A weighty situation

[Brett Buck]

In all my time in this sport, the very few failures I’ve seen were all, save one, were where the wire got damaged,  mostly where the ends were made by either working back and forth at a hard point where the cable exits the ferrule or a kink.  The only other failure was a brand new set of Sullivan’s from years ago shredded in the middle on the first flight- an obvious flaw in the cable.  The line weight really wouldn’t have mattered very much other than the heavier line will hold with more damage not yet seen.  Line condition I think is more important than weight.  You can only hope a pull test will find the weak point on the ground.

    Right - we are hardly treading new ground here. This sort of issue is a common one in the aerospace industry - trading off increased safety/margins for performance. You can't build spaceflight pressure vessels to the same margins as a stationary steam boiler, for example.

    I think that the line pull test/line size requirements follow common safety factor rules for performance (roughly a factor of two after a single failure) and that's a good standard to use in this case. The previous chart had some real anomalies, in both directions, so the latest change was to even that up. It just happened that the most critical break point fell right in the middle of the current range of airplane weight at 64 ounces. That's what the engineering said, so that's what it is.

     If people are willing to move past the requirement (apparently mandatory in the past, maybe not mandatory now) line size requirements, then the issue essentially goes away - from an *engineering* standpoint.

     I dispute the "fairness" aspect as it appear to have more to do with looking bad to some people for some reason. Weigh the airplanes with or without the battery or fuel, you are barely affecting the safety due to the other tolerances in the system, and if if makes someone feel better to say the airplane weighs 55 ounces than 64, then fine with me. It's entirely cosmetic, and if someone is all hot to fly their 60-sized electric at a liftoff weight of 64 ounces on .015 stranded, or .012 solids, breaking loose and hitting someone is not the biggest issue.

     Brett

[Ken Culbertson]

Just out of curiosity, has anybody ever devised a method of measuring line pull in the air?  Other than combat I have only seen two in flight line failures and both of them had just passed a pull test.  We pull both lines together yet the "ah sh**" situation usually hits one line full force.  If you don't break a line you sure do put a lot of stress on the bellcrank and flap horn.  I am sure there is a reason but why don't we use "stops" on the bellcrank to limit movement if one line is yanked.   How many of our ships could stand the pull test if each line were done separately, even at lower lbs.

[Jim Svitko]

I have also been curious about measuring the line pull in the air.  With the proper equipment (instrumentation?) I suppose it could be done if someone wanted to go thru the steps.  But, is it worth the time spent?   Maybe, for some, but for me, it is easier to do the math.  I know the weight (mass) of the plane, the radius of the circle, and with a standard lap time (5 seconds, give or take a few tenths?), I plug the numbers into the formula.

[Trostle]

I apologize for posting bad info. I didn’t look at the date close enough. It appears this proposal was dropped. So I deleted the post.

No need to delete your post.  The basic proposal to allow GSUMP lines (spectra) did pass the initial vote of the Contest Board 6-5, where a simple majority is needed to pass the initial vote.

Keith

[Randy Cuberly]

Just out of curiosity, has anybody ever devised a method of measuring line pull in the air?  Other than combat I have only seen two in flight line failures and both of them had just passed a pull test.  We pull both lines together yet the "ah sh**" situation usually hits one line full force.  If you don't break a line you sure do put a lot of stress on the bellcrank and flap horn.  I am sure there is a reason but why don't we use "stops" on the bellcrank to limit movement if one line is yanked.   How many of our ships could stand the pull test if each line were done separately, even at lower lbs.

A stop on the bell crank wouldn't limit the force on the line when it hit the stop.  It would simply make it occur sooner...and possibly more often!

Further, if one line breaks when it hit the end of travel the other usually does NOT.  I have see stunt planes do a dozen or more loops on one line before crashing or in a couple of cases run out of fuel!  Of course if it's the up line that breaks there is probably not enough time left before the crash to even blink....still NO flyaway!

I'm of the opinion that all of this is a non problem but would be highly in favor of a simple pull test requirement like the FAI has...If it passes the pull test...It flies!  Simple and effective in my opinion.

In other words a line diameter requirement is unnecessary.  If you can find lines that are strong enough to pass the pull test requirement why should anyone besides the pilot care if they stretch, etc, etc, etc...

