Over Runs

[John Rist]

At our last club meeting the subject of over-runs cam up.  Ty pointed out that 2.4 radio engine cutoff was legal.   As I read the AMA rules it is indeed legal for retracts and engine cutoff.  Looking into the hardware available it would not be that hard to set up.  My question is anybody using a 2.4ghz setup to prevent over-runs? 

[Brett Buck]

At our last club meeting the subject of over-runs cam up.  Ty pointed out that 2.4 radio engine cutoff was legal.   As I read the AMA rules it is indeed legal for retracts and engine cutoff.  Looking into the hardware available it would not be that hard to set up.  My question is anybody using a 2.4ghz setup to prevent over-runs? 

  I am not aware of any of the usual suspects using it for either cut-off or landing gear. It's not a critical issue because with 8 minutes, it's pretty easy to make the limit without a radio cutoff. And, it's only been unambiguously legal since January.

    Brett

[Dan McEntee]

  I made up a "throttle pack" for my new profile "Dusty" so I could fly it in profile scale contests. I used a small Spektrum reciever, a really small servo, and a 7.4 volt, 250mah battery pack controlled with a dummy plug. It all fits in a small box that attaches to the side of the fuselage with 4 screws, and connects to the throttle with a simple wire pushrod. The whole throttle pack only weighs aboput 1.5 ounces. I hang the transmitter from a clip on my belt to work the throttle. I never intended to fly it this way in contests, the R/C carb is too flakey. If I fly stunt with it, I remove the throttle pack, replace the carb with a venturi and needle valve and fly as usual. So it can easily be done at that kind of weight pretty easily. I think the thing to do if you must try a fuel cutoff, is to adapt the device that some F/F guys use on F/F models. It's a hand held single channel device with a button. Weighs only a few grams. My son Sean uses one on his discuss launched glider for dethermalizer. Great for small fields and trim flight. The same device could be rigged up on a fuel cut off on a stunt model at very small weight penalty. But in my opinion it is one more thing that can go wrong at the wrong place of a critical maneuver if accidentally triggered!  Much more traumatic than an over run!
  Type at you later,
   Dan McEntee

[Mike Scholtes]

The RC setup would only need to trigger a Free-Flight-type pinch-off valve, no RC carb needed. Or, use a new FF electronic timer to trigger the shut-off device, as modern FF models are now mostly using. That would eliminate the RC stuff entirely. See Texas Timers web site, or Star Link web site, for details. They weigh only a few grams and are easy to program in the field.

Or, as Brett notes, just figure out how much fuel to put in the tank based on experience with temperature, altitude, nitro content, etc. With the 8-minute AMA rule there is no reason for an over-run, and it peeves the judges to stand there watching while you do an extra 30 laps until fuel exhaustion.

[Jared Hays]

Is it really that hard to pull fuel out of your tank?  Why add weight with batteries and radio gear for a cutoff.  I just got back from Denver 5500 feet altitude to where I normally fly 1000 feet altitude.   Only took me 1 flight on each plane to know how much fuel to pull out to compensate for the altitude difference which makes your engines run longer on the same amount of fuel. 

[Brett Buck]

Is it really that hard to pull fuel out of your tank?  Why add weight with batteries and radio gear for a cutoff.  I just got back from Denver 5500 feet altitude to where I normally fly 1000 feet altitude.   Only took me 1 flight on each plane to know how much fuel to pull out to compensate for the altitude difference which makes your engines run longer on the same amount of fuel. 

  In my case I pretty much always extract the same amount of fuel, even for FAI. It's not always the same type of fuel, however. If you adjust the nitro to get the same power, you get about the same run run time. I checked my indicated flight times at the last TT I went to and I was between 6:20 and 6:35 for all of the flights.

   What *is* critical is to get a tank that cuts off reliably with almost no warning. It has to run through the 4-leaf with little or no leaning out, and then cut off a few laps later. I use the high-circling-flight cutoff that I learned from Whitely, unless it is really windy, in which case I revert to the cutoff loop. The overhead flight allows you to dive to get speed for landing.  The windy day at the NATs this year, I did my first cutoff loops in about 5 years. You start a little *before* dead-downwind (reverse-bias), allow it to whip up, and then again get a bunch of speed built to be able to reliably control it through the upwind section of the last lap. I probably exited on my second flight at about 85 mph with the engine quit, and then it's easy to get on the ground 45 prior to dead downwind at relatively high speed.

   If you just fly around level and wait, you have no control over the landing position. If it's windy and it cuts off around dead downwind or sometime in the next 90 degrees in level flight, you are going to be super-screwed.

     Brett

[Ward Van Duzer]

"Super-Screwed"!

Great phrase Brett!


