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Author Topic: Fuel and shut-off systems  (Read 1465 times)
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RobinB
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« on: October 09, 2009, 09:03:20 AM »

I'm completing a 57/58 Lucky Lindy (the 'big' 500 sq.in. version) which will probably have an OS MAX .19. A clubmate has an FP20 in a Lindy, but it's a bit leery!

Under UK Classic Power rules any fuel system is allowed, so I'll have a latex balloon supplying the pressure.

But here's the question - is it necessary to have a flood-off, or will a pinch-off work ok?

All of the flood-off systems I've seen in the UK are for very high-revving engines (F1C, J, etc), but I notice that a lot of U.S. AMA gas models have a bladder with pinch-off. Is it down to the rpm as to which method to use?

Robin
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Scottl0413
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« Reply #1 on: October 09, 2009, 09:44:06 AM »

Robin, your F1C guys use flood off because of the high rpm's they're turning there afraid (and rightly so) that with the pinch off you'll lean out the engine and possibly freeze up the motor. Running your OS 19 with a bladder and pinch off will work fine with no ill effects. I have Super Tygres, OS's, and Cox's all running on pinch off timers with no problems.

Scott
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applehoney
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« Reply #2 on: October 09, 2009, 09:52:55 AM »

Agree with Scott - pinch-off is fine. I've been using pacifier, pen bladder, surgical tubing, etc. since the early 70's on everything from 1/2A to .40's and have never found any need for floodoff, least of all for the additional plumbing required.

Incidentally, a friend in the US flys a Lindy in Nostalgia with greater power .... impressive and faultless.
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glidermaster
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« Reply #3 on: October 09, 2009, 12:19:39 PM »

Treat us to some pictures, Robin (Robin builds a nice model, guys).

Our old friend George Fuller is a bladder man, of course, and I think he exclusively uses flood-off. Having said that (and I'm not a bladder man, of course), pinch-off seems to work just fine with a bladder. The only thing I can think of that might possibly constitute a down-side to bladder/pinch-off is that it does (of course) lean out the engine, and there might be a plug life penalty to that - I don't know for sure, it's just a thought.

With suction/pinch-off there is a benefit to getting the pinch very close to the spray bar - it gives a cleaner stop. I don't know if the same holds true for bladder.

John
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RobinB
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« Reply #4 on: October 12, 2009, 11:57:29 AM »

Thought it was a question of revs - logical, really. George always says that he tried the idea of flood-off to stop those piped G15s that John B referred to in another post.

Jim, my clubmate John Deeming has a 'Cranfield' Lindy with an OSFP20 which he's modified. Goes very quick, and he's had to repair it more than once. He did up an FP20 for George, who obviously put it in a Dixielander (pic attached)

I'll do a snap of my Lindy if you really want - it's a butt-ugly plane! I don't understand how it gets away with such a low pylon, though the subject of pylon height is a bit of a mystery - I suspect most designers use half the prop diameter and add half an inch. The Lindy pylon is nearly as wide as it is high.

Robin
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Re: Fuel and shut-off systems
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RobinB
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« Reply #5 on: June 30, 2010, 11:39:18 AM »

This just in:.... A suggestion to the UK's Free Flight Technical Committee regarding timing engine runs has actually brought a response in favour of pressure feed systems.
Extract as follows :

>>>>Rule 3.1.6.2(a) change---- "when all audible noise from the engine ceases." --------to------- "when engine power strokes cease."

Reasoning is as follows:

Cessation of power strokes is easily heard and recognised by timekeepers and is an almost instinctive cue to stop the watch. The present rule requires the timekeeper to disregard this cue and wait until he is SURE that the engine is not going to make another sound, e.g., a "diesel cough", resulting in an over-run being given if he is "keen", or not if he isn't. The result is inconsistent standards of engine timing , with the competitor being unsure of this standard. This can lead to an increased risk of an over-run, unless the competitor sets his engine run conservatively and probably penalises himself. Frankly, under the present rule, engine timing is, and always has been, a lottery , the recorded time being largely dependent upon the 'attitude' of the timekeeper.

The engine rundown , with the engine producing no power and the propellor slowing, probably produces insignificant thrust irrespective of the length of the rundown for engines not fitted with propellor brakes. Models with engines which are fitted with brakes may be disadvantaged, only practical experience will tell.

Adopting my proposal will ensure accuracy and consistency in timing engine runs, across all timekeepers,experienced or otherwise, 'keen' or 'generous', with all competitors having confidence in timekeeping standards adopted by all timekeepers.

The method I propose is the official timekeeping method of the AMA, and has been in use in the U.S.A. for many years.

Northern Area power competitors have been canvassed and there is broad support for this proposal.

I suggest that the rule change be adopted for a 1 year trial period, during which its operation and acceptability can be assessed.


