# Wrapping Fiberglass around Aluminum t increase strength?

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#### wanttobuild

##### Well-Known Member
The other thing to consider from a structural perspective is the coeficient of thermal expansion of the two materials. No matter how good the initial bond, the CTE differences can be a significant percentage (or even exceed) the shear load of the bond. In theory, you can overload and fail the bond just by changing temperature in the hangar.
And that is a FACT

#### wanttobuild

##### Well-Known Member
Wrapping a section of large diameter (5-6”+) thin walled alloy tube in fibreglass will increase its resistance to buckling failure irrespective of the bond or no-bond between the glass and the tube, this is a good way to re-inforce the junction of a tail boom with the forward fuselage of a pod and boom pusher at the maximum bending moment, the thickness of the fibreglass would be tapered to lessen the shear force where the tube exited the glass.
I am glad you posted this.
Why not break the bond with plastic or tape then wrap away @ 0deg. Would personally use thin Carbon Tow, because I have fell in LOVE with carbon

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Ok, let's start with stiffer. Three possible modes. First is axial. Stiffness is sum of E*A of the materials. EA of the metal plus EA of the composite to get Sum of EA

Bending. E*I is bending stiffness. Compute for each layer of structure and sum to get the total.

Torsion. G*J is torsional stiffness. Similar approach.

While you can just look up E and G for metals, composites are a little trickier, as you need to figure out how much fiber you have in each direction to get to E along and across and in shear...

Now getting into strengths, you need the yield strength of the metal and the first fiber failure strength of the composite in the direction of the load, then figure out which one happens at the lowest strain, then figure out what the part load is that first failure strain.

ALL of these figures vary with the metal, the fiber resin system, fiber angles, how much of each, how the fibers are aligned and so on.

So, we can not answer the question asked except to say, yeah, you can make an existing metal part stiffer and stronger (when it is new), but it might not be the lightest nor simplest way to get to strength or durability. The final answer is going to be dependant upon how and how much and then how long you want it to last under what circumstances.

We did give the basics - but finding the right answer for your circumstances might take some serious searching of the design space... that is what the engineering school training is for - to enable the design search to be done with lessons learned and analytically ( mostly) as opposed to making many examples and then running tests on them all.

Lessons learned? Long ago, NASA put out lists of acceptable and not acceptable materials for use in coastal Florida. DoD has a similar set for their equipment. These lists came about as a result of hard learned lessons. There are others...

So, what if? Well, you get to figure out the favorable ones for your work. Sorry, it is a multivariate problem...

Billski

#### Dan Thomas

##### Well-Known Member
So, we can not answer the question asked except to say, yeah, you can make an existing metal part stiffer and stronger (when it is new), but it might not be the lightest nor simplest way to get to strength or durability.
Or the cheapest.

Some of this sort of thing strikes me as a way to make an inadequate design adequate. There are plenty of instances in certified airplanes. ADs (which force) or service bulletins (which recommend) the addition of some patch or stiffener to strengthen some spot that has turned out to be failing in service. For the homebuilder, sometimes it's just better (and cheaper and sometimes lighter) to make a new, stronger part rather than to start adding a bunch of different material that might not stay put.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Building on my previous post, aluminum is about 5 times stiffer (per unit volume) than BID fiberglass and about 2 times the density.

As an example, doubleing the axial stiffness of an aluminum element with bidirectional fiberglass will require adding 2.5 times as much fiberglas weight as you have aluminum, making the part 3.5 times heavier, while the same stiffness upgrade in aluminum would only require it to be 2 times heavier. The new element is much heavier with a fiberglass reinforcement than by just using a bigger aluminum element

To do the same thing in bending and torsion is not quite as dramatic, but the weight penalty for this sort of thing is still large....

For our OP, I need to say this - apologies to everyone else : WEIGHT IS THE ENEMY. Anytime you are working on something in an airplane, you really must figure out several ways of doing it and go to or near the lowest weight way. This because extra weight always: Increases runway length needed; reduces climb rates; reduces ceiling; reduces payload; increases forced landing energy. In powered airplanes, you need good reasons to add any weight, and a lot of good reasons to make something a lot heavier.

