Update 18 May 2016:
Sometimes all that is missing is the right name, so here it is:
Update 17 May 2016:
Our initial sketches involved tilting and swiveling motors, but of course they did not comply with the requirements. However, apparently a swiveling mechanism is allowed. Therefore we did some quick sketching and analysis and came up with a slightly modified aircraft (see new image). The aim was to fit the hover system inside a large fairing in cruise flight – the fairing was inspired by the optional conformal fuel tanks on the latest model F-16.
Unfortunately further analysis showed, that the increase in weight and wetted area eat up all the form drag savings. Therefore, we are sticking to our baseline aircraft.
Update 09 May 2016:
The latest layout from the Red team is in: Refined fuselage-lifting surface intersections/fairings, refined values for the hover propulsion system size, winglets - and a landing gear!
We abandoned the bicycle landing gear approach, as analysis predicted very little aero and weight advantages. The aircraft can be configured with both a conventional tricycle gear (for additional conventional take-off capability) and skids for rough terrain. (Skids are not shown in the pictures, yet.)
10 days to go - we'll continue with maximum effort!
Update 09 May 2016:
Analysis have shown that the Blue approach with the strutted horizontal stabilizer suffers from increased drag compared to the Red Team baseline.Interference at the junction is of far greater impact than the weight savings due to the decreased bending moment.
We'll now concentrate our final efforts on the basic three surface configuration (Red). Fortunatly the structure is strong enough to enable an increase in aspect ratio to about 17. At the moment we are confident that the design will put us in a very competitive position.
Update 04 May 2016:CFD results are here...Putting 4 stopped Rotors into the wind is draggy. Really draggy!Update 03 May 2016:All new Fuselage and redesigned lifting surfaces.
First analysis showed we had too much unused space in the initial layout of the fuselage. This is great for adding equipment for a diversity of missions later on, but we decided to go for improved flight performance for our primary mission instead.The much shorter fuselage not only decreases drag and weight, but also improves packaging when disassembled.First structural analysis showed we have a lot of strength left in the wings, so we decided to go with a larger aspect ratio. This, together with the changing lever arms for the control surfaces made a redesign of the stabilizing surfaces necessary. Static stability should now be just like we want it - we are expecting results by tomorrow, followed by new CFD data.
The first new image was released by our Red Team - the Blue Team will update their design by the end of the week.
Update 19 April 2016:Our Blue Team presents a preliminary picture of an alternative configuration:
The basic fuselage layout is kept, as is the forward wing. The main wing, however, is given a much larger aspect ratio to further improve L/D over the basic (red) configuration. To alleviate the wing bending moment the aft rotors have been moved to the wing. Further structural weight savings are facilitated by using the horizontal tail as a strut.This configuration is more challenging from the aerodynamic and flight-mechanical standpoint - but the payoff might be higher than the red-configuration.
Update 18 April 2016: First CFD analysis (check out the new pictures) show that we are on the right track with this configuration. No seperation regions are discovered in the first runs, L/D ratios look very exiting and are expected to further improve as the design further matures in the refinement process.Structural and flight-mechanical analysis are underway and we will keep you updated on our progress.
Update 16 April 2016: Slightly changed the fuselage geometry to properly fit all components. Also Attached the engine/rotor mounts for the hover propulsion system.
A three surface design is chosen for minimal wetted area and maximum efficiency (L/D).
The front wing is vertically separated from the main wing to reduce interference effects with the main wing (major issue with the original Quadcruiser design) and is also given a slight anhedral to supplement this effect.
For the same reason the T-Tail configuration is chosen – the aft wing is well separated from the wake of the front and main wings, and also from the influence of the cruise propeller.
The main wing is of moderate aspect ratio (AR=8.2) to keep the weight down – the most important step for VTOL designs. A high L/D is achieve by the selection of laminar flow airfoils and the addition of winglets.
The vertical stabilizer does need a somewhat higher thickness to carry the loads from the aft wing and the lifting rotors. However, by adding a strake, the actual thickness-to-chord ratio can be kept low enough to not cause a significant drag rise.
Additionally, the pusher configuration will reduce boattail drag in cruise flight, also contributing to a high L/D.
The lifting rotors are placed on the smaller span front and aft wings, to keep the lever arms to the plane of symmetry short, and thus reduce the bending moment. This will yield significant weight savings over the Quadcruiser configuration.
Hover download is kept to a minimum by placing the rotors and motors forward of the lifting surfaces. The forward placement also helps with regards to flutter, even though at the low dynamic pressure at the maximum required speed, flutter is not expected to be an issue.
To reduce complexity, weight and cost the minimum number of engines is chosen.
The fuselage is sized to the payload and battery size requirements. It is shaped to achieve laminar flow on the front third, significantly reducing cruise drag.
The landing gear (not shown) is planned in the bicycle configuration with outriggers, again to achieve the minimum mass solution.
Constructed of carbon fiber laminate (where radio transparency for antennas is required: glass fiber laminate) for the best strength-to-weight ratio, the design is suited for moderated rain. It is probably going to lose some efficiency in rainy conditions, due to the boundary layer tripping to turbulent flow. Maintenance provisions are addressed by providing access doors, to save weight, these must be kept to a minimum number and size, however.
For scaling reasons, the fixed equipment fraction is lower for larger aircraft. Additionally, larger aircraft offer improved empty mass fractions. Therefore the maximum allowed mass (25 kg) is chosen as the maximum take-off mass.