Best place for the engine to cut off

[Tim Wescott]

If you could choose where in the circle the engine cuts off, where would it be?

Would the answer be the same for high wind as low, and for turbulent conditions vs. steady?

How much would "bad spots" in the circle affect your decision?

[John Stiles]

Tail wind... The only bad spots are the fire ant hills!

[dave siegler]

not before you complete the clover?   

[Tim Wescott]

not before you complete the clover?   

I was thinking more on the lines of up wind, down wind, into the wind, 90 degrees off from that pothole, etc.

[john e. holliday]

Down wind for me as I can control the landing better for me.   Just have to remember to not let the plane balloon up.  Also keep tension on the lines and a little down once the wheels contact the surface.

[Dane Martin]

at our field, just a little after the take off spot. then the glide from there is nice.
right about here....

[Dave_Trible]

Tim,  in front of the judges.  Then you go around and touch down in front of or just past them.

Dave

[bob whitney]

getting the plane to land where u want it to is a very important part of racing without a shut off . most times the engine will shut off at the same place  ( think it has something to do with the wind ) ,. after u have picked where u want to land  see where the plane lands on a normal landing ,from there u can determine wheather  u need to whip it or hold it back all the time keeping a smooth steady decent.

[Tim Wescott]

OK.  Let's go back to my original question, because most of you are answering as if the engine will shut off any old where.

If you could make the engine shut off right where you want it to, where would that engine shutoff point be?

[Steve Fitton]

It shuts off dead downwind in your kill loop, allowing you to glide one lap to a downwind landing.

[RC Storick]

The best place for it to shut off is at the end of the flight. However I saw them cut off sooner at the NATS.  

[Tim Wescott]

It shuts off dead downwind in your kill loop, allowing you to glide one lap to a downwind landing.

It shuts off downwind in your kill loop.  My kill loop lets you adjust how long it runs afterwards before it cuts out.

[Steve Helmick]

Mine won't respond to a kill loop, what with it being a clunk tank. It tends to shutoff going upwind, due to the uniflow, I think. Muffler pressure would fix that, if it needed fixin'.

It lets me glide about a lap and ground roll is another 1/2 lap or so. That's what I'd like to fix. Come up with a brake design that will work inside wheel trousers and be adjustable externally with a micro-screw adjustment. The CF wheel trousers are not stout enough to get involved. I'm thinking about epoxying a disc (CF, Alum. or Brass?) to the inboard side of each wheel and just have a nylon screw rubbing on it. Or maybe a lever rubbing on it, with a screw pushing on the lever. The wheels are retained by a "C clip" with a flat washer between clip and hub, so can't push too hard. 

At Auburn Muni, I can almost always touchdown in the same place within a few yards, and happily, that's the good place to land, tho it has nothing to do with where the judges are. But then again, I make lots of 40 point landings and get 28-32 points for them.  Steve

[Tim Wescott]

But then again, I make lots of 40 point landings and get 28-32 points for them.

I have that problem, too.  Particularly when you're judging.

When you're experimenting, try using a bit of mild steel, like from a tin can (a pineapple can would do).  Then locate a 1/4" or 3/8" diameter neodymium magnet close to it.  If it works you'll have a hysteresis brake.  Assuming that you can make the disk run true, you should have a pretty consistent braking, but I'm not sure if it'll be enough.  You can then adjust the amount of braking by the spacing to the magnet, and possibly the number of magnets (alternate them N-S-N-S).

I'm not sure if the hysteresis brake will work -- you need steel that's magnetically soft enough to get magnetized, but magnetically hard enough to hold onto the magnetization.  If it's too hard the magnet won't affect it; if it's too soft it'll let go too easily.  Some experimentation may be in order -- fortunately, for plain old carbon steel the magnetic hardness roughly tracks the physical hardness.

If you use aluminum or brass instead of steel you'll have an eddy current brake.  It'll slow you down fast at high speeds, but not give you any braking at all at low speeds.  A hysteresis brake should work all the way down to a stop, although at high speeds it'll probably have an eddy current component as well.

Edit:  You probably need to do some lathe work to get the disk running true enough.  I don't know how true it needs to be -- just give it to Haverly and tell him that some engineer said it needs to be "close".

More edit:  And don't blame me for the wad of rusty washers, cotter pins, and iron-bearing sand gumming up your wheels.

