Pull tests

Pull tests, properly done, help provide assurance that the model is safe to fly as well as perhaps warn the flyer of an incipient failing line or other control device before his ship gets splattered on the asphalt. All in all a good deal.
Note I said "properly done". Unfortunately, all pullers are not always up to speed on proper pull testing. I have personally had a couple of bad experiences and am aware of some others.
This is not a knock on the testers as they are earning way under minimum wage, stand in the sun most of the day, sometimes are prevented from flying if the demands on their time are great, etc.
Instead, perhaps an admonition to CD's to brief the testers on proper proceedure, etc. A wise thought I heard was that if you think you are pulling the proper weight and are urged to pull more, stop and recheck with the tester to be sure ya'll are on the same page.
This is wise. If you are directed to pull harder than usual-stop pulling!
The pull test device at the VSC seems foolproof but there is still the chance that an improper setting could be used. Other devices are also subject to failure so it is not a totally human failure problem either.
Comments?
Jim

Actually, this could be the subject of a safety column in Stunt News. What kind of pull testing equipment are we using for our various contests, and which designs are safer to use. And then, we are all supposed to be pull testing our lines even when we go out to fly in non-contest situations, which of course we all do religiously, yes? (no?) The truth of the matter is, even at the Nats, you don't see people pull testing their lines when they go out to practice. What type of testing equipment might we use for these purposes? If anyone has pictures, sketches, or simply ideas, maybe they could post them here and send me larger pictures by e-mail. This should be in keeping with the thoughts of this post. What do we do (or should we do) for pull tests?

Len,
Out here on the West Coast, pull test rigs seem pretty popular. The photo shows a version that was used at the 2008 Cabin Fever Racing contest. Very similar versions are used by the Knights Of The Round Circle and by the Valley Circle Burners. Once calibrated, they seem to work well. The VCB version has a switch and a buzzer so that when the flier lifts the weight they know when to stop pulling. Works good if no engines are running and if the flier isn't deaf yet. :)

Dave "McSlow" Hull
LA_Flyer

[photo not recovered: 29122.jpg]

Attachment #1, (jpg file)

Looks similar/identical to the device used at the VSC. Seems to shrink error margin, perhaps to zero assuming it is set properly.
I like it!
Jim

>Looks similar/identical to the device used at the VSC. Seems
>to shrink error margin, perhaps to zero assuming it is set
>properly.
>I like it!
>Jim

It should look similar, it's the same one!

This tester works fine for the current stunt pull tests. It will NOT work properly for pull tests that vary according to the weight of the model. At CabinFever, we used this tester and just set it at one of the pre-set values that would cover the needs of a specific event.

Bill Lee

>This tester works fine for the current stunt pull tests. It
>will NOT work properly for pull tests that vary according to
>the weight of the model. At CabinFever, we used this tester
>and just set it at one of the pre-set values that would cover
>the needs of a specific event.
>
>Bill Lee


How about adding a sliding platform for the weight. That way it could be adjusted for pull tests that vary according to the weight of the model.

>Len,
>Out here on the West Coast, pull test rigs seem pretty
>popular. The photo shows a version that was used at the 2008
>Cabin Fever Racing contest. Very similar versions are used by
>the Knights Of The Round Circle and by the Valley Circle
>Burners. Once calibrated, they seem to work well. The VCB
>version has a switch and a buzzer so that when the flier lifts
>the weight they know when to stop pulling. Works good if no
>engines are running and if the flier isn't deaf yet.

Perhaps you could add a light to this along with the buzzer. Even if the flyer were deaf (or sound was drowned out by other motors running, he could still see. And if he is blind...well, he is probably not flying.

>[photo not recovered: 29122.jpg]
>

Note that this type of pull tester has the handle end fastened about 12" above the ground. Now, the flyer/owner typically stands (!) some 60 feet away with the model approximately 4 to 5 ft. off the ground and ABOVE the elevation of the handle. Now, a little trigonometry here. You are ACTUALLY pulling MORE than required if you hold the model while in a standing position. Therefore, I always hold the plane while in a kneeling position with the lines as close to horizontal as my knees will permit.

Floyd

A 25 # pull test at that angle (3'/60'=2.86°) is 25.03# actual on the lines, insignificant!

don Burke
Menifee, CA
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways - body thoroughly used up, totally worn out and screaming, WOO HOO, What a Ride!

How and where do you hook the plane up for pull testing?
Do the ropes go around the fuse. fore and aft of the wing?
I've only seen the two-man/ fish scale method.

Doug,
The contraption just replaces the fish scale. The underpaid, (sometimes maligned?) pull test official first arranges the appropriate weights on the horizontal arm of the contraption, then loops the rope thru the handle and the pilot/owner holds and pulls on the plane.

