Fuel Cutoff ??

[Hoss Cain]

Has anyone experimented with using a FF dethermalizer timer such as the Seelig and/or Texas Timer for a fuel cutoff in a CL stunter?  It seems to me that a tank with an extra ounce or so fuel and a positive cutoff at a time to make a landing within the 8 minutes could be a positive thing to keep the mind on flying.
I left Cl Stunt in the early '70s as I owned a hobby shop then and RC was what was selling. I guess I could check it out on my Ringmasters but thought maybe someone could save me labor.
My last real stunt competition was in '72-73 time period. The timing was always in my mind. At the 71 NATs I was talked into flying a pre-production Testor's McCoy 40 grey-case which was simply a K&B series 71 dykes ring .40  in a super ugly case. Just as I was finishing the hourglass, knowing I had just performed a barn-burner flight which the flight scores backed-up, that hunk-of-junk went into rat-race lean and I had a 12+/- minute flight. As you well know the second flight was set a bit rich and then I wallowed through the air like I was making my first ever CL flight.    Needless to say that my report to Testors was not what they would place in a magazine review! 
So in these past 40 years, I wonder just what great revelations have been accomplished to ensure a precise time solution. I have not observed much about that here in the forums, but I miss a lot, or so wifey tells me! 

[Larry Fernandez]

Has anyone experimented with using a FF dethermalizer timer such as the Seelig and/or Texas Timer for a fuel cutoff in a CL stunter?  It seems to me that a tank with an extra ounce or so fuel and a positive cutoff at a time to make a landing within the 8 minutes could be a positive thing to keep the mind on flying.
I left Cl Stunt in the early '70s as I owned a hobby shop then and RC was what was selling. I guess I could check it out on my Ringmasters but thought maybe someone could save me labor.
My last real stunt competition was in '72-73 time period. The timing was always in my mind. At the 71 NATs I was talked into flying a pre-production Testor's McCoy 40 grey-case which was simply a K&B series 71 dykes ring .40  in a super ugly case. Just as I was finishing the hourglass, knowing I had just performed a barn-burner flight which the flight scores backed-up, that hunk-of-junk went into rat-race lean and I had a 12+/- minute flight. As you well know the second flight was set a bit rich and then I wallowed through the air like I was making my first ever CL flight.    Needless to say that my report to Testors was not what they would place in a magazine review! 
So in these past 40 years, I wonder just what great revelations have been accomplished to ensure a precise time solution. I have not observed much about that here in the forums, but I miss a lot, or so wifey tells me! 


There is no need for such complexity on your stunters.
Get to know your powerplant. Know what your lap times will be for a given RPM. Monitor and note how much fuel you put in and how long it flies. Try keeping a log, making note of temperature, type of fuel used, prop, line length, fuel quantity, RPM, lap times, and flight duration and so on.

After you have everything sorted out you will know that five laps after the four leaf clover, your motor will go lean for about a half a lap and then quit. No surprises

Larry, Buttafucco Stunt Team

[Tim Wescott]

Or get a helicopter governor, a Hubin timer and a little battery.  Have yourself an "electric" run with slime power.

(Excuse me while I duck and cover...)

[Steve Helmick]

Dick Mathis used a Seelig Mini-Combo mechanical timer to trigger his retracting landing gear, so there's no reason that you couldn't use one for engine shutoff as well. There are much lighter mechanical timers available now, if you are interested.

Most interesting to me is the concept of a timer tank that has no moving parts. See the .pdf attached. I think it's a very cool concept, but I have to agree that the alternative is to just practise enough to know how long the IC engine is going to run in various situations.  Steve

[Howard Rush]

This is an example of dissimilar redundancy.  You can take two kinda flaky components to make an adequate system.  Most folks have chosen to solve this particular problem without the additional component.  A good engineer could design a system that makes all four engines of a B-17 stunter quit consistently between the clover and the 7-minute F2B time limit without a timer.

[phil c]

A Sullivan SS-6 tank fitted for uniflow does the same job.  You can see exactly how much fuel is needed for a certain run.

The problem with using fuel amount to control the flight time is the weather.  Last year at one contest I got an over run on the first flight, an extra 1.5 min.  I took out 3/4 of an ounce of fuel on the second flight in the afternoon and got an underrun, it quit exiting the cloverleaf.

