Stefan Hafner

Most of the stuff i use is heavier, but then thats for actual composites construction, but most folk seem to use the Grams per square meter designation.  As for suppliers, I use these guys , its about the cheapest place that i've found so far. The cloth you're talking about at 1oz/sqYd is about the same as the 25 g/sm that they do, not quite as cheap at the stuff you got though, thats about 50p/ yard, they may as well be giving it away :P

So, after too long away from the build i finally get to get on with it again, but at least now i can get on and buy most of the stuff i need to finish it :D Since my last post, i've glassed and sanded the fuselage, but not got any photos, and to be fair it still looks the same, and i've also added the instrument panel cover.  The main changes are on the wing, which has been sanded and primed. This was then sanded down so i could make the gear doors. I started off by marking the position of the doors, and covering them in cling film, makming sure that the cling film wasn't lifting at any point of the doors. Then i laid up 4 layers of glass cloth, 3 coarse cloths to give a bit of thickness and strenght, and a finer layer on top to save a lot of effort on the sanding front. This give me a thickness of about 1mm, which sould easily be strong enough to survive most things.  Once the resing had cured i could just see the outlines through the doors. From this i could mark the outlines onto the glass, and separate the doors from the wing. I was pleasantly surprised at how easily the glass released from the cling film, think i'll be using it as a barrier for molding again. Annoyingly there were a few pinholes in the cling film, so a bit of resin got through these, but that can just be sanded off. Next jobs, detail the insides of the gear doors and add the panel lines to the wing.  

The ailerons are 'Junker' type aswell, so hang below the wing, with an off-set pivot, so the aileron LE & TE will decrease the gap between the wing upon deflection, which I also believe helps keep the air 'on' the surface..??  I think in this case the main benifit of having the ailerons is to keep them in the cleaner airflow below the wing, which means control is maintained better at higher angles of attack,as the airflow coming from the wing will most likely be turbulent.  I think what you'r thinking of is slotted flaps, like those that are used on big airliners, which work by allowing some of the air at higher pressure under the wing to flow over the top surface to re-energise the boundary layer on the top surface to keep the flow attached, as once it separates it stalls the wing.This diagram from my uni notes probably explains it better

Spot on Chrisie Using the full length would increase the camber of the wing, and so the angle of attack, so using only 50% movment on the outer section will reduce the angle of attack on the outer section of the wing, which has the same effect as when we build washout into our wings.   Drooping the ailerons will of course help with STOL performance, as it increases the camber of the wing, so more lift and so a shorter takeoff run.  All you need to add then ar some leading edge slats

Its a compressed air engine, to quote Doc Brown, " spark plugs..... where we're going we don't need spark plugs"

Very impressive indeed, but you're gonna need a big compressed air tank for that spit james Try putting one of these in it though, or some of these ones shown here

Do you mean carburetter ???

If you want to have it look relatively scale you'll need to make some sort of housing, but for the mounting the actual fan casing if you look carefully at the picture there are mounting lugs on the outside (just visable under the top of the H of the hobbyking logo) that will hold the fan in place. The 16 and 18mm refer to the dimensions of the motor mounting holes.

I think you would be out of fuel in the first engine by the time u get the last one started

Altering the CoG will mainly affect the static margin, which affects how sensitive the elevator control is, reducing the angle of attack as you suggest I think will have better results. Clinbing will be caused by the wing producing too much lift, and this changed will reduce the amount of lift by reducing the angle of attack. Just my 2 pennies worth

Looks like its gonna be a good one, carefull on gray days tho, somone at my old club had a chrome plane and lost sight of it about 30 seconds after take-off

Had a look at the manual, and with the engine at that angle it shouldn't be causing any problems. It may be that the tank is a little low, but its hard to tell without seeing the plane in the flesh.  Have you checked if the needle valve is blocked, i've had that cause problems in the past. To check this you just take out the needle valve and try and pump some fuel through or blow through the fuel line, if it runs out easily its not blocked, but if its blocked you may need to try blowing through it down the fuel line, and that should soon "eject" any blockages in the valve.

Sorry if I confused you a bit, I'll try and explain it a bit clearer Its usefull to know which way up the engine is mounted, ie: is the cylinder pointing up or down when the plane is the right way up?  This pic shows the best way to line up the tank and the engine You can see how the centreline of the carburetor is just above the centre of the tank. No as we're talking about a Mustang I expect you, put the engine in upside down, but the rule about tank height should still apply, I've edited the pic (badly:P) to show how it should be. Here if anything the tank will be even lower in the plane than with the engine the right way up, which may be causing problems on the transition.  I also just thought of a plane i had with long fuel line causeing problem on the trasnition, how long are your fuel lines? For fuel coming out the exhaust, when the engine is running normally, the line that comes from the silencer pressurises the tank , to push fuel through to the engine, and this obviously depends on the revs of the engine, as at high speed more exhaust gasses are coming out of the engine and creating a higher pressure. Now this pressure line usually feeds into the top of the tank, so that when the plane is the rightway up, it is above the fuel level and fuel cant get in to it.  When the plane is inverted it is now submerged and fuel can get into it, but is prevented from doing so by the pressure in the line coming from the silencer. I suspect that when you throttle back this pressure is becoming less, and is letting fuel drain out through this line. This hasn't happened to me, but each engine will have a different pressure in the silencer, so seems a rerasonable explanation to me.   I don't think i'd be too worried about this, as most of the time you're inverted you'll probably have power on anyways  Hope this is a bit clearer.