What's next lines can't be too shiney because they'll blind the pilot or judge...

Randy Cuberly

[Ken Culbertson]

A stop on the bell crank wouldn't limit the force on the line when it hit the stop. 
Randy Cuberly

I was thinking more in line with damage to the rest of the control system if there is no practical limit on bellcrank movement.  You are right about the 2nd line not usually breaking but once the loops start there is little or no centrifugal force to break it.  There is however a very valid reason to keep the line size rules.  Without stupid rules like that one to argue about we would have to do something constructive.  My vote goes to pulling the "cr**" out of the plane then fly on the lines you did it with, even if it is dirty kite string.

[peabody]

I've been pondering......
A tuna piped IC set-up weighs around a pound (or more) when all is said and done....
I was told that an electric motor of similar power weighs 6 ounces....and a battery that is probably too much weighs 10 ounces....
Same same water buffalo....

EXCEPT that batteries are always getting lighter.

Who has the advantage?

[Randy Cuberly]

I've been pondering......
A tuna piped IC set-up weighs around a pound (or more) when all is said and done....
I was told that an electric motor of similar power weighs 6 ounces....and a battery that is probably too much weighs 10 ounces....
Same same water buffalo....

EXCEPT that batteries are always getting lighter.

Who has the advantage?

Yeah and don't forget the empty fuel tank weighs up to about 1 3/4 oz.

Personally I believe that on the larger competitive setups on both sides the difference is insignificant with possibly the advantage going to the electric!  In fact I think I pointed that out, with the actual weights, in a previous post that received NO comments!

Plus the fact that it's easier to build an electric lighter since the vibrations loads are much lower on the fuselage!

I'm beginning to believe that we are being Conned guys!   

Whatever happened to common sense?

Randy Cuberly

[Gerald Arana]

Whatever happened to common sense?

Randy Cuberly
[/quote]


It went out with the Obummer administration! 

Jerry

PS: What's common cents? 

[peabody]

Yup Randy...the con is on.....
Checked weights (WITH Battery v. dry IC) at the recent contest.....very close....PLUS the 6 or so ounces of fuel....I reached out to Paul Winter....his electric Yatsenkos with battery weigh what empty IC versions of the commie planes.....Have fun!

[Frank Imbriaco]

 Composite aircraft can weigh less than traditional wood /painted finishes.

Can't say  I agree that building lighter aircraft is easier ; IC or electric.

[Brett Buck]

Yup Randy...the con is on.....
Checked weights (WITH Battery v. dry IC) at the recent contest.....very close....PLUS the 6 or so ounces of fuel....I reached out to Paul Winter....his electric Yatsenkos with battery weigh what empty IC versions of the commie planes.....Have fun!

  I know I will regret it, but what "con" are we talking about now?  There is virtually no one flying today at a competitive level that thinks Electric is at a disadvantage in any way, if anything, Electric has an advantage. Great, something works slightly better than the last thing, that's a wonderful thing. Most people are completely incapable of even evaluating it in either direction, because they can't get either one to work properly and optimally, so they are comparing the mistake they make with the mistakes someone else is making, not comparing a perfect working system to another.

     No one cares, it's not important, and it's not a "con".

      Brett

[peabody]

Brett
My examples demonstrate that electric has NO disadvantage as far as weight...more likely, IC engines are heavier at take off.
Just sayin

[Brett Buck]

Brett
My examples demonstrate that electric has NO disadvantage as far as weight...more likely, IC engines are heavier at take off.
Just sayin

  Suppose they are (in fact the current rules more-or-less guarantee that they take off with less margin over the pull test than electric - something everyone has long accepted and was designed into the rules)  - who cares? What difference does that make and why is it relevant?

     Brett

[peabody]

The thread began with a thought that an EMERGENCY safety proposal be made....
It morphed into proposing a rule change that would compensate for the "weight advantage IC engines had over electric"....
My statement of fact is that there is no real weight advantage for IC engines.....
Just sayin

[Air Ministry .]

Think over this ' PARITY ' is the word , I think .

With all the supposed ( reported ) advantages of Electric , I.C.E. need ' the Boost ' .

