Hello all,
Where to start... Well, My name is Justin, and aviation is my life. I grew up in a family with aviation in our heart and blood. Everyone in my family has been in some sort of aviation, whether it is Full scale helis, prop jobs, jets/airliners, hang gliders, or even home built aircraft. I solo'd at 18 yrs old with only 9 instructor hours, and continue to enjoy every aspect of aviation. I am currently serving in the USAF as an aircraft electrician, in order to finish my Aerospace engineering degree. (Which is not far from being complete!)
Onto the project!
The albatross UAV project came to me one night while laying in bed (so original isn't it?!). My goal was to provide a high grade, inexpensive UAV platform with unrivaled performance.
My goals?
A standard 4-6kg+ MTOW
Plenty of room for sensors, batteries, and equipment
Easy 1 hour flight times, and up to 4 hours (which is the goal... of course we can't be sure to initial flight tests)
Breakdown, and transportation ease!
Wide flight envelope
Sexy and appealing looks
Last but certainly not least, EFFICIENCY!
Airframe introduction.
The wing: The wing will have a wingspan of 3000mm, and wing area of 68.38dm^2 (in other words, 118" span, and 1060in^2). It consist of an optimized foil, and a forward swept planform. The foil is designed to ensure low stall speed, while maintaining a high max efficiency, and large cruise window. The wing planform Utilizes this foil nicely. It is a relatively high aspect wing with a ratio of 13.2. I have found that this moderate aspect ratio is preferred at RC Reynolds numbers for numerous reasons. an Aspect ratio of 12-15 allows for easier, and stronger wing structure, it allows for slightly higher Reynolds numbers, allowing airfoil's to work properly, over a wider speed range, and allows for easier built in retract, and or component bays. Obviously, we want to achieve all of the above, with minimal impact on performance. Of course a Higher AR wing would be more efficient, but at a significant cost (both in actual price, and giving up benefits.) The wing will be built with built in component bays, allowing for RC rx install in one wing, and Vtx install in the other. Not only does this allow for more room in the aircraft, but it allows for proper separation between Vtx and RC rx. The wing is forward swept, which helps minimize the chance of tip stalling while on approach with your UAV, which may as we all know, be overloaded. (there is nothing as horrible as losing your beloved UAV platform and equipment!). The downturned style tips aren't just for sex appeal, they actually reduce drag and tip vorticites, as well as decrease stall, while improving stability!
The Fuselage: The fuselage is designed around the user. It is designed to have plenty of usable storage space. Whats this mean? Well why would you have a tall narrow fuse? This not only makes is a huge PITA to work in, yet it limits how YOU want to lay out your components! The fuselage is approximately 740mm long, 150mm deep and 200mm wide. To avoid excessive fuselage/wing intersection drag and interference the fuselage is built in a slight trapezoidal shape, only to an extent that wouldn't hinder storage capacity to much. This translates into a fuselage with more usable space than the popular SkyHunter. I haven't mentioned efficiency yet. Lets not forget about that! The fuselage is actually a very efficient shape, minimizing the drag left behind. (even though it will only get chewed up by a prop...). It is also efficient in cooling. It will be designed with a NACA duct in the nose, which is a high pressure region. It will consist of an exhaust right above the motor, which is the lowest pressure region. think suck and blow. While creating a pressure differential it actually pulls air through the airframe keeping necessary components nice and cool.
Tail/s: The tail is an Inverted V design. Why? Simple really, an Inverted V improves efficiency while decreasing drag. It is also naturally more stable in a banked, and coordinated turn. The Inverted V allows for twin tail boom design, allowing for a large diameter prop. It also raises the ground clearance of the tail on landing and takeoff.
Breakdown and transportation: The number 1 reason for keeping airframes small is due to transportation and storage. The Albatross is designed to fit into a box no larger than .35m X .5m X 1m. In reality the case could be much smaller. How does it do this? The fuselage is 740mm X 200mm X 150mm, needless to say, it was designed within the required specifications. The wing is 3m long! However, it simply breaks into 3 1m long sections. The twin carbon-fiber tailbooms are 700mm each. The tail will be hinged at the center, and consist of two 440mm halves, allowing it to fold into one 440mm piece. Not only does this make it easy for the end user, but it reduce's shipping costs to your door. No more paying as much as 50% of your aircraft on shipping alone!