Ward

[Gary Mondry]

I clearly fall into the "super screwed" category as I simply fly around level and wait (and hope).  So what is it that allows a cutoff loop to work?  Is the tank vented a particular way or is it dependent on some maximum amount of remaining fuel?

[Brett Buck]

I clearly fall into the "super screwed" category as I simply fly around level and wait (and hope).  So what is it that allows a cutoff loop to work?  Is the tank vented a particular way or is it dependent on some maximum amount of remaining fuel?

   The acceleration of the loop (or high circling flight) pulls the fuel towards the bottom of the tank, and away from the pickup. Note that it works better on insides than on outsides, analysis is left to the reader.

   The key to being able to get it to fly through the 4-leaf at low fuel is to have the correct wedge angle. A Veco T-21 worked OK when you couldn't corner to hard, but you generally need it to be a bit steeper nowadays. Canting or tapering the tank in plan form also helps.

    Brett

[Gary Mondry]

Well, that makes sense, but won't help me much with my Hayes clunk tanks...

[Dave_Trible]

Well, that makes sense, but won't help me much with my Hayes clunk tanks...

Nope.  Get out the soldering iron Gary.  Clunks don't work well in this.  You DON'T want a clunk following the fuel around.  You may still have to pull some amount of fuel out to get the fuel level low enough for a good cutoff.  Usually you'll need to hear the engine starting to go into its leaner almost- out sound before the loop is a sure bet.  You may need to extract some fuel to find that place a few laps after the clover.  The loop simply pre-emps the several more laps of burp-scream-burp.  As Brett was talking about,  not enough slope angle in the tank wedge makes that a harder guess and the plane may think the first turn in the clover is your cutoff loop.  Ask me how I know.  The clunk has to go!

Dave

[John Rist]

Reading all of the posts I am hearing words that indicate that a predictable cutoff would be a good thing.  Nothing is fool proof so if you add cutoff electronics it could inadvertently kill the engine at the wrong time.  However running short on fuel and have it die in the clover is not a good thing. Also  a well designed system most of the failure modes should leave the engine running not kill it unannounced.

I am just beginning to look at a possible solution, But my first thought is that the battery could replace part of the tip weight.  The transmitter could be mounted on your belt.  The weight gain could be close to zero.

Another advantage would be the ability to abort a bad engine run eliminating  the need to fly in circles for 5-10 minutes.  It could also be used to save an engine from a lean run.

Additionally the top pilots don't need or want a cutoff.   Through hard work, at our hobby,  they have it down pat.  The rest of us need help.

PS if and when I do decide to try a stunt contest I will probably fly an electric which, by design, will have an electronic timer. 

[Steve Helmick]

I've been using clunk tanks for some years and haven't had any significant problems with run-time. The key thing is to get some practice flights in and treat them just like a contest flight. I don't often time my flight times, but I can certainly tell that it's running too long, so I adjust from there.

The "mustard pump" is my favorite way to fuel up. Each full stroke (after purging the pump of air) gives EXACTLY one ounce of fuel into the tank. With my current plane (piped .46VF), I run 5.5 to 6 oz of 10% nitro. I can adjust the flight time by adjusting the amount of oil in the fuel (more oil = shorter run), increase the prop load (more prop = shorter run), increase the nitro content, or reduce the fuel load. Reducing the fuel load is easy enough. I'm planning to make a spacer thing with a handle that will limit the fuel delivered on the last stroke of the pump...1/4 oz increments, I hope. Good enough!    Steve

[Target]

Yep, certainly flying an electric stunter with a timer is simplest.
But I find all the glow fuel info fascinating none the less.
Hence my subscription to this thread.

[Brett Buck]

Yep, certainly flying an electric stunter with a timer is simplest.
But I find all the glow fuel info fascinating none the less.
Hence my subscription to this thread.

  I haven't figured out how to make the electric cut off when I want WRT the wind, without 2.4 gHz, anyway.

   Brett

[Tim Wescott]

Reading all of the posts I am hearing words that indicate that a predictable cutoff would be a good thing.  Nothing is fool proof so if you add cutoff electronics it could inadvertently kill the engine at the wrong time.  However running short on fuel and have it die in the clover is not a good thing. Also  a well designed system most of the failure modes should leave the engine running not kill it unannounced.

I am just beginning to look at a possible solution, But my first thought is that the battery could replace part of the tip weight.  The transmitter could be mounted on your belt.  The weight gain could be close to zero.

Long cables can make electronics unhappy.  If you're going to use the electronics for tip weight you probably want to run the battery and receiver together, with a long wire to the servo.

The latest el-cheapo Hobby King car radio is 3-channel, with a button on the grip for the 3rd channel.  You could use that for cutoff, and have a transmitter for flying carrier planes.