Dave Hull
LA_Flyer

>Len,
>Out here on the West Coast, pull test rigs seem pretty
>popular. The photo shows a version that was used at the 2008
>Cabin Fever Racing contest. Very similar versions are used by
>the Knights Of The Round Circle and by the Valley Circle
>Burners. Once calibrated, they seem to work well. The VCB
>version has a switch and a buzzer so that when the flier lifts
>the weight they know when to stop pulling. Works good if no
>engines are running and if the flier isn't deaf yet.
>
>Dave "McSlow" Hull
>LA_Flyer
>
>[photo not recovered: 29122.jpg]
>

I don't like these type of pull test machines.

Why?

It takes more than the "set" weight to actually get the weight moving.
The larger the ratio between the two arms, the worse they are.

( The static force would be the arm ratio times the weight, but to get it to move you have to accelerate it.
The rate of acceleration of the weight compared to what you apply to the model is also multiplied by the arm ratio.
So the force you have to put in to actually get the weight to move can end up being proportional to the square of the arm ratio.)


A 1:1 ratio would be the best.
At the Muncie W/C for F2D the machine had a huge ratio, about 10:1. It felt like you were pulling against a brick wall.

If you are forced to use one of these machines pulling very slowly will minimize the error.

Spring scales are by far the best since they eliminate this error.

Pat MacKenzie

>Spring scales are by far the best since they eliminate this
>error.
>
>Pat MacKenzie
>

At the Nats they used a pully arrangement with a weight that you changed for the varioius pull tests. This should be linear. And the force that you pull never exceeds this amount (unless you jerk it). It has a light and buzzer that activates as soon as you have "lift off". Lift it off fractionally, and set it down. That's it.

The problem with spring scales is there is no upward limit. You can pull and far exceed the needed pull test and actually damage your plane because of the excess force exerted.

I have a feeling that if you feel that you are pulling against a brick wall using one of the above pull testers, that your plane doesn't have much pull in flight so the pull test seems very excessive. Matt says his plane feels like it will actually out pull the pull test at times. I remember watching one of the Juniors fly at the Nats once. A scrawny little guy. He had to lean way back just to hold on to the plane while flying level. Did a real good job, though. Some of these planes pull a little more than others.

The official pull test in England is completely invalid and useless, assuming it is intended as a safety measure, e.g. to reproduce the conditions that would apply if a flyer let go the handle. I believe our pull test is copied from the American one.

>The official pull test in England is completely invalid and
>useless, assuming it is intended as a safety measure, e.g. to
>reproduce the conditions that would apply if a flyer let go
>the handle. I believe our pull test is copied from the
>American one.

Huh? Let go of the handle? That's why you pull test the thong, too, but never have I heard the opinion that the pull test has something to do with letting go of the handle.

Brett

Speaking of pull tests, did anyone happen to notice that pull test for the Perky given in the new MA? It says 25grams, me thinks 25lbs to be more appropriate. What say ye?


Randy Ryan <><
AMA 8500
SAM 36
BO all my own M's

I didn't look (so could be wrong), but I think it may be 25 "g"s, not g(rams). So a 1 lb Perky would pull 25 lbs, a 2 lb Perky would be 50 lbs (and be seriously overweight!).
Remember in speed they actually try to go faster than 5s laps!!

Randy,
You are right, it did say "grams". I tried to check various places for more info (Perky is an unofficial event) and got more confused. I have seen both 25 lbs and 25 g's. It doesn't help that a Perky is a little over one lb in weight, so it is hard to infer what the rule is meant to be. I am pretty sure 25 "g" is correct. Also there may be more than one version of the rules since it is an unofficial event.

Still need to get mine finished!

Brett,
It is possible that what Ian is saying is that since the pull test has to be performed by the pilot, it is a demonstration that he possesses the strength to hang onto the model. It doesn't seem particularly representative on small stunt models, but it certainly is for speed models. I don't think I have the body mass to pull a D-speed or jet--so I don't get to fly them... :(

The safety strap mitigates this by containing the bulk of the wreckage to the circle even if the pilot loses grip or control.

I tried to raise a related question here on SSW a while back when the allowable engine displacement was increased for stunt. Apparently I worded my question poorly because the universal response was that you won't get a unmanageable flight (excessive pull) because you use a low pitch prop/high rpm setup and etc., etc., etc. Since all the likely users of monster motors are probably expert stunters and I am not, I quietly folded my tent. I KNOW you can get a runaway on smaller planes. A really good runaway on a .40 can be an 8 minute strength trial. I remain unconvinced that you "can't" get a runaway on a .76 or a .90 or a ...? In which case, we are back to whether the pull test is representative of the load at the maximum speed for the least tolerant setup.

What say you, Ian?

