Boomerang conversion

[jimwalker]

Inspired by last months article concerning a Boomerang, I decided to try my hand at it. The LHS owner had one laying around and had given up on it because it was hard to control and would not climb. When I told him about last months article, he immediately handed it over and bid me do as I would....

I took my conversion a step further and gave it full elevon control. I cut off the fixed tip elevons and added full length hinged elevons. I layed the servos down in the wing ala a Razor. The feather reciever and FMA SC5 ESC fit nicely in the factory servo pocket under the rudder. I glued the rudder solid and used the foam from the cut off factory elevons to fill in all the holes from the factory equipment. It looks sharp!

I have some 720mah Nimh batteries on order to replace the stock battery pack. The stock pack of 300mah Nicads and 720mah Nimh batteries are the same physical dimensions as AAA drycells. They snap into a plastic holder underneath the fuselage. The stock pack is 5 cells and I'm going to make a 6 cell pack just as the RCMicroflight author did and see what happens. I may add yet another cell for a 7 cell pack depending on the results.

I was a little impatient yesterday and decided to give the little flying wing a test in the small park across from my house using the stock battery pack. I did some power off test glides to get the positive incidence set correctly on the elevons. After 3 tries I knew I had it correct because the little wing surprised me by gliding several yards and then landing softly on the grass. I fired up the little ducted fan and let it go. I didn't give it much push and it just nosed over and bounced off the ground. I then remembered that ducted fans need a pretty good shove to get going and so I tried again with a good toss like I had done when test gliding it. Before I knew what was happening it had flown across the length of the park. Some kids who hadn't noticed me before were startled by the strange plane and exclaimed, "What was that????"

I can't wait to get my battery order now that I know this thing will fly. If anybody wants to see what it looks like, let me know and I'll post some photos....

Jim

[ 09-10-2001: Message edited by: Jim Walker ]

[pease1]

Jimbo - post 'em!

[Micro Rotors]

As if you needed to ask us Jim :D

[jimwalker]

Ok, here they are......
http://www.rcmicroflight.com/upload/boom1.jpg

http://www.rcmicroflight.com/upload/boom2.jpg

http://www.rcmicroflight.com/upload/boom3.jpg

http://www.rcmicroflight.com/upload/boom4.jpg

It will weigh about 8.5 ounces with the new Nimh battery pack (6 or 7 x 720mah). Gear is a Hitec feather, FMA SC5 ESC, 2-GWS pico servos, stock Cox fan unit.

Jim

[jason stevens]

hey jim hows this thing coming? I just picked one up on ebay lastnight for 25 bucks. the only thing wrong was tip of rudder looked broken. can you get replacement parts for this?

[jimwalker]

OK, here's the flight update.....

I did get my battery order and made up a 6 cell 720mah NIMH pack. The motor definitely had much more power. after cartwheeling the thing 4 times in the deep grass (no damage) I finally got the elevons set with the correct incidence. It climbed out nicely after a short level run to let the ducted fan get up to speed. I did some gentle turns and then was able to back off to half throttle to maintain level flight.

Gaining confidence I tried some sharper turns and the boomerang nearly fell out of the sky due to horrible adverse yaw. The thing would literally point it's nose in the opposite direction of it's bank. During this "wallering" it would lose altitude at an alarming rate. I kept things very smooth after that and brought it in for a nice landing.

On the second flight the wind picked up and the more I tried to turn into the wind, (away from an eight foot fence), the more it kept wallering and heading toward the fence. I finally got desperate and tried a hard bank. It snap rolled, went inverted and augered in. Fortunately it hit in soft dirt and damage was minimal.

I took it home and Zagified it. I cut the elevons down to about half and added vertical wing tips like a Zagi. I don't know if this will help, but I didn't know what else to do.

Yo Mama,

If the part of the rudder that is broken off came with the boomerang you bought, just glue it back on with 5min epoxy, white glue, or oderless C/A. If not, and you're going to do a conversion like mine, then either reshape what's left of the rudder (it's not that important), or use some of the foam bits from the conversion to build it back up.

Jim

[KSU Flyer]

Jim,

Just curious... Why did you choose to place the EDF unit in the front of the plane. Maybe thats what the plans state, I dont know....I'm not familiar with the plane. Some of the info I found stated that the EDF unit is more efficient if it is placed at the back of the duct? This seems to makes since...
The turbulent flow behind the fan will create more shear stress on the inner walls of the duct if it has more wall surface area to interact with. Anyway, the plane looks sharp! Good luck, and keep us up to date. Also, do you know how much static thrust you're getting with this setup?

