Potential Aircraft Purchase - Wooden Spar Concerns

[dillardrg]

This thread got me to wondering how we have arrived at this point where it is an “accepted fact” that Aluminum is superior to Wood as a material for building airplanes (specifically wings). So, here are some thoughts on the subject.

Up until the end of WW II most small airplanes were built using a lot of wood because Aluminum was hard to get and expensive, even more so with the war. An airplane manufacturer had to hire a team of Craftsmen to build their wings for them. A labor intensive process, but hey, labor was relatively cheap and you could find artisans who knew how to work with it.

During the war a lot of airplanes were manufactured and they needed to be built as quickly and cheaply as possible, stamp out the parts and rivet them together. It wasn’t difficult to train unskilled labor to do this and a lot of machines could be used in the making of the parts.

The war ended and Aluminum became readily available and cheap. There were a lot of people available trained in the metal airplane process. Labor costs started to rise. In 1946 Bill Piper changed his J3 wing spars from wood to aluminum. Not because they were better, but they were cheaper. There were some aircraft manufacturers who resisted the change. Bellanca was one of them and gained a reputation of making an incredibly strong and tough airplane. Why? Because they retained the wood, they didn’t go to aluminum like the “spam cans” at Piper. Everyone knew at that time that wood was stronger, lighter, and more flexible than aluminum. But economic and marketing forces are impossible to over come. Soon advertiser were asking the new to aviation customer, “Why fly in the old fashioned wood airplane when you can have a new, modern aluminum one?”

Wood wings didn’t go from stronger, lighter, and more flexible to inferior overnight, it took a lot of years of marketing before that was an accepted belief. Think about this, with a wood spar a competent inspector can tell if it is airworthy. You can’t say that about aluminum. Aluminum has its own problems including fatigue and corrosion. A friend of mine just a few weeks ago had to replace both wings on his 172 because of corrosion, advanced corrosion. When it was found it was way beyond unairworthy. These kinds of stories don’t stop people from buying aluminum wings. Why? Because everyone these days knows that aluminum is what you make wings out of. So if you have a problem now and then, so what?

Sorry for the rambling on, but it just bothers me that we are such slaves to marketing and technology that we lose sight of the fact that in a lot of cases the old ways were better. I think that wooden spars is an example of this.

Ron

 

[Baron2PG]

This thread got me to wondering how we have arrived at this point where it is an “accepted fact” that Aluminum is superior to Wood as a material for building airplanes (specifically wings). So, here are some thoughts on the subject.

Up until the end of WW II most small airplanes were built using a lot of wood because Aluminum was hard to get and expensive, even more so with the war. An airplane manufacturer had to hire a team of Craftsmen to build their wings for them. A labor intensive process, but hey, labor was relatively cheap and you could find artisans who knew how to work with it.

During the war a lot of airplanes were manufactured and they needed to be built as quickly and cheaply as possible, stamp out the parts and rivet them together. It wasn’t difficult to train unskilled labor to do this and a lot of machines could be used in the making of the parts.

The war ended and Aluminum became readily available and cheap. There were a lot of people available trained in the metal airplane process. Labor costs started to rise. In 1946 Bill Piper changed his J3 wing spars from wood to aluminum. Not because they were better, but they were cheaper. There were some aircraft manufacturers who resisted the change. Bellanca was one of them and gained a reputation of making an incredibly strong and tough airplane. Why? Because they retained the wood, they didn’t go to aluminum like the “spam cans” at Piper. Everyone knew at that time that wood was stronger, lighter, and more flexible than aluminum. But economic and marketing forces are impossible to over come. Soon advertiser were asking the new to aviation customer, “Why fly in the old fashioned wood airplane when you can have a new, modern aluminum one?”

Wood wings didn’t go from stronger, lighter, and more flexible to inferior overnight, it took a lot of years of marketing before that was an accepted belief. Think about this, with a wood spar a competent inspector can tell if it is airworthy. You can’t say that about aluminum. Aluminum has its own problems including fatigue and corrosion. A friend of mine just a few weeks ago had to replace both wings on his 172 because of corrosion, advanced corrosion. When it was found it was way beyond unairworthy. These kinds of stories don’t stop people from buying aluminum wings. Why? Because everyone these days knows that aluminum is what you make wings out of. So if you have a problem now and then, so what?

Sorry for the rambling on, but it just bothers me that we are such slaves to marketing and technology that we lose sight of the fact that in a lot of cases the old ways were better. I think that wooden spars is an example of this.

Ron

Well said.

 

[dmccormack]

Well said.

Exactly.

