Pull Test Machine

[frank williams]

One of the best things I did this winter was to build a copy of the Tulsa Gluedobbers pull test machine from the Bob Reeves plans available on this site. http://stunthanger.com/smf/index.php/topic,12162.0.html It has ball bearings at the fulcrum and an easy a/c weight scale pointer.

This thing is great!  You know you've had a pull test, but not a potentially destructive event.  The trip drops the flag instantly and there is no fear of over pull by either the puller or the flyer.  Thanks Bob for a great design. 

This thing is better than sliced bread.  Even the design of leather handle holder is superior to others that run the risk of slipping to one side or the other and putting all the load on one line.  A great design.  We used it at this years Houston contest and it was far better than the usual fish scale we have used in the past.

PAMPA should invest in a pair of these for the NATS.

[bill rutherford]

Frank I did not know that you made the pull tester. Good on you.  Bill

[sleepy gomez]

I too have made a pull tester. See attachment.

[BillLee]

One of the best things I did this winter was to build a copy of the Tulsa Gluedobbers pull test machine from the Bob Reeves plans available on this site. http://stunthanger.com/smf/index.php/topic,12162.0.html It has ball bearings at the fulcrum and an easy a/c weight scale pointer.

This thing is great!  You know you've had a pull test, but not a potentially destructive event.  The trip drops the flag instantly and there is no fear of over pull by either the puller or the flyer.  Thanks Bob for a great design. 

This thing is better than sliced bread.  Even the design of leather handle holder is superior to others that run the risk of slipping to one side or the other and putting all the load on one line.  A great design.  We used it at this years Houston contest and it was far better than the usual fish scale we have used in the past.

PAMPA should invest in a pair of these for the NATS.

Works great until you want to pull a model weighing less than 36 ounces. 

[frank williams]

I too have made a pull tester. See attachment.

Hi Sleepy
I was going to also make one using a digital torque wrench module.  They are cheap, about $30, and I was going to tap into the readout to light a light when the pull was accomplished.  I never got the light circuit finished, but I realized that the "Tulsa Guledobber" machine had the benefit of never pulling more than the test limit.  The torque wrench method, if exceeded past the signal, will keep on applying more load.

Bill
I need to make the scale a little bit longer on the low end.

[Bob Reeves]

Frank, happy to hear about your success. Ours have really worked out well, everyone that comes to Tulsa really appreciates the safe, accurate and easy pulls tests.

[Allan Perret]

I used it in Houston, works great.  Every club that puts on contest should build one for their site.  Only thing that might be a hassle is contest sites where they have multiple pits, unless it is portable enough to move from one pit to another.

[Mike Anderson]

I too have made a pull tester. See attachment.

Note that this will work correctly only if the torque wrench is set to click when the (Applied Force) x (L) exceeds the required pull.

So if L is 1 foot, then set the wrench to the required pull.  If L is other than 1 foot, you must set the wrench to F x L lbs.

[sleepy gomez]

Hi Mike, I should have mentioned that I use a 1/2" drive wrench.  At the handle the wrench set at say 40 will click at a 40 pound pull.  I use my torque wrench to torque bolts at as little as 20 pounds.  The click is still there but it is soft. 

[Mike Anderson]

If you set the wrench to '40', it will click at 40 ft-lb of torque, not 40 lb of force.  If the handle is 1 foot long, then 40 lb of force is 40 ft-lb of torque but if the handle is longer, then 40 ft-lb (and the click) will happen at LESS than 40 lb of force.  For instance - if the handle ("L") is 2 feet, then 20 lb of force will produce 40 ft-lb of torque (and a click).  If a piece of pipe 4 feet long is slipped over the handle, then only 10 lb of force will click the wrench set to "40".  Likewise, a 6 inch handle would require 80 lb. force to clilck the handle, if set to "40". 

[sleepy gomez]

Hi Mike, I don't think you understand torque wrenches. Go to the store and look at a 1/2" drive torque wrench.  40 pounds of torque will be 40 pounds of pull at the handle.  I can assure you that 40 pounds of torque will require 40 pounds of pull for the click.

[Mike Anderson]

Hi Mike, I don't think you understand torque wrenches. ...

I understand the difference between torque and force.

[Bob Reeves]

I can see what Mike is saying, my understanding has always been torque wrenches are calibrated in either inch pounds or foot pounds. One Foot pound is one pound of pull at one foot. The scale on the wrench is calibrated to compensate for the handle length. If the handle on the wrench is two feet long then you are doubling L. Now if the wrench is set to 1 Foot Pound you are actually only applying 1/2 pound at the handle.

In any case I don't care for the idea, even if the pull is accurate I would bet 9 times out of 10 (maybe 10 of 10) the airplane is over pulled simply due to human reaction time. Also Click torque wrenches are only accurate if you ease off the spring and reset every time. Last but not least is you still have to do the math, ounces to pounds etc.

