Scratchbuilt Gasbag needs a name

[artmonster]

It's getting close to the summer Thermal season ( actually it's here I think ), so I thought I'd build a gasbag from scratch.

Paul (arbo) and I cut some cores out of blue foam ( MH32 airfoil ) with the hotwire bow.

I put a small hardwood spar in the wings, glassed the polyhedral joints, put a little strapping tape for rigidity, sprayed the foam with Krylon ( be careful when spraying with Krylon directly on foam, the base likes to eat foam, so spray from a good distance ).....and as soon as the clear Mylar 1.5 mil laminating film arrives, I will cover with that.

The fuse is blue foam cut on the bandsaw, then I put a small carbon rod in the tailboom for strength. then I glasses the fuse, and painted with Krylon......I dont think it will need to be covered, I glassed pretty much the whole thing, I may put some tape on the bottom for skid landing....and it's light light light !!

The tail feathers are Fan Fold foam and Depron for lightweight and ease of replacing if needed.

I will put a 2 channel system in it, with HS-55 servos, and a light battery, and probably do pull/pull ( maybe ).......I hope to make the wing loading in the 4 to 5 oz per sq/ft range....wheeee !!! it should be able to find the slightest thermals !

what do you think? Pretty good for nearly zero investment eh?

It needs a name though........any ideas? :rolleyes: ;) :D :rolleyes:

[ejett]

How can you possibly call a foam plane a "gasbag"??? :D

Looks like you should be able to snag some thermal time with it. Get yourself a name and put together some kits.

EJ

[artmonster]

How can you possibly call a foam plane a "gasbag"??? :D

I call all thermal planes gasbags....bad habit I guess. :rolleyes: :rolleyes: :rolleyes:

[ejett]

Get out there and give it a good test and let us know how it flies. Might make a good, cheap one design plane for clubs to have fun with.

EJ

[artmonster]

Get out there and give it a good test and let us know how it flies. Might make a good, cheap one design plane for clubs to have fun with.

EJ

Thats exactly what I had in mind......

A plane you can build quick, cheap, and parts that are easily and redily replacable.

[flybaby2000]

thermal chopper........still awaiting those orphan plans?....apparently its gonna cost about 20aud..... to send eeks

[artmonster]

no thanks, I cant justify the shipping.

I can get a CD rom motor for that.......hmmm........
:rolleyes: :D

[Peytr]

Gabadefobo would be a nice name, which is short for Gas Bag Derived Foam Bomber. I once named a plane Dadefobo which is short for Dart Derived Foam Bomber (the Dart was a HLG by MPX). Gabadefobo sounds more square though, and is still free :D.

[artmonster]

LOL that's awesome.

GaBaDeFoBo is great !!!

can even say it with a stuffed up nose.

My other scratch built blue foam thermal plane is called Quasimoto ( its a bit uglier thatn this one )....so gabadefobo works well as a brother !

rofl

[nuevo]

like that bumper sticker !! :D :D No wonder you call all thermal planes gasbags.

[artmonster]

Ya......I'm a sloper.


leadsleds and gasbags.........now that's living !!! :D

[artmonster]

OK I got the plane finished finally.

The AUW for flying is a whopping 16 oz !!

That makes the Wing Loading 4.25 oz/sqft. ! Whoop !

(( this is darn near a handlaunch glider....well actually it is I guess......))

It should find the tiniest thermal and be able to work it.

Wingspan is 67.5 with an 8 inch chord.

Plane is made from blue foam, horiz tail is FFF, and vert tail is depron.

I glassed the fuse with lightweight glass, and the wing has a hardwood spar and is covered with 1.5 mil laminating film.

Electronics are 5 HS55's, a cheap 2ch AM reciever and TX ( what I had on hand, and these work good for thermal planes ), a 750 NiMh battery....and thats about it.

(( that's what makes the plane so light ))

I am going to try and maiden it here before the end of the weekend.

