Zenith STOL CH 750 - Page 3 - RC Groups
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Nov 15, 2010, 11:05 PM
Retired CAD guy
birdofplay's Avatar
What I attend is a Scale Aero Tow event.
Big Gliders and Big Tugs for three days a glorious Soaring.

Foamys are the last thing on the agenda. ( after 5 pm )

Now if we made a 100cc version of the CH750 and put a tow point on it
THEN we'd have something of interest!

Look at Scale Gliders Forum for the schedule.
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Nov 16, 2010, 01:13 PM
Retired CAD guy
birdofplay's Avatar
I have finally managed to get a cowl and front end look.

See pix.

On the foamy I have been thinking that maybe WE COULD USE
CONTROL HORNS as hinges.
Put some on the bottom of the wing
and some on the Top of the Flaperon
and a small screw between them and WAH LAH
you have articulated an offset surface.

I've been looking at some of the interesting HK "plastic" Parts.
Like the Canopy Hinges et al

This Might work as opposed to the whole foam ply rib sandwich thang !
Nov 16, 2010, 03:35 PM
Yes, "that" Karl...
karl k's Avatar
HOLY crap!!

My plane will not live up to those drawings...
Nov 16, 2010, 05:12 PM
Retired CAD guy
birdofplay's Avatar
Well, um .. Thanks , I think

You gotta realize that I like CAD as much as I like Modeling !
Like sometimes I just do a 3D CAD of a plane I like and never get past that !

So foam at 119" span is going to weigh quite a bit even if it is foam.

Yes I know this is the Scratch built Foamy forum.

My plan is to go with something ~ 1/2 that size or ~ 60".
Make IT out of mostly Foam a bit of CF a smidge of ply and maybe a sprinkle if balsa.

I have a Great Plane Cherokee at ~ 60" and I love the way it flys !
So I EXPECT the 60" Foamy CH7XX to fly similar except STOL !

IF it does fly well, THEN I'll Jack UP the Drawings to be Larger - MUCH Larger ! :-)

I just ordered a variety of those canopy hinges and horns and stuff from HK.
It's all cheap plastic stuff so no biggy if it ends up in the stock drawers.
Oh and I got some 75mm Lite Wheels while I was at it too.
I have plenty of motors and ESC's of various sizes already.

It this thing has a much lift at the original I might do a set of floats too !

If the Plastic hinge idea pans out then I can eliminate the Ply ribs altogether
by adding some Slat Standoffs for mounting on the LE .

I welcome any design idea towards reducing cost , weight, complexity ???

I may actually try cutting some of the parts tomorrow.

Test BUILD #1 !
Nov 16, 2010, 07:56 PM
Registered User
biznak's Avatar
that looks awesome!
I've always liked those Zen's
I'd love to build one if you wanted to kit it for cheap, maybe stop in on your way to mission?
Nov 16, 2010, 08:05 PM
Retired CAD guy
birdofplay's Avatar
yup yup yup - been thru Bellingham :-)

If everything works out per the plan I will probably offer the parts in 6mm depron
for the 60" version.

Karl !!!

I was feeling sorry for you since you started this thing
and I kinda started on the design but not the one you wanted.

So see the pix this time !

I scaled it to fit 119" span and dimensioned the views presented.
There are some dashed lines OFFSET 1/2" from the outside lines.
I assume that you were going to slab it out with 1/2" sheeting.

The wings build will be the trickiestpart if you are shooting for all the STOL effects and features.
If you cover with 6mm depron or 2. FFF Blue then I would suggest more stringers( spars)
to support that surface.

How much engineering help do you need ?

I suppose I could offer to CNC the ribs from 1/2" sheet.
( up to 1" thick would be doable )
WITH all the extra stringer slots

I could save as PDF if the jpg is too blurry.

Also check the that build PDF offered earlier !
Lot of good info in there.
Last edited by birdofplay; Nov 16, 2010 at 08:18 PM.
Nov 17, 2010, 11:51 AM
Retired CAD guy
birdofplay's Avatar
I fired up the CNC bright and early this AM - well maybe not so bright ...

So here are the results of my efforts so far except for the Ply parts.

Test fit and assy come next :-)



BTW that's 1" PINK used for those Big Ribs.
Last edited by birdofplay; May 12, 2012 at 03:31 PM.
Nov 17, 2010, 12:16 PM
Yes, "that" Karl...
karl k's Avatar
Don't worry about taking off with your drawings, build, etc...

I decided to post the idea before I had started so others could build as well.
Nov 17, 2010, 01:12 PM
Retired CAD guy
birdofplay's Avatar
I've stopped drawing and started bulding the 60" foamy version.
I just cut the Big ribs to tantelize you :-)

I'll only be drawing CHANGES as they become apparent while building.

Ya know I think they MAKE Pink Foam sheeting Near Portland OR or Vancouver WA.

