Hatch Lift Struts Calculation

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Hatch Lift Struts Calculation

Postby ssample » Fri Dec 27, 2013 11:35 pm

My TT is now completed except for installing the galley hatch lift struts. For now I raise the hatch with one arm and place wood supports at each side. The hatch is heavy for my wife and kids to lift. I want to install a pair of automotive type gas lift struts such as is seen on auto hoods or rear lift gates. The hatch is 48 inches long and weighs 23.5 pounds at the end opposite the hatch hinge. Can anyone provide a reference source which will guide me on how to determine the length, strength and positioning of these struts? Thanks, Steve
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Re: Hatch Lift Struts Calculation

Postby danlott » Sat Dec 28, 2013 10:03 am

I just happen to have made a strut calculator not to long ago. Here is a link to the post: http://www.tnttt.com/viewtopic.php?f=21&t=58263

If the calculator works for you please post a comment and your results in the calculator thread.

Dan
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Re: Hatch Lift Struts Calculation

Postby ssample » Sun Dec 29, 2013 7:19 pm

Thanks for the quick reply. I am studying the calculations in the Excel spreadsheet within the limitations of my dimensions and have some questions?

How did you arrive at the 60% ideal gas spring length percentage? This is about the size of extended gas spring that I can get into my TT above the galley counter.

Also, how did you determine that the ideal hatch attachment point should be 85% of the gas spring stroke length?

Finally, I did not understand that the attachment point inside the galley should be placed along a radius measurement from the (hatch) hinge center point equal to the extended length of the gas spring. This might work on the configuration in the hatch and galley layout that you show in the diagram that you provided in the post; but in my TT, the gas spring will be installed nearer to vertical and the extended gas spring hatch attachment location will be about 8 inches above the hatch hinge point with the hatch fully open. For now I have attached a photo crop that shows my configuration to help explain my situation and to assist you.

Thanks for your assistance. Steve
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TT Hatch Layout.jpg
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Re: Hatch Lift Struts Calculation

Postby ssample » Sun Dec 29, 2013 9:59 pm

Hi, I have one more question? Is the calculator solution for the required force of the gas springs for one spring or is it the total for both springs? Thanks, Steve
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Re: Hatch Lift Struts Calculation

Postby danlott » Mon Dec 30, 2013 3:16 am

I got the ideal length, mounting locations and calculations from various strut manufactures websites. All I did was try and make sense of the calculations and show how to apply the information to teardrop hatches.

You can go with shorter struts than the ideal length struts. This will require different mounting locations and higher strength struts to be used. This will also not support your hatch as well at the ideal length struts would. I also believe the higher strength struts will place more stress of the hatch hinge. As far as I can tell lots of people have used smaller struts and have had no issues.

The ideal mounting locations are to try and prevent the strut from compressing more than 85%. This again was found on the various manufactures websites.

As I stated in the spreadsheet it may not be possible to use the ideal length sturts due to the design of your trailer. You may very well have to use smaller struts to fit your design.

The calculator determines the force required for each strut. Make sure to put the number of struts that you will be using in the right box.

Hope this makes a little more sense now.

Dan
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Re: Hatch Lift Struts Calculation

Postby ssample » Mon Dec 30, 2013 9:55 am

Hi, Please see the attached calculations that I did. I used both the center dead weight and the outer end weight using the levers theory and arrived at the same 140 pounds that the Excel calculator did, but for a TOTAL. This would be divided by two for each gas spring. Does anyone else have any ideas? Thanks again, Steve
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Re: Hatch Lift Struts Calculation

Postby danlott » Tue Dec 31, 2013 1:09 am

ssample wrote:Hi, Please see the attached calculations that I did. I used both the center dead weight and the outer end weight using the levers theory and arrived at the same 140 pounds that the Excel calculator did, but for a TOTAL. This would be divided by two for each gas spring. Does anyone else have any ideas? Thanks again, Steve


I had a chance to review my formulas in the calculator and it did have an error. Thank you very much for helping bring this to my attention, so I could figuring it out. I have updated my calculator with the corrected formula.

Thanks again,
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Re: Hatch Lift Struts Calculation

Postby ssample » Tue Dec 31, 2013 1:36 pm

Thanks for posting your updated gas spring calculator and validating my calculation. Can I get to the new spreadsheet using the same link in the earlier post? I understand that the result is for each single gas spring. I am thinking that I might also do a follow-up weight test using a scale set at the hatch spring attachment point, that will give me an empirical validation of our theoretical calculations. Of course this result would not have the safety factor. I will post the result if I do this. Steve
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Re: Hatch Lift Struts Calculation

Postby danlott » Tue Dec 31, 2013 2:21 pm

Yes the link above will go to the updated spreadsheet. I deleted the old one and uploaded the new one in it's place.

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