 

[BiffJ]

Intragranular corrosion is a good example of aluminum problems.....I inspected a 172 that had flown in for an annual and found the spar roots were affected with this problem. Not always obvious from the outside. It didn't fly back out and the cost of replacing aluminum spars in an aluminum or fabric wing is as prohibitive as replacing the wood. Both types of spars have their issues so look at the plane not just the spar material.
Good luck
Frank

 

[ebetancourt]

This thread got me to wondering how we have arrived at this point where it is an “accepted fact” that Aluminum is superior to Wood as a material for building airplanes (specifically wings). So, here are some thoughts on the subject.

Up until the end of WW II most small airplanes were built using a lot of wood because Aluminum was hard to get and expensive, even more so with the war. An airplane manufacturer had to hire a team of Craftsmen to build their wings for them. A labor intensive process, but hey, labor was relatively cheap and you could find artisans who knew how to work with it.

During the war a lot of airplanes were manufactured and they needed to be built as quickly and cheaply as possible, stamp out the parts and rivet them together. It wasn’t difficult to train unskilled labor to do this and a lot of machines could be used in the making of the parts.

The war ended and Aluminum became readily available and cheap. There were a lot of people available trained in the metal airplane process. Labor costs started to rise. In 1946 Bill Piper changed his J3 wing spars from wood to aluminum. Not because they were better, but they were cheaper. There were some aircraft manufacturers who resisted the change. Bellanca was one of them and gained a reputation of making an incredibly strong and tough airplane. Why? Because they retained the wood, they didn’t go to aluminum like the “spam cans” at Piper. Everyone knew at that time that wood was stronger, lighter, and more flexible than aluminum. But economic and marketing forces are impossible to over come. Soon advertiser were asking the new to aviation customer, “Why fly in the old fashioned wood airplane when you can have a new, modern aluminum one?”

Wood wings didn’t go from stronger, lighter, and more flexible to inferior overnight, it took a lot of years of marketing before that was an accepted belief. Think about this, with a wood spar a competent inspector can tell if it is airworthy. You can’t say that about aluminum. Aluminum has its own problems including fatigue and corrosion. A friend of mine just a few weeks ago had to replace both wings on his 172 because of corrosion, advanced corrosion. When it was found it was way beyond unairworthy. These kinds of stories don’t stop people from buying aluminum wings. Why? Because everyone these days knows that aluminum is what you make wings out of. So if you have a problem now and then, so what?

Sorry for the rambling on, but it just bothers me that we are such slaves to marketing and technology that we lose sight of the fact that in a lot of cases the old ways were better. I think that wooden spars is an example of this.

Ron

Yep, Classic Waco is a perfect example!

 

[Diana]

Sorry for the rambling on, but it just bothers me that we are such slaves to marketing and technology that we lose sight of the fact that in a lot of cases the old ways were better. I think that wooden spars is an example of this.

Ron

Ron, I agree.

We recovered our 1977 Citabria in 2006. The wood spars were in great shape and we left them on. They are inspected every year and no problems have been found with them.

 

[Baron2PG]

Looking at a possible purchase (1966 Citabria) and have a concern about the wooden spar.

This particular aircraft has damage history -1983 hard landing - collapsed gear and damage to wingtips.

Left spar was replaced in 2000.
Right spar replaced in 1982 (before the accident)

Aircraft was painted in 2008.

The overall condition of the aircraft is very good. My concern from a purchase standpoint is the right wing. The paint (2 years old) is starting to chip and flake off along some of the rib seams. There is no paint chipping on the left wing, but the left spar is obviously much newer. Could this be a sign that the right spar is in need of replacemement and how much do spar replacements cost? It would seem to me that there is clearly more flex in the right wing vs left.

Obviously, a thorough pre-puchase inspection would answer my questions. Since I don't have any experience with maintaining a wood spar plane, I am mostly just wondering if given the info above, if it is worth paying the money for the inspection or if I should forget about this bird entirely and move on.

So, what was the outcome on the Citabria? Did you buy it?

 

[somorris]

We recovered our 1977 Citabria in 2006. The wood spars were in great shape and we left them on. They are inspected every year and no problems have been found with them.

It probably has a lot to do with whether or not the airplane has been treated with TLC like Diana does hers. If the spar is looked at and is in good shape and the pilot doesn't over stress it, why would it crack?

 

[Fearless Tower]

So, what was the outcome on the Citabria? Did you buy it?

Nope - I had the advantage of a fellow flying club member taking it for a pre-purchase inspection ahead of me - never got a look at the spar - his A&P didn't look any further than the condition of the fabric. Plane was airworthy, but probably going to need a recover within the next few years - not something I wanted to get saddled with right now.

