R/C VTOL XR-2 Ravenstar

[NuttyPro67]

Hello Guys! I work for a company that designs R/C Foamy parkjets and I've been working on a new Vertical Takeoff project. After spending many days doing it wrong with a model of the F-35 I sat down and spent a long while thinking about how I could make a VTOL parkjet just WORK.

If your curious, here is the F-35 prototype I built, flew, and crashed many times.

This design, based off the idea of the Verticopter, uses two motors in the center with counter rotating propellers to remove torque roll from the frame. This particular design had too much drag and the motors stacked ontop of each other ended up canceling each other out.
So essentially, I have two motors rated at 30 oz of thrust each kicking out a total of 40 oz of thrust at full throttle. Thats bad. Not only that, but with 100% of of the thrust so centralized, I was balancing an egg ontop of a bowling ball when it came time to hover. Solution: spread the thrust out.

With that being said, I spent a long while looking for a twin engine design to base the second concept off of that would also have room for a lifting motor in the front. Then I remembered the XR-2 off Orbiter, a sim I have spent MANY hours playing around with and it hit me like a ton of bricks.

I have already built a parkjet variant that is 400 class(rather small) to test the airframe and design itself, with great success.

I had to simplify the curves of the XR-2 down to a few faceted edges to save weight, complexity, and time. I also had to make a couple additional changes to the shape and form to make the design more parkjet-esque. The second phase of this project will be twice the size of the parkjet variant and include a triple motor setup.

Here, you can see a concept render of the model in Google Sketchup in VTOL mode. The two rear motors will pitch down 90 degrees and the front motor will engage, giving the model excellent stability (hopefully!). Just thought you guys might find this stuff interesting.

If you have some time, you can check out my website:
www.RCPowers.com
and my Youtube Channel
www.youtube.com/nuttypro67

Thanks guys!

 

[RisingFury]

OMG!!! Scott Lott!

I love your stuff man! I'm working on a RC DGIV, check it out!

http://www.orbiter-forum.com/showthread.php?t=8509

 

[Dambuster]

You're right, that is extremely cool!!!

Good luck, and welcome to the forums! :speakcool:

 

[Messierhunter]

Welcome to the forum, I've been a fan of your company's foamy jets for a while now, and if you guys do start selling an XR-2 VTOL kit that's going to become a must-buy for me!

 

[NuttyPro67]

The VTOL design won't ever make it to our "for-sale" page thanks to its complexity. We have to keep our designs pretty simple because our customers are sometimes as young as 13. Imagine having to go back and forth in e-mail between an average 13 year old trying to make a VTOL work. *smacks head*

However, I would be more than happy to share the ideas and design here FOR FREE.

 

[Messierhunter]

The VTOL design won't ever make it to our "for-sale" page thanks to its complexity. We have to keep our designs pretty simple because our customers are sometimes as young as 13.
However, I would be more than happy to share the ideas and design here FOR FREE.

That's understandable. My own model building experience has been limited to rockets or non-flying vehicles so far, but my little brother has plenty of RC-building experience I can call on for help. I look forward to the design, free is always good!

 

[NuttyPro67]

If anybody has 1/4" foam laying around and wants to put together the parkjet variant XR-2 I have a photo of, I'd be happy to post the plans on here. It's a PDF document that is sized at 2'x4', the size of a sheet of 1/4" foam board insulation from Lowes. Thanks!

 

[Brycesv1]

hey could u give me a good deal on a simple foamy to start with? just getting into RC planes and model rockets

 

[RisingFury]

EasyStar.

 

[the.punk]

Hey welcome.
This looks realy cool.
Keep on this.

 

[NuttyPro67]

Ok, so, as it stands here are the specifications of the project:
-Triple motor setup, all 480 class motors that push ~35 oz of thrust with a 6x4inch prop. This should give a maximum vtol liftoff weight of around 6 pounds.
-Total Estimated weight is 3.5 pounds with a length of 95cm and a wingspan of 80cm. Wing area is ~4.2 sq ft.
-Final VTOL plane will need atleast a 9 channel radio to work fully.
-Redundant triple axis active gyro stabilization.
-Powered by dual 2000 to 3000 mah 4-cell 14.8 v Li-Po batteries.
-Maximum power: 1500 watts at full throttle all the way around.

