Building light vs. durability & Wing Loading vs. Stability

[payne9999]

I finished the balsa and the spruce/balsa fuselages. Here are some pictures:

Balsa:


Spruce/balsa with doculam covering:


I am really pleased with the spruce and balsa combination. I need to find my electronic scale to see the difference in weight but it seems very light.

Next step is to begin painting the fuse while building the wing up.

Dave

[kyleservicetech]

Originally Posted by payne9999

I finished the balsa and the spruce/balsa fuselages. Here are some pictures:

Balsa:


Spruce/balsa with doculam covering:


I am really pleased with the spruce and balsa combination. I need to find my electronic scale to see the difference in weight but it seems very light.

Next step is to begin painting the fuse while building the wing up.

Dave

Wow, that is incredible work, keep wattflyer posted

[payne9999]

This kit and plan remind me of days gone by when I was about 10 and building every Comet rubber powered FF model I could get.

The spruce/balsa fuse required less bracing because it was stiffer. I hope this offsets the increased weight of the spruce.

The credit goes to Pat Tritle for a masterful design. The only reason I am changing it slightly is because of my clumsiness and hard landings.

I would recommend his short kits more than any other right now especially if someone is into scale aircraft that are light but large and will fly in parks (48-60"). I wish I could just plunk down the money for 2 of every short kit he offers.

http://www.patscustom-models.com/

I am also a big fan of Mountain Models (Brian is great and he ships stuff very promptly):

http://www.mountainmodels.com/index.php?cPath=25_74


Dave

[kenchiroalpha]

Hi Dave
Outstanding
Thats a wonderful job your doing, very nice
Take care
Yours Hank

[payne9999]

Thanks. The paint went on nice. I do like doculam although I always wonder about paint adhesion.

Here it is with the white paint. I have to wait a week or so before adding the trim to allow the paint to fully cure.




Dave

[Captain Dunsel]

Very nice work!

I take it you're painting with spray latex (I used Valspar on my latest ship, a PA-12). If so, you definitely need to let it cure for a few days.

CD

[payne9999]

I used Behr latex exterior thinned. I like it because Home Depot willl mix and computer match colors in the pint samples which are only $1.98 each. It is the perfect size for models.

However, this white I am using clogs the airbrush when it is not real thin and then it goes on transparent and I have to watch for runs. It seems like only the white gives me this problem. I am going to look for a small touch-up gun or a larger airbrush that can handle more volume of material.

Maybe I should try some acrylics from the art store and hand mix/match for the military colors.

Dave

[Captain Dunsel]

I've tried several types of paint, including Apple Barrel (a pain to spray as the different colors often have grossly different pigment sizes) and Tamiya acrylics (easy to spray, but mediocre coverage), plastic model enamels (mainly Testors), Krylon, and, latest of all, Valspar spray latex.

Of all of them, only the Valspar has stayed on when masked, provided I buffed the Doculam and wiped it down with acetone before painting. If I don't do both, it lifts when masked.

So far, I'm fairly happy with the Valspar, having painted my latest, a PA-12, with it in cream and red. I actually had more trouble getting the red to cover than I did the cream, and I think I got on too thick a coat of the fuselage nose, because after almost a month it's still slightly soft and picks up marks from the storage rack.

The other unpleasant thing I learned about the Valspar paints was that CA kicker attacks it. On the other hand, the spray cans work well and I have no complaint about them.

I haven't tried it as a top coat over latex, but I have found that Polycrylic sprays on well over all of the other paints I've used, so if you need a top coat to make the glosses/flats match, that may be viable.

CD

CD

[payne9999]

Is Valspar a Miller product? Who sells Polycrylic? I would like to do a gloss topcoat and for flat military colors I have been using Dullcote form Testors but it is expensive.

Thanks,

Dave

[JackM]

Dave,

Generally speaking, spruce is twice the weight as balsa and 10X strength. I plan on using spruce in some of my future builds since I have a large stash of very old, high quality, rough cut spruce lumber.

I am learning to fly using a all balsa aileron trainer (mini-telemaster) and on windy days (about >5mph) the plane can be lifted off the ground and is also knocked about pretty bad in the air unless going upwind. In wind it is all I can do to get it to land. Not fun and not a good learning experience. I am thinking of adding a 6-8oz weight at the CG just to stabilize it.

In the future I will be more worried about balance and not about weight when it comes to high flat bottom wing floaty planes.

Can't wait till I can fly well enough to handle a plane with better wind penetration.

Jack

[Captain Dunsel]

In our part of NJ, Valspar is carried by Lowes, and Rustoleum by Home Depot. From what I can tell from the can and the Web, Valspar appears to be a US product, but it's sold overseas. So, it may really be an overseas product, with a subsidiary in Illinois.

Polycrylic is a Minwax product. It comes in gloss and satin finishes, and can be sprayed with very little thinning. When I do thin it, I use clear Windex (which is what I use for just about all of my spraying). My primary airbrush is an ancient Miller brush, run via a cheap compressor I've had for close to thirty years. The only thing I had to do was put a water trap in the line (got it from Harbor Freight). I prefer the satin finish, as it looks more realistic to my eyes.

To keep things straight, I've used rattle cans for the latex and Testor's enamels. For the acrylics, I've used my airbrush.

My PA-12 is about 450 squares, and I was able to do all of the painting with two cans of Valspar, with paint left over. I'm including a shot of the PA-12.