Goals:
My Short Term goal is to finish analysis and development. I am planning on starting a kickstarter to fund the initial molds and production costs. The current Design consists of a fiberglass fuselage, twin carbon fiber booms, and either a foam core/obeche covered wing, or an all built up wood wing. It will come with optional fuselage formers/inserts. These will be laser cut, allowing the builder the option of using them or not. These peices will consist of a retract mount (offset similar to an A-10c aircraft nose wheel, to allow for minimal effect on usable space) as well as numerous mounts and shalves for components and or batteries. Of course, as mentioned this will be up to the customer whether or not he/she will choose to install them. It also allows for some open source design in case anyone wants to improved upon, or create their own after market laser cut parts. This airframe would be available at a goal price of around $500 usd. This may or may not be achieved, but it is my GOAL. I consider this a reasonable goal considering similar aircraft such as Hobbykings UAV-3000 are capable of being produced around $300. I hope that my few added features are not enough to out-reach my goal.
Specs:
Albatross:
Wingspan; 3000mm
Wing Area; 68.38 dm^2
Root Chord; 300mm
Tip Chord; 160mm
Fuse Length; 740mm
Fuse (max) Width; 190mm
My Long Term Goal is a Albatross Pro version. The Albatross Pro will have a slightly enlarged fuselage, more wing area, higher MTOW, change in airfoil, fully molded wings and tail, and more precise construction. These changes would increase MTOW, and cruise speed/efficiency to a more specified range. It would also consist of a few ease of operation features such as built in Cannon-plug style connections for easy quick-disconnect assembly. This means that when you take off the wing, there is no servo connection to fumble with. It would also consist of some ease of assembly mods such as quick disconnect wings, booms, and tail, requiring no tools to use. (Think, Crutch/cane style push button. This would be located under the flaps.)
Specs:
Albatross Pro:
Wingspan; 3000mm
Wing Area; 75.216 dm^2
Root Chord; 330mm
Tip Chord; 185mm
Fuse Length; 890mm
Fuse (max) Width; 230mm
Here is a more in-depth design log on my RCG account. The wing planform, and laminar foil research was originally from a previous project, before I realized its potential in FPV/UAV. Although the introduction of my UAV/FPV platform is fairly new, a lot (many years worth) of prior personally research has been incorporated.
I am currently in communication with a few different OEM manufacturers for an initial Hobby version, and a long term Pro Version. If you know of, or you are another OEM manufacturer feel free to contact me! It would be much appreciated!
Please, feel free to comment, discuss, and provide constructive criticism! After all, this is my first post on DIY Drones, so please be nice!
Comments
Thanks Reto!
Magnets are so far the most promising on the hobby version. The hobby version will also rely on normal servo connectors, as well as customer-provided extensions etc. (just like any other airframe). Of course tape is always recomended, and I always use it on my models as well, however, it is not needed and it will be up to the customer to use it or not.
Stuff such as fancy all-in-one electrical connectors will be included on the Pro model (when and if it is available). The developments for simple and reliable connectors and such will be funded by the hobby versions success. It will also feature a more secure locking mechanism, as I feel magnets should not be a solution on high end aircraft.
As for an update, the search for manufacturer is still going. I am in contact with a few different OEM companies, and I imagine this will take some time. My criteria is quality and business ethics first, then stuff like price, etc. As for the Pro model, although it is a looong way out, I believe I do have my ideal manufacturer in mind.
I like your solution of having just one flap and accordingly only one flap servo on the center wing section. Makes a lot of sense on a wing having three sections. I also like the wing fixature with magnets. You could even do without and just rely on tape. Tape is highly recommended anyway to cover slots between the wing sections to improve aerodynamics. This method proved to be simple, reliable and efficient on many of our models.
Think about all the wires running through an UAV. Quite some more than in a normal RC plane. They need space, e.g. in the wings and the tail booms. Another crucial point are electric connectors. Even large RC companies like Multiplex have hard times to find reliable solutions to connect electrically and mechanically in one move, e.g. at the wing connections. From our experience it is better to first connect electrically, then store the connectors and wires and finally connect mechanically.
I am looking forward to your commercialization!
