What Device is used for Pull tests?

I really don't have a clue to what device is used for the tests. I remember as a kid I had a fish scale that weighed up to 3o pounds, attached to the fish and then holding the other end with my hand, it was spring loaded. Advice more than welcomed.
Thanks.

Paul H.

Some people still use fish scales.
A more accurate approach involves a pulley and a weight.

I believe that an accurate fish scale is terrific....the key is to have the competitor pull the model against the scale. That way he may determine if there is a problem.

I would take the pulley / wheel contraptions being more accurate to task....they are even more susceptible to error and problems because there is more stuff going on. I know that Woody and Warren spend a whole lot of time making sure that the units at the Nats work properly....

See Ya

>I would take the pulley / wheel contraptions being more
>accurate to task....they are even more susceptible to error
>and problems because there is more stuff going on. I know
>that Woody and Warren spend a whole lot of time making sure
>that the units at the Nats work properly....

I think it's good that they are very careful for the Nats.

But I wasn't proposing anything complex.
A thirty-pound weight sitting on the ground,
a little framework supporting a pulley above,
and a piece of wire making a 90-degree bend around the pulley.
KISS and all that.

Unfortunately, "fishing scales" are terribly inaccurate. Digital fishing scales may be accurate for awhile (or not), but they don't seem to be consistent over a period of years. The only fishing scale worth carrying home is a "Chatillion", available from Cabela's for at least $50, and they need to be calibrated before use. My bass fishing club has a scale calibration program, and I have run that program in past years. It was quite an eye-opener.

The "pulley and weight" or "lever and weight" type pull scales need to be operated by somebody who can read the pull test for various engine sizes, and can deal with the math. The ED needs to put the engine size on the info on the clipboard, next to the flier's name. Then too, the weights need to be calibrated, and friction needs to be allowed for. It's not "Rocket Science", but it could surely be a problem if the weights (typically weights from barbell sets) are not calibrated and there is no adjustment for friction. Steve

The ones used at VSC are really cool. A weight is placed on a board at a precalibrated spot (and held there with a pin). The board lays flat on the ground and has a perpendicular upright (I know, redundant) that the plane pulls against. Due to geometry, once the weight gets off the ground, the pull gets easier. No reading scales, only one hinge, can't overpull. Can be used solo if the thing is anchored to the ground. Contact the Cholla Choppers for plans, OR call me tomorrow and have me go dig through the office and I'll FAX them to you! OR email me a suitable fas number. If you don't get it soon enough, FOLLOW UP, I'm not known for my superior administrative acumen.

At VSC, the pull tester operator usually slips his fingers underneath the weight as soon as they'll fit and lifts up on it. That signals a successful pull and TOTALLY eliminates any chance for an overpull. The puller can immediately feel the slack and knows it was a good pull.

Mike Danford
817 313 1593
706 375 7092

Several years ago, Bob Emett (snowbird in the Tucson area) took a thought I among others raised at a Cholla Choppers monthly meeting and developed it into what is used at the VSC and other Tucson contests...

Using the AMA pull test schedule, and a few barbell weights, we came up with a simple "leverage" pull tester. The vertical arm is a known value, and FIXED to a horizontal base with pegs for standard weights. A little 4th grade arithmetic finds the ratio of the vertical arm and the horizontal arm is used so that a 5 lb pull for a 1/2A needs no further weight and the other AMA values need a 5 or 10 lb weight on various pegs to match the required total pull.

The vertical and base arms are pivoted at their intersection, so when the model is pulled against the vertical arm, ANY lift off the weighted base means that the lines, bellcrank and clips have met the required pull.

Doodle it out! No pulleys. No (whatever accuracy) fish scales.

All that is needed is the AMA rulebook and some arithmetic. We have the pegs marked for which weight on which peg matches the engine displacement. The pull test guy just checks with the flier about the engine displacement, places the right weight(s), and lets the guy lift the weights off the baseboard.

Saves a lot of worry about things...

That's what we use for the Bladder Grabber combat contest. I copied it from one I saw at the 1990 WC. I have committed to make one for the 2004 F2D WC. I'll post a picture or drawing one of these days, but I think the device is in the attic now, where it spends the winter.

Here's a picture of the one I made from Bob Emmett's plans. Very clever, in my opinion. It's easy to transport, cheap and easy to make, easy to adjust, and takes only 15 pounds of weight to handle all the different pull-test requirements. You can stand on the longer board during the pull, or nail it to the ground if you want flyers to come to you.

Commercial: "Folgers for that real pick me up." Sorry, couldn't resist.

Another advantage is that it helps measure line length, too. The handle holder is in a fixed position until the requisite pull test force is applied. Well, it's an advantage in combat, where all have the same pull test, so the handle end can be left unattended. The pull test officer sits at the airplane end-- farther from the circle, hence safer-- and checks line length while he's pulling.

>The vertical and base arms are pivoted at their
>intersection, so when the model is pulled against the
>vertical arm, ANY lift off the weighted base means that the
>lines, bellcrank and clips have met the required pull.
>
>Doodle it out! No pulleys. No (whatever accuracy) fish
>scales.
>
>All that is needed is the AMA rulebook and some arithmetic.
>We have the pegs marked for which weight on which peg
>matches the engine displacement. The pull test guy just
>checks with the flier about the engine displacement, places
>the right weight(s), and lets the guy lift the weights off
>the baseboard.
>

And, ideally, as soon as it lifts, the force begins droppping off, so it's self-limiting.

Emmit taught Ted Fancher everything he knew -except how to put an overflow tube in his fuel tank! Watching Bob fuel his airplane is like watching Trostle start his; both require about a dozen carefully practiced gynmastics moves.

The fishing scale is OK, just you need precise pointer – like I got on my scale.

The front side till 100 kilo with big hook is called B-17 side – it is also for heavy 4C 15 ccm fighters - bombers, but I use backside with smaller hook for my light subtle LA powered ships – 16 kilo is far enough.

igor

… I am running back to museum

Thanks for all the input.
I like Igor's neat pictures of his scale.
Paul H.

We use professional spring scales at work for human factors evaluations. I assume they are pretty accurate. I know for sure that they are pricey. Currell