elnato aka the_nuts

Hi all, I am an aircraft engineer apprentice in New Zealand and am new to the modeling scene.
This is my query: recently i picked up an XPV, which is a gimmiky rc aircraft with a li-po battery and twin electric motors. It is 2 chanel and basically it climbs/descends by varying the thrust of both motors and turns/banks by varying the thrust of either motor. I couldnt resist it because it was 5 dollars from the neigbors garage sale.
I want to use the components to make a twin engine autogyro, using the same method of control as the original aircraft. What i want to know is if it will be controlable or even fly with a fixed empanage and rotor hub or if i will need to resort to more chanels to make the idea fesable. Your thoughts would be greatly appreciated.

rcflyerfl

My Feedback: (1)

Sounds like a good assignment for an appentice aircraft engineer.. I would not do it but play with it a little.. But first get a Autogyro flying so you know it will fly then try your twin motors. Good Luck.

Jim

elnato aka the_nuts

thanks for the suggestions Jim, unfortunatly at the monent any spare cash i have is going towards my AME licence exams and also living in newzealand makes it expensive for me to import kits etc. i think i will just have a play and see what i learn. this is my concept so far: twin 3blade rotors with the motors mounted directly under the rotor shafts and the battery and RX in a centre fuselage with a single conventional tail. the motors produce bucketloads of thrust, the original plane went pretty damn fast so im hoping the have enough grunt to get the thing airborne. what im worried about at the moment is that having twin rotors will make it slow to turn becuase of the drag they create and the large moment arm they will have in relation to each other (the slower spinning engine being the axis of rotation for a turn).

floridagyro

Hi,

I would recommend a 3 blade single rotor and if balanced correctly it should fly. Because your control will come from the motor thrust, the rotor could be fixed without pitch or roll control.

Using a gyro stick, I built a single rotor gyro using two electric motors that were mounted on each side and using servos I could change the pitch of each motor. This would cause a similar control as you are attempting.

Set your hang angle by suspending the gyro by the rotor shaft at minus 10 degrees. The rotor shaft should also be about 10 degrees positive.

Good luck,

Phil

elnato aka the_nuts

Thanks for the advice Phil, i will be sure to follow it. At the moment, changing to a single rotor, the whole assembly including battery, RX, motors and hub but minus the blades wieghs around 100grams or 3 1/2oz, but i haven't any undercarriage yet. If i use a clark-y shape blade with zero incidence what sort of rotor disk area should i be looking at using?

cheers for the info.

Mike

floridagyro

Hi Mike,

It's pretty hard to calculate the rotor diameter for something that small but I would start with about 15" to 18" diameter. I would also use the SG6042 rotor blade profile instead of the clark-y. You can sand the clark-y blades a little thinner and sand a small channel on the under side of the blades near the trailing edge. That's the difference between the clark-y and the SG6042.

Phil

elnato aka the_nuts

Thanks for the advice Phil, all I need now is a couple of bits and peices and I'll be ready to go. I'll keep you posted on how everything turns out.

Mike

Flymo

Great idea, Mike, and a very interesting suggestion from Phil - is that you, Phil P?

Because my experience is mostly with bi-rotors, I would suggest going that route if it is not already too late. With decent blades they are (in our experience) more efficient (fly on less power) than single rotors. Stable, too.

Like Phil, I'd suggest a 'Stick' design with something like SG6042 for the blade profile - the difference would be that I'd suggest two rotors, one each side.

The other main benefit from this layout is that the stability is usually far better than a competent single rotor design. The best single rotors are equal in this regard, but they are rare, and (we find) harder to set up than a bi-rotor.

So far the bi-rotors we have built have only needed a CG shift or a bit more control throw to fly perfectly, and you don't have any control throws to worry about!

One of my first bi-rotor 'designs' was a crude, cheap, RTF foamie twin monoplane that had the same control method as yours. After prising off the wing, I bodged the rotor assembly from an Air Hogs XT-9 birotor just to see if it worked. It was a bit low on power, but flew as steady as rock and steered where it was pointed. But it would not so much climb as gain altitude, very slowly! Heavy as sin, so that didn't help.

Apologies if this is too late - and all the best with your project.

Ben

PS some info on bi-rotors at: www.BRAGgroup.com
XT-9 article at: http://discovermagazine.com/2001/aug/featreviews

XE521

Hi Ben,

recommend that you edit your post and knock out the comma after the .com in the BRAGgroup link, otherwise 'it ain't gonna wurk'.

Regards

Karl.

Flymo

Ooops, sorry folks, and many thanks to Karl for pointing out the blooper. [sm=red_smile.gif]
Now edited to show website correctly!

All the best, Ben

elnato aka the_nuts

Gidday Ben, thanks for the feedback. Its not too late at all for me to change to a twin as i still have the bits and pieces for the original twin design and modifying them from a 3 blade to a 2 blade will be a piece of cake and make the hub assemblies lighter and simpler to boot. A twin definatly looks more apealing if it will be less power reliant to fly and if it is more stable and forgiving, well then sweet as. Nothing wrong with trying eh?

Cheers, Mike