The Tulsa pull test machines though a little difficult to build eliminates every short coming of any pull test system being used.
No math, the only number that has to be known is how much the airplane weighs in ounces.
Impossible to over pull an airplane.
Under pulls do not happen because the guy holding the scale with his fear of breaking something is eliminated.
Sliding weight means no compromises (however small) as sometimes must be made with fixed weights.
You simply can't get more accurate than moving a known weight at a given distance.

The down side is complexity and portability.
Frank made a few changes from the original design using material and means he has access to which is great. Am sure it reduced the build time without compromising accuracy.
Potability is a real problem, we solved it by building three machines but fully understand the reluctance to build just one much less two or more.

[frank williams]

The first thought I had when starting the build was, "where and I gonna get all this metal? .... I'll be driving around town for days trying to gather it up."

No problem ... speedymetals.com ..... I'd like a piece of 2x6x9 inch cold rolled steel  (weighs about 30 lbs)..... some 1x2 steel tubing ... some aluminum channel and some blocks cut to 1x1x2 .......  bingo, a few days later it arrives on the doorstep ... all cut to size ready to start construction.

I had to pay more than I thought I would for the welding ($55 to strike an arc) I know that if you know someone that can be done cheaper.  The leather was from HobbyLobby.  They sell assorted leather scraps in bags for a couple of dollars.  While I was at it I used some of the leather to make some nice "finger sheaths" for engine starting .... stitched up with kevlar thread.

[Howard Rush]

As a person who has made some pull-test machines, I'm impressed by Bob's.  He is one clever guy and really not all that grouchy.

[dale gleason]

I haven't won many contests, but I've flown in a lot of'em- Bob Reeves' pull test machines are "the best, Jerry, the BEST!"
Frank's in Houston worked exactly the same as Bob's in Tulsa. They should, they're the same. They beat fish scales, cotton scales, lever scales, pulley scales and strain gauges. Smooth, no "stacking", no "over-center". I sneaked in a test of my own to check for accuracy, they are dead-on, but so smooth it seems like a lesser pull. If AMA had these on the "L"Pad, Linda Bob wouldn't have to lift all those different weights for each and every pull test, just slide the pointer to the weight on the scale, let the pilot drop the flag, done.

Thanks, Frank, nice contest, maybe better wx next year, or the next...

dg

[Joseph Patterson]

  Dale, you are right on!! They should have a couple of these at the NAT'S. They are so easy to use for the pull testers, so quick, accurate, and a lot less abusive to the airplane.
           Doug 

[Doug Moon]

...grouchy.

That word makes me laugh every time I see it.  Haha!!

[Doug Moon]

"the best, Jerry, the BEST!"

 

[Andre Ming]

Works great until you want to pull a model weighing less than 36 ounces.

Not a problem. The two times I've flown at our (Gluedobbers) field, I pull tested all of my sport-flyer vintage combat ships, the heaviest is about 18 oz.  Worked great.

The Reeves/Gluedobbers pull testers are the Cadillac's* of the pull testers.

* Spare us the berating of what Cadillac may/may not be now/etc, I merely used the term to mean "the cream of the crop".

[pmackenzie]

The Tulsa pull test machines though a little difficult to build eliminates every short coming of any pull test system being used.
No math, the only number that has to be known is how much the airplane weighs in ounces.
Impossible to over pull an airplane.

It is very easy to over pull, just pull quickly and the inertial loads will be far higher than the static ones. Or  once it trips let it back down and then stop before it hits the bottom stop.
This gets even worse if there is any mechanical multiplying going on, since the inertial loads will go by the square of the ratio of the two arms.
At one F2D W/C they had a machine that had about 10:1 ratio, and it felt like you were pulling against a brick wall

I would take a spring pull any time over these sort of machines.
If you find yourself at the end of one of these machines do yourself a favour and pull very slowly

Pat MacKenzie

[Bob Reeves]

It is very easy to over pull, just pull quickly and the inertial loads will be far higher than the static ones. Or  once it trips let it back down and then stop before it hits the bottom stop.
This gets even worse if there is any mechanical multiplying going on, since the inertial loads will go by the square of the ratio of the two arms.
At one F2D W/C they had a machine that had about 10:1 ratio, and it felt like you were pulling against a brick wall

I would take a spring pull any time over these sort of machines.
If you find yourself at the end of one of these machines do yourself a favour and pull very slowly

Pat MacKenzie

You have got to be kidding 

[BillLee]

Kidding about what, Bob?

Pat is dead-on with his concerns about the inertial load and his suggestion about always pulling slowly and steadily.

Perhaps his reliance on a spring pull tester?

[Bob Reeves]

Kidding about what, Bob?

Pat is dead-on with his concerns about the inertial load and his suggestion about always pulling slowly and steadily.

Perhaps his reliance on a spring pull tester?

Only an idiot would do anything he is suggesting. I better just leave it at that as everyone already knows I'm a grouchy old man.