So, I continue to happily rent while keeping my eyes open for the right opportunity.

 

[Tom-D]

It probably has a lot to do with whether or not the airplane has been treated with TLC like Diana does hers. If the spar is looked at and is in good shape and the pilot doesn't over stress it, why would it crack?

Cracking isn't usually the cause of failure, elongated bolt holes and dry rot are the most popular causes that are not accident related.

The spars in my Fairchild 24 were cut in 1946 they are as good as the day they were made. they've been varnished and wrapped in uv protective covers all their life. and were removed cleaned and re varnished with UV protective varnish in 2007.

 

[weirdjim]

Do they make catholic and jewish varnish as well?

 

[stagecoachco]

Do they make catholic and jewish varnish as well?

Indeed they do, as well as Islamic varnish. But note that the use of Islamic varnish on aircraft is prohibited by the Department of Homeland Security as aircraft with Islamic varnish tend to crash into government buildings...

 

[Richard]

Ron D, thanks for saying that. From my boatbuilding days I recall a series of articles detailing the superior characteristics of wood as compared to alum and steel. Modulus of elasticity is important in building aircraft and boats. Lb for lb, wood species are as durable and share equitable maintainence costs with steel. Actually, some hardwood species costs less to maintain than any of the types of steel or alum.

Every material will have it's weakness, design can overcome some of that but it comes down to maintaining the orgininal characteristics of the material. I'm biased towards wood.

 

[kyleb]

Every material will have it's weakness, design can overcome some of that but it comes down to maintaining the orgininal characteristics of the material. I'm biased towards wood.

Wood is great stuff. The problem is that in older airplanes that weren't worth much 30 years ago, they probably got wet and stayed wet periodically when the <then> cheap aircraft were tied down outside for a couple of decades.

Now, a lot of those spars are in bad shape. It seems like every time a new owner opens up the wings on a '46 Champ or Chief, they find spars that need replacing. I sure did. After 65 years, that isn't a big surprise.

Airplanes that were always hangared don't have that problem.

 

[Richard]

And other than the suceptability of the material, none of what you state is the result of an inherent deficiency of the material. Every one of those you mentioned is due to improper or lack of maintenance.

A couple years ago the proud new owner of a J-2 taxied in. After I had pointed out a serious crack in a cylinder shroud and said I would call the A&P over, I pointed out the pine needles I pulled out of drain hole. By then another pilot had wandered over because one doesn't see many J-2s.

He started to argue keeping the drain holes clear was a minor detail. I could just roll my eyes. The matter was settled when the A&P authoritively stated keeping the drain holes clear was very important. Again, a pilot needs to know the care and feeding of the aircraft he flies.

EDIT: would it make a difference if a 65 yr old spar was made of metal? Suppose the answer is, Yes. The ultimate concern here is why is one waiting to the life limit for replacement? Everything will fatigue. A planned maintenance program will combat that evolution by being proactive. I recognize this is made more problematic because planes trade owners every so many years and so does the perspective of the importance of maintenance.

 

[Henning]

Getting back on the subject of Wood Spars. I too am looking to purchase a Decathlon which is subject to the same wood spar AD as the Citabria. A "friend" advised that I only look at planes that have had the wood spar replaced with the aluminum spar or buy a newer 90's Decathlon that came from the factory with the AL spar.

Unfortunately, there are only a few '70s with the spar replacement and they are out of my price range. The new planes '90s onward are outside of my budget. There are a couple very nice '70s wood spar aircraft available. However, the seeds of doubt have been firmly planted and I'm not sure I'm comfortable with a wood spar aircraft. 1) I don't want the wing to fail (duh) though I know this probably is highly unlikely and there haven't been any documented wing seperation failures 2) I don't to get stuck with a $20K repair bill for a $40K airplane; this is the major concern. I buy a $40k plane and the 1st annual they find a cracked spar. Now I'm SCREWED.

Yes, there is inspecting to do, and yes, there have been some problems, but for an aerobatic airplane, especially a used one, I would much prefer a wood spar to an aluminum one.

A couple quicky tests you can do when looking at the plane that you can use to eliminate that plane before spending money on a proper and complete inspection. First, lift up and pull down on the wing tips with as much force as you can apply, What do you hear? If you hear crackling, you can walk away (creaking on the other hand can be normal, it's those sharp edged reports in the noise that are of immediate concern) . Open an inspection panel in the wing and stick your nose in there, if you smell a sickly sweet smell, walk away, that's the smell of rot.

These are the two primary preflight checks I make on a wood spar aircraft to decide whether I'm going to ferry it or not.