[Derek Barry]

It shuts off downwind in your kill loop.  My kill loop lets you adjust how long it runs afterwards before it cuts out.

 One full lap later plus enough time to do another kill loop (or at least half of one). The object of the kill loop is to gain speed to drive you around the circle through the up-wind side and land back on the down wind side.

Derek

[Derek Barry]

I have that problem, too.  Particularly when you're judging.

When you're experimenting, try using a bit of mild steel, like from a tin can (a pineapple can would do).  Then locate a 1/4" or 3/8" diameter neodymium magnet close to it.  If it works you'll have a hysteresis brake.  Assuming that you can make the disk run true, you should have a pretty consistent braking, but I'm not sure if it'll be enough.  You can then adjust the amount of braking by the spacing to the magnet, and possibly the number of magnets (alternate them N-S-N-S).

I'm not sure if the hysteresis brake will work -- you need steel that's magnetically soft enough to get magnetized, but magnetically hard enough to hold onto the magnetization.  If it's too hard the magnet won't affect it; if it's too soft it'll let go too easily.  Some experimentation may be in order -- fortunately, for plain old carbon steel the magnetic hardness roughly tracks the physical hardness.

If you use aluminum or brass instead of steel you'll have an eddy current brake.  It'll slow you down fast at high speeds, but not give you any braking at all at low speeds.  A hysteresis brake should work all the way down to a stop, although at high speeds it'll probably have an eddy current component as well.

Edit:  You probably need to do some lathe work to get the disk running true enough.  I don't know how true it needs to be -- just give it to Haverly and tell him that some engineer said it needs to be "close".

More edit:  And don't blame me for the wad of rusty washers, cotter pins, and iron-bearing sand gumming up your wheels.

Cool ideas but all you really need is a lock-nut and washer on either side of the outboard wheel. You can then adjust the amount of break that you have to your own personal preferences by tightening the nut against the wheel hub.

Derek

[Crist Rigotti]

When I did cut off loops, they were performed downwind.  So I would like my electrics to shut off downwind.

[Steve Helmick]

Cool ideas but all you really need is a lock-nut and washer on either side of the outboard wheel. You can then adjust the amount of break that you have to your own personal preferences by tightening the nut against the wheel hub.

Derek

Yes, well, that won't work, 'cause there's no lock nutz anywhere. See the diagrams. The screw through the LG strut is a 4-40, and the rest is 'luminum, except for the 'c' clip. These are from Central Hobby, Billings, Montana. Funny thing is that I can't find any sort of brakes on their site. I thought R/C pattern models usta have 'em. I was just looking for ideas there, not to buy their stuff...tho that's not totally out of the question.  Steve

[Tim Wescott]

Steve, as pictured I cannot recommend that axle -- the parts flying off mean that your airplane will not get any points for the flight!

Take that arrangement of stuff, and put a spring between the wheel and the shoulder on the axle.  You probably want to make the spring out of a folded-over piece of springy brass, but folded spring steel may work, or a small coil spring.  Adjust the spring tension for the amount of braking.

[Steve Helmick]

Steve, as pictured I cannot recommend that axle -- the parts flying off mean that your airplane will not get any points for the flight!

Take that arrangement of stuff, and put a spring between the wheel and the shoulder on the axle.  You probably want to make the spring out of a folded-over piece of springy brass, but folded spring steel may work, or a small coil spring.  Adjust the spring tension for the amount of braking.

Tim, those parts are being installed, not flying off. There's about enough room for a couple layers of typing paper between the axle flange and the wheel hub. I kinda like your disc/magnet plot, but I'm thinking of mounting an alum. bracket under the axle flange (pointing aft or up) and then doing something from that. Just not sure of what to do with it!  Steve

[Ted Fancher]

"O" rings between both wheel hubs and their wheel retainer.  Adjust for "like" tension on both sides so that the airplane still rolls forward when pushed but stops after only a few feet of roll after a moderate push.  This does three things: 1. Limits the landing roll even after high speed touchdowns in strong winds to avoid the dreaded roll back into the wind. 2.  Allows virtually silent touchdowns as the 'rattle' between the wheel and the retainers and washer is silenced. 3. The resistance to turning adds just the tiniest bit of nose down rotation when touching down which acts to minimize the chance of bounces.

