Some questions ...............
I’m in the early stages of investigating different airframe possibilities – looking at the pros & cons of different layouts, shapes, sizes, wing profiles etc etc ……… which inevitably leads to a whole bunch of questions
Integrated Dynamics – a Pakistan company which manufactures UAV’s & Target Drones, has amongst their products a UAV called the NISHAN II - best described as a rear delta wing type wing setup with forward canards (have I described that correctly?). The NISHAN II airframe is also available with a turbine in place of the conventional piston/cylinder type engine.
What interests me about this design (and any other airframe with rear main wing and front canards) is a point noted by builders of a home made aircraft called the VELOCITY (which adopts a very similar wing layout), is: if velocity drops to stall speed (for whatever reasons), the airframe automatically drops its nose to avoid stalling i.e. as the nose drops the airframe will start to accelerate. As acceleration builds up, the airframe starts to level off ……..
I would imagine in a UAV scenario, with total power loss and in a passive mode (i.e. with no power to implement correction inputs of any sort) there is going to be a “yo-yo” type response to some degree i.e. a "stall/nose drop/acceleration" cycle will keep repeating its self until the airframe gets back down to earth, at which point, depending on what point in the stall/nose drop/acceleration cycle the airframe is in when it touches the ground, the impact will vary from very mild force to max force (max been that combination of velocity and angle that results in max force)………… (?) That of course is a worst case scenario - it shouldn't be to hard to setup a degree of independent powered correction, even if only to help a state of equlibrium to be arrived at, at which a balance between airframe attitude and speed can be arrived at to avoid the "stall/nose drop/acceleration" cycle repeating its self constantly down to ground level. But thats another issue altogether .......
Just how much speed has to be gained each time to level off is largely down to airframe COG and mass/weight distribution, and how big the front canards are i.e. the larger the front canard for a given airframe mass/weight distribution the sooner it will level off ….. … and again, how accurate my understanding of all this is, is also another story (I’m sure there is considerably more to all this than I am grasping?). In other words, a model builder could tailor their UAV’s centre of gravity and mass/weight distribution to ensure whatever rate of recovery/response they felt appropriate (?)
My knowledge on aerodynamics & UAV model design is very poor at best - but any wing setup that results in an aircraft or model which looses power, to “automatically” fall into a recovery orientation as described above, has to be a rather cool solution/response to loss of power/stalling.
Now, all the above comments/questions are rhetorical (just ideas bouncing around my little brain), but before I throw loads of time into researching the viability of building a model along the above lines, I would be grateful if one of you more experienced members on the forum could share an opinion on the general overall stability of airframes with the wing layout as described in these note (i.e. airframes with rear delta type wing & front canard)
The whole “automatic recovery” characteristics of airframes with this sort of wing layout is one matter, but importantly at this stage for me is how stable do they tend to be (suitable for a video camera?)?
Do they tend to be setups that require constant input (autopilot or manual ) to keep on course/heading/orientation? The comparison of course is against conventional airframe layouts (i.e. airframes with large forward wing and small rear wing).
Any other general comment regards the suitability of this sort of layout for a flying model would also be appreciated.