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Apr 13, 2009, 12:55 AM
"Watch out for...CRUNCH!!
Ok, Thanks. I have a few boards of foamboard and was looking for some good plans and I think I have found them
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Apr 13, 2009, 09:00 AM
Jack
jackerbes's Avatar
dean 85 wrote:

"..What esc is he using, that seems really heavy..."

I thought the same thing, he posted a link to it, it is this Hobby City 18 Amp ESC and that is the weight they list for it. That weight is probably part of a program to escalate shipping costs and add "hidden profits" by over stating the weights.

http://www.hobbycity.com/hobbycity/s...rogrammability

They are so stupid at Hobby City... They probably don't realize that a lot of people are not buying that ESC simply because of the 69 grams weight listed there. If you asked them about it they would probably think you are trying to cut into their profits and ignore the question or fend you off with a stupid reply.

I don't do Hobby City any more... And with their prices, it takes some self control.

Jack
Apr 13, 2009, 09:12 AM
Jack
jackerbes's Avatar
I cut a Divinity out of FFF yesterday and starting getting it glued up also.

I have the KFm strips glued on and now the center and top panel on the top. The thing is impressively stiff for not having any spars or other stiffening in it. Just the bonding of the multiple layers is working real well.

I left the plastic layer on the FFF and the plastic side down on the wing panel. I removed the plastic where I glued the KFm strips and center and top panels on so most of the structure is getting some additional stiffening from the plastic.

Considering the light weight of the rest of the components and stuff, I think the wing loading on this is going to be fine.

I have the leading edgwe rough sanded as you see it here. Not very pretty, the top panel shifted after I weighted it down but it looks like it will work...

Jack
Last edited by jackerbes; Apr 13, 2009 at 10:26 AM.
Apr 13, 2009, 09:35 AM
John 3:16
Daddy-O's Avatar
I took Divinity out for her maiden flight this morning. It was a little windy. I played around with the cg by putting a key (I forgot my lead weights) under the battery pack, then right in front of the motor on the back. I think it needs more rear cg than what was on the plans. It rolls very slowly, and I could only get it to do an inside loop. The outside loop didn't want to go over. I also need to put a skid on the back near the motor since the motor takes a hit every time I land. I flew 6 flights this morning with it. Thank you ApachePilot for the plans. I will try making some adjustments and try again either this afternoon or on Wednesday. The video of the first flight is here: https://www.rcgroups.com/forums/show...2#post12018770
Daddy-O
Apr 13, 2009, 10:29 AM
Jack
jackerbes's Avatar
Good one Daddy-O!

Looks like you were out there at the crack of dawn. That is usually the best time for flying up here in Maine too.

We are going to be getting into the black fly and other annoying bugs season pretty quick but right now it is wonderful, cold enough to keep the bugs down and warm enough to be out there.

Jack
Apr 13, 2009, 10:47 AM
Crash Test Pilot
caeman's Avatar
A very nice flying wing, indeed.
Apr 13, 2009, 11:45 AM
John 3:16
Daddy-O's Avatar
I forgot to do the nice transitions, but here is another video of today's flights.
Daddy-O
Divinity with KFm airfoil (1 min 50 sec)
Apr 13, 2009, 12:44 PM
treefinder
springer's Avatar
Dad: Utube works! great vid She's a real floater (or is it just your expert control?) Looks great.
Apr 13, 2009, 01:18 PM
John 3:16
Daddy-O's Avatar
Hahaha! You're so funny, springer! Yeah, my expert control has a lot to be desired. It is a floater, though. I may go back out later today with a variety of props to try (9X5, 8X6, 7X3.5). I also have some lighter 2s and 3s packs to put on the front so that the cg will be shifted towards the rear a little.

I am hoping to improve the roll rate just a tad, and get it so it will do both inside and outside loops. I was looking at my other motor options also. After weighing other motor/battery combinations, I found out that I can easily knock 2 ounces off the AUW. I will probably make the change once I figure out where I like the cg. Experimenting can be fun!

Daddy-O
Apr 13, 2009, 01:41 PM
Jack
jackerbes's Avatar
You're having too much fun!

I think nose heavy is the best way to start though. On Tony65x55's Zagnutz wing they recommended a CG at about 7.5" back from the nose but most of them are finishing up at 8 to 8.75 inches back depending on the components.

On the Zagnutz one of the CG location tests is that when you have it trimmed out to fly a level and steady cruise, if you start a gentle 30 degree or so turn it should be aable hold that rate of turn without losing or gaining any altitude. That is the CG "sweet spot" for that plane.