[Brett Buck]

The thread began with a thought that an EMERGENCY safety proposal be made....
It morphed into proposing a rule change that would compensate for the "weight advantage IC engines had over electric"....
My statement of fact is that there is no real weight advantage for IC engines.....
Just sayin

   There is certainly no emergency and if you dismiss that, the rest of it is a "don't care"/"in the noise"/irrelevant. Change the weight for electric, change the weight for IC, it doesn't make any consequential competitive or safety difference either way.

     And as always, you have immediately jumped to the conclusion that this is a "con", again spewing nonsensical accusations over a minor difference of opinion, and alluding to some sort of plot or conspiracy. One would have though you had learned your lesson in the 93-2005 time frame, but I guess not.

      Brett

[Randy Cuberly]

   There is certainly no emergency and if you dismiss that, the rest of it is a "don't care"/"in the noise"/irrelevant. Change the weight for electric, change the weight for IC, it doesn't make any consequential competitive or safety difference either way.

     And as always, you have immediately jumped to the conclusion that this is a "con", again spewing nonsensical accusations over a minor difference of opinion, and alluding to some sort of plot or conspiracy. One would have though you had learned your lesson in the 93-2005 time frame, but I guess not.

      Brett

I must take the blame (credit) for first mentioning the term "Con".  I did it however as a joke indicating that the reason for the requested change was simply to provide an advantage for the "Evil" Electric Guys!  it wasn't intended to be a serious challenge!

I believe this whole  fact that we have required line diameters and a pull test to be just more belt and suspenders "seudo" safety regulations that have no real foundation in fact or necessity!  Of course I really don't think Electric guys are "Evil"...well maybe one or two of them... and they know who they are!  But I have many friends and good nice people that have gone to the dark side and still remain NICE PEOPLE!  I certainly confess that I don't believe that the electric systems are better than the best IC systems but that they do have the technical advantage to become so!  I don't believe they are there yet however.  There is some small experimentation going on with IC engines that may level the playing field again.  Experimentation with air boxes and potential fuel injection systems while expensive could easily advance IC beyond the electrics and give more consistency...potentially of course!  Electrics are cheap and easy so they will have the high ground for a while.  It may simply happen that there is not enough remaining energy or desire in the old crowd that has an interest in Stunt to really worry about future advancement!   I would think if there are any real advances in either it will likely be from the Europeans.  They seem right now to have a bit more development interest! 

Right now even R/C Competition other than the stupid drones (and certainly the commercial usage for those has a determined place in the future) is highly questionable and on a big down turn!

Personally, I find disappointment in the fact that my period of greatest interest so far in stunt also comes at a time when my physical abilities due to age are also on a steep down slide!  RATS!  Nothing ever seems to come together...such is life!  Oh well I've hopefully got a few more years wiggleing the handle even if I don't ever actually win anything!

Randy Cuberly

[Jason Greer]

This post is in reply to several comments regarding the actual weights of a full size/competitive electric model.  I thought I’d add a few real world examples of my last few completed electric model weights. These models were built per the plans with no extreme measures to save weight.  For example, the engine bearers were left out of the fuselage construction, but no other structural changes were made. All of the wood used to construct these models was purchased from Tom Morris. These weights include the battery and are ready to fly.

Geo-XL built in 2011: 53 ounces (5 cell battery)
Impact built in 2013: 53 -54 ounces (5 cell battery)
Impact built in 2016: 57 ounces (6 cell battery)

All of these models were finished with monokote except for the 2016 model. It has a silkspan/doped fuselage and monokote covered flying surfaces.

I shared the component weights of a typical 6 cell 60 size electric power system in an earlier post. These are actual numbers weighed on a trustworthy scale. 

Please note that I don’t personally have any issue with how we are currently weighing/pull testing electric models. The purpose of this post is to simply inform the guys who have no experience with electric power systems of the true weights of a typical ready to fly electric model.

Jason

[Randy Cuberly]

This post in reply to several comments regarding the actual weights of a full size/competitive electric model.  I thought I’d add a few real world examples of my last few completed electric model weights. These models were built per the plans with no extreme measures to save weight.  For example, the engine bearers were left out of the fuselage construction, but no other structural changes were made. All of the wood used to construct these models was purchased from Tom Morris. These weights include the battery and are ready to fly.