I just edited in a few pix from the Slow Building day I've had.
I discovered tht I have NO fast setting glue like Sumo or even Gorilla fast set White.
So I'm giving a few other types a "chance" but they are slow going.

This thing is looking kinda Large !

So far with a bit of sanding/cleanup everything is fitting well.
Ya gotta love 3D CAD design :-)
Last edited by birdofplay; Nov 17, 2010 at 05:41 PM.
Nov 17, 2010, 09:38 PM
Retired CAD guy
birdofplay's Avatar
HELLO !!! is anyone else interested in this design ?

I guess I'm just doing it for me.

Later this PM I decided that the top sheeting needs a shelf to mount to.
So I glued in some 1/4 triangle balsa stock.
A strip of 6mm x6m would have worked just as well.

I did realize that, 3D or not, I forgot to allow to the intersection of two parts.
The angled instrument panel and the window frame former intersect.
I should have slotted them.
Too late for this build but I'll correct it on the drawings.

The Top sheeting was cut to go all the way to the front where the wind screen starts.
That leaves little access to the interior.
I may cut it off a the rear cabin former and just use clear plastic over that area
as the Full Sized version does.

I do have the fire wall glued in as well as a 2" wide 1/8 ply piece
across the bottom for the LG mount.
That may end up getting one on the inside too.

Tomorrow I may get going on the wing panels.
I'm thinking that a servo in each wing would be better than trying to make
some arrangement to mate the controls to the fuse when plugging them in.
Unless I'm inspired.

HK has still not even processed my order so those experimental hinge parts
wont get here until AFTER Thanksgiving, if I know HK !
Last edited by birdofplay; Nov 17, 2010 at 09:52 PM.
Nov 17, 2010, 10:55 PM
Yes, "that" Karl...
karl k's Avatar
Excellent job!

What are the chances since you've got this amazing talent with CAD to do a set of designs for the 119" plane? Is it possible to make the tail removable, maybe with a series of bolts to undo?

I visited my friend Jessie to take a look at some gas engines to convert to possibly use in this plane. He's a bit of a redneck, but he knows his engines and can get them to purr.

He has a habit of not putting exhaust on things, though.
Here he is testing the motor without a muffler.
Kind of neat to see the flame front at the exhaust port.
The sound is quite crumby as the sound pulses were overloading the mic on my phone (camera)

Weed eater conversion without muffler (0 min 53 sec)
Nov 17, 2010, 10:57 PM
Yes, "that" Karl...
karl k's Avatar
Later, I convinced him to put a muffler on the thing so we could hear when we're 40...

Weed eater conversion with muffler (0 min 28 sec)

Jessie is quite the character...
Nov 17, 2010, 11:10 PM
Registered User
biznak's Avatar
looking good BoP!! that thing is FAT!!! 8" wide fuse or is it closer to 10?

so you are doing conventional heat shrink cover?, are you sheeting the rib surface for the covering or just ironing to the foam??
Nov 17, 2010, 11:45 PM
RC Adddict
Wilfor's Avatar
1100 views in 4 days hmmm maybe a little interest I know im interested in what your doing
Nov 18, 2010, 12:42 AM
Retired CAD guy
birdofplay's Avatar
Ah signs of life out there !

I've been busy deleting old programs and trying to get my Downloading to work better !
They just seem to HANG UP forever.
Something is screwy with my net lately.

Karl, I have a guy near hear that just grabbed up a motor like that and started it while just HOLDING IT !

He put it on some home brew Swamp buggy thang !

Compared to the rest of this Bird the Emenage parts are relatively small !
I dont see why you couldnt use a chunk of PLY back there
with some sandwiched blind nuts and bolt down the H-stab easily.
Heck on the 119" version you could probably put the servo IN THE STAB
so all you would have to do is Plug it in them bolt it down.
NO mechanical connections :-)

I'd probably do cable to the flying rudder.

Biznak: Re Covering - I haven't decided.
But I do have some of the real thin Laminating film.
I might try that 1st.
I think that stuff is paintable.

I've never been one to get too juiced up decorating Foamys.
But in this case I think its worth considering.
For the Wings I was thinking of covering over the ribs with 2-3mm depron 1st.

I used to think a foamy should BE a Foamy 1st and Foremost.
Then along came some CF then a little ply then even some balsa here and there.
Now were talking COMPOSITE construction !

I'm hoping this 60" version will not weigh very much at all.
I want a real AIR FOILED Foamy with serious Lift and STOL capability.
None of the silly KFM mystery lift , voodoo lift kinda stuff !
A BIG Park Model kinda thang that will still fly in the park or small spaces.
Maybe even indoors this long winter !

Lastly a few more progress pix.

Instrument panel slot cut and inserted.
The Top is on and the Fin insert and the H-stab is just sitting there
with the Rudder for the Pic.

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