[Russell Shaffer]

Phil has a very good point.  There are too many variables for firm predictions.  I would buy a good, cheap electronic timed fuel shutoff.  Then I could run with enough fuel to ensure that the engine really would run and still shut off when the time arrived. Get rid of all the annoying end or run issues, too. It would really help us aspiring fliers. It works for the electric guys.  Tim Wescott to the rescue?

[Tim Wescott]

Ah, the dilemma of the innovator: is no one doing this cool thing you've thought up because you're smarter than everyone else?  Or do you mistakenly think that you can make it work because you're an over ambitious dolt, about to chuck a whole bunch of man-hours down a rat hole?

While I had my tongue in my cheek about the response that one may expect at the idea, I was quite serious about the potential for the system to work: a Hubin timer, a helicopter engine governor, a servo and a small battery (and an RC carb), and you're all set.  You'll probably add at least an ounce for all the pieces.  On the bright side you'd also get a dead-steady run (or at least as good as the governor will get you), meaning that you wouldn't need a super-special razzle-dazzle black-magic stunt-tuned carbon-fiber-piped engine -- just go to the local hobby shop and pick out anything that is reliable and that'll haul your plane around at 1/2 or 3/4 throttle in the level laps.  You'll have power to spare for when you go straight up, and "shut down" to spare going down.

Or if you just want the timing capability without the governing, you can save a part and some weight and do it with a Hubin timer, a servo, and a battery.  If you can figure out a reliable way to cut the power under servo control without a carb, you can use your favorite ol' reliable CL stunt engine.

Ways that I know that the free-flight guys use to cut power are a pinch-off timer, where the timer actuates and pinches the fuel line, making the engine run out of fuel, and a flood-off timer, where the timer actuates and un-pinches a fuel line that is directed into the venturi.  Obviously a flood-off timer requires a pressurized fuel system, but I think that muffler pressure would be more than enough.

In either case you'd really want to talk Will into modifying his timer software to start up at the full power setting, stay that way when the button is pressed, and only go to low power at the end of the flight. You could work around that, but it'd be awfully nice.

After that, the rest is just mechanical ingenuity.

[Hoss Cain]

//SNIP//
Or if you just want the timing capability without the governing, you can save a part and some weight and do it with a Hubin timer, a servo, and a battery.  If you can figure out a reliable way to cut the power under servo control without a carb, you can use your favorite ol' reliable CL stunt engine.

Sounds interesting. Will probably check that out.

Ways that I know that the free-flight guys use to cut power are a pinch-off timer, where the timer actuates and pinches the fuel line, making the engine run out of fuel, and a flood-off timer, where the timer actuates and un-pinches a fuel line that is directed into the venturi.  Obviously a flood-off timer requires a pressurized fuel system, but I think that muffler pressure would be more than enough.

Unfortunately commercial FF fuel-off timers are restricted to generally not more than 30 seconds. I used those back in the '60s and early '70s when I flew competition FF along with CL stunt.
As I first stated: "....FF dethermalizer timer such as the Seelig and/or Texas Timer for a fuel cutoff in a CL stunter? Those can be set for up to 10 minutes depending on the series. I still have some. I would prefer mechanical over electric but right now I am not ruling anything out.

In either case you'd really want to talk Will into modifying his timer software to start up at the full power setting, stay that way when the button is pressed, and only go to low power at the end of the flight. You could work around that, but it'd be awfully nice.

After that, the rest is just mechanical ingenuity.

Yep, here I have ideas of being a 20 to 35 year old again and now I have trouble keeping a half dozen RC and a couple Ringmasters flying. YUCK !!

Thanks to all with your inputs.  And to Larry, you really are very correct, yet I have too many irons in the fire to try to best the young-guns anymore, but I do wish to build a couple more of my very successful machines that I designed and won with in the '69-'72 time period. There are several very different versions of control systems in my mind, yet I have observed very little changes in current in-use systems over the past 40 years other than RC connectors. I really wonder why. Hope to have some on the field next Spring.

Again, Thanks to all for your help.

[Brian Hampton]

I used one of the mechanical FF D/T timers about 35 years ago in my stunter with absolute reliability until someone at a competition informed me that timers were no longer allowed under FAI rules. I had it flush mounted on the fuselage side and the release wire trapped a short length of very soft tubing which was Teed into the fuel line close to the needle valve. When the timer tripped it opened up that short tube so letting only air be drawn in through the needle valve. I'd set the timer to 6 minutes before starting the engine then after engine start I'd move a little arm to "operate" and the timer would begin to tick.

[Lauri Malila]

 Hi.

