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cable tension on a hot airplane

seagull

Well Known Member
I am doing my conditional and cable tension check is on the list. The maintenance manual emphasizes that the hangar temperature should be 70f for the test, if not the tension measurement will "change significantly".
My hangar is at 105f and I am getting a reading of 55 lbs, and the manual says I want 35-45 lbs.

Is there a conversion chart for higher hangar temps. I am in CA and it is hot this time of year.
 
Paul,
Good resource, thanks.
That chart is for 1/8 cable at 70 degrees and 62 lbs. Vans wants our cable to be 35 - 45 lbs at that temperature. This would take some guess work to get an exact number. It isn’t exactly linear but looks like in their example a 30 degree rise changes the tension 18 lbs.
 
Your probably ok at 55 lbs at that temp...I'd be more concerned about having less tension instead of a little more ...Vans doesn't want the cables too slack where they sag and rub on structure...best bet is recheck early in the day when not as hot.
 
Based upon Van’s recommended tension and the chart, the values fall in the range for 3/32” cable. What diameter is our stabilator cable?
 
F-01247C/D/E/F stabilator cables are 1/8 7X19, but as pointed out, the correct way to use the chart is to find a curve that intersects the spec from Van's or interpolate between two curves. Based on the chart below I'd say the nominal tension at 105F looks to be about 51lbs. Wouldn't hurt to check with Van's support.
 

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The graphs shown here just seem to align with 3/32” instead of 1/8” cable diameter. Maybe I’m misinterpreting the data or being overly pedantic? I start my condition inspection next month so would like to be sure I’m using the correct value.

I'm certainly no expert, but my impression is that these graphs may not be one-size-fits-all-applications. The only ones I could find were simply described as "examples" or "typical" with no other information, source citations, etc. Note the top of the one I shared says "Values include 10 percent structural deflection." Perhaps that's not a valid assumption for the RV-12? Could be other assumptions behind each plot as well?

At any rate, it sounds like Van's already answered your question, no? Did you share your chart with them to verify that's what they meant? It seems reasonable, although the slope is a little lower than the sample graphs.
 
I had the same question. It's getting hot in Charlotte and I was going to tighten up the cables after my inspection. I assumed when it was hotter the cables would expand and the tension would go down ! Why does the tension go up?
 
I had the same question. It's getting hot in Charlotte and I was going to tighten up the cables after my inspection. I assumed when it was hotter the cables would expand and the tension would go down ! Why does the tension go up?

The expansion coefficient of aluminum in relation to temp is quite high.

The warmer it is, the longer the airplane is.

Since the aluminum expands at a higher rate than the steel cables, the cable tension gets higher when temps are hot and and lower when they are cold.
 
The expansion coefficient of aluminum in relation to temp is quite high.

The warmer it is, the longer the airplane is.

Since the aluminum expands at a higher rate than the steel cables, the cable tension gets higher when temps are hot and and lower when they are cold.

Thanks Scott, I was trying to think of a way to explain in a few words what you said………the reason I asked the question in the first place.

Every airplane has a different length of cable vs aluminum so there is no “one size fits all” formula.
 
I adjusted my elevator cable tension at annual. I guess they stretched a bit over 9 years. I noticed it as a “soft feel” in the elevator control.
 
The expansion coefficient of aluminum in relation to temp is quite high.

The warmer it is, the longer the airplane is.

Since the aluminum expands at a higher rate than the steel cables, the cable tension gets higher when temps are hot and and lower when they are cold.

Ahhh! That makes sense Scott!
 
Update

I was able to get a 70 degree morning and checked the cables, they were 43 lbs.

For those that may be in the same situation I was in the hangar with an inside temperature of 105f and the cables measured 55 lbs. with no adjustments when the ambient was 70f they measured 43 lbs.
 
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