[Howard Rush]

Pat has a point, and it's my fault.  The F2D pull tester at the 1990 world champs was a clever linkage that caused a lever to pop up from the ground when the pull reached the prescribed value.  It took less force to hold the lever up than it did to get it to rise initially.  This device was so cool that I copied it for the Bladder Grabber, where we used the copy successfully for many years.  I never noticed any adverse inertial effect.  I helped Pat Willcox make one for F2D for the 2004 world champs.  I must have gotten the dimensions wrong, because lots of people, many of whom are not idiots, hated it.  I'm sure Bob's doesn't have the inertial trouble that the 2004 F2D machine had.

It would be wonderful to have a couple of Bob's for the Nats.  An alternative would be to hack a strain-gauge luggage scale, http://www.amazon.com/WeiHeng-Portable-Digital-Hangging-Luggage/dp/B00FDO6F7K  , and have the pull tester dial in a value on a pot such that a light would come on at the requisite pull.  I'm fixing to hack a pair of these scales to measure differential line tension, hence stunt hinge moment, but don't hold your breath.

[BillLee]

Only an idiot would do anything he is suggesting. I better just leave it at that as everyone already knows I'm a grouchy old man.

Or someone trying to prove that pull testing damages models.

[john e. holliday]

I always thought the pull test machines in Tuscon at VSC worked pretty good.  Right Bill Lee.

[pmackenzie]

Only an idiot would do anything he is suggesting. I better just leave it at that as everyone already knows I'm a grouchy old man.

Unless I missed something the only things I suggested were pulling smoothly, and backing out without stopping. 

FWIW they used both spring and weight based machines in Poland. The former in F2B the latter in F2D.
In F2D they had a very short vertical arm and it was low to the ground. By standing up when you did the pull you could "game" the system a bit
Pulling against the spring in F2B was a non event.

The machine in the OP at least uses a heavy weight, so the inertial ratio is fairly small.
Just for fun change the weight to 5 pounds and move the handle mount down on the arm to 3.3 " and you will see what I mean about pulling against a wall.
The static forces are the same, but the inertial ones will be 36 times higher for the same rate of acceleration. (Not allowing for any increase due to the weight of the horizontal arm)

I assume they build the high-ratio machines to make them lighter and more compact.

[FLOYD CARTER]

These high-zoot pull machines are OK, but:

WHO'S AFRAID OF A PULL TEST?

Certainly not me.  My control systems will survive any method of pull test.

I'll be happy with a spring scale.

Floyd

[sleepy gomez]

Dear Bob Reeves,  I strongly resent being referred to as an idiot.  I am proven to be more intelligent than 96% of the populace.  Unless you are proven to be in the top 4% I suggest you shut your idiot mouth.  If you are in that 4% then I can understand your making complex things, like some engineers you just throw more parts at until it works.  I post on this forum hoping to help someone.  Maybe it is just because I am not a name or famous flyer that I get picked apart.  I strongly resent negative comments from people who have not tried or used things from my posts. This has been done before on this forum by one of the gurus.

I SHALL POST NO MORE,  GOODBYE  SLEEPY   

[Dane Martin]

Wow, sleepy. Chill.
Being in the much lower 96% I read that completely different. In fact, Mr Reeves comment was not directed at you in any way
I read it as " only  an idiot would jerk his plane against a pull test". Of course we want to pull slowly. In fact, his comment was
a reply to another individual about a method of pull testing. Not your torque wrench tester. In fact, most of us would agree the
torque wrench method works great when used properly.
I am not trying to speak for anyone, But mr Reeves has helped me a lot through this forum, and I find him to be a great person
to deal with. Been in some contests with lots of his friends also. Seems like a nice knowledgeable guy to me.

[Bob Reeves]

Hi Sleepy,

Sorry you took what I said personally, really wasn't aimed at anyone specific. If you look at it from a different direction I was really saying I believe CL people are sharp enough to not jerk on the airplane or drop the weight then try to catch it. Now wished that is the way I would have said it in the first place.

Like you, I kinda got a little defensive when someone pointed out a possible short coming, don't you call my baby ugly gerrrrrr 

[BillLee]

Sleepy, you say that you use a 1/2" torque Wrench. Can you supply me the dimensions of the wrench? Specifically. the distance from the center of the socket to the handle attachment point?

Both of my 1/2" torque wrenches are about 18" long, is yours the same?

[frank williams]

This is what I was hacking to make a pull tester.
http://www.harborfreight.com/12-in-drive-digital-torque-adapter-68283.html
Inside its a 3" extension with strain gauges attached and some electronics.

[Howard Rush]

This is what I was hacking to make a pull tester.
http://www.harborfreight.com/12-in-drive-digital-torque-adapter-68283.html
Inside its a 3" extension with strain gauges attached and some electronics.

It already has a P/T button, presumably Pull Test.