Heres the deal. I am not 100% sure the final layout of the plane because I still have a boat load of thrust calculations to do so I know exactly where to put the weight of the model.

I have a special problem with this design. The two motors in the back will be producing twice the thrust as the single one in the front, obviously. This means the center of thrust will be 2/3rd back between the front motor and the two in the back.

The obstacle I face is the center of lift for the model itself has been found to be 16 cm forward of this position. Which means to hover, I need the center of gravity next to the tail, but to fly like an airplane, it needs to be WAY forward of this. The solution, no doubt, will be mixing the rear motors so they are at a lower throttle level than the one in front, which means I won't be tapping 100% of the models lifting capability.

With all that being said: Here is my plan of attack on this whole, massive, project:
1. Build small scale model to find the CofG and flight characteristics. (Done)
2. Install dual motors into the small scale model to test thrust vectoring and stability handling. (To-Do)
3. Build full scale model with no VTOL capability and no front lifting motor. This will allow me to test the model's CofG again and get it balanced and working properly before I start strapping VTOL hardware to it.(To-Do)
4. Get the plane to hover on its tail, still with no third motor. This will allow me to tune the gyros and get the plane in the shape needed to hover like a helicopter.(To-Do)
5. Finally, install the second set of gyros as needed(may not need all 6) and front lifting motor. The final step will take the airplane that one final extra bit into the wonderful world of VTOL. There is a 5% chance it will actually make it this far.(To-Do)

I doubt I'll be able to finish off this before the year is over, but that is my plan of action. With enough luck it might actually work.

 

[Biscuit]

hehehe ... Shame you can't just have a servo drag the battery back and forth to change the COG (in imitation of what the XR-2 does in Orbiter).

 

[NuttyPro67]

As it is I will probably be right at my weight limit for VTOL, so I am going to avoid every bit of extra modification weight I can afford to, especially in the beginning.
Especially when you look at how much difference between the two points there is:

 

[RisingFury]

9 chanels and 3 gyros? Oh man... that thing's gonna turn into a Dave Powers wiring job pretty soon :lol:


I can't wait to see it fly! Good luck!

 

[thomasantony]

Maybe you should check out some brushless motor based electric ducted fan systems. They put out a lot of thrust .

 

[RisingFury]

Even the most powerful ducted fans are pitiful when it comes to thrust and response time.

 

[thomasantony]

Oh well ok .. I am just starting out in R/C hobby. Still getting the parts .. hehe.

 

[NuttyPro67]

I am going to use three of these, all with 6x4 props:
http://www.graysonhobby.com/catalog/product_info.php?cPath=22&products_id=645
There is a chance I'll use something like 7x3's instead. This will give the motors higher acceleration if its needed. Additionally, I use a 4-cell lipo rated at 14.8 volts to run the whole works.

With the 6x4's, though, the motors are rated at 35 oz or 900g of thrust each, giving me a total lifting capacity of 6.5 pounds or nearly 3 kg. More than likely, I can count on about 80% of what those numbers say. So while the performance numbers say 3kg, I'll try to keep the first one around 2kg and add extra weight to find the ACTUAL lifting capacity. My hunch is it will be around 5 pounds or 2.3kg. Not too bad, still.

There are so many variables still...

 

[RisingFury]

Scott, you're quit big into electics... you should get yourself a good volt/amp meter and something you can measure thrust and RPMs with.

I can tell you have to measure these things on the budget, without having to buy expensive equipment.


By the way, have you seen FCO3? They've improved the picture quality quite a lot!

 

[NuttyPro67]

I can measure thrust with a scale, but I found that there are two very different numbers. The thrust the motor produces against a scale is much higer than the weight it will actually lift for some odd reason...and yes I have seen it, have yet to see some real world sample footage, though.