Comments. Keep the rule unchanged from Jo'D. Allow pressure and hence clean cuts in all classes from Peter Watson. The FFTC are so far inclined to take the route of introducing pressure and hence flood off and clean cuts.

>>>>>>>>>>>

Thank you, Peter Watson!

RobinB
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applehoney
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« Reply #6 on: June 30, 2010, 01:23:53 PM »

Not a new idea. I pushed that scenario to no avail about 30 years ago, arguing that 'run down' time served little purpose regarding gaining further altitude. It's interesting to see the wheel go full circle and it appear as a new suggestion. The Northern Area, of which I was Chairman at that time, was supportive then but it was turned down by the SMAE/BMFA F/F honchos. As was noted, it's been the rule in North America for many years..

BMFA. it was the NA Delegate of the time who, when the Society changed its name, christened it the 'Bought Model Flyers Association' and had his wrist slapped by Council (as if he cared!) .. yet maybe an increasing ring of truth to it as time passes.
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PeeTee
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« Reply #7 on: June 30, 2010, 01:48:52 PM »

Jim

It hasn't been submitted as a 'new' suggestion. The Northern area, and other power flyers submit this every year or two, and it regularly gets rejected. As a timekeeper for some southern power flyers my finger invariably goes on the button as soon as the main noise stops.The descriptive part of the submission is spot on, how long do you wait? I can always blame my 'tin' ear Grin

Peter
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applehoney
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« Reply #8 on: June 30, 2010, 03:30:11 PM »

The existing rule was always particularly hard on diesels which so often tend to fade out and 'burp' a little before quitting, all of which presently counts as engine run. The change in attitude of the model from the last full power stroke always indicated that such 'after-run' did nothing for increasing altitude.

Good to see that my past compatriots in the NA are still pushing and shoving!

Jim
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« Reply #9 on: June 30, 2010, 03:36:30 PM »

You probably cannot research the original author of the "timer" rule now in use by the AMA, but it was my proposal that is the now established rule.

I offered it as an alternative to the then existing rulebook item in the early 1980's. At that time I was regularly competing in AMA power events as a member of the Texas "Pearl Team".

Same arguments were presented about "rundown" and a few flyers devised engine braking systems..some worked so well that connecting rod failure was a common problem.

It's really easy to hear the last power stroke, even with my hearing loss from too much pistol shooting without ear protection...

Duco
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RobinB
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« Reply #10 on: July 01, 2010, 03:37:58 AM »

I forgot to credit the rule change suggestion - it's from Dave Limbert, a top SLOP competitor. (He's fairly Northern, Jim)

I agree that this suggestion comes up regularly, but this time it sounds as though it might get the ok.

Interesting that flood-off is automatically associated with pressure feed. They shoulda read this thread Grin

Robin
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RobinB
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« Reply #11 on: October 05, 2010, 03:54:23 AM »

Just received the latest news from FFTC on the rule change proposal mentioned above:

"1.I.C. Engine run timing. No change. The extensive arguments put forward by both proponents of change (to either the American "last power stroke" approach or the adoption of pressure) and the "it has been OK for 50 years" lobby were considered at length. At the end the committee felt that any change was simply going to raise a fresh set of problems."

So, yet again, no change. We're still stuck with gravity feed for Slow Open Power.

RobinB
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applehoney
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« Reply #12 on: October 05, 2010, 09:47:58 AM »

Time for a new forward-thinking committee ?  If you can find anyone willing to serve, of course.

There is another approach ....  if, say, the Northern Area ran all power events (other than Area Centralised and FAI) to pre-publicised rules that specified engine timing to the last power stroke - and maybe pressure feed for SOP optional - then competitors would become used to the idea which - after a season (or two) would spread further afield and ultimately become official policy by default.

Run it by the Morley lads ... they might like it .. and take it to the NA Committee. Any FF people on same these days? The NA was never reluctant to be pro-active and innovative in the past and hopefully things haven't changed. Often wish I was back and flying there.

Thinks.... "lads" .... huh! Say 'Hi" for me ?
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Dimeflyer
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« Reply #13 on: October 09, 2010, 12:06:37 PM »

Jim
Why don't the rules committee give this a 90 day trial period just to see if it would be agreeable with the guys in the field? Better yet the guys in the northern area could get things going by allowing the local field contestants to choose which way they do their timing for each contest??

Just an Idea !?!?
George
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glidermaster
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« Reply #14 on: October 11, 2010, 03:26:50 PM »

George raises an interesting point - why not try it first!

What occurs to me however, is that it (the engine run timing thing) has already been tried - for donkey's years in the US. To a large extent, of course, 'the last power stroke' is exactly how we time engine runs already, though I do note the point about audible run-on in diesel models. The f/f sub-committee then, have passed over a chance to put the rule book in line with established practice, to align the rule book with established practice elsewhere in the world, and have ignored substantial accumulated evidence that this is indeed the way to go.

