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A Grassna on the building table

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A Grassna on the building table

Old 04-28-2012, 11:09 AM
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SBS_Pilot
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Default A Grassna on the building table

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I've finally begun my building of a Grassna. OK, I know what you're thinking:What on earth is a Grassna? Well, here's the story:

A long, long time ago was I trawling this forum when I suddenly stumbled upon a remarkable plane. It was the Grace by dieFluggeister, and I fell in love with her immediately. I was hooked as soon as I saw the first pictures and I am still, several years later, in love with her. The only catch is that I am not a very experienced builder. In fact, I haven't built much at all (even though I have been repairing quite a lot). Grace have always been among the top five on my building list, but because I've assumed the task of building her would be over my head she's never got to the top. Until now.

A couple of months ago one hobby-store here in Sweden had a sale for some spares to some planes they weren't selling anymore. One of the items was a crash-kit, consisting of wing, stabilizer, fin-and-rudder and landing-gear to ParkZone Cessna 182. The price was set to the symbolic sum of 10 kr (approximately $1.50) and I got the last one in Sweden

So, now I have wing and tail-feathers to a Cessna, which I am going to put on a Grace-fuselage, and –ta-daaa– a Grassna is born!

My goals for this project are:

    [*]I want to learn how to scratch-build[*]I want to learn to fly 1/2A-sized planes[*]I want to begin to build a Grace[/list]

    The Grassna will have a small electric motor. The plan is that when (if?) I manage to fly her I will build a new wing and mount a Surestart.

    By the way; the link to the original Grace-thread is here: http://www.rcuniverse.com/forum/m_5062550/anchors_5062550/mpage_1/key_/anchor/tm.htm#5062550

    The link to ParkZone Cessna 182-370 is here: http://www.parkzone.com/Products/Def...ProdId=EFL2200

    I began to build two days ago with the intention to take a lot of photos and write an extensive build-log, but a couple of hours later the fuselage was half-way done! I had no idea scratch-building could be so fast. So, the first picture is of the fuselage sides with glued formers. Oh, yes, before I forget. My hobby-budget is depleted for several months to come (but I now have an almost new electric glider), so I have decided to make this one solely with materials I already have. That means that I don't use the same thicknesses as per the plan. As an example is my fuselage sides from 3 mm balsa, instead of the recommended 2.38 mm (3/32&rdquo. To the top and bottom of the fuselage is recommended 1.59mm (1/16&rdquo. I had no 1.5mm so I used 2mm. On the other hand I think I have saved some weight by using 3mm lite-ply for the formers instead of the 1/16” plywood as per the plan.

    OK, here's the first pictures:

    1. The beginning of the fuselage
    2. I couldn't resist attaching the wing and tail just to see what it will look like.

    More to come soon

    /Stefan

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Old 04-28-2012, 11:31 AM
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Default RE: A Grassna on the building table

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The fuselage is ready for covering. I have no clue if it's considered light or heavy but my scale stops at 72 gram for the fuselage (without servos and receiver). The tailfeathers are another 22 grams, so all together I get 94 grams (3.3 oz).

In the first picture you can see the beginning of my cowl. I know the plan shows a flat balsa-plate, but it's so fun to build so I couldn't resist building a built-up one. I realized I hadn't taken any picture of the cowl, so this is just before the top layer is attached. You can see the still wet glue in the picture.

By the way. The firewall and the first two formers are glued with epoxy. The rest of the glue-joints are white-glue thinned with water. The future will tell if it's strong enough.

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Old 04-28-2012, 01:00 PM
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Default RE: A Grassna on the building table

That's a good plane you are building. I don't see any fundamental problems with what you are doing. Is this your first scratchbuilding/ kit bash
project?
Old 04-28-2012, 01:39 PM
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Default RE: A Grassna on the building table

Yes, this is my first kit-bashing. My building experience is limited to:
    [*]A glider kit 20 years ago (still flies that plane, by the way)[*]Radio installation in an ARF electric glider[*]Scratch-built a pod-and-boom fuselage after I smashed that glider on it's maiden. The new fuselage was too large, too heavy and I was never happy with it, sp it is now in the garbage[*]Scratch-built a depron-trainer[/list]The pod-and-boom fuselage mentioned above gave me a lot of experience even though (or maybe just because) it never turned out well. It made me build, rebuild and repair several times, and - most of all - it re-introduced me to balsa building.
Old 04-28-2012, 02:40 PM
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Default RE: A Grassna on the building table


ORIGINAL: SBS_Pilot

I couldn't resist attaching the wing and tail just to see what it will look like.

Don't worry, we all do it. Looks like you've a good start underway.
Old 04-28-2012, 04:07 PM
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Default RE: A Grassna on the building table

Something you may be interested in reading. Wings across America 2008. About the same as Grace but all electric. I forgot to say I got to fly the SQUIRT
Old 04-28-2012, 04:16 PM
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Default RE: A Grassna on the building table

Looks good. I've spent a lot of potential building time mocking up parts to visualize and enjoy what it will eventually look like. It's an enjoyable part of the build to mock up the newest parts, sit back, have the beverage of your choice, and just enjoy your latest aeromodeling creation. Try to enjoy the process as much as possible. Most other folks will never appreciate the thought and effort it takes to see a model go from the building board to the RC flying pattern. Even a lot of modelers will be critical of your efforts. The internal satisfaction of flying something that you created will be worth it.
Old 04-28-2012, 04:39 PM
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Default RE: A Grassna on the building table

Thank you all for your encouraging words.

I have begun covering her, but so far i've only done the cowl. I'll report back tomorrow with any further achievments.