I'm kinda proud....being my very first plane built entirely from scratch. :rolleyes: :cool: :D :D

[barefootbass]

Go AM go! :D

[artmonster]

OK....I maidened it.

The conditions were light wind lift with thermals....so slermally....nice, easy conditions for thermal planes at the slope.

The toss was great with the plane rising nicely, good sign.

Then I tried a turn...hmmm........not very much response at all, so I tried my best to get it back around and land it, it was hard, but I did it.


So with my limited knowledge and logic, I decided that I had to make the rudder bigger....I increased the rudder to be about twice the area of the original one. (see pic)

I went back up to re-maiden it.....


tossed, and it wanted to fly again nicely, until I tried to turn ! :confused:

same thing ! hardly any response at all. The throws for the rudder were set to about 75 degrees either way at max throw as well, and still no turning.

The elevator works fine, and it doesnt need much throw at all to work it seems.

I got it on the ground after a battle with the headwind, and did minor damage to the tailboom, which I fixed easily.

So what do I do now? Is there something Im not seeing thats obvious?

Is it too tail heavy? I put an ounce of lead in the nose to try again, to see if that is the case. (( the cg calc I inputted numbers into said the CG is at 2 to 2.5 inches from the LE { the wing is an 8" chord}......I put lead in to move it up to 1.5" for the next round ))

what do you guys think? Is there something else I should check?

-M
"newbius-confusicus"

[nuevo]

The wings look very flat. Not much EDA (effective dihedral angle). I'm betting this is your issue with turns. From the front-end photo, I'm guessing the tips are each 7 degrees above horizontal. Just from guessing, this would give you an EDA of 5 degrees or less. I suggest adding additional dihedral in the center of the wing. You may also consider trying a larger angle where the tip panels join the center section of the wing.

You've got to have some dihedral/polyhedral for a rudder to be able to initiate a turn.

Try this Google search (http://www.google.com/search?q=EDA+%22effective+dihedral+angle%22) for a few good articles commenting on EDA.

Here's nice Excel spreadsheet to calculate EDA.
http://www.mmaa-modelairplanes.org/tools/effectivedihedralanglecalculator.xls

There's no reason you should need anywhere near 75 degrees of throw from the rudder.

About the CG, what % of MAC (mean aerodynamic chord) is the balance point? Try 25-30% MAC as a starting point. You can safely go further back than that, depending on your skill/comfort level.

[artmonster]

cool thanks for the tip.

(( funny I didnt use the calculator.......I designed the mmaa website...lol ...I got it on my main sailing site too coloradogliders.com .......funny how you overlook using the tools you got. ))

anyway.

As calculated, if I split the center section in half, and raise the center panel an inch on each side, I will be within good EDA limits......


....so now to cut my purdy wing !!! :eek: :eek: :eek:

Hopefully I an have this done quickly and let you guys know how it goes.

:D

[artmonster]

Quick enough??

I got it done today....but wont be able to fly it until tomorrow or the next day.

I didnt cut the wing at the center, asd I would have to have adjusted the wing saddle as well, and I have pushrod tubes and antenna running just below the surface of the saddle.....

so what I did was; cut the center panel out 5 inches frm the center, which gave me a center panel that was 10 inches wide that would stay horizontal.

I then raised the wings about an inch and a quarter at the next joint.

according to the calculator, this woudl give the whole wing a good running Efective dihedral angle.

It actually looks right now as well, when compared to my other thermal planes.....go figure.

anyway, I am hoping that this will make it more apt to turn when I give it rudder input :rolleyes: :rolleyes: :rolleyes:

keep your fingers crossed. :D

[artmonster]

re-maidened it today !

very very light slope lift, and hot poppy thermals.

It flew beautifully !!

That little extra dihedral is exactly what it needed, thanks for the dead on tip JonStone :) :) :)

it reacts very nicely to lift, the tail and wingtips dance around, so it is a very easy thermal indicator.


specked it out a couple times.....made the whole day worth it. :rolleyes:

I learned a hell of a lot about sailplane design with this project. Im a happy camper.