I believe my little VAPOR has a wing loading of .9 oz per sq ft- at a wing area of aprox 75 sq inches.
If I build a model having 110 sq in wing area - (same aspect ratio), how heavy can it be to have aprox same slow speed flying ability?

Dick, I think you meant 9 oz and not 0.9, correct?  If so it means that your Vapor weighs 4.7 oz.

The 110 sq inch version would fly at the same speed if it has the same wing loading.  The difference in sizing not being enough to make a noticable difference in Reynolds numbers that you'd see.  So you could allow the bigger model to weigh 110/75=1.46 times as much.   But obviously if you can make the bigger model more like 1.2 to 1.3 times as much so it's got a lighter wing loading then it'll fly that much slower.

The VAPOR weighs 17 grams ready to fly (60% of one ounce).
If it weighed one ounce - and had 144 sq inches -
it would figure out at - one ounce per sq ft
N/Y?
my math was done in my head ( SWAG)
I was going to try for one ounce.
This little bitty stuff is a real challange -
My UMX300 weighs 32 grams and the wing loading is higher than I would like.

My mistake Dick.  I just assumed that a VAPOR was another of the flat foamie 3D models.  I've since looked it up and see that it's a spider web like model with some superlight gear.

Seems to me that what you're looking at as a bigger version already exists.  I don't remember the name but there's a model that's been around a while with the same bent carbon rod and film flying surfaces and that uses a small carbon tube for the fuselage.  It has around a 30 inch span as I recall and a V tail.  Although it used regular RC gear instead of the specialized small stuff of the VAPOR.  Sorry, no idea of what it weighed.  But it did slow down really well so it couldn't have been much more, if any, over 4'ish oz.

Same idea of the oval bent and curved up hoop for the wing that when covered and shrunk automatically gives a cambered arc airfoil to the covering.

The key to keeping the weight of a bigger version down will be finding the optimum small gear, motor and battery pack.  But if you're talking about a double size one then you can let the wing loading creep up a little and still fly the bigger one at the same speed.  And with the wing area going up by a factor of 4 times this means you can aim at a 3.7'ish oz weight for a 30'ish inch span.  That should be doable with care.

I am doing a profile Cassut Racer with large flying surfaces -and we shall see how "low" we can go - weight wise
I just recieved the new ESC/rx and outrunner motor from HH The A6400BL ultra lite rx two inc servos and esc -weighs 7.8 grams This one will be on the large side but I will scale it down for the all out attempt using a tiny cored motor
I am putting together a H9 BEAST at the same time for a friend - kinda a contradiction in model approachs n sizes!

Wing loading might be just a tad high but I sure am having a blast with my UMX300.

yes I bought another - also my new 125 sq in Cassut is very interesting - and slower but it is tooheavy at 44 grams

Dick if you want to have the same .9 oz per sq ft wing loading on a 110 sq inch wing, you are talking about a AUW of .68 ounces (just over 27 grams) from what I got.

Sounds like a very interesting project!

Dick my math was off it is 19.3 grams for the AUW, sorry; glad I double checked...

OK anyway -thefinished plane - 125 squares / 44 grams inc battery
The wing loading is OK-it takes off is airborne (about 6"high)and lands in fifteen ft!
Powerloading is a bit weak tho
I love these projects -
For peanuts -you can check out concepts .
I was once ,one of the modelers who believed airfoils were crucial to performance of our models -
The actual shape -Clark Y /24 12 symm etc- do make basic differences but switching from say a flat to a sharp le on this little stuff means absolutely nothing.
The ability to do some basic cambering -really showed up on this one- flaps work with elevators just like on a U Control
The 6400rx and servos weigh a few scant grams and are extremely accurate
Actually more fun than the larger stuff I flew for years
wing loading is about .8 oz per sq ft-
(125/1.5)
I used 28.349 as one ounce

Your talking just a bit over 1.5oz/ft wing loading, that's not bad!
I bet it does more than just takeoff.

You built a 4 channel airplane, with landing gear, and it came out at 44 grams that is great work!

my math-was terrible and done backwards in my head
so 1.5 ounces (44grams)
divided by .86 sq ft (125 sq in) =1.74

Dick,
Regarding flat plate airfoils, I recall back in the late 50's or early 60's NASA or it previous incarnation experimented with a flat airfoil for use in the hypersonic region, I think it's designation was NADA or something along those lines...
The one thing I remember is that it actually worked fairly well for them, it was essentially a flat plate that had a rounded LE and tapered TE, and other than that just a flat plate between.

I can not wait to see how my "flat plate" airfoil works on this one at 2 lbs AUW on 516 Sq inch wing.

If it does not flex under loads -it should be great
I found that holding shape on the aerobatic stuf really made a difference.
some stuff was flexible and was always hunting Pretty modle also - my little foamie is a SWAG to se if power and or weight needs adjusting
So detail work is minimal
I once did scale stuff - this design was 2.nd in Sportsman Scale in 1984 at Nats - The one I entered was detailed .

Well that plane has the diagonal ribs you suggested to stop the flutter issue, how it holds up under flight loads has yet to be seen.
I have to wait for the snow to melt, and the swamp that is our flying field dries out, before she gets put into the air.
I just did the fancy paint work to hide the Clorox bottle look it had going, no real detail work just a little camouflage. (I guess I was overly sensitive to some comments about pictures of it that I posted of it before)
I use to do some scale stuff myself but have really focused on late on just the structure and performance.
I have a few foamies that really look nasty but fly pretty good, I am really don't care much about how they look anymore, yours looks a lot better than mine do.
My Easy star with carbon tow on the wings and fuselage would be a good example of nasty looking...
That's a nice looking scale model, I wish mine looked as good!

Right now for the most part I focus on the structure and keeping the weight down, that seems to be the best approach from what results I have seen thus far.
This model is not typical for the type of plane I like to fly, it is basically nothing more than an experiment to see if a 3/8 inch thick wood structure wing can withstand the rigors of the flight envelope it was originally designed for.

Tho some may think otherwise - structure and weight outweigh calculated airfoils when it comes to performance
All are necessary -obviously but model or full scale - it's all a compromise and I will take a common sense airframe guy over all the rest.
I always wondered why the Wright Bros airfoil got all the credit when getting a machine which was light and strong enough was really what made it work

That's heavy; mine weighed about 12 grams including the battery, well below 1/2 oz. What a superb little plane....ez hovering, consecutive loops, inside or out, inverted flying, and even managed a roll or two with it. Alas, my grandson, for whom it was intended, stepped on it more than a year ago. No more Vapor

that is a lighter Vapor than we typically see.
we have a bunch of em here- the new Nite Vapor is quicker.

The new Vapor appears to have a lighter battery and electronics.

weight is about the same - the motor is apparantly wound for a tiny bit more draw.
I have both