EDIT, I am not condoning you fly with 45,000mah of batteries. It is also not an official statement. If is however a useful comparison to show the true volume of the fuselage, at or under the CG. I find many people prefer to have batteries clumped together, where as video components,and/or autopilot to have plenty of room and working area. These components are intended to be place in the forward section of the fuselage.
Good morning Reto,
The fuselage I have been working on a compromise between storage and volume as well as minimal wing interference. Currently there is still PLENTY of room under the fuse. Infact in the region right under CG there is more room than the "bulge" in front. It is only 185mm wide as oppose to 200, however it is significantly taller as well. It then starts to narrow towards the motor mount. To put this in perspective, directly under CG, you can fit 45,000mah of 4S If you felt entitled to do so. This is 9x zippy compact 5000mah 4s 25c, standing on edge (46mm high and 29mm wide), it fits 5 side by side on the base, and another stacked 4 on top. (no shelves included, in this estimate).
As for tips, they are actually rather easy to gain an advantage. It is hard to squeeze the last little bit. Swept/Raked are excellent, but they have no stability, or stall benefit at all. All a swept or raked tip achieves is minimizing drag. The downturned tips have close to the same drag reduction, however they can drastically soften the effects of a tip stall. Instead of a sharp stall it becomes more "mushy." That is the major advantage. Yes if I were only chasing drag, I probably would just stick with raked/swept tips.
As for wings, the current plan is 1 servo operation for flaps (this should be feasible due to the one piece center). The center section will be rather busy, including cut outs and hardpoints for retracts (which of course do not have to be utilized, yet at the same time they add little weight to the overall design), one bay on each side for RC Rx, and vTx, and the tail boom hardpoints.
I already have a plan for the Pro version as far as wing and tailboom disconnect/quick release mounting and mechanism. As for the Hobby (which is my current priority), I am still trying to figure this out. Currently I think it will be more of a clamping "sleeve" for the tailbooms, and probably magnets for the outer wings. (yes magnets are plenty secure, with wingspar and anti-rotation pins, two neodymium magnets have proven to hold the wings on 4 of my models with no problem. This is also rather cheap for manufacturing)
Glad to read you mount the tail booms on the upper surface. You really have gone through many good thoughts for your design.
I still think you should add some more volume to the fuselage underneath the wing. Your maximum fuselage cross section seems to be in front of the wing. From there it gradually narrows to the trailing edge of the wing. I would keep the large cross section until near the trailing edge and start narrowing from there. It doesn't matter or even helps if the motor and prop are not right at the trailing edge of the wing, but have some distance to the rear. Then the prop gets some distance from the disturbed air of the wing.
To me wingtips are black art. Even the largest aircraft constructors of the world like Airbus and Boeing are still developing, hiring some of the smartest guys on the planet, keep changing design and still not knowing what is best. To me the popular swept/raked wingtips used in F3F, F5D and DS make most sense.
After having the general design settled you will have to go through a lot of design details. Stick to your idea of placing stuff in the wings, especially the radio equipment (RC, FPV, GPS and telemetry). We tried a lot and it proved to be best to have these components separated as far as possible to minimize interference. The airframe must be easy to manufacture, easy to assemble, must have good solutions for connectors (both mechanical and electrical), have some good propulsion, RC and payload solutions.
Point out all the awesome advantages your airframe has and people will buy it!
Alex, the tail booms are planned at 20mm this has proved to be more than plenty in many large sailplane applications, let alone having two of them Fortunately having a semi-triangulated tail will increase rigidity (theoretically) much more than say a T-Tail
Stephen, The plan is to build at least one, or more, prototypes prior to production. Due to the size and structure of the wing, a hotwired foam wing will not work. However, I may be able to hotwire a wing then cover it in balsa/ply. Tails and fuselage will be easy, and carbon tailbooms are easily outsourced. As for span-wise flow, I feel it is often underestimated at low Re's. I have done some work with forward swept wings on Discus launch gliders which often fly between under 60k for the majority of their flight envelope. The stall characteristics are still noticed. This isn't so much due to span-wise flow, but more so due to the fact that in a coordinated tight turn, the inboard wing creates more lift than the outboard, THIS is what reduces the chance of tip stalling in a tight turn. The wing does have washout, almost every wing RC or full scale incorporates washout. Whether it is indicated or not, generally the airfoil progression simulates washout, whether it is indicated or not. (by indicated I mean designed at a negative incidence, etc...) However, this wing does include washout both in the progression of the foil series, as well as actual washout built into the wing... This is mostly for stability and drag reduction. It is almost always ideal to have an elliptical lift curve, which translates into less lift at the tips (IE, washout). This also translates into less of a vorticity at the tips. Vortcities are one of the largest negative impacts on efficiency. However, keep in mind that the forward swept wing is also useful to keep your CG further forward. This makes it easier to load up a fuselage with components, and worry less about getting enough wait in the back. for example, you shouldn't have to remove the wing to access 90% of your equipment because it doesn't have to be placed in the rear.
