Cost effectiveness of buying new struts

[Guest]

Interesting comments on other threads about the economics of getting new struts.

After reading them I did a present value calculation for strut inspect cost and I figured $200 and $250 per year. That translates to $400 and $500 per NDT inspection every other year.

I am convinced that you can buy a set on Univair struts for $2700 + shipping. In fact I think I can sell them to you for about $2650 + air freight. So the target present value is about $2700.

I assume that 4% interest is a reasonable rate that most of us can get on our money.

Using all those assumptions I calculate that it takes 14 to 20 years to make it worth buying new struts based on the financials alone. 14 years if you spend $500 per inspection and 20 if you spend $400 per strut inspection.

If the interest rate that you can get on your money is higher than 4% then the number of years it takes to make it worth buying gets greater. For example if you get 6% on your money then the number of years it takes jump to 18 and 28 respectively.

[N96337]

Re: Cost effectiveness of buying new struts

I guess it's also going to depend on what the owner wants to put up with as far as hassle goes. Like Tom said in another post, it's not worth it to him to pull the struts and go through the NDT every couple years.... I can understand that. I'm sure there will also be others that factor in the feeling of knowing the struts are new and the latest/greatest part... I can understand that too. They both are very legitimate factors! I guess it's going to be more of a "personal" thing to some, and more dollars and cents (sense?) to others.
Being an IA, I have no problem doing the inspections every couple years, as long as my struts are good, but that's just MY thoughts.
JH

[NY86]

Re: Cost effectiveness of buying new struts

Another thing to consider is that if the inspections come up empty the AD may be revised or rescinded as was the Cherokee wing AD of years past, in which case the inspections would be less frequest or unnecessary all together and the payback infinite...

Maybe the Association or another interested party could keep records of the inspection results for use in the future to get the AD defanged.

[DannyDot]

Re: Cost effectiveness of buying new struts

There is talk of a second AD coming out to inspect the fitting. If I have to pull the struts every 2 years to do this AD, even if I have new struts, I will lean toward keeping my unsealed struts. I will wait to see what happens with the fitting inspection AD.

Danny Deger

[Guest]

Re: Cost effectiveness of buying new struts

There is talk of a second AD coming out to inspect the fitting. If I have to pull the struts every 2 years to do this AD, even if I have new struts, I will lean toward keeping my unsealed struts. I will wait to see what happens with the fitting inspection AD.

Danny Deger

excellent point!

[1938BF50]

Re: Cost effectiveness of buying new struts

Dave,

I like your line of thinking!

In fairness to the calculation, should you be compounding the NDT cost (linear for simplicity) as a rising cost over "X" years? Kind of working the formula backwards, but more representative of a "worst case" break even analysis (in my non-financial mind anyway).

Leave the $2700 alone and plug in a compounded cost resulting in $1000-$1200 for the NTD in (7) years. What do 'ya get?

[Guest]

Re: Cost effectiveness of buying new struts

Dave,

I like your line of thinking!

In fairness to the calculation, should you be compounding the NDT cost (linear for simplicity) as a rising cost over "X" years? Kind of working the formula backwards, but more representative of a "worst case" break even analysis (in my non-financial mind anyway).

Leave the $2700 alone and plug in a compounded cost resulting in $1000-$1200 for the NTD in (7) years. What do 'ya get?

yes- BUT- My engineering economic book is at home and all I have here is a spreadsheet tool.

I like your idea it is correct as the ndt cost will inflate. Will try that later tonite.

[Ragwing nut]

Re: Cost effectiveness of buying new struts

Interesting comments on other threads about the economics of getting new struts.

After reading them I did a present value calculation for strut inspect cost and I figured $200 and $250 per year. That translates to $400 and $500 per NDT inspection every other year.

I am convinced that you can buy a set on Univair struts for $2700 + shipping. In fact I think I can sell them to you for about $2650 + air freight. So the target present value is about $2700.