John
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RobinB
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« Reply #15 on: February 01, 2011, 04:35:01 PM »

Anyone got any views on installing latex tube pressure systems in relatively slim fuselages like Creep or Dixielander?

I've noticed from bench running with latex that it tends to balloon out to a spherical shape. If it's confined into a compartment inside a fuselage, does it adapt to a shape that fits? If so, does it need any extra strengthening to prevent it from bulging the sides out?

I'd rather fit it inside somehow than have it tied to the outside.

Robin
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FF Bruce
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« Reply #16 on: February 01, 2011, 09:33:56 PM »

I have all my Nost. models on bladders and will never ever stick that ugly thing on the outside. You must widen the body so the bladder never touches the sides. It would give you uneven pressure until it shrinks down. I've built a .020 Creep and scale the body's only about a 1/2" wide at the front I widen it to match the 020 mount giving just enough room for the bladder.You can also use different dia. bladders. The sizes I use are 3/16,1/4, 5/16 & and one more called a "Red Cap" it's sold at hardware stores to seal caulking tubes after there opened.Also use the least amount of fuel you can,7cc for 1/2A's works for me, that's about 30sec.of fuel.12 to 14cc on my .15's &.23 you get the idea. I seal the bladder area with epoxy and put a small hole or tube(3\32 dia.) at the back of that area on the bottom, this is to let me know if there is a leak and to make cleaning out easier if there was a broken bladder.Hope this helps.
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glidermaster
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« Reply #17 on: February 02, 2011, 04:21:22 PM »

I think if you look at the picture of Mr Dixielander (Fuller) himself further up the page you can deduce the answer - well, George's answer; turn the engine upright, widen the fuselage, and create a decent size cavity for the bladder. I think you can see that he has a fairly long fuel line going to the engine, and thus the bladder is fairly well back.

George uses (or used to use) water balloons from the Joke Shop - 2 of them - one inside the other. One piece of advice with bladder - don't use too much fuel.

John
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RobinB
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« Reply #18 on: February 04, 2011, 05:17:56 AM »

John, that Dixie is standard size behind the mounting fairing - perhaps George's water balloons expand like a sausage so that they fit in the fus ok. I'll ask him when I see him next, tho' I fear he's been drawn so far into the electric cult now that he scarcely mentions i.c. engines.

This question of bladder installation came about while I was looking at the Beatnik plan - that has a 5/8" wide fus! Most of these old (sorry, Classic) UK power models had narrow fuselages due to sidewinder mounting. UK Classic rules allow any combination of engine, mount and fuel system so I was wondering how to convert some of these designs to bladder feed.

One piece of advice with bladder - don't use too much fuel.

I know that - now. It was an old shirt,anyway

Robin
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danberry
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« Reply #19 on: February 04, 2011, 08:23:15 AM »

You could hang the bladder in the wind. Bob Hanford does this. Of course, he really doesn't have much success.....
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glidermaster
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« Reply #20 on: February 04, 2011, 12:45:01 PM »

Well, if you are going to do away with the bearers/sidewinder layout, and put the engine upright, you have to 'transition' back to the plan type fuselage with cheeks/fairings of some sort, so surely there is a region behind the bulkhead where one can create a cavity.

20cc of fuel implies a (spherical) tank of 34mm diameter, where most 2.5cc engnes require a bulkhead of over 40mm.

Just a thought.
John

p.s. note for our U.S. based friends - 1" = 25.4mm  Wink  (sorry, a bit cheeky)
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applehoney
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« Reply #21 on: February 04, 2011, 02:02:57 PM »

You could hang the bladder in the wind.

I've been hanging out pacifiers, penbladders, etc. in the wind since the mid-70's* - attached to the landing skid. Quick, convenient, easy to access and no cleanout problem when one bursts. Good enough for me.

* I think I was one of the first to consistently use bladders in F/F in the UK. The classic comment came at a 70's Barkston Nationals when an arriving Northern Area member greeted me with "I knew you were here when I saw the power model gliding above with a condom hanging from it"
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glidermaster
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« Reply #22 on: February 04, 2011, 09:28:24 PM »

Yeah, you can..................
.........but it's not very stylish, is it?
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FF Bruce
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« Reply #23 on: February 04, 2011, 10:43:23 PM »

Yeah like a five gallon can and hose hooked to your door if it was a car.
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danberry
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« Reply #24 on: February 04, 2011, 11:58:23 PM »

Goin' up like a scalded cat and then floatin' up in a thermal........ priceless.

If I worried about how my planes looked, I wouldn't get to do much flying.

Bob doesn't even suspend the bladder. It just hangs from the pincher.
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