/Stefan

Old 04-28-2012, 06:12 PM
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Default RE: A Grassna on the building table

That's really great. Scratchbuilding is in fact a lot easier than most people think. I know that nowadays just about every flier grew up on ARFs and foamy electrics, so scratchbuilding from free forms or plans is something they just don't conceptualize. There is nothing in the world quite like having a unique airplane at the field that you built yourself from a pile of wood and sticks.
The options for airframes is literaly unlimited when you "roll yer own". Good flying!
Old 05-09-2012, 05:16 AM
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Default RE: A Grassna on the building table

The Grassna gets closer and closer to be finished. It's just that the last few steps seems to take forever. There's been some small mishaps and adjustments. Nothing big enough to be worth mentioning and most of it due to my inexperience, but nevertheless I feel it's so fun to build this way and I allready start looking for what my next project should be.

Currently there are just some small things to fix up before maiden:I had to redo the front "window" so it needs to be re-covered. I forgor to cover the firewall (but that isn't very obvious at the pictures). I havent built anything to hold the battery in the fuselage. She needs some more colour to make it easier to see her in the air. And I also need to stuff some scrap balsa under the trailing end of the wing to keep it fixed.

As you see there isn't much left to do, but Ihave underestimated the time consumption so much earlier so I don't make a schedule anymore.

Oh, almost forgot to mention:current AUW is 332 gram (11.7 oz) including a 3S-500mAh battery of 47 gram (1.7 oz).

/Stefan

P.S. I get the message "Internal server error" when trying to upload pictures, so they have to wait until next time.
Old 05-09-2012, 02:05 PM
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Default RE: A Grassna on the building table

I try once again to upload the pictures.... I had a new error-screen in my last attempt a couple of minutes ago - this time it said that I have been editing too long


EDIT:Now it worked! As you can see in the pictures she isn't very pretty (yet). I hope the appearance improves a little bit when I re-cover the 'windscreen' and add some stickers. On the other hand - the whole purpose with this bird is to learn to fly with ailerons and have as much fun as possible while doing it. I don't think the fun-factor improves very much if I build a plane that is so beautiful that I don't dare fly her....

/Stefan

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Old 05-09-2012, 11:58 PM
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Default RE: A Grassna on the building table

OK, I'm back with a few questions:
  1. I have now run my motor attached to the plane. I get 12500 rpm static with a 7x3.5 propeller. According to the thrust calculator I usually uses (personal.osi.hu/fuzesisz/strc_eng/index.htm) that would equal a static thrust of 460 gram (16 oz) and 81 W power. Would that be approximately tha same figures as a Surestart, at least in the meaning that it wouldn't be too much difference when I switch to glow?
  2. I haven't changed any thrust angles from the Grace-plan. I think that any error in thrust-angle needs a little (but not much) correction with rudder and/or elevator, and that the needed corection differs with throttle usage. Is that right, or have I misunderstood anything? Is there any preventive measurements I need to do before maiden?
  3. I haven't got a clue to control throws. Parkzone have the following recommendations for their Cessna 182 (where my wing and stab comes from) Ailerons: 1/4 in (6mm) Up/Down, Elevator: 5/8 in (16mm) Up/Down, Rudder: 1/2 in (12mm) Right/Left. First of all, theese figures, should they be measured from centre-to-extreme or from extreme-to-extreme? Are they a good start for my Grassna or should I increase/decrease any of them? What about expo and dual rate?
  4. It's going to be windy for the next few days so my maiden have to wait, but do you have any tips for the maiden? My idea is to hold her under the belly, set half open throttle and give her a good, straight throw. Any better ideas?
  5. This wing has a lot less dihedral than anything I've ever flown. Do you think she will have any tendencies to self-correction due to CG far below the wing, or is ailerons the only way to keep her level?
  6. As you can see from my previous questions I'm getting a little bit of cold feets, and I would like to practice a little before maiden. The only simulator I have is ClearView (and FMS of course, but that doesn't count), does anyone of you have ClearView and can recommend a plane whose behavior is closest to my Grassna?
Thank you for your patience with theese admittedly quite stupid questions.

/Stefan
Old 08-10-2012, 01:07 AM
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Default RE: A Grassna on the building table

I know it's been long time since the last update of this thread, but here I am.

The Grassna has finally flown successfully. I say finally because there have been a few hickups and bumps in the road. First of all, the motor i selected turned out to give quite marginal prestanda. I have now switched to a EMax CF2822 (39 gram, kV950) which I find adequate. With this motor I use approx 100mAh/minute, so I get 3-4 minutes from a 500mAh battery.

The initial rudder throws were far to big, so I've had a couple of crashes due to that circumstance (and due to the fact that I'm far, far away from being skilled enough to handle such situations). As you can see in one of the attached photos the wind shield is still missing from such a minor crash.

Anyway, now she flies and I have had about ten successful flight with her. (To me, any flight is successful if I can have another flight without the need for any repair.) It turns out she can handle much more wind than I would have thought, but she can get a bit wobbly in the turbulence.

Edit:Sorry, no video. I've flown alone almost every time so far. Once I had the kids with me and my five year old daughter approved to take care of filming. But I'm afraid she forgot all about the camera, because the picture just follows the plane for three seconds after launch, then it wobbles everywhere, but nowhere close to where the plane was.

I still haven't decided if I want to keep her electric or if I want to build a new wing and convert her with a Shurestart. Currently I've got two Surestarts, one Cox Viper and a Baby Bee and they are all screaming for a plane to live in. Hmmm, got to start planning.... Convert Grassna to Grace, build a Blink, or maybe a Papillon, or perhaps an All-Star, a Saab J21 would be nice, or.....

/Stefan
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