Lipo Man Posted September 23 Share Posted September 23 I’m planning on going to the Laser and Best of Britain event this weekend at Buckminster. Plan was to take my Warbird Replicas FW190, my big foam “cartoon scale” Bearcat and, last but not least, my 3d printed EDF F16. The latter is decidedly unbritish in every way but I thought people might be interested. The main interesting feature is “direct drive” all flying tailerons - the surfaces simply glued directly onto the servo horns. The plane was designed as a 50mm but mine was upscaled to fit a 64mm fan. I was very conscious that the method of fixing the control surfaces was a bit sketchy, especially when mine were bigger carrying higher loads at higher speeds. And of course as the tailerons were the only control surfaces, a failure of either would be catastrophic. So - to cut a long story short whilst turning fairly tightly at moderate speed I saw something rapidly flutter away from the plane, at which point I had no control. I think it was inevitable it was going to happen eventually… I’m therefore without an EDF to fly this weekend. It might be unrealistic but I’m going to try to design and build something in five evenings. It will be a simple box design from foamboard, “inspired” by an F16 XL (I’ll need the extra wing area to cope with the weight of the heavy Hobbycraft foamboard, plus I can fit proper control surfaces with hinges). Evening one - rough sketches and wing planform marked out ready to cut. I’m going to need to pick up the pace! 2 Quote Link to comment Share on other sites More sharing options...
Lipo Man Posted September 24 Author Share Posted September 24 Second evening and a sort of plane is emerging! Pretty sure I could stick a tail on this and fly it, but I suppose I’ll make it look a bit more plane-like before I call it done! 1 Quote Link to comment Share on other sites More sharing options...
Lipo Man Posted September 25 Author Share Posted September 25 Third evening of “work” and I’ve got a sort-of F16 XL, albeit a boxy cartoon version. Feels very rigid and light for all that wing area. I’ll put a top skin on the wings to give some airfoil shape, a canopy just to capture the look a bit more, finish off the tail structure and that’s it done. It might even fly! 2 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 26 Share Posted September 26 LiPo man It looks like the inlet duct area is rather below the minimum 1.2 times the fan swept area (FSA). I would also add that installing the EDF with its bell mouth in a rectangular "box" fuselage is not ideal for inlet efficiency. It would be better if the inlet duct gently changed from the rectangular inlet to a circular duct that exactly matched the EDF's body diameter. This way the air travelling down the duct will not have to negotiate any sudden changes in direction prior to meeting the fan blades. I appreciate that using foam board it would not be easy to make such a shape. The rule is that anything that restricts the inlet air flow just means the EDF has to do work to restore the planes air flow speed before it can start to speed up the air flow to create thrust. Compared to props EDFs are pretty inefficient to start with, particularly when used in a model based on a airframe specifically designed for supersonic flight! I suspect your design will rely rather heavily on the power of that EDF to fly but I am sure it will. Quote Link to comment Share on other sites More sharing options...
Lipo Man Posted September 26 Author Share Posted September 26 3 hours ago, Simon Chaddock said: LiPo man It looks like the inlet duct area is rather below the minimum 1.2 times the fan swept area (FSA). I would also add that installing the EDF with its bell mouth in a rectangular "box" fuselage is not ideal for inlet efficiency. It would be better if the inlet duct gently changed from the rectangular inlet to a circular duct that exactly matched the EDF's body diameter. This way the air travelling down the duct will not have to negotiate any sudden changes in direction prior to meeting the fan blades. I appreciate that using foam board it would not be easy to make such a shape. The rule is that anything that restricts the inlet air flow just means the EDF has to do work to restore the planes air flow speed before it can start to speed up the air flow to create thrust. Compared to props EDFs are pretty inefficient to start with, particularly when used in a model based on a airframe specifically designed for supersonic flight! I suspect your design will rely rather heavily on the power of that EDF to fly but I am sure it will. Couldn’t agree more - it’s rudimentary, but it should fly. Intake area is bigger than it looks - it’s definitely more than 1.2 FSA. The boxy intake isn’t great, but I can 3d print something to smooth the transition from the box intake to fan if I decide the plane is enough fun to fly to merit the effort! You’re right - it’ll rely on brute force rather than elegant engineering. I’m afraid ’twas ever thus with my designs… 😳 Quote Link to comment Share on other sites More sharing options...
Lipo Man Posted October 4 Author Share Posted October 4 Well it flies. Surprisingly fast and has way more thrust than it needs - can cruise at less than half throttle and full power scoots it along more than quick enough. It’s behaving a bit “oddly” - not sure what’s going on so I’ll get a few flights in to feel it out. At one point in the maiden I managed to get into a flat spin that was almost unrecoverable - I bet I can’t get it to do that deliberately! 4 Quote Link to comment Share on other sites More sharing options...
RICHARD WILLS Posted October 4 Share Posted October 4 I can go into a flat spin at the slightest provocation . Nice work though David . Maybe put a strake down the back bone leading to the fin . That should sort it . Can you remind us all of the spec , ie fan size , cells esc ? Quote Link to comment Share on other sites More sharing options...
Lipo Man Posted October 4 Author Share Posted October 4 1 hour ago, RICHARD WILLS said: I can go into a flat spin at the slightest provocation . Nice work though David . Maybe put a strake down the back bone leading to the fin . That should sort it . Can you remind us all of the spec , ie fan size , cells esc ? The plane is about 1.1m long, wingspan about 750mm. It’s a 64mm EDF unit currently running on a 4s 2200. It has so much power I’m actually going to try it tomorrow off a 2200 3cell. That will be very light for that wing area - might do OK. I’ll try to get some video… 1 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 4 Share Posted October 4 Well done! Remember with a delta the fin is not that far back from the CG when compared to a conventional wing/tail layout. They need big fins as far back a possible to provide the necessary aerodynamic force to resist a spin. With a delta it will nearly always be a flat spin! 1 Quote Link to comment Share on other sites More sharing options...
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