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Precedent Stampe 1/4 Scale


cymaz

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  • 2 weeks later...

Stampe now has laser 150 fitted. Nearly ready to test fly. Getting a car on/off field a challenge.

A few questions please;

1. As the carb is lower than the tank has anyone tried a perry pump?

2. Does anyone know the propshaft size so I can get a domed nut for both laser 150 and 180 please.

Thanks

Bill

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9 hours ago, William Macleod said:

hi Jon,

          unfortunately  the undercarriage is in the way. Looks like a hopper system then..or should I just test fly it as it is?

 bill

 

Cut it out. Whatever is in the way just cut it out and make the space you need. Its why they invented power tools ? 

 

That bay behind the firewall is probably big enough for a 12oz tank anyway so you might not have to cut a hole in the former, but given the awful undercarriage that comes with the kit i would bin that anyway and make a new one that attached from the bottom. You can then cut through the bulkhead without a worry. 

 

There is no point flying it as is. The engine will go lean and probably stop whenever you do a loop or roll. Header tanks do not work unless pressure isolated from the tank above. This means the tanks need modification and you still need to find room for the lower tank anyway. If you attempt this and have any problems i cannot help or offer any technical support as the problem will probably be with the implementation of the tank setup so all i will do is say...lower the tank. Its guaranteed to work and its why i recommend it. 

 

 

 

 

 

 

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That wont work either.

 

If you are in a long right turn or wingover with less than a full tank of fuel left the clunk will be high and dry causing the engine to stop. You could shorten the clunk line to combat this but you will then have the clunk high and dry in a left turn at less than half a tank remaining and this will, again, cause the engine to stop. 

 

Cut a hole in the bulkhead and fit it the right way round. 

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58 minutes ago, Jon - Laser Engines said:

That wont work either.

 

If you are in a long right turn or wingover with less than a full tank of fuel left the clunk will be high and dry causing the engine to stop. You could shorten the clunk line to combat this but you will then have the clunk high and dry in a left turn at less than half a tank remaining and this will, again, cause the engine to stop. 

 

Cut a hole in the bulkhead and fit it the right way round. 

If you are in balance flight in a long right or left turn for that matter, the fuel will stay in the same position as it was when you were flying straight and level.  That is, unless you resort to a long slipping or skidding turn.  So, I would disagree with your comment if you were flying the aircraft in a normal turn.  The other point is to make sure the pipe connecting the clunk to the feed tube is flexible enough to allow the clunk to follow the fuel.  Indeed, if it were flexible, the clunk would just follow the fuel wherever it went.  

 

Don't see the problem unless you are flying a control liner!

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15 hours ago, GrumpyGnome said:

Good point, well made....... but, won't the same thing apply with a long dive if the tank is rotated 90 degrees ?

 

Yes, it can be a problem. 

 

Peter. While i know what you are getting at this simply isnt true im afraid. 

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Well, Jon, that's how physics works in a balanced turn.  If you use an unkinkable but flexible tube (I have some) the clunk just follows the fuel around pulled by gravity.   If you fly with a lot of slip or skid in your turns then there might be the chance of a dead stick if your clunk cannot follow the fuel.

 

As it happens, I have a pumped OS up front on mine, I just have 2 tanks one above the other and there have been no problems.  I would have needed a more complex tank arrangement had I not had an OS pumper up front of course.

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Another devils advocate. Just what i needed. 

 

Yes the physics works that way in theory. But you cannot cancel out gravity completely no matter how nicely you turn, at least not without a rather substantial g force being applied. There is a great video of bob hoover doing a barrel roll while pouring ice tea into a glass. Maintaining sufficient g to keep it pouring even when inverted. its clever stuff for sure and proves the physics.  The issue is that its highly doubtful any model is being flown as accurately as you would need to do this, and the forces required to have the effect you mention are substantially beyond something like a stampe doing a long 45 degree bank turn, especially if its descending. Also what about a spin, or a knife edge, or anything else that forces all of the fuel to one side of the model? 

 

I have seen it done and it didnt work. I have even half done it myself when a tank shifted in flight and was diagonal across the fuselage. Long descending turn to land and the engine died half way through as the fuel was at the front/bottom and below the clunk. 

 

I dont just make this stuff up and i am beginning to think that modellers in general look at the simple and easy way to do something, and instead decide to completely reinvent the wheel. Why? just do it the easy way so you know for sure that its going to work. Why take the risk on some radical solution? 

 

As for pumped engines, they dont give a monkeys so the tank can go on the top of the fin for all it matters so their performance is not really too relevant. 

 

 

 

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Jon

 

You may recall that I said in my original post that provided there wasn't a significant amount of slip or skid in the turn the force of turning the aircraft generated by the wing has to both maintain the required level of lift (enough to sustain a climb, level or descent) and to accelerate the aircraft to cause it to turn.  Lift force acts at 90 deg to the wing, ergo the fuel will stay at the bottom of the tank.  If there is a slip or skid in the turn then the fuel will, as you say, go off to one side.  If the clunk is attached with sufficiently flexible tubing (Dubro do some in neoprene) then the clunk will travel with the fuel maintaining fuel flow.  I did stress that the fuel tubing had to be flexible enough to allow this without causing a kink.

 

Bob Hoover's famous video, widely available on YouTube, shows a correctly executed barrel roll while he simultaneously pours ice tea from a flask into a glass on the cockpit coaming while the viewer sees the horizon rotate through 360 degs.  I accept not all of us are quite as good as Bob but generally speaking people are going to fly the Stampe relatively sedately.  Some may wish to perform either point rolls or knife edge and then your point about fuel rushing to one side comes into play BUT so too does my suggestion of using a flexible but not kinking tube to connect the clunk pickup to the feed pipe.  YES, if you don't have a flexible and non-kinking tube then you have a problem.  I still have a supply of Dubro No 199 neoprene fuel tubing that can be used for gas, oil, diesel or glow fuel and that is what I've used successfully for long lasting clunk connections.  When the tank is turned so it's pointing at the ground the clunk ends up at the front (now bottom) of the tank without kinking the tube.

 

If Bill wishes to use that tank arrangement, I would urge him to check that the tubing he proposes to use will allow the clunk to travel around the tank without causing the supply pipe to be pinched and so stop the fuel flow.  If he cannot find tubing that meets that purpose then he'll need to resort to major surgery.

 

By the way, I'm not acting as a devil's advocate.  Just like to see advice given on this forum being correct and arrived at by considering the forces acting on an aircraft in flight.

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I’m a bit confused. Why does skip, or skid cause a problem, Put a force on a clunk. It is driven by the force.
Skid or slip is still a force vector. Why does fuel follow a different path. 
And a fuel tube so flexible that it fall by 180 ° in a dive in a Slec/Dupro dimensioned tank I’ve never yet encountered. Start high enough, strong airframe, brave enough, it will die when the airframe gets to terminal velocity if the tank is not full. 

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Hi Don

 

I did say that I have a situation where I can point the tank at the ground and the clunk will fall to the front of the tank.  That's what I call a flexible fuel tube but one that doesn't kink and cut the fuel flow.    You are right that slip or skid is irrelevant if the clunk connection is flexible enough to be influenced by forces in flight.

 

I have to say, I've never seen anyone brave enough to start really high and dive vertically to terminal velocity to demonstrate your point.   

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