How is the engine mounted in the plane, if inverted and the tank is above the centreline of the carburettor barrel the its too high, it wants to be below the centerline of the carb, i seem to remeber about 1/2" below.  As for the fuel coming out the exhaust, is it definately fuel, or just some oil that is sloshing around the silencer and its easier for it to escape when its upsidedown. If its fuel, i assume you have a pressurised system, in which case is it possible that the fuel is running back through the pressure line, as you say it only happens below half throttle which is when there will be less pressure from the silence and it may be possible for the fuel to get through.

Posted by Dizz on 21/10/2011 13:58:50: 2 of my models have definitely generated more thurust once moving than when stationary I would think this lies in the design of the fan, if the setting angle of the blades is a very high then when static it may be that the blade is effectively stalled, and therefor will have a very high drag figure and be putting a large load on the motor. When it starts to move the relative angle of attack (effetive anlge of attack) of the fan blades will reduce, as in the diagram in my previous post, and the angle of attack of the blades will then be lower than the stall angle, meaning that the power that was being used overcoming drag prviously is now available for going faster :D   Agreed. Better to leave supersonic aircraft out of this discussion.   Aww, no-one want to try and go supersonic

Posted by Richard Sharman on 20/10/2011 20:49:34:For example, no one has commented yet on the relationship between static thrust and dynamic thrust -- what is it? Because it's not obvious. Static thrust is when the fan is fixed, fairly self explanatory for this part I think Dynamic thrust is the trust that is being generated when the aircraft is moving through the air, and will be less than static because the relative angle of attack of the airflow over the blades is reduced due to the velocity of the aircraft. This is a lecture slide from at uni, where it can clearly be seen that when going faster that the effective angle of attack is lower, and as the prop can be treated as a wing at lower angle of attack the trust (lift) will be less. this example is for a propeller but the same princlple will apply to a fan. Posted by Keith Simmons on 21/10/2011 09:05:10: Also on SR71 Blackbird, there is more thrust generated in front of the engine cone at M3 so is that due to a vacuum effect due to pressure shock wave generated in front of the aircraft. I wasn't aware of any engine generating more thrust in front of it, but the SR71 is a tricky example because of the science involved. At low speed the engines worked in a conventional low bypass engine, but at about M2.3 I believe the engines started to operate on RAMJET principles as the forces were too high for a conventional engine. As for shock waves, the cones on the front were variable geometry (they moved back and forth) to create the shock waves, the reason being that the engine would not work with supersonic flow in the combustion chamber, and the shockwaves reduce the flow speed, and increased the pressure, but i've never heard of the lower pressure at the intake.

Myron, I know the actual principles of the engines are worlds apart, i'm intrigued to see if the same ducting principles can be used, ie: use a diverging duct to increase the pressure and reduce the velocity at the fan to create a higher enegy gain in the flow. Richard, I would think the longer the pitot tube is the better, as the calculation done for airspeed relies on the difference in static and dynamic pressure, and at the nose of the plane i would expect boundary layer effects and flow stagnation will occur for a reasonable distace in front of the nose and affect the pressure.

On my T180 the side windows are just stapled on, bit rough and ready but works well, and with some covering over the deges it looks not half bad. as for glueing, id be interesed to know wat othe folk say too, as its usually a real pain

Sounds like this could be an interetsing thread, and will be interesing for me, as I had to do a whole class on Turbine design at uni, so might be able to bring something usefull to it too  Also, will be handy as i'm designing an A-10 at the moment that I'm hoping to sell later on as a kit

missing text here??

Pilot might just be a bit short person  I know the small lathes are fairly cheap, problem is i want to use one for other stuff too, so saving up for a bigger one, really wanting something with about 300mm swing, sorry, bit off topic, no more machine related posts

Looks very nice Tim,  Am slightly jealous, I wish I had a lathe for that sort of stuff, filing to shape get a bit tedius

Hmm, this has got me thinking now, never really thought about it before.  I'm not sure if the tip vortex would have anything to do with it as I would only expect it to be affect ing the very tip of the wing if anything. My thinking would be that the lack of tailplane would have more to do with it, as the sections used on wings and tail-less planes all have a reflexed camber line to cancel out the pitching moment created by a normal section.  The tailplane on a conventional plane at high angle of attack, will be stalled at the same time as the wing, most likely before the main wing due to the smaller chord length meaning that its at a lower reynolds number (like for like will stall earlier), so the force created by the tailplane to counter act the pitching moment will dissappear, which means the pitching moment of the wing then dominates, and will create the nose down movement or snap that we all know.  With a wing or delta the pitching moment that is cancelled out by the tailplane on a conventional plane is non existant as the section is designed that way, so that the stall is simply the wing losing lift and descending while still flat.  The rounded leading edge, I would expect keeps the flow attached longer, so delaying the stall, and would it be fair to say that these models are fairly light??   Sorry, bit technical, but i think this sort of explains the aerodynamics of it Edited By Stefan Hafner on 27/09/2011 20:46:49

I'd have to agree with you there Doug, i think they were only used to slow the Spit down for landing, if i remeber correctly they moved about 80 degrees and just sort of stuck out like a plank If the old topflite mustang i had a few years back then this one should fly a treat Myron

Was typin while you posted there Steve, I wonder if putting a big funnel on the carb would work, not sure what it would do for the drag though . I have noticed th ehigher pitch improving things a bit, purely as a dinged one and the only spare was higher pitch, but did help a bit. The main difference I noticed was the take-off, and then just kept the speed up a bit.