VTOL

[Ash]

i don't know why but lastweek i decided to attempt to build a vtol aircraft (something like the bell v22). now being a i.c man i thought about using my two OS FS 30 surpass buy decided that they ma be hard to match for individual speed and the fact that they must rotate in the same direction. i have decided to against my better opinion use electric motors. i want the craft to weigh less than 800g. there will be two vertical thrust motors and two small ducted fans for foward thrust. i am planing to buy all items off e-bay in Hong Kong because the items are cheep. i have foam cutting and vac forming capabilites at home so no problems in that department. what i would like to know is how to reverce brushless motors and any propeller/motor setups for max thrust. also if anyone has any infomation or thoughts on this matter i would love to know. just quickly does anyone know where i can buy carbon fiber tubes and mats in Australia.

Thanks

[Bruce Richards]

Ash,

Some time ago I was following a thread on one of the US forums RCGroups I think where several people were discussing how to approach this very task. There where some great ideas. You may want to search this out just to get the brain cells working.

Good Luck and keep us posted on how it goes.

[birdy]

Hi Ash. If you ask me, buy three 'leccy motors, 120 degrees away from each other, and tell your tx they are ccpm servos. Possibly a central motor too, for torque and throttle reasons? The original toughts were for a flying sorcer, and it wouldn't be very plane like.

[Ash]

thanks for the advice and ideas it all helps.

[Aero120]

Ash,

 Just to propose an alternate design concept. Some years ago I "accidentally" built a great VTOL plane. It was a Precendent Hiboy that I'd modified to carry a camera and I fitted with large flaps. On full flap and full throttle the plane would climb vertically and the elevator could be used to adjust forward speed and the rudder would control roll / yaw. The plane was only being kept aloft by prop wash so the ailerons had no effect. The planes natural stabilty helped too. I fitted finlets to the out edges of the flaps and it worked even better as when the flaps when drooped to about 80 degrees, they deflected most of the prop thrust downwards, and created a load of drag to counter the forwards thrust that remained. The remaining propwash over the tail was enough to allow the rudder and evelators to have some effect. The result was like a basic version of a Bae harrier and it would hover and even fly backwards with a head wind. Landing approaches could be vertical too but a final roll out / flare was neccessary. This worked very well, it cost next to nothing and was able to operate from small clearings to photograph specific objects.

Your proposed design is more interesting, but both the V22 Osprey and the upcoming Joint strike fighter  that uses lift engines are very complex and have / are taking ages to develop. Hover stability is a major issue and the complexity of the systems to achieve this. More rotors means more things to co ordinate and to go wrong. Hence why there are so few multi rotor designs in both the model and real world.

I would recommend that you fit some form of auto stabilisation in the form of a couple of giros to control roll and pitch so you only have yaw and vertical speed to think about. If your model is carbon fibre and foam and hence very light it will have very little static inertia and will be upset by the slightest draft. When hovering you will need some sort of fan or air blast to control yaw and react to the change in torque from the speed variation in the lift motors, Ideally you might need a giro to control this too.

 Most Ic model engines create far more thrust relatively than their full size equivalents hence why a basic trainer flies more like a jet fighter than the Cessna 150 that it resembles so you could use a conventional IC engine / prop and duct the thrust through the fuselage / wings to give hover control.

 Hope this helps

[Ash]

I like the idea with the flaps. it really simplelifies the design.

thanks

[Bruce Richards]

Ash,

I would agree that flaps are the answer for VSTOL. From what I remember of the RCGroups thread they were struggling to get anywhere using lift engines.

[Ash]

well if large flaps and a good single ic engine is the answer than i hace an old boomerang 40 trainer with a Royal 46 on the front of it i might put some large flaps on, but i think that i will build something of a more scale appearance. what do you think. high or low wing.

[Bruce Richards]

I find my electric powered models, generally,  take off in a shorter distance so you may want to try a light weight electric powered model with flaps. Low KV motor turning a large prop while keeping it light. This may be a problem because most low KV motors are also large. Not sure about high or low wing my feeling is that high wing will catch more of the prop blast in the flaps.

[Tim Mackey]

To "reverse" an electric brushless motor, simply swap any two of the three wires.

As you seem a reluctant leccy flyer, as per your statement

" I have decided to against my better opinion use electric motors. i want the craft to weigh less than 800g"

then I suggest you need to gen up a bit more on the foibles of the power-trains a bit - especially as you plan to complicate things further by using multiple motors.

[Aero120]

Ash,

 It has to be high wing so the majority of the prop blast goes below the wing and can be diverted downwards by the flaps. If you use a low wing, the flaps have little effect on the airflow over the top of the wing. Plus you need the pendulum stablity of a high wing in slow flight to control roll. I'd recommend starting with a proven trainer design, put the biggest engine in that you can and shorten the nose a bit if possible to keep the balance point, then fit flaps on the inboard section of the wing only, to avoid tip stalls and enlarge the tail control surfaces. Make it a tail dragger with chunky wheels and main undercarriage to take vertical landings and its nearly a Storch! I think wing fences in line with the outer edge of the flaps would help duct the air onto the flaps. I only went as far as fins on the flaps themsleves. These worked well though

[Aero120]

I haver a low wing Travelair with flapperons and there seems to be no thrust vectoring effect with the flaps down and the full length flapperons rob aileron authority and make it a bit prone to a tip stalling except when just dropped a few degrees.

[Bravedan]

I built a really good VTOL plane over a year ago................then I corrected the CG..................

As Timbo says, read up a lot more on EP, and look around RCGroups for others work in this area.

[Ash]

i've started drawing up plans for my vtol craft. it has a 900mm wingspan and is about 1.2m long.to save weight the wing is foam core and the fuselarge going to be made out cross members and sheeted from the nose to the CG. the wing will be mounted high.the engine will be a Royal 46 turning a large prop. the flaps on the wing are quite large as well as all of the other control surfaces. as i said i am only drawing up the plans so if you can think of any modifications or improvements than please let me know, also any flying tips might help.

 thanks.

[Former Member]

[This posting has been removed]

[Aero120]

Ash,

As Eric says, take a look at something full size for general layout. The Westland Lysander is another design along the same lines.   I'd recommend copying the basic design proportion of the the Lysander  or the planes listed by Eric  and see what fits you needs/likes best. Don't keep scale control surfaces though and as Bravedan says, allow room to play with the C of G to get the best out of it. Might be worth doing a prototype first to test the C of G and dihedral so that the rudder gives some roll control. Alternatively build it in modules so you can change engines complete with noses, wings, air ducts and tails etc like the BAC lightning propotype

[Ash]

i was thinking that i might make a short wing because it is not going to be providing lift bot vectoring the air flow from the prop. however i don't know how far out the prop will push air. any idea?

[Bruce Richards]

A large lifting wing area and low weight (low wing loading) is necessary as well as the directed prop was for a good short take off. The prop wash alone will not lift the aircraft. Also a a motor and prop combination which will provide good acceleration, this is why I think electric power is good for short take offs. A good target would be to get under 6' take off run.