hello!
I'm trying to build my first RC model UAV i have the airfoil cut out of polystyrene clark-y and with wing span of 1.5meters but i want a way to build a very lightweight fuselage i tried using PVC before but it turned out too heavy plus with a 5200mah batery weighing 400grams there is already too much weight to carry my motors are 1000KV with 11x7 APC props so please suggest some better materials and designs that i can make do with
Note: foam is not an option too hard to work with my limited supply of tools
Replies
What kind of tools do you have? It sounds like you need to find a good hobby shop that still has construction materials and get yourself a nice hobby knife, some sanding blocks and a razor saw or two. I can't imagine doing anything in this hobby without these tools. They've been my house literally as long as I can remember. (My dad started flying RC when I was 5 years old, back in the 70's.)
If you need light weight a simple and fast construction would be a traditional box from balsa with an aircraft plywood skid plate. On my electric sailplanes I laminated some fiberglass over the skid plate and you can barely tell it touched the ground. Added advantage that wood is very easy to repair and transparent to RF.
Once you get more sophisticated in your construction you can make a single-use male plug and laminate that with your favorite fabric. Understand that carbon is conductive and will attenuate any RF significantly. Many sailplanes use Aramid (kevlar) fabric for the majority of the structure and carbon where needed for rigidity. These things are literally flown into the ground like javelins in contests so the material can take relatively ungraceful landings.
And now for the questions. I'm not trying to be abusive, only get a better idea of the design objective. How much wing area do you have? You said the wing is 1.5m in span but what is the chord length at the root and at the tip? How much payload do you expect to carry or more importantly what is your AUW? You said 'motors' which implies that this is a multi-engine design correct? That much motor on a 1.5m wingspan probably won't give you much for range. Generally aircraft have multiple engines for redundancy and speed at the cost of efficiency. Engineering truism here: Efficient, Fast, Reliable. Pick two. :)
hello tim!
Tools ? yes i do have the basic tools.. a cutter and sand paper and i used to build myself a wing and a fuselage made of Styrofoam and then i got all fancy and built myself a triangular frame made out of cardboard and used Styrofoam board to act a s panels on it but the upon mounting the entire wing the end result was a very heavy fuselage that did fly to my surprise(guess all my lift and stall speed calculations were right) but was unstable...so it um crashed and well never flew again... i then tried a short cut..bought a PVC pipe and hooked my entire wing assembly to it since i made my previous design a modular one and the wings survived the crash! but this one almost being as heavy as the previous one doesn't fly(i balanced the CG on both the axes no nose or tail heavy). and since i have only these two resources available in my locality i don;'t know what else to try using these materials any ideas wild ones are most welcome.
Secondly, here re the vitals of my wing
Root cord : 323.800 mm
Tip cord : 223.816 mm
AUW : 2.0 kg
Motors : 2 Avionic 1000KV BLDC out-runners
Wing area : 4107.120 sq cm / 4.42087 sq ft
Calculated stall speed 30 km/h
Airfoil used : Clark-Y 11.7% smoothed
and now with the aspect ratio of 5.48 i think i should get a decent range on this thing but since I've used the PVC pipe it refuses to stay in the air, banks right and crashes on the wing tip I thought it would be the counter torque causing the aircraft to roll right but when i checked the direction my motors run that dint prove to be the scenario now my suspicion is on the weight but I'm still not clear perhaps a light weight fuselage will help my plane lift with easier efforts. Each of the motors juice out 17 amps at full throttle and i'm using two 20 Amp escs with a Li-Po of 5200 mAh so the combination turns out just fine but i dont't why its not working out
Let me start this with saying that I'm a software/systems engineer by day and a tinkerer by night. I know how to drive the software and the models that I've designed perform within reasonable margins of the simulations.
It sounds to me like FRP will be your best option if you can get glass fiber and laminating epoxy. Boat/Marine shops often have these in small quantity for boat repair. If you can get appropriate sized model rocket kits I've seen people make sailplane fuselages from those laminated with fiberglass. You could also make a male mold from foam, laminate that with a few layers of fiberglass and melt the foam out with acetone. Do that outside and don't put the resulting goop in anything you care to re-use. Then you can epoxy in hardwood square stock for equipment rails and use aircraft plywood as the platform to mount your equipment to.
2kg seems quite heavy for 1.5m wingspan. I made some assumptions and ran a 2kg Clark Y with those values, 4.0 deg dihedral and -2.0 deg washout at the tips. XFLR suggests that it stalls at 36kph and cruises at 0.0 +/- 0.1deg Alpha at a speed of 76kph.
In comparison the Skywalker 1900 I just assembled has a 1.9m wing with an area of 3550cm2 and it is hugely undercambered. I just measured the AUW at 1.57kg. The measured cruise airspeed is right around 15m/s (54kph). I fly it at that speed on less than 200W with my objective being a 60 minute duration. That should give me plenty of time to fly out several km, do my survey and return. That said I'm also designing a replacement to give me slightly better cruise speed.
Thanks tim!! i will run some simulations further using new specifications on XFLR and let you know the results