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Old Nov 27, 2007, 03:12 PM
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Houston, TX, USA
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Wow I happened to look into this section Sunday and by the end of the day I had already downloaded and printed a plan and cut parts. Last night I did a quick sharpie "paint" job and assembled all but the rudder and top profile, all of the CF supports, and is ready to mount electronics. This foamie building is fast!

I like the idea of flying a small plane that can be very precise. I know this is probably blasphemous to say on this forum but since I really don’t have any access to an indoor flying area my goal is to have a small plane I can fly outside on calmer days. Considering how reasonable the prices are for equipment it is worth trying and I could always find a suitable indoor space if I looked and maybe joined a club.

Attached is a picture from Sunday night. So far building has been easy but my plane is a bit heavier than yours, the completed airframe with CF supports is right at 50g. I did use Cellfoam 88 since my LHS does not carry Depron. Mine might be a bit overweight but I am still hopeful that it turns out to be a good flier:

- Plane – 50g
- Park 270 w/ mounting hardware – 17g
- APC 8x4 prop – 8g
- Berg 7 RX – 9g (I might remove the case)
- 480 2S Lipo with plugs – 25g
- 3 HS-55’s with hardware – 26g
- Castle thunderbird 9 ESC with plugs – 10g

So far that is a total of 145g without any aileron push-rods, pull-pull strings, hinge tape, or Velcro for the lipo pack. The APC prop seems like it may not be the best choice so I may need to look for something else. I could probably save a few grams with a 300mAh pack or a smaller Rx but I already had these. Also, the airframe before gluing or adding the little mounting discs for the CF rods was 45g. I did use 1mm CF for the wings and .8mm CF for the fuselage supports. I used a medium CA which worked great except for the CF rod mounting, I’d rather use something with a little give like epoxy but think that would weigh too much. Maybe on the next one I’ll use a combination of CF rods and foam bracing, similar to what yakwrecker did.

I can’t wait to fly it! Maybe this weekend, weather permitting…
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Old Nov 27, 2007, 03:47 PM
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PabloM,

Did you mean Park 250 for the motor? If so, the APC props I have used didn't pull very well, and the amp draw was high.

I would suggest the GWS HD 8 x 4. This prop works great with the park 250. You can also save some weight by using a smaller battery, like a Thunder power 350.

I get 7 -8 min. flights with the TP 350 lipo.

Mini ifo
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Old Nov 27, 2007, 04:48 PM
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Houston, TX, USA
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Quote:
Originally Posted by mini ifo
PabloM,

Did you mean Park 250 for the motor? If so, the APC props I have used didn't pull very well, and the amp draw was high.

I would suggest the GWS HD 8 x 4. This prop works great with the park 250. You can also save some weight by using a smaller battery, like a Thunder power 350.

I get 7 -8 min. flights with the TP 350 lipo.

Mini ifo
You're right, I did mean Park 250...

Are the GWS props lighter? it seems like the APCs are pretty heavy. And the metal insert needs alot of hand fitting, to the point that it may be possible to get them out of center by the time it fits.

I had the 480 packs already so I'll just start with them first. But if the finished plane can come in at 150g or less I'll be happy and it'll be a good place to start. I could always shave off another 16 grams with 5g servos and smaller battreries.

All I really need to do now is mount the electronics and make some control horns. Maybe 1/64 ply? Or maybe I'll make a sheet of fiberglass and cut them out...
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Old Nov 27, 2007, 04:52 PM
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Pablo,
yes the GWS props are lighter.

Do you plan to use pull/pull? Its very easy, and doesn't require horns. I just use small pieces of carbon fiber, and attach fishing string. Very light and works great.

Mini Ifo
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Old Nov 27, 2007, 06:54 PM
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PabloM,

Here's a way to mount the battery that may be a little lighter than Velcro. I saw the idea on Dick & Derk van der Vecht's site.

I flew the Index for the first time today in our backyard which is smaller than a gym. I was a klutz with it the first 2 flights but settled down on the last two. I'm still pretty new at 3d/pattern but it was so easy to do rolling circles and torque rolls that I was amazed. Mine doesn't have a landing gear yet but it just parachutes down with a little power to land at almost zero forward speed. Lots of fun and lots to learn. Thanks again Aiden!
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Old Nov 27, 2007, 08:43 PM
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Hey Tow,
Good idea, however i like to mount my batteries throught the fuse. it seems like it keeps the wieghtng of the battery from working the foam and fatigueing it. Plus it keeps the weight over a central location which i think helps them fly more neutral and track better.