To answer the original question: a cut off loop should, IMHO, always be an option to help the pilot select the best place to touch down...which should essentially always be downwind...the O ring (or a "slice" of fuel tubing) brake becomes essential when landing in high winds to prevent the airplane from rolling around into a headwind with the tail dropping, risking an unwanted re-entry to flight.

A cutoff loop should always initially be a large loop at a time in the engine run the pilot knows the 'time is right'.   Large because the cutoff is the result of positive G's pulling the fuel down and away from the fuel pick up tube and you need to keep the fuel away long enough for the engine to quit or it'll just start up again...which looks un-cool.  If it doesn't quit, tighten the radius and do a second loop at a higher g level which--if you know your engine run well enough--will be enough to shut down the engine.

Note the cut off loop only works if the fuel pick up tube is "fixed".  This is exactly the reason I own no competition airplanes with clunk tanks.  In bad weather it will almost always cost you points as you'll be unable to "begin" your landing approach from the ideal location to allow a downwind landing...with all the benefits of control that provides.

Ted

P.s.  A big thank you to Al Rabe for these pearls of wisdom...among his many other contributions to the art.

[RC Storick]

I run a clunk tank and when I hear the first charge at the end of the flight wait a lap and do a cut off loop and it will quit.

[Steve Helmick]

Robert...I'll try that! Mine has a very noticeable "charge" when it's getting ready to shut down, does a couple laps at about 75mph and shuts off cleanly. I can't imagine that a cutoff loop would increase the speed beyond that...I'd be happy with a reduction.   Steve

PS: I was shocked to see you flying I.C. at the NATS. How come not 'lectrons?

[RC Storick]

Robert...I'll try that! Mine has a very noticeable "charge" when it's getting ready to shut down, does a couple laps at about 75mph and shuts off cleanly. I can't imagine that a cutoff loop would increase the speed beyond that...I'd be happy with a reduction.   Steve

PS: I was shocked to see you flying I.C. at the NATS. How come not 'lectrons?

I discussed this issue with Brett and seems no one can put a finger on my issue with electric yet. Just about everyone I watched this year has some of the issue I don't like. The feeling of Lock. Maybe we can get Brett to chime in and explain this. Something to do with laminar flow and vibration. Not quite sure but I sure can feel it, and see it now because I know what I am looking for. My electric planes have wonderful power delivery but its just a feeling in all 6 planes I have built I will need to learn to live with.

Dennis Adimisson thinks it might be prop rotation and I just have not got to it yet. All 6 planes I have built run clockwise prop rotation.

My entry next year will be electric but it will suprise you on what it is.

[FLOYD CARTER]

The first thing to do is determine how far your plane will glide after a clean engine shut-off.  They are all different.  One of my large planes will easily do 1 1/2 laps without coaxing. Others, barely 3/4 lap.  Touchdown downwind is the best to prevent any headwind raising the plane on roll out.  I think the roll-out is important, for realism. 1/4 lap is good.

How you coax the engine to stop at your chosen spot is the only remaining problem  I've never been able to manage it.  The only reliable way is a 2.4 GHz transmitter to a throttle servo.  I don't like that.

Even electrics are problematic, because they stop after a fixed time-out.

Floyd

[Tim Wescott]

How you coax the engine to stop at your chosen spot is the only remaining problem  I've never been able to manage it.  The only reliable way is a 2.4 GHz transmitter to a throttle servo.  I don't like that.

Ah, Floyd, you haven't been paying attention.  I have a gizmo that'll do that reliably.  Gyro+microprocessor+lots-o-code.  Use it in an electric and you can do cut-off loops.  For IC you have to add a servo and some plumbing, but it'll work there, too.

Even electrics are problematic, because they stop after a fixed time-out.

Howard Rush has devised a solution to that problem, too, which is implemented in Tim's Universal Timer: toward the end of a pattern, you start flashing a gawdaful bright LED about once every 5.2 seconds (you choose a time that's a bit faster than a regular lap).  Then you use the flashing light to tell you how to adjust your lap time (by inserting stunts, or flying high, or whatever) so that at the appointed time (on the last flash), you're right where you want to be.

[FLOYD CARTER]

April 1 is long past.

[Tim Wescott]

April 1 is long past.

I'm not joking.  I've done it.

[Trostle]

OK.  Let's go back to my original question, because most of you are answering as if the engine will shut off any old where.