-Mike

[jimwalker]

KSU,

The boomerang is a Cox RTF made out of high impact foam. I don't know why they put the fan in the front of the model. My guess is that was the only way to get the thing to balance with the "extra heavy" radio gear that comes stock. When I disected the thing to change radio gear, it was obvious that I would have to leave most things as they were. It balanced just fine because I substituted my ESC, reciever, and 2 servos for their one heavy servo and circuit board.

I have read the same thing about keeping the exhaust end of the duct as short as possible due to friction and sheer turbulence. Another thing that doesn't seem right is how much the exhaust duct converges inside the plane. My understanding is that the exhaust should at least be 85-90% of the fan swept area less the spinner. This usually translates into around 70% of the duct diameter. Looking in the boomerang, it looks more like a convergence down to 50% FSA.

I wish I had a way to measure static thrust so I could gather that data for myself and share it. I built a small pulley and arm rig to transfer horizontal force into vertical force for my triple beam gram scale. Unfortunately I found that there are too many bearing surfaces involved with this rig using my triple beam and friction messes up any readings I might get. I think it would work with a digital scale if I can ever get up the $30-$40 for a nice digital I saw at Walmart.

Jim

[pease1]

Jim,

did you replace the motor in the Cox fan unit with a GWS IPS motor? I hear that's a good way to get more thrust out of it.

Al

[jason stevens]

Hey jim, do you have the parts # for cox? I think it is in the manual that comes with the boomerang. I need to order parts for mine, Just got it from ebay and funny enough It wasn't as pictured in the auction. both wings broken in two places, Rudder severly damaged and a dead battery. that really sucked. Thought if I can order an empty fuse, then I could just put the fan into it and start from scratch.

[jimwalker]

Allan,

The GWS motor may indeed make the cox fan more spunky. Unfortunately the can motor that comes in the cox unit is of radically different dimensions than the GWS motor and would take serious modification to make work, if it is possible at all. Someone mentioned using a DMC20BB because it fit right in the unit, I wish I had known that before, since it's too late now. I don't think I could get the thing apart without destroying it. However, power is really not the problem. With the 6 cell pack I'm using (comes with a 5 cell pack) I have plenty of climb once it gains speed. The problem is the adverse yaw since I converted it to full elevons.

Jason,

I'm sorry, no I don't have the original paperwork. The LHS owner just handed me the plane and nothing else. I'm also sorry that it sounds like you got ripped off on Ebay. I'm not sure you can even get parts for the thing. I still think your best bet is to get some oderless C/A and glue it back together if all the parts are present. I've had to patch mine up a few times already and it goes back together fairly well....

Jim

[jimwalker]

Here's the final update.......

After trimming down the elevons where they are pretty much constant chord, and adding vertical wingtips ala a Zagi, the Boomerang is now very controllable and I don't see any more adverse yaw. I also decreased the reflex a couple of degrees which makes the plane fly with much more authority. I think I had too much reflex causing the thing to be in a constant mild stall. It's not a screamer, but it will maintain altitude at half throttle. With 720mah Nimh pack, I'm getting about 8 minutes depending on throttle management. If I ever catch a thermal that time would definitely increase. The boomerang has execellent glide performance, in fact I've had to learn to setup a lot farther out than I'm used to for landings because it just wants to keep on flying.

Maneuvers have to be open and scale-like with the ducted fan or speed goes quickly just as I've read from other EDF threads. Finally, I've had to relearn turns somewhat. I'm used to adding a slight amount of up elevator during turns to maintain altitude with my conventional flyers. With this ducted fan flying wing, it seems to like just a touch of down elevons through the turn. This keeps the nose down and the speed up giving the elevons greater authority. If I don't add some slight down through turns, the nose pitches up slightly and speed bleeds off and the controls lose effectiveness.

This was a fun conversion and once I got the elevons to the right shape and reflex setting, it's a great flyer. The guys at the flying field are still talking about that funny looking plane with no tail and no prop. It is quite a sight......

[jason stevens]

Do you have any pics of your boomerang in it's final stage? I am almost done with mine and don't know how big to make my elevons.

[RAMTech-RC]

I gave up on my boomerang about a year ago. I was going to put a rocket motor in there, but I'll have to tryt his first. Any pictures??

[JTracker99]

Hey There,

This is my first post in a really old thread.

I'm looking for the photos referred to by the 4th post by Jim Walker that were viewable in the archive, which are:

http://www.rcmicroflight.com/upload/boom1.jpg
http://www.rcmicroflight.com/upload/boom2.jpg
http://www.rcmicroflight.com/upload/boom3.jpg
http://www.rcmicroflight.com/upload/boom4.jpg

Any idea why I can't view them?

Thanks,

JT

[JohnR]

Most likly they were on a website that is now gone. :(
sorry about that.