Reto, The major difference is that this is intended for, and designed with UAV and FPV flight in mined. When I mentioned retrofitted, I meant it is not performing an act that it was not designed for. In this case the Hugin and Cyclops would be my biggest competitors. The Huggin is lacking in transportability (is that a word?!), and efficiency (in comparison to most other airframes), The cyclops can break down, however not quite as compact. It also does not accept LG, and has a more limited MTOW. The plan was already to mount the tail booms to the upper surface. The drawbacks are disrupted airflow on the most sensitive surface on the airframe, however I feel the benefits outweigh. For instance, the root chord thickness is about 30mm (almost a 10% thick foil, so rather thin for this application, however pretty standard, even thick, for Sailplanes) This translates into either send the booms out the TE, or out of the top. If they were to come off the bottom they would need to be faired and it would be plain ugly. Once you take flaps into consideration, top mounted booms is a must. The fuselage is already designed for usability. Much more so than many other models such as the popular Skywalker. It is not designed to be tall and narrow, rather wide,flat, and rather square. This gives you more of an option for component layout. Also due to the forward swept wing, CG is moved further forward, thus allowing more room in the fuse that isnt covered by the wing. However, the work I did to the fuselage was with minimal impact on aerodynamics. When it comes to the tips, there is no doubt that even at low Re's there is an advantage to reducing tip induced drag. Generally on almost all high efficiency aircraft, much work goes into tip design. There are many ways of reducing tip rag, however the most common (as seen on a number of sailplanes) are the swept (blended or raked) tips. These work great for reducing drag, however almost any form of properly design winglet can increase lift, while minimizing drag, rather than just minimizing drag. As for the turn-down hoerner style tips, they do not decrease drag as much as conventional winglets (however they are generally on par with raked/blended tips). In general, the efficiency gain of winglets decreases with reduced Re's (although still noticeable), however with hoerner style tips they seem to soften the effects and onset of a tip stall, an in all making a bad situation more controllable. This has been replicated MANY times at RC Re's.
PS, most, if not all F3F, F5D, or Dynamic Soaring airframes fave swept/raked tips.
I had a quick look at Esprit, SoaringUSA and Skip Miller. I found the Grob G 103C (500 USD), the Fox 2.75S/E (480 USD) of TopModel CZ. They can be considered competition as well, similar to the mentioned ASK-21 of HobbyKing, just not quite as cheap. I didn't see any other highly efficient models with voluminous fuselages and electric propulsion, but am sure there are more somewhere.
Some design recommendations from your experience with the Y-UAV and UMARS:
Attach the tail booms on top of the wing, like the UMARS. If you attach them in line with the wing, you will suffer flap length, like the Penguin. If you attach them underneath the wing, they will conflict with the extended flaps, like the Y-UAV.
Design the fuselage for maximum usability. Don't overengineer its aerodynamics. Make sure you have a lot of volume underneath the wing (at the CG) and have it well accessible. That area is the most valuble place for payload, especially variable and heavy stuff. Best might be some tray formed fuselage, open on top on the full length (also underneath the wing), screwed to the wing from its side panels.
Concerning your downturned style wing tips I have some doubts they are a good choice. I can hardly imagine all high performance and competition aircrafts having upswept wing tips are wrong.
The prop diameter might not be as critical as you expect. We found rather small ones to be more efficient in cruise than excessively large ones. See this thread.
Looking forward to your final design!
You should build one and see how it flies. Just hotwire it out of foam.
Forward swept wings are an interesting choice. I think you overestimate span-wise flow for such low Re. Why not just washout like everyone else?
Ok, no problem :-)
From my point of view the tail boom should be larger in diameter, at least 1"1/2
In this case, it would prevent torsion and vibration the Stab. and rudder
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