Dave "McSlow" Hull
LA_Flyer

Another much more likely scenario is when a flyer has trouble with a warp or gusty wind and the plane comes in and cuts across the circle. Any plane that can pull 8-10 lb. in level flight can hit the end of the lines with easily enough force to snap at least one line, usually followed quickly by the other line breaking.

Dave,
Having experienced 4 second per lap "runaway" with ST60s and 70+ oz airplane I can tell you that the pull is enough to make one very tired by the end of the flight. Certainly not in the category of a D speed model, but enough to make my 200+ lbs lean a little. It is likely more than the pull test....but not a lot.

Randy C [photo not recovered: sipcof.gif]

>Dave,
>Having experienced 4 second per lap "runaway" with
>ST60s and 70+ oz airplane I can tell you that the pull is
>enough to make one very tired by the end of the flight.
>Certainly not in the category of a D speed model, but enough
>to make my 200+ lbs lean a little. It is likely more than the
>pull test....but not a lot.
>
>Randy C [photo not recovered: sipcof.gif]

So what is your point concerning the original thread, other than to tell your rather boring little story?

>>Dave,
>>Having experienced 4 second per lap "runaway"
>with
>>ST60s and 70+ oz airplane I can tell you that the pull is
>>enough to make one very tired by the end of the flight.
>>Certainly not in the category of a D speed model, but
>enough
>>to make my 200+ lbs lean a little. It is likely more than
>the
>>pull test....but not a lot.
>>
>>Randy C [photo not recovered: sipcof.gif]
>
>So what is your point concerning the original thread, other
>than to tell your rather boring little story?
>

Well....
Since you're an Idiot I'll patiently try to explain it to you.
Dave made the point that runaways could increase the pull of the airplane. I simply confirmed that they do in fact happen and they do increase the pull significantly beyond what would be considered "normal". However, my opinion is that it is unlikely that it is more than the 40 lbs used for the pull test.

Understand????

Now go resurect some other very old thread and take someone else to task. After all you must uphold your reputation.

Randy C

>(snip)A really good runaway on a .40 can be an 8
>minute strength trial. I remain unconvinced that you
>"can't" get a runaway on a .76 or a .90 or a ...? In
>which case, we are back to whether the pull test is
>representative of the load at the maximum speed for the least
>tolerant setup.
>

Sure, it is possible to get a runaway on any engine set-up You get dirt in the needle, injest a bug in the venturi, whatever. However, airplane speed is still a factor of rpm and pitch. Whether you get a runaway with a 40 or a 75 using the same set-up, the rpm and prop pitch will still be very similar--as will be the flight speed of the airplane. And even if you are using a bigger prop, you will get better "grip" in the air, but when you are at a certain speed, you are at a certain speed. All in all, it shouldn't make a lot of difference. (And the 75 is using heavier lines and subject to a greater pull test than the 40).

Cant see why anyone would be scared of a bit of overkill in the
control system mounts.

Having old 4mm titanium bolts , I epoxy and brace the B/C mount.
And attempt to have continuity structuraly to the fuse doublers.

A sacrifice of a few extra ounces thereabouts is money well spent.

If the plane does cut across the circle,its preferable the controls dont get sucked up the inside wing. They tend to bind like that.

If the plane can hack it on a pull test , and the lines dont ,
youve potentialy saved yourself an aeroplane .

If you look at the pull test as a Minimum Requirement , youve
the option of putting it together to take TWICE the 'minimum' .

Its not a bad idea ,if you indulge in 'any weather' flying .

A piece of 1/2 x 3/8 engine bearer epoxied to inside the iner fuse. side, running down through the bellcrank mounting platform,with no
overhang (moment) on the bolt. should stay in in most forseable coditions.

I think most of us remember seing the odd team racer or stunt ship doing a 'Hard Left' , and 'wot happened' at the other side,when it was compelled to do a ' hard right ' .

Fair weather flyers , disregard all of the above . ? .

Actually the above scenario was usally observed in ' Fair weather '.

Such is life .

I prefer the system to be of sufficient strength to enable a test of the 'line stretch ' , or ,to find the line 'elasticity'.In tecnical
terms.

Sorry guys. Apparently I do not know how to post a picture file of a table.

For comparison:

Dave Hull
LA_Flyer

[photo not recovered: 29150.jpg]

Attachment #1, (jpg file)

Jim,
I was busy doing most of the pull testing at the NW Regionals, let alone flying, runner, tabulator and what not. At least that's how it started out till I got some other helpfull ladies. I had a real nice pull testor that Scott Riese uses, wish I had a photo of it for ha. It was a slick fish type scale, a black tube about 1" diamater X 10" long. It had two finger type hooks to set around the handel, the other end a T handel to pull with. The tube had a plastic slider that was around the tube that could slide to a preset marked position fo the certain engine size. The idea was to first ask the flyer what size engine was on the plane, hook the two fingers on the pull tester to the handel and when the flyer held the plane up, most of the flyers seemed they wanted me to do the pulling, which I find it better that the flyer holding the plane should do most of the pulling, then when the marker on the pull testor marks the test point that is when I gave the slack and it was done. Some flyers had no fear and pulled away which was the way to go. All pull tests had no problems.

