Hatch Gas Spring/Strut Calculator

[danlott]

TA huge thanks to Dan Lott

Another perfect install!

I followed the instructions and it went like a dream.
Just had to fab my weird lower mount, and Bob's your auntie

Very glad this has help several people.

Dan

 

[Thommyknocker]

pic for reference, I couldn't pull it of mobile

 

[ZachR-TNT]

Thanks Dan! Your calculator and suggestions worked perfectly for me.

 

[pmeyers-ClassB]

In the final stages of my tear drop build and I am at the strut installation. Tere is something that I don't understand: The dimensions that I am working with are very similar to those of the hatch calculator. 48" hatch, 28 " strut and 12" stroke length. If the attachment point inside the galley is determined by the strut length as a radius from the hinge point then it would seem to be that when attached to the hatch it would be long enough to even open the hatch. This would be made worse by the fact that the attachment point on the hatch is calculated on 85% of the stroke. My trailer is a Benroy shape and the hatch curves down at the hinge. Not to bright, any help understanding this would be appreciated.

 

[pmeyers-ClassB]

Correction:
In the final stages of my tear drop build and I am at the strut installation. There is something that I don't understand: The dimensions that I am working with are very similar to those of the hatch calculator. 48" hatch, 28 " strut and 12" stroke length. If the attachment point inside the galley is determined by the strut length as a radius from the hinge point then it would seem to be that when attached to the hatch it would not be long enough to even open the hatch. This would be made worse by the fact that the attachment point on the hatch is calculated on 85% of the stroke. My trailer is a Benroy shape and the hatch curves down at the hinge. Not to bright, any help understanding this would be appreciated.
pmeyers
Teardrop Inspector

Posts: 1
Joined: Thu Oct 06, 2016 3:48 pm

 

[danlott]

The dimensions that I am working with are very similar to those of the hatch calculator. 48" hatch, 28 " strut and 12" stroke length. If the attachment point inside the galley is determined by the strut length as a radius from the hinge point then it would seem to be that when attached to the hatch it would not be long enough to even open the hatch. This would be made worse by the fact that the attachment point on the hatch is calculated on 85% of the stroke. My trailer is a Benroy shape and the hatch curves down at the hinge.

Take a look at the picture that is in the first post.

One end of the strut attaches to the side wall of the galley wall at a point from the hatch hinge point that is equal to the overall length of the of the strut. The other end of the strut attaches to the hatch at a point equal to 85% of the strut stroke length.

In your case the strut should be attached to the galley wall 28" from the hinge point of the hatch. The other end of the strut should be attached to the hatch 10.2" from the hinge point. The measurements should be taken in a straight line from the hinge point and not follow the curve of the hatch.

When the hatch is closed the strut will be compressed to length of approximately 17.8 inches. This compression force is what allows the hatch to open and stay open.

The overall clearance height that you will have with your hatch open depends mostly on your hatch design and the height of the hinge point from the ground level. If you desire more or less overall clearance height then you will need to adjust the recommended strut attachment points.

If you use the dimensions provided in the calculator spreadsheet the overall clearance height should be sufficient for most normal height people.

Dan Lott

 

[Jeepnick-TNT]

I made an account specifically to post here that the calculator worked for me!

My hatch is oversized at 68"L x 57.5"W and I built it with the intention of making it very strong (and therefore heavy at 74 pounds). I was quite worried about attaching the gas springs in the wrong place and putting holes in my siding where I don't want them. After reading a bunch, I finally settled on using Dan's excel sheet to perform the calculations and it couldn't have turned out better! Nothing like installing something the right way the first time. Thank you!

Nick

 

[danlott]

I made an account specifically to post here that the calculator worked for me!

My hatch is oversized at 68"L x 57.5"W and I built it with the intention of making it very strong (and therefore heavy at 74 pounds). I was quite worried about attaching the gas springs in the wrong place and putting holes in my siding where I don't want them. After reading a bunch, I finally settled on using Dan's excel sheet to perform the calculations and it couldn't have turned out better! Nothing like installing something the right way the first time. Thank you!

Nick

Very glad to hear the spreadsheet worked for you/

Dan

 

[Tony Latham]

I have made a calculator to help determine the proper gas spring length, placement and force required to properly open and support my galley hatch. I searched the internet for formulas and recommendations for the proper placement of gas springs. This is what I came up with to use. I have not actually used it on my own trailer yet, but I figured I would throw it out there and hopefully it will help someone.

If you do use the calculator please post your results on this thread to help determine if it is accurate and useful.

Here is a picture that goes along with the spreadsheet below.

Hope it helps.

Dan

Dan:

Check your PMs, please.

Tony

 

[bknowles86]

This is great and extremely helpful - thank you. I am in the final stages of design for my build and trying to get as many things figured out as possible before starting construction. I am planning on doing a rear hatch and front roof "hatch" per the attached drawing. I'm doing 1.5" thick insulated walls, so I'd like to ensure that I have wood backing/blocking in the proper locations ahead of time. I've estimated the rear hatch to be approximately 121 lbs TOTAL weight (will include a spare tire mount) and the front at approximately 69 lbs. TOTAL weight. My question is: is there a way to calculate the dead weight from total weight, per the configuration in the sketch? Thanks!