Geo-XL built in 2011: 53 ounces (5 cell battery)
Impact built in 2013: 53 -54 ounces (5 cell battery)
Impact built in 2016: 57 ounces (6 cell battery)

All of these models were finished with monokote except for the 2016 model. It has a silkspan/doped fuselage and monokote covered flying surfaces.

I shared the component weights of a typical 6 cell 60 size electric power system in an earlier post. These are actual numbers weighed on a trustworthy scale. 

Please note that I don’t personally have any issue with how we are currently weighing/pull testing electric models. The purpose of this post is to simply inform the guys who have no experience with electric power systems of the true weights of a typical ready to fly electric model.

Jason

Hi Jason,
Thanks for the post!  It confirms what I basically have believed to be fact.

My Geo XL built in 2006 weighed 54 ounces with no fuel in the 4.5 ounce tank (no nitro fuel) and the wood was very carefully selected to be as light as possible.  It used a Belko long shaft .56 which is a fairly light engine at 11.5 ounces with the rear exhaust muffler.  It was finished in the traditional silkspan Dope finish on the entire airframe with considerable fiberglass reinforcement on the fuselage and internal areas of the engine compartment.
Had it used a typical tuned pipe arrangement on a PA65 it would have weighed significantly more.  Probably as much as 6-7 ounces more plus the weight of the fuel!

It was a terrific flying airplane at that weight and perfectly matched to the power!  I still miss it!  It was unfortunately stolen from the flying field!

Randy Cuberly

[Dave Hull]

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Re: A weighty situation

« Reply #105 on: May 03, 2018, 01:11:20 PM »


Quote

 

"I have also been curious about measuring the line pull in the air.  With the proper equipment (instrumentation?) I suppose it could be done if someone wanted to go thru the steps.  But, is it worth the time spent?   Maybe, for some, but for me, it is easier to do the math.  I know the weight (mass) of the plane, the radius of the circle, and with a standard lap time (5 seconds, give or take a few tenths?), I plug the numbers into the formula."

Yes, there was at least one in-situ measurement of line tension. The results were published back in probably the early 1960's. As I recall, it was done by the racing guys. They probably used load cells at the handle, or less likely, strain gages on the lines. (I remember looking at the photos and trying to decide what type of transducer was being used. I couldn't tell, other than there were electrical lead wires to some electronics strapped the pilot's belt.) They plotted the loads and compared them to the straight "centrifugal force" calculation. Their conclusion was that the actual loads were higher than the simple mass/centrifugal force calculation. I would have to find the article to see if they characterized the uncertainty of the test results. The biggest question I would have is whether they grabbed random instantaneous values or were able to collect max/max value.

A few other cautions:  pilots often whip at times, which increases the line load temporarily beyond the simple centrifugal force calculation. Also, I suspect that trim can cause a significant offset in the straight and level line tension. Lots of line rake, rudder offset, engine offset, etc. These cause aerodynamic loads that are not accounted for in the simple centrifugal force calculations. Bob mentioned in one of his posts that he could show us how to reduce the excessive line tension--I liked his oil painter metaphor. I used a different one when I tried to describe motor skills and strength to guys at work: try holding a suitcase in one hand and then try to take the cap off a tube of Chapstick and apply to lips. The extra weight demolishes your fine control. Go ahead, no one is looking, try it!

Also note that increased line tension in the wind--which everyone can relate to--occurs from two sources: so-called wind-up where the plane speeds up, and also from the "crosswind drag" on the plane. Planes are not very streamlined along the lateral axis, and you can feel it. So the first one is mass related and the second is aero related.

The team race (F2C) guys experimented years ago with engine in-thrust and banana fuselages to try to reduce the in-flight drag. Not sure how much that achieved--but it made the planes a real #$@%?! to take off. Not sure anyone is still building/trimming that way. However, I know that racers trim for least out-thrust of any of the events that I have participated in. Zero everything and then push the leadouts forward until you have trouble on takeoff. Not sure how the old B-TRs in the study were trimmed, but I would start by assuming a stunter would have more aerodynamically generated line tension.

One of the other posts implied that a centrifugal force calculation wasn't valid during maneuvers. I disagree: the component of force that is solely due to the accelerating mass is always valid--if you put in the correct velocity and other inputs. However, as I tried to list above, it is only one of the vector components.

Dave