Another advantage would be the ability to abort a bad engine run eliminating  the need to fly in circles for 5-10 minutes.  It could also be used to save an engine from a lean run.

Modern ABC and ABN engines are fairly tolerant of lean runs -- and lean runs are few and far between if you've got your setup right.

Additionally the top pilots don't need or want a cutoff.   Through hard work, at our hobby,  they have it down pat.  The rest of us need help.

PS if and when I do decide to try a stunt contest I will probably fly an electric which, by design, will have an electronic timer. 

[Igor Burger]

an electric which, by design, will have an electronic timer. 

You can use the same timer, small Lipo 1 cell battery and micro servo, it will be less then 1/2 oz

[Tim Wescott]

  I haven't figured out how to make the electric cut off when I want WRT the wind, without 2.4 gHz, anyway.

Use a TUT with a cutoff loop programmed in.  It's how Howard Rush does it.

[Dick Pacini]

There was some discussion a while back about cut-off loops being considered grandstanding.  I always liked them.

To me, the absolute best cut-off loops were done by Al Rabe.  Perfect control and consistency and watching that big Sea Fury do exactly what he wanted when time came to shut down and land was a thing of beauty and a joy to behold.

[Norm Furutani]

Here's the link to Airtek radio DT.  http://www.airtekee.com/RDT.php. Airtek, Kenny Bauer has been a pioneer in electronic FF goodies. There are two basic versions, a stand alone system that operates a servo or other actuator and one that interfaces with an electronic timer. Ken speaks controline so make sure he is aware of its use. Example: some have an immediate response and some have a battery saving delay.

Norm 

[Target]

 I haven't figured out how to make the electric cut off when I want WRT the wind, without 2.4 gHz, anyway.

   Brett

I hadn't thought of that, but being the person I am, I could say that a "smart guy" might have the timer run timed, trusty Seiko S321 watch in pocket, and manipulate the last laps of flight to be in the right place at the right time.
I would think its doable with some practice....
But I do get your point, and your plan certainly gives some added flexibility once its mastered.
Again, exactly why I subscribe here.

R,
Chris

[Tim Wescott]

I hadn't thought of that, but being the person I am, I could say that a "smart guy" might have the timer run timed, trusty Seiko S321 watch in pocket, and manipulate the last laps of flight to be in the right place at the right time.
I would think its doable with some practice....
But I do get your point, and your plan certainly gives some added flexibility once its mastered.
Again, exactly why I subscribe here.

I see Paul Walker checking his watch toward the end of the flight.  I think he flies high or low laps to move where the airplane will cut out (I've also seen him do a "cut off loop" right as the time runs out).

Howard Rush had me program one of Tim's Universal Timer outputs to time the flight.  He runs that output to an LED in the plane so that toward the end of the flight it starts blinking once every 5.2 seconds (or whatever he programs in).  It's bright enough that he can see it even in direct sun.  It's timed so that at the end of the last blink the timer cuts out, so he flies his last few laps fast or slow to the same effect as Paul does, only he keeps his eye on the plane.

http://atomiczombieworkshop.com/tut/tut.html

[Target]

Good to know I'm not that far off base.
I never thought so, but being tested occasionally isn't a bad thing...
And I'm still very interested in being able to manipulate a glow engine run.
I'll have to discuss that with my engine mentor before I convert him to electrics.
Kind regards to all.
Chris

[Igor Burger]

Howard Rush had me program one of Tim's Universal Timer outputs to time the flight.  He runs that output to an LED in the plane so that toward the end of the flight it starts blinking once every 5.2 seconds (or whatever he programs in).  It's bright enough that he can see it even in direct sun.  It's timed so that at the end of the last blink the timer cuts out, so he flies his last few laps fast or slow to the same effect as Paul does, only he keeps his eye on the plane.

And we, with tired eyes after flight, not looking to model last laps of flight have beeping and vibrating stopwatches in pocket telling us exactly the same, so I not only know exact place where motor stops, but I can also manage him to stop wherever I want (for example regarding the wind direction or even large rocks/holes on some official FAI WCh circles  ) ... and they even allow us measure lap time as a bonus 

[Tim Wescott]

And we, with tired eyes after flight, not looking to model last laps of flight have beeping and vibrating stopwatches in pocket telling us exactly the same, so I not only know exact place where motor stops, but I can also manage him to stop wherever I want (for example regarding the wind direction or even large rocks/holes on some official FAI WCh circles  ) ... and they even allow us measure lap time as a bonus 

True.  But you have to admit, when it comes to a proliferation of blinking lights, Howard's plane has yours beat down to the ground.