Just my 2 cents
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Old Nov 28, 2007, 01:40 AM
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towgadget, I like your battery mount, but I'll also center it in the fuselage like yakwrecker suggested. And I also like Mini Ifo's suggestion for the control horns. I suppose it’s not so critical to have the pivot point over the hinge line since the offset will only be slightly more than 1/8”. I might also add little balsa stiffeners to help minimize flexing of the surface... if it's even needed at all.

I do have to keep in perspective how small and light the planes are and that the force required to bend or twist a part probably exceeds the weight of the plane! I'm also thoroughly impressed with how stiff the fuselage is too with the CF rods. Much stiffer than some 16oz balsa profile planes I've had that were roughly the same size.

Here's a picture of it so far. I wanted to mount electronics tonight but had other stuff to take care of this evening. I should have it ready to take to the skies this weekend and I'm really looking forward to it. Not too shabby for 2 evening's worth of time...
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Old Nov 28, 2007, 12:53 PM
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It's great to see a few Indexes (Indices?) being built. It's very satisfying when other people feel it's worth putting some of their time into building themselves something you designed! They're looking good too.

Glad to hear you're happy with yours so far towgadget!

Pablo - that looks like a really tidy build. I like the paint too. I agree the carbon bracing works great to stiffen the fuselage. My newest one uses 0.7mm rod instead of the 1mm I used for the fuselage on the original. I stayed with 1mm for the wing. The fuselage is still plenty stiff enough. There's only a fraction of a gram of weight saved so I'd suggest using whichever is easier to get.
As far as control horns go I'd suggest keeping them in line with the hinge as far as possible. Otherwise you may be introducing unwanted differential which could ruin those axial rolls! What you really want is 90 degrees between all the linkage components when the servo is at neutral. I don't stick rigidly to that but I do keep as close as is practical.

For mounting the battery I strap it to the side with a narrow strip of velco looped through the fuselage. It's pretty light and very easy. I don't like using velcro on the cells and sticking them to a piece on the plane because it puts too much stress on the airframe when you pull it back off again and it's not as secure anyway. I've been meaning to try the elastic band approach like in towgadget's photo. It's similar to my velcro solution but lighter and maybe a little neater. Might try it on the 810mm version I'm working on.

I don't worry too much about mounting the cells on one side or other of the centreline. Providing it's mounted to the vertical profile you're only talking about a few millimeters and I put most of the radio gear on the opposite side to counterbalance the battery.

Keep up the building and keep posting pictures!
If you do have any problems with the design, let me know. I'll update it if I can to address any issues if we find them.... but so far I'm happy.

Aidan
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Old Nov 28, 2007, 02:29 PM
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Houston, TX, USA
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Aidan,

I see this type of pushrod to servo and pushrod to control horn used by you guys but after a quick search I can’t seem to confirm what this is… Is it simply heat shrink tubing that grips the parts and provides the bendable joint? Maybe wire insulation? For a pull-pull connection, how do you connect the strings to the servo arms and control horns… is it just glued or do you tie a loop of some sort? That would be a hard knot to tie at just the exact length needed… is there a trick to making it adjustable?

Sorry to ask so many basic questions but I’m still out of my element here…

I mocked up the parts for balance locations and ended up with a weight of exactly 141 grams. This still lacks only hinge tape, landing gear, and final control linkages. I did lay a few CF rods to account for the weight of push-rods and taped a few scraps of balsa to account for the weight of the control horns, though. And I may not even use the landing gear since I initially plan to fly over short, soft grass and the gear may snag and cause more harm than good.

thanks for posting plans. I have a few scratch-builds I have made (small 36" balsa 3-D style planes) and I'll have to return the favor to the site. somebody else might enjoy them as much as I did...
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Old Nov 28, 2007, 03:47 PM
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Pablo,

Yes I do the type of joint you've shown with just some heat shrink and a little CA. It works well. It's also very light, cheap and simple. The down side is that you can't adjust it, you have to re-make the joint but it's fairly easy to get right. My prototype used 1.2mm pushrods for ailerons and rudder (1mm should do) with 1.5mm heat shrink linkages at the servo end. The Dymond 47 type servos I'm using have very slim output arms and you'll probably need bigger heatshrink diameter for other servos. I just shrink on the tube leaving a small gap (maybe 1mm at a guess) inside the heatshrink between the end of the servo arm and the end of the pushrod and then apply a drop of thin CA to fix in place. I used adjustable fittings at the control horns but I think I'll use heat shrink both ends for the one I'm building now.