The only place where anyone deliberately adds weight is in racing sailplanes on a day with good lift. That raises the speed of best L/D, and allows higher ground speeds. And they dump the water if lift goes weak and before landing.

Billski

#### proppastie

##### Well-Known Member
Log Member
I believe the RVs had to have a metal stiffener added to the nose strut

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#### wsimpso1

##### Super Moderator
Staff member
Log Member
Nose gear landing strut.
That still does not tell us much. Please describe the parts and the loading types. Or maybe cite what the "strut" looks like: a C152 or a RANS S6 or an RV6A.

#### Yellowhammer

##### Well-Known Member
That still does not tell us much. Please describe the parts and the loading types. Or maybe cite what the "strut" looks like: a C152 or a RANS S6 or an RV6A.

Yes sir.

My Nose Gear Strut is for a Pulsar I series aircraft. The Nose gear strut, from Aero Designs, has been a constant issue over the years. Several folks have modified their forks and struts to compensate for the weak structure which has, on many occasions, broken upon landing causing prop strikes and major damage to the aircraft.

Ill post a picture of the assembly when I get home later today.

Thank you all for your willingness to help out.

Sincerely and Most Respectfully,

Yellowhammer

#### Yellowhammer

##### Well-Known Member
I believe the RVs had to have a metal stiffener added to the nose strut

View attachment 103295

I have seen these before. The Anti Splat device. I think I could build my own and save money. What are your thoughts?

Thanks,
Yellowhammer

#### Yellowhammer

##### Well-Known Member
Building on my previous post, aluminum is about 5 times stiffer (per unit volume) than BID fiberglass and about 2 times the density.

As an example, doubleing the axial stiffness of an aluminum element with bidirectional fiberglass will require adding 2.5 times as much fiberglas weight as you have aluminum, making the part 3.5 times heavier, while the same stiffness upgrade in aluminum would only require it to be 2 times heavier. The new element is much heavier with a fiberglass reinforcement than by just using a bigger aluminum element

To do the same thing in bending and torsion is not quite as dramatic, but the weight penalty for this sort of thing is still large....

For our OP, I need to say this - apologies to everyone else : WEIGHT IS THE ENEMY. Anytime you are working on something in an airplane, you really must figure out several ways of doing it and go to or near the lowest weight way. This because extra weight always: Increases runway length needed; reduces climb rates; reduces ceiling; reduces payload; increases forced landing energy. In powered airplanes, you need good reasons to add any weight, and a lot of good reasons to make something a lot heavier.

The only place where anyone deliberately adds weight is in racing sailplanes on a day with good lift. That raises the speed of best L/D, and allows higher ground speeds. And they dump the water if lift goes weak and before landing.

Billski

Thank you sir!!

#### Yellowhammer

##### Well-Known Member
Greetings,

Please except my apologies for not providing more information about my situation. It has been extremely crazy at work and this has been the first time I have had to get caught up on my correspondence. I will supply all the relevant information needed as soon as I get home and can refer to my manuals tonight.

Again, thanks for ALL for your help, input, wisdom, time, and guidance. I value you all and I am Blessed to be apart of such an outstanding forum.

Sincerely and Respectfully,

Yellowhammer

#### proppastie

##### Well-Known Member
Log Member
I have seen these before. The Anti Splat device. I think I could build my own and save money. What are your thoughts?

Thanks,
Yellowhammer
If it were for a RV then Van has a new design with rubber compression disks in the cowl for some aircraft....yes you have pictures and probably could find an RV to look at so yes you could save money.....however the purchased item is engineered, tested, and fabricated for you......I did not think it was an unreasonable price for "aircraft part" .....were it Mooney it would probably be 1AMU (Aircraft Monetary Unit $1,000) plus A&P professional installation (4 hr at$85/hr?). As for your bird....careful here..... gear design is not trivial, perhaps someone with an aircraft same as yours has a successful design/fix to copy.

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