I assume that 4% interest is a reasonable rate that most of us can get on our money.

Using all those assumptions I calculate that it takes 14 to 20 years to make it worth buying new struts based on the financials alone. 14 years if you spend $500 per inspection and 20 if you spend $400 per strut inspection.

If the interest rate that you can get on your money is higher than 4% then the number of years it takes to make it worth buying gets greater. For example if you get 6% on your money then the number of years it takes jump to 18 and 28 respectively.

I don't think you took into consideration the cost of paying a mechanic to R&R the struts as required by the regs. Unless you already have a fixture made to hold them up, you should consider 1 hour to make fixtures plus the cost of material, 1 hour to remove the struts, time or cost to deliver or ship to a certified NDT inspector, and 1 hour to reinstall. At $50 per hour and $50+ for the fixture material, that becomes $450+ every 2 years not including transportation costs whether delivery or shipping. And that does not cover any touch up painting that may be required.

Mike

[Guest]

Re: Cost effectiveness of buying new struts

I don't think you took into consideration the cost of paying a mechanic to R&R the struts as required by the regs. Unless you already have a fixture made to hold them up, you should consider 1 hour to make fixtures plus the cost of material, 1 hour to remove the struts, time or cost to deliver or ship to a certified NDT inspector, and 1 hour to reinstall. At $50 per hour and $50+ for the fixture material, that becomes $450+ every 2 years not including transportation costs whether delivery or shipping. And that does not cover any touch up painting that may be required.

Mike

So basically you are saying the costs are twice what I guessed?

[1938BF50]

Re: Cost effectiveness of buying new struts

yes- BUT- My engineering economic book is at home and all I have here is a spreadsheet tool.

I like your idea it is correct as the ndt cost will inflate. Will try that later tonite.

ENGINEERING ECON! That gave me an involuntary shudder and brought back nightmares. I hope I never have to retrieve that book! One of two classes in my pre-calculator college days that I was thrilled to just get a passing grade in.

[1938BF50]

Re: Cost effectiveness of buying new struts

Good point Mike.

Dave,

I would agree that the "starting" point for NDT should be somewhere around double for Mike's very applicable observations. Compound that again as a (7) year projection. Boring as this may be to a lot of us, this data will help tremendously in helping to make test/buy decisions for a lot of us. Maybe chart a best case/worse case scenario?

[Ragwing nut]

Re: Cost effectiveness of buying new struts

So basically you are saying the costs are twice what I guessed?

yes. As an A&P/owner I doubt you are not far off if you are close to a NDT inspector. For those that are an owner only, there are more costs involved.

When the Piper AD came out and required a Maule puch test, it ruined the finsih on the struts and required repaint. I never trusted what might be hiding under the paint and required we have the struts blasted to verify the condition of the metal surface. When we told customers it would cost $500 10 years ago to do the inspection and repaint, most chose to buy new ones when they were still reasonably priced (under $1000 for a set). Maule punch testing was time consuming and screwed up the paint every time I did one.

[cpirrmann]

Re: Cost effectiveness of buying new struts

You could assuage some of the cost by having it done at annual time, if your IA has the equipment. Does anyone know the theoretical life span of the sealed struts?

[Ragwing nut]

Re: Cost effectiveness of buying new struts

You could assuage some of the cost by having it done at annual time, if your IA has the equipment. Does anyone know the theoretical life span of the sealed struts?

time is still time and most IA's may flat rate the inspection, but any repair work would be extra.

Thoeretical life span will depend on the enviroment, but I am betting no longer than the originals

Mike

[Guest]

Re: Cost effectiveness of buying new struts

I doctored up my .xls spreadsheet for figuring the present value of a series of strut inspections.

You can enter your own inspection fees and interest rate.

Was hoping to post it here but I don't see a way to do it.

Any clues?

k- think I figured out a way, I attached it as a zipped file to teh next post, download it, unzip and give it a whirl.

If you know what you are doing and want to edit it the password is strut.