And to get full elevon travel so you can do all the different maneuvers, without it being way too pitch and roll sensitive, try cranking in a lot of Expo. Like 80 or even 90 percent. That will give you that precise and gentle movement at the center and you can still have full control surface travel with the stick at the stops.

Jack
Apr 13, 2009, 02:41 PM
Jack
jackerbes's Avatar
ApachePilot,

Did you ever get an AUW on your Divinity as you are flying it?

I just finished the airframe for the one I'm building out of FFF and it is right at 140 grams now. That is the finished wing with elevons and tip plates mounted and a motor mount on.

I think it will finish up at about 250-260 grams ready to fly with with a 2S battery (850 mAh, I don't have anything smaller). That is with the 9 gram motor. If I decide to kick it up to the 24 gram motor, it will go up about 15 grams more.

The 9 gram motor is about 30-36 Watts I think, the wing is going to be a little less than 1/2 pound, so it should fly with 9 gram motor. At least by the generally accepted 50-70 Watts per pound minimum rule anyway. If it doesn't, the 24 gram motor will double the watts and that will be the next thing I'll try.

Jack
Apr 13, 2009, 03:53 PM
John 3:16
Daddy-O's Avatar
Jack, Your 140 grams is 4.9 ounces for your wing without gear. I don't see any way possible to have a completed wing in the 3 ounce AUW range if it is made from blucore. I knew there must have been something wrong with my scale the other day. I have it working right now, and my wing weighs almost exactly 9 ounces with a 2s 740-800 mah lipo or 3s 400mah lipo pack. That is what I am trying next.

With these packs, my cg is moved more toward the rear. I will be taking some lead out with me this time to fine tune the cg point to my liking. It will be hard to get exactly right if the wind is blowing as hard as it is right now, but I'm going to give it a shot. All in all, we are looking at the same basic numbers for an AUW for our Divinity's. I thought about going with the 24 gram motor also. I have a 10 gram motor that I could use. I think I would have to prop it with a 5X? prop and fly it with 3s packs. I have a hard time believing that it will make this 9 ounce plane fly well. I'm looking forward to seeing how your 9 gram motor works for you. Please keep us updated.
Daddy-O
Apr 13, 2009, 04:17 PM
John 3:16
Daddy-O's Avatar

Pictures


Here are some pics of my Divinity as it was flown today. I added the skid on the bottom to protect the motor. **EDIT** All of my wires are imbedded into the foam with a piece of packing tape over them. It is difficult to see, but the receiver and esc are also flush with the surface and covered with a piece of packing tape. I attached my elevons with strapping tape using the over / under method to help save some weight there. It also give full (easy) deflection of the control surface by the servos.
Daddy-O
Last edited by Daddy-O; Apr 13, 2009 at 08:11 PM.
Apr 13, 2009, 07:41 PM
Jack
jackerbes's Avatar
"..Jack, Your 140 grams is 4.9 ounces for your wing without gear. I don't see any way possible to have a completed wing in the 3 ounce AUW range if it is made from blucore..."

Nor do I. I said the other day that davor21's airframe was 62 grams but that was based on subtracting the known weights from the AUW and using the remaining weight as the airframe. I know now that it was not right.

If there is a material that is any lighter than FFF I don't know what it is. There is nothing in that airframe, at 140 grams, but FFF, PU, and a few feet of clear package sealing tape. I used that for the hinges and also taped the leading edge to smooth that up from the sanding. And like I say, the stiffness and strength is certainly adequate for this plane.

I don't have much in the way of small props, I ordered a few 6x3 and 6x4's today. I have one 5.5 x 5.5 that I used for testing the motor. And I have a couple of 7 x 4 or 7 x 5's that have too big a hole in them for the prop saver right now. I'll cobble something up to let me try one of those probably. If it pulls too many amps I can trim it down some.

I know that the 1811-20 9g motor I bought is a 7V motor but I tried it with a 3S for a few seconds just for the heck of it. It quickly overheated in a few seconds so now I know that it is a 7V motor that really *is* a 7V motor.

Our winds are waning finally, I should get a chance to fly this tomorrow or Wednesday and will let you know how it does.

Jack
Apr 13, 2009, 08:15 PM
John 3:16
Daddy-O's Avatar
I went back out to the field this afternoon to fly in the extremely windy conditions that we had. A 9 ounce plane should never be flown in the winds that I flew the Divinity in this afternoon. It didn't do great, but I didn't crash either. I am amazed at how slow this thing can fly without falling out of the sky. I have full airfoil wings that will drop out of the sky when flown too slow, but the KFm airfoil on this just keeps it floating. It is really amazing!
Daddy-O


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