 

[Tony Latham]

This is great and extremely helpful - thank you. I am in the final stages of design for my build and trying to get as many things figured out as possible before starting construction. I am planning on doing a rear hatch and front roof "hatch" per the attached drawing. I'm doing 1.5" thick insulated walls, so I'd like to ensure that I have wood backing/blocking in the proper locations ahead of time. I've estimated the rear hatch to be approximately 121 lbs TOTAL weight (will include a spare tire mount) and the front at approximately 69 lbs. TOTAL weight. My question is: is there a way to calculate the dead weight from total weight, per the configuration in the sketch? Thanks!

I'll chime in here since your post is sitting here unanswered ––but to cut to the chase, I think you're just going to have to build it and weigh it.

I like your profile but question the elephant in the room. The spare on the hatch.

I build Fredrick style hatches which are strong, and not overweight but I wouldn't want to hang a spare off of them. If I tried to build a hatch to support a spare, it'd probably be pushing eighty pounds without the spare. The heavier the hatch, the heavier the gas springs or course. Keep in mind, when the hatch is closed, there is a tremendous amount of pressure coming from those springs.

Spare tires are a problem. We carry a spare in our truck bed. With this new build I'm working on, I thought about looking for a donut spare in a wrecking yard with the right bolt pattern and include a lift on the chassis. That thought has come and gone.

I apologize for not being of much help, but I think folks aren't responding because of the elephant.



Tony

p.s. And think about moving the door a bit closer to the rear. You want it even with your hips.

 

[bknowles86]

Thanks Tony. I'm sure it's going to require a significant amount of force per strut to lift the spare, so I'm trying to configure the struts in a way that will be most efficient, using Dan's formula, but flipped in this case. (see attached images).

My plan is to build the hatch frame out of aluminum tube to give it the strength it needs without making it too heavy. My reasoning for having the door so far forward is to accommodate a twin bunk near the rear (we have a 5-year old daughter) which actually "pops out" of the sides a bit. I've attached an updated image.

As per the struts, I suppose as long as I have a general idea of the attachment points I can make sure I have backing in place and then as suggested, weigh the hatch once it's built.

 

[bknowles86]

I did find this sizing guide online - although it's in metric, it seems like it would work as long as the conversions are made correctly. Any thoughts?

 

[Tony Latham]

I suppose as long as I have a general idea of the attachment points...

Sounds good. I buy my struts at McMaster.com. They have detailed drawings of the struts plus a no-questions-asked return
policy.



T

 

[bknowles86]

Keep in mind, when the hatch is closed, there is a tremendous amount of pressure coming from those springs.

Tony, one more question: regarding your comment above about pressure when the hatch is closed, could you further elaborate? Thanks!

 

[Tony Latham]

Keep in mind, when the hatch is closed, there is a tremendous amount of pressure coming from those springs.

Tony, one more question: regarding your comment above about pressure when the hatch is closed, could you further elaborate? Thanks!

When you close the hatch and compress two one-hundred-pound gas springs, they are exerting that force while closed. So you've got two hundred pounds pushing against the hatch.



Tony

 

[bknowles86]

Thanks - so does that mean the hatch will come flying open when released? Is there some sort of gradual opening option similar to the way a car hatch opens, where it requires a bit of an assist to get it started? Also, what does that mean for the amount of force required to get it closed from a fully open position?

 

[Tony Latham]

Thanks - so does that mean the hatch will come flying open when released? Is there some sort of gradual opening option similar to the way a car hatch opens, where it requires a bit of an assist to get it started? Also, what does that mean for the amount of force required to get it closed from a fully open position?

If the geometry is right, the spring will nearly fully compress and then start to lengthen and hold the hatch closed. Just don't ask me what that geometry is.

Tony

 

[Tom&Shelly]

Thanks - so does that mean the hatch will come flying open when released? Is there some sort of gradual opening option similar to the way a car hatch opens, where it requires a bit of an assist to get it started? Also, what does that mean for the amount of force required to get it closed from a fully open position?

If the geometry is right, the spring will nearly fully compress and then start to lengthen and hold the hatch closed. Just don't ask me what that geometry is.

Tony

Seems to me, if you draw a straight line between the hinge and the attachment point on the galley wall (or maybe a mental straight line), the correct geometry is that, when the hatch is closed, the attachment point on the hatch should be just below the line. I think.

The idea is that the spring is fully compressed when the strut is along the line, so any past and it is slightly less compressed.

But I haven't seen anyone say anything like that on this forum, and it doesn't seem to be something that would happen automatically with a curved hatch (just the opposite). So maybe my thinking is wrong...

Tom

 

[Tom&Shelly]

Sure wish I'd paid more attention to this paragraph in Dan Lott's gas calculator directions earlier:

"To allow for proper mounting support, the attachment points should be figured out early in your build using a drawing program or the old pencil and paper method."

I didn't put enough skeleton in the upper galley portion of the skeletonized walls. I can compensate by attaching the struts to the galley counter, but, in that case, it would be better to make the struts' "extended length" longer than the calculator recommends by an inch or two. Does anyone see a problem with that?

An alternative is to use long brackets to hold the pivots, but, besides being unsightly, there is the structural strength issue, currently being discussed on another thread.

Tom