> Huh? Let go of the handle? That's why you pull test the
>thong, too, but never have I heard the opinion that the pull
>test has something to do with letting go of the handle.
>
> Brett

In England we have to use a thong, which is a safety device. A thong only comes into play if for whatever reason you let go the handle. To be relevant a pull test should test the conditions that will apply if the pilot does let go the handle, so the system should be pulled duplicating these conditions. That means as one, holding the thong one end and the model the other. For some reason most pilots in England attach the thong at the bottom of the handle, so if the pilot lets go, all the load is applied to the down line. Ergo that is how the system should be tested. Testing the lines to model first, applying the load through both lines, then testing the attachment of the thong to the handle separately, does not test the conditions which will apply. With the thong at the bottom of the handle, if you let go you get a snatch loading on the down line alone, whereas you have tested the system with the load being shared between both lines. Bad practice. Personally I attach the thong at the middle of the handle so any snatch loading is shared between both lines, and hopefully the safety factor has taken care of the rest. No it doesn't feel uncomfortable, the palm of the hand is "cupped" to a small degree and the knot can sit quite comfortably in that space. I do recess the knot into the handle a little also.

>
>In England we have to use a thong, which is a safety device. A
>thong only comes into play if for whatever reason you let go
>the handle. To be relevant a pull test should test the
>conditions that will apply if the pilot does let go the
>handle, so the system should be pulled duplicating these
>conditions.

Oh! I hadn't thought of that.

Brett

I get strange looks because my leather safety thong is connected to the UP-side of my handle. Here's my reasoning: chances are if the handle is somehow let-go the plane will pitch up because upright flying is the flight attitude in the stunt pattern more often than inverted. So maybe a recovery is possible. If the thong is on the down side, the ground comes up much quicker if you are in some sort of non-inverted attitude.

I've never had a plane come in at me and then snap at the other side of the circle. But if that ever happens, you can bet that my handle grip would suddenly increase by 500%, because that would be the natural reaction.

If a line breaks, well, it doesn't m atter WHERE the thong is connected; you are not going to save it.

Floyd

Dr. S,
Strange things can happen when faced with that situation. Your comment about increased grip when the plane transits the circle is probably a natural instinct. But it probably won't help most of the time. Why? Can you hold your handle and break the lines during a static pull test?

Cross-circle "excursions" seem to happen more often with racing planes, where experience has shown that:

(1) After you have lost the battle trying to extend your arm to regain tension and the lines are loose you need to get the handle back close to your chest or at least pointed 90 degrees forward of the airplane.
(2) When the plane approaches the end of the lines again you need to let your arm give, softening the jerk and reducing the line loads. It helps to step toward the plane at the same time.

Certainly no guarantee of recovery, but you do the best you can in a bad situation. And don't give up until the engine quits running and the pile of balsa chips stops moving! It seems like the natural reaction is to get a death-grip on the handle anticipating the jerk. The strong grip isn't a bad thing, but almost invariably, the arm is mostly extended pointing at the plane and all the muscles there are tensed up (rigid) too. A sure way to break some part of the control system. Pull the handle back in close and relax the arm to reduce the jerk. You have to train past the instincts. Easy to say, but some fliers have demonstrated they can do it.

Dave "McSlow" Hull
LA_Flyer

Looking at the combat column in Flying Models. Combat fliers have the thong in the center of the handle, and use a short thong in the hopes that if they lose the handle it won't go very far, and they can recover it before disaster.

Yes, you can break two .018" lines without letting go of the handle. I've done it hundreds of times. You stunt guys are a bunch of armchair line breakers.

Howard Rush
Bellevue, WA

Yes, it's amazing how much force a piloto can exert on the lines when faced with a blind panic!

>>The official pull test in England is completely invalid
>and
>>useless, assuming it is intended as a safety measure, e.g.
>to
>>reproduce the conditions that would apply if a flyer let
>go
>>the handle. I believe our pull test is copied from the
>>American one.
>
> Huh? Let go of the handle? That's why you pull test the
>thong, too, but never have I heard the opinion that the pull
>test has something to do with letting go of the handle.
>
> Brett

You don't get it..it's called the "letting go test" in England.Those limeys actually have lower IQ's than Texans

Saw on another forum that if you google safety thongs you get some interesting results.