Later!

--Coop
 

Q-Aero

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you seems to have a very long base in the front of the fin. I will first glue the fins together, then sand it to make it thinner, remove the fillets (especially in the back part to have more grip on the left over of the base) and FB only the fin on both side, I think the front base is large enough to hold everything.

Beside, why trash it, worst case, you can glue the fins, repaint and hang it on the ceiling of the shop
 

BDB

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Here's what I just did for a similar situation tonight.

Sanded the paint off using a 50 grit pad in my orbital sander. Then I filled the break with Titebond II, wrapped the area with wax paper and clamped it between two 1x6 boards. I just applied the glue to one side. Tomorrow morning I'll flip it and apply the glue to the other side. Then I'll do tip-to-tip with 6 oz glass and a 2 oz veil layer.
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Maxitout

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Reading through all this, I think Handeman has the right idea, that's how I would go about it.

Several years ago, I took some advise from Andy Woerner, (started What's Up Hobbies), about fin installation that I use to this day. I butter up the root of the fin, and stick it in. After that cures, I put a fillet on the outside, usually not a very big one. This results in a firmly attached fin, but if it does hit, will usually just knock the entire fin loose, without breaking it. I've had a couple of hard landings that have done this, just wiggle the fin, pop it out, clean it up, and re-attach. Then, of course, re-fillet and paint. This method has worked for me for years with great success, and I fly on a dry lack bed. To be honest, I see some people put tons of epoxy on internal fillets that I feel is excess. You're going to fly that thing, not run an Abrams tank over it.

Phil L.
 

MaxQ

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More on that Fiber Glassing over Quantum Tube thing:

I located an article in Sport Rocketry - May/June 2009.
"Keeping The Fins On: Tip - to - Tip Glassing" by Mike Konshak NAR 896 L3

Here is a statement from this article on tip to tip fin fiber glassing, and I quote:

" This will accomplish two goals, one is laminating the fins together with the airframe to make it a one-piece structure.
It doesn't matter if your airframe is made out of G-10, phenolic or Quantum tubing, the technique will be the same.
The second goal is to change the resonant characteristics of the fins by using layers of both Carbon Fiber and fiberglass cloth.
Sandwiching the two different materials together will eliminate the likelihood of fin flutter."

I'm not an engineer, but he is.
He has written several articles on CF glassing and Level three builds.

I'm going with his advice on fiber glassing over Quantum tube.
Until someone can provide first hand evidence to the contrary.

I think there is a reason PML buried that little statement about Quantum tube "not being intended for Fiber Glassing" three or four tiers deep into their website...they just don't know for sure themselves.
 
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