For the pull-pull elevator I fed the thread through the outer holes in the servo output arm. I slipped two small pieces of brass tube onto the thread and then tied it off at the control horns on the elevator making sure there was a little tension in the system. Then I centered the servo and the control surface and crimped the tubes onto the thread against the servo arm. This fixes the thread in place in relation to the servo arm. It means there's only one critical knot and that's just to get enough, but not too much, tension. I'm not sure I explained that very well so hopefully the pictures will make it clear!

Aidan

P.S. I find a heat gun necessary to properly shrink the tubing. Make sure you don't point it at the plane - depron will melt very quickly!
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Old Nov 28, 2007, 03:56 PM
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Easy Servo Connection

PabloM,

I personally like to tighten my pull/pull strings, so I just glue the string to the carbon fiber horn, and at the servo, I use Dubro ez micro connector, and just tie the string to a fish hook that has been cut, and you can adjust the string anytime.

The weight of the connector is minimal, since its made of alum.

Mini Ifo
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Last edited by mini ifo; Nov 28, 2007 at 04:05 PM.
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Old Nov 28, 2007, 05:00 PM
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Airbrakes

Here's some pictures of the airbrakes I tried on Sunday.
The small rectangels are what I thought seemed about right. I added the two additional strips on a bals stick with double sided tape to see how far would be too far. It flew OK with the big airbrakes but I needed high-ish throttle the whole time and it just didn't feel right. I then broke off half the length of the strips and tried again. It was better but still felt like too much so I removed the add-ons altogether. With just the rectangular brakes it seemed about right. I'll try cutting them down a bit later after I've flown it like this a while. I don't think they need to be reduced further but I suppose I should try it for completeness

The airbrakes are 50mm deep and 70mm long.
The center of the airbrake is 180mm outboard and the gap between the trailing edge and the center of the airbrake is 18mm. The gap is not constant as the brakes are perpendicular to the direction of flight not parallel with the trailing edge.

The brakes didn't seem to do the handling any harm but it did prevent the plane from accelerating much in dives or when throttle is applied. I'm not sure if I prefer it with or without the brakes for fun flying - probably without. However for F3P I think it will definitely be easier to fly accurately with the brakes.


I've also included a couple of shots of the 810mm version.
The profile blanks weighed 42g compared to 35g for the 750mm version which works out about as expected given that the scales are only accurate to 1g.
With all the depron (except the upper LE strip) and the carbon bracing done it weighs only 47g. Looking good for the target AUW of 135g.

I've taken pictures of the 810mm build so far and I might put together a build thread when I've finished.

Aidan
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Old Nov 29, 2007, 11:00 AM
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Good job on trying air brakes! I've added some very small SFG's to mine and will try small rectangles attached to them on the next indoor meet.

Last night i managed to maiden my index indoors! It was nice and light feeling, rolled and did all moves nice expect for some strange warp out on and inside loop where it would just twist and flip over. Also the KE was bad, it seems to need some down in it as it wants to do a KE circuit on its own, it does not couple out, but instead i just need to add down in on both left and right KE!

Any ideas guys?
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Old Nov 29, 2007, 12:10 PM
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How much trim do you have on the elevator?
Is the amount of down needed for knife edge similar to the amount needed for inverted flight?

The more up trim any plane needs to maintain level flight the more elevator it will need inverted and it will also need some in knife edge. However with the fairly rearward CG you're using very little trim should be needed for level flight so I wouldn't have thought that's your problem.

What do you mean when you say "it does not couple out"?

Aidan
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Old Nov 29, 2007, 06:04 PM
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Coupling is when the plane wants to either go inverted or back to level flight in KE, it just wants to loop in the KE position. I might have some twist going on.

Anyways a rebuild is on the books as the wing was almost sheers off after dodging a heli and hitting the deck!

I want to make a larger version, any chance you could post the A0 plans for me today as i would love to get them printed of ready to build for saturday!

Hope this is okay, i'll do a full report on it.
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