 I'm working with an electronical cutout/timer at the moment. (for IC engine) It's lighter and more reliable than the mechanical clockworks, and also more accurate. It's built from Roger Morrell / Ken Bauer free flight "Magic" timer, RDT (Radio DeThermalizer) unit and a micro servo that operates a mechanical fuel line clamp.
 Actually, the timer option is kind of extra, I feel no need for it as I know my engines. But in testing differend setups, and in a situation where something goes wrong (like a broken blade, lean/rich run etc.), the remote cutout is really handy. Of course it's not allowed in rules to have a remote cutout like that, the rules state that the signal must go via the line(s). L

[john e. holliday]

And what happens when you pick up your handle signal for take off and remember you forgot to start the timer?   Been there and done that on an electronic throttle control carrier plane.

[PerttiMe]

I used one of the mechanical FF D/T timers ...
... the release wire trapped a short length of very soft tubing which was Teed into the fuel line close to the needle valve. When the timer tripped it opened up that short tube so letting only air be drawn in through the needle valve.

Was there need to isolate the timer from engine vibrations?

On a glow powered aircraft, I'd rather not use electronics at all. Just "because".

[Dan McEntee]

  Up until the recent advancements in electric stunt, cut off timers were not allowed. If you fly stunt and are half way serious about it, you then should be flying fairly often, enough to become very familiar with your power plant and how much fuel it requires. Pencil and paper can make up for the lack of sufficient memory. It's common knowledge and basic high school physics that cooler air and lower altitudes requires more fuel and warmer air and higher altitudes require less fuel. How much more or less is determined by the before mentioned practice flights. The most high tech thing you need to buy is a fuel syringe and a stop watch and most of us already have those anyway. So basically, since I couldn't use them before I see no need for them now. I occasionally have an over run or run out too soon, but that is usually attributed to some lack of attention or failure on my part. Catching up on that stuff is part of the hobby, and makes you look at and pay attention to other ares while you are under the hood. For those who like to tinker with such things, more power to them, for that is where other discoveries sometimes come from. I would not have a problem with some one using them, I just don't want to have one more thing to check and maintain. I like KISS stunt, " Keep It Simple, Stupid!" 
   Good luck with all the experiments.
    Dan McEntee

[Brett Buck]

  Up until the recent advancements in electric stunt, cut off timers were not allowed.

   I really have no idea how that idea got so firmly entrenched. You could have used a timer at any point since Jim Walker first flew. There has never, to my knowledge, been a prohibition on timers in AMA stunt.  FAI disallowed them until recently, for no good reason that anyone can provide.

    The real reason that they were very rare is that it's not at all difficult to get the run time right. And if your engine is set up properly, it's not particularly sensitive to the external conditions. At the TT, I was running 6:32 +-5 seconds all week long, cold and rainy, warm and humid, etc. Timers are just not needed and provide no advantage - and create one more point of potential failure. Unless I take a hammer to my fuel tank and alter the shape of the wedge, it's going to run exactly the same every time.

    The one and only trick, which almost everybody knows, is to shape the tank so you can get through the 4-leaf with about 30 seconds worth of fuel, but without uncovering the pickup.

   I have judged 1000's of flights over the years and overruns are exceptionally rare. Take out the incidents where someone took 2 minutes to get started and flew anyway, and it's in the single digits. You don't need a timer.

    Brett

[Andrew Tinsley]

I have run big diesels in stunt, with these, you definately need a timer because of the very big difference one can experience in run time. A small electronic timer and a little ingenuity is all that is needed, it is not rocket science to achieve a suitable cutoff mechanism.

Regards,

Andrew.

[Sean McEntee]

"FAI disallowed them until recently, for no good reason that anyone can provide."

          My highly uneducated guess to that would be the recent introduction of electrics.  They have timers, so I would think that it would be an unfair advantage to allow electrics to have timers but not IC engines.

          Im with the "burn fuel and figure it out" crowd.

[Brett Buck]

"FAI disallowed them until recently, for no good reason that anyone can provide."

          My highly uneducated guess to that would be the recent introduction of electrics.  They have timers, so I would think that it would be an unfair advantage to allow electrics to have timers but not IC engines.

  Oh, that's why they permit them. My point was, and the much better question (that has absolutely no good answer, I have tried) is why they didn't allow them all along. They even banned the "fill only when inverted" hopper, which permitted perfectly reliable cutoffs *WITHOUT* a mechanical timer. I have yet to find anyone who actually believes that "accurate fuel volume measurement" is a fundamental element of stunt competition.