Again, these checks are not used to EXCLUDE potential issues, a negative test doesn't mean you have no problems, just that a positive result indicates you have a problem that has grown to a proportion that safety of flight is a concern (and most likely a significant cost to repair). In your situation I would just use it to eliminate that airframe from further inspection/consideration unless it is priced correctly for one that is advertised as known defective.

 

[Henning]

It probably has a lot to do with whether or not the airplane has been treated with TLC like Diana does hers. If the spar is looked at and is in good shape and the pilot doesn't over stress it, why would it crack?

That's the thing, you aren't going to "overstress" a proper wood spar and make it crack, overstress is an issue you face with aluminium which is why I prefer wood in an aerobatic aircraft.

 

[Tom-D]

When I built a new vertical stab for my 24, i needed to open the old stab to reverse engineer it and found the interior like new.

pictures, some are the old some are the new.

 

[Tom-D]

Do they make Catholic and Jewish varnish as well?

Fixed it for ya..

 

[Tom-D]

FWiW The super cub and Husky wings I re-cover usually have a lot fewer repairs to do than wooden structure

the new 5 year clear varnish I use is $140.00 per Pint kit. http://www.fiveyearclear.com/
WoW,,,,,,,,, sure am glad I got enough when we bought last.

It does cost more to restore wooden structure than metal. Aviation grade spruce is getting expensive, this bundle was $5 bucks 10 years ago.

http://www.aircraftspruce.com/catalog/wppages/bargainbag_spruce.php

Metal aircraft are easier and quicker to repair than wood, you can buy ready made parts and they fit, and the wooden structure usually must be repaired by glue up and dwell times.

 

[weirdjim]

Fixed it for ya..

Well, since you didn't capitalize Protestant, I figured I didn't have to cap Catholic or Jewish either.

 

[AcroBoy]

The last time I checked, the factory will not repair a wood spar. I seem to remember that Safe Air Repair in MN has a DER with an STC to replace wood spars. ACA is located not far from my house, and they will give a tour, which is pretty interesting.

ACA is in the business of replacing wood spars, so be careful. They will talk about the dangers of wood spars, but there have never been any catastrophic failures of wood spars. However, the wings do require careful inspection for compression cracks at the top, nails backed out, and broken nose ribs and aileron attachment fittings. It takes lots of inspection covers, and I kept a stash of them since they always were going missing.

I put 400 hours in a Super Decathlon, which had a different airfoil, and the whole family of planes were otherwise great.

 

[d.grimm]

Really??? "there's never been a catastrophic failure of a wood spar"
Why the AD?
Dave

 

[dillardrg]

Dave,

If you are really interested in why the Citabria AD was initiated the Bellanca-Champion club has a very thorough explanation on their web site.

 

[Ken Ibold]

Really??? "there's never been a catastrophic failure of a wood spar"
Why the AD?
Dave

Two schools of thought:

1) Why wait for an accident before addressing something you see as a hazard? The FAA and other industries have been moving to proactive safety measures for some time.

2) Aircraft manufacturers have learned what it takes to get the FAA to issue ADs requiring owners to buy parts. Voila, instant cash flow. American Champion had certified the aluminum-sparred wing, and this was their chance to sell some of them.

Which one you believe is entirely up to you.

 

[tonycondon]

Two schools of thought:

1) Why wait for an accident before addressing something you see as a hazard? The FAA and other industries have been moving to proactive safety measures for some time.

2) Aircraft manufacturers have learned what it takes to get the FAA to issue ADs requiring owners to buy parts. Voila, instant cash flow. American Champion had certified the aluminum-sparred wing, and this was their chance to sell some of them.

Which one you believe is entirely up to you.

similar to the taylorcraft lift strut AD

 

[tonycondon]

i have to admit, after reading Liz's trials with the carrythrough on her Cardinal I like my wood spars even more. It does help though that I have local guys who see a broken in half wood wing and think "fun!". at least spruce and douglas fir haven't gone extinct yet, like the castings for cardinal center sections.

 

[somorris]

I agree with you, Tony. Wood rules!

 

[Tom-D]

I agree with you, Tony. Wood rules!

74 years old and still in great condition.

 

[flyersfan31]

Two schools of thought:

1) Why wait for an accident before addressing something you see as a hazard? The FAA and other industries have been moving to proactive safety measures for some time.

2) Aircraft manufacturers have learned what it takes to get the FAA to issue ADs requiring owners to buy parts. Voila, instant cash flow. American Champion had certified the aluminum-sparred wing, and this was their chance to sell some of them.

Which one you believe is entirely up to you.

GASP!!! Number 2???? Even a possibility????? NONSENSE!!! That could NEVER happen. It's all about safety. And the kids. It's all about the kids!!!!