If you could make the engine shut off right where you want it to, where would that engine shutoff point be?

I will do a kill loop which means the engine cuts out on the down side of the loop.  Because of inertia and all, the props still tuns for a quarter lap or so depending on the engine and wind.  I have already determined where I want the touchdown to be which is when the airplane is heading with the wind.  When it is really windy, this part of the landing when the airplane is heading down wind is even more important.  That kill loop gives the energy needed to come around to that dead downwind touchdown.  Sometimes some whipping might be needed but normally, not much.  And again, the touch down is when the airplane is traveling with the wind, NOT the downwind side of the circle.   

The above is for a contest flight.  On the local practice circle, I still use the kill loop which normally gives plenty of energy in the airplane so that with judicious use of whipping, I can touch down where the plane will stop on the side of the circle, near the pit area, where the mechanics do not have to walk completely across the circle to move the airplane back to the pits.  But if the wind is a serious problem, I will still try to get the model to touch down when it is traveling with the wind.

Keith

[wwwarbird]

The best place for it to shut off is at the end of the flight. However I saw them cut off sooner at the NATS.  

 

[Steve Helmick]

It happened that we went flying this evening...Pete Ferguson, newbie Kris Millard (40 years since last CL flight) and myself. I flew 3 flights and tried the shutoff loop per Robert's suggestion, with nothing positive to report. Big loop. Didn't seem to faze it at all. Waited one lap, did big loop, keep going. Next flight, I tried the loop at first downwind side after rpm increase...nothing. If I wait 2 laps, it'll quit...but it would have quit anyway, so can't see it's worth the risk, is it? 

I think the size and shape of the clunk is a factor. For those tempted to use a sintered bronze filter/clunk thing...I see no way they can work well for our application. When any part of it gets uncovered, the engine will suck air and not fuel.  I suspect it would tend to not shutoff cleanly, but with lots of burping and belching. I think a small & heavy clunk should be best. While it's tempting to throw some technology at it with a tungsten clunk....but......  naaaah!  Steve

[John Stiles]

The best place for it to shut off is at the end of the flight. However I saw them cut off sooner at the NATS.  

I thought once I'd put a wheel in the top of the canopy...make it look similar to a wheel barely sticking out from wheel pants. I got the idea after seeing all those planes with their vertical stabs chopped off!

[Trostle]

It happened that we went flying this evening...Pete Ferguson, newbie Kris Millard (40 years since last CL flight) and myself. I flew 3 flights and tried the shutoff loop per Robert's suggestion, with nothing positive to report. Big loop. Didn't seem to faze it at all. Waited one lap, did big loop, keep going. Next flight, I tried the loop at first downwind side after rpm increase...nothing. If I wait 2 laps, it'll quit...but it would have quit anyway, so can't see it's worth the risk, is it? 

I think the size and shape of the clunk is a factor. For those tempted to use a sintered bronze filter/clunk thing...I see no way they can work well for our application. When any part of it gets uncovered, the engine will suck air and not fuel.  I suspect it would tend to not shutoff cleanly, but with lots of burping and belching. I think a small & heavy clunk should be best. While it's tempting to throw some technology at it with a tungsten clunk....but......  naaaah!  Steve

The loop cut off works for me.  I use metal uniflow tanks, no clunks, and can normally tell when the tank is nearing empty.  A single loop will normally cut the engine.  Sometimes, it will take two consecutive inside loops to do the trick.  I do not know about the clunk tanks.  If you know your equipment, there is no risk doing the inside loop cut off.

Keitih

[Paul Walker]

I prefer mine to shutoff heading directly into the wind, i.e. 90 degrees past down wind. This gives me the most potential energy heading into the wind without power. It also keeps from having to touch down with a tailwind after it slows down.

I would do this wind or no wind if I had a choice.

[Tim Wescott]

I prefer mine to shutoff heading directly into the wind, i.e. 90 degrees past down wind. This gives me the most potential energy heading into the wind without power. It also keeps from having to touch down with a tailwind after it slows down.

I would do this wind or no wind if I had a choice.

OK.  Now I have another question -- in a system where the plane went to high throttle right after you straightened out from a cutoff loop (which is presumably downwind), would you want 90 degrees of high throttle and then a cut, or 450 degrees of high throttle and then a cut?

[Paul Walker]

90 degrees only.