   FAI contests, even the TT with the best fliers in the world, actually take longer than AMA contest since if the engine doesn't start instantly, you have to take an attempt. If you tried FAI with Intermediate fliers, you'd be cranking out about 3 officials an hour!

    Brett

[PerttiMe]

3 minutes is "instantly"?

... shouldn't be too hard to manage that with electric.

[Brett Buck]

3 minutes is "instantly"?

No. The problem is that you need to run from about 6:15 to 6:30 for a comfortable margin with an instant start. If you take even 45 seconds fiddling around with starting, you will go over at the end. Similar issue with staring points. So you take your time to get into the circle, signal, then take an attempt, and have to do it again. With the 10 minute slots like at most WC its even worse, since the whole 10 minutes is wasted.   That's why the FAI 7 minute time limit actually makes contests take longer with anything but the most skilled competitors.

  It's even worse if you fly particularly slowly, you might need to run maybe 6:45 from signal to wheel stop, so you have only 15 seconds of engine flipping before you have to take an attempt. And that's with no margin at all. I run about 6:30 in FAI and I give myself about 15 seconds to try to start, if it gets over, I call an attempt.

    In AMA you have 8 minutes total and no starting points, so can screw around for a while and still have a good chance of making it, so you keep trying for much longer, and don't lose the flight. Most flights are finished in under 7 minutes anyway, so the 8 minute time limit costs you almost nothing most of the time and save a few flights a day.

    Brett

[Tim Wescott]

I really have no idea how that idea got so firmly entrenched.

For what it's worth:

I read a story somewhere on Stunthanger that in the 70's the Russians had a mechanical fuel cut off device that worked by letting the lines go slack and giving a good yank -- the resulting pull on the bellcrank actuated the cutoff.  But the idea of intentionally having such a jerk on the lines every flight worried the officials, and instead of trying to disallow just that the FAI disallowed mechanical shut off devices altogether.

[Steve Helmick]

For PA, Classic and Profile, one of the better plots, if you have trouble starting within 1 minute (for AMA) is to go ahead and fly, but don't pull out inverted in the RWO. That gives you a practise flight for the cost of the "attempt" you're giving up anyway, if you just call an attempt. Not that I've ever done it, but it is ok by the rulebook. A mucho better rule would be to make the attempt start upon release.  Steve

[Sean McEntee]

      Steve I dont think that I have ever seen anyone do that, although you are correct about the legality.

      Problem is the current window for declaring an attempt is to allow for a bad needle setting, or some other type of problem.  This isnt so much geared for the upper skill classes as it is for beginner/intermediate.

[Steve Helmick]

Avoiding the wingover completely works. I've seen that, but it wasn't done on purpose. Another way is to not install the safety thong on your wrist. Saw that, too. Just sayin'...  Steve

PS: I need to read the OTS  rules, but I think if you just don't give the hand signal to start the pattern, you're good to go on an "unofficial". Tho, I don't think over runs are much of a problem with OTS.

[john e. holliday]

Yep, OTS, no signal, no score.       Even then in our local meets if I am on my last attempt, I will start engine and fly no matter if it takes 3 1/2 minutes to start.   

[Jim Kraft]

I have been thinking about a timer for my ignition planes. It would be easy to shut off the ignition at say 6 minutes. That way I could run gasoline which is much harder to adjust for as far as time goes. That would also eliminate having to worry about shutting down the ign. after the plane lands to keep from running down the batteries if the points are close upon landing. The Don Hutchinson ign. does shut down as soon as the motor stops, but it would be nice to have it timed. Hmmmm!

[Larry Cunningham]

This is an example of dissimilar redundancy.  You can take two kinda flaky components to make an adequate system.  Most folks have chosen to solve this particular problem without the additional component.  A good engineer could design a system that makes all four engines of a B-17 stunter quit consistently between the clover and the 7-minute F2B time limit without a timer.

But WHERE would we find a good engineer, Howard? ;->

Just have them all run out of fuel at the same time.. Or, simply do a Kervorkian - no engineer required..

L.

"From error to error one discovers the entire truth." -Sigmund Freud

[Howard Rush]

But WHERE would we find a good engineer, Howard? ;->

Beats me, but somebody ought to be able to make a reliable pressure reducer.

[Larry Cunningham]

..needs a microprocessor 

L.

"If hard work were really a virtue, then mules would be saints." -James D. Richardson