BTW, I did cheat with the numerals on the wing top. They're white Econokote, scuffed then painted with Valspar and CAREFULLY ironed into place at the minimum heat that would make them stick. Any more heat, and the red started bubbling. I made up a test block and made my goofs on that before trying them for real! I also left off the wing bottom numerals, to make it easier for my wife to fly the plane (I built it for her).

CD

[JackM]

Valspar is an old company that used to make "long oil" based boat paint back when we had wooden boats so I assume it is still American. I just painted my house with it and liked it.

Jack

[payne9999]

I am in Oregon and Valspar is sold by Miller locally.

I will give it a try. Very nice looking PA-12. I have a Pilot 1 ARF version of that same color scheme. It is the only ARF I have ever owned but I want to recover and paint it since it has been through a lot including a crash caused by the latest Spektrum recall.

Thanks,

Dave

[payne9999]

Here is a wing section. Again I just changed it to deal with my clumsiness and bumpy landings but the leading edge is very light Engleman spruce, the tiny 1/16" square stringers and the trailing edge.

After breaking the main spars loose from the bowed wing tip, I added some small gussets from light balsa.





I wasn't intending to make this a build log but OK....

Tomorrow I think I will check the weight on a scale at work.

Dave

[payne9999]

I did a weight comparison. These values are for a covered and painted fuselage with completed and covered tail assembly, motor and servos. No landing gear or wheels yet but I am using very light foam scale tires.

Fuselage that is all balsa: 5.3 oz.

Fuselage that is mostly select Engleman spruce: 8 oz.

So, for a 2.7 oz. difference I think the spruce is best for my flying style and clumsy nature. I am thinking since the wings only have spruce for the leading and trailing edges that the all up weight will only be 4-5 ounces heavier than the original all balsa design for a total weight of about 23 oz.

I should be receiving the paulownia lumber this week so I may build another prototype from it.

Dave

[JackM]

Dave,

Interesting weight comparison!

I've been thinking of building a "steam punk" plane ever since seeing an article in Model Aviation. I am thinking of fuse longerons being very straight sticks, possibly willow.

Jack

[payne9999]

Willow is light but not as strong as other materials. Stronger than balsa though. Is the Steam plane going to fly or is it static? If I remember the article it looked as though it was about concept aircraft for the Jules Vern era. I know they had at least one photo was of a real flying steam plane. I remember the photo showing the engine running with a huge puddle of water under it.

Dave

[JackM]

Dave,

"Steam Punk" is a genere or style, not necessarily steam powered. It will fly and will be electric. I figure willow can be cut and hung with weights to straighten as it drys. It will look so funky people will wonder if it will fly!

Jack

[payne9999]

I received the paulownia wood today and re-sawed it into model size dimensional lumber. It planes and saws very nicely. It was easy to slit even down to 1/16" by 1/16".

From what I can tell it is about 2x stronger than most balsa. I say most because it seems a little stronger than the hardest balsa I have worked with (in 30 plus years of building) but significantly stronger than medium or soft balsa.

I responds to CA slower than balsa but not as poorly as spruce. Many of the spruce glue joints I made took over 20 minutes to cure but held well in the end. This wood does not bond in an instant the way balsa will with thin CA.

It cuts a little harder than balsa and your X-acto knife needs to be in good shape in order not to tear.

Overall it looks like a nice material option that could be used for a lot of structures where weight is critical but you need a little more strength and rigidity.

I am mostly into park flyers that are around 48" and up in wingspan and typically weigh 17-34oz. for these planes I don't think I would opt out of using spruce because it is so much stronger without a lot of weight penalty but maybe use a combination of balsa, paulownia and spruce. I think it might be great for a really light plane that would be too fragile in 100% balsa.

Dave

[JackM]

Dave,

I hadn't heard of paulownia so I did a quick search to learn about paulownia. None of my personal library has any specific info on it but I did find some general info on the web. Amazingly I couldn't find any info regarding strength which I can find regarding most other woods. From what i gather it is similar to poplar but a bit more porus. Biggest plus for paulownia is that it is quick to grow and will start from a stump being environmentally friendly.

When glueing spruce higher viscosity CA might work better for you. I use a variety of CA glues and "zip kicker" accellerant. I find zip kicker very useful. I have been tempted to try Gorilla glue.

Jack

[payne9999]

Here is some data (breaking strength is quoted as almost exactly 2X balsa):

http://www.paulowniasupply.com/paulownia_vs_balsa.htm

It does grow fast and some folks in the U.S. are farming it.

I have used "kicker" before and I will have to go get some especially for use on spruce. I just don't like the smell and some times when CA goes off quickly it is really irritating.

I think if the balsa supply ever got scarce paulownia would be a great substitute.

Dave

[pmullen503]

Around the great lakes states, Aspen (Populus tremuloides) is available at specialty lumber yards, and some home centers and also makes an good substitute for spruce and balsa. It's similar to basswood in that it has a very fine tight grain and carves easily. About double the density of balsa. Around here, it's dirt cheap too!

Like Paulownia, gram per gram it beats balsa in all important strength characteristics. I use it for spars in foam wings and for vacuform molds. Saws and sands well too. I rip thin sheets on a band saw or table saw. Good alternate material if you can get it locally.

[JackM]

Kicker does stench! When I plan on using it a lot I do it in front of my cardboard box spray booth! Generally speaking I'm not keen on CA but it is fast.

One thing to consider with wood is the grain structure. Both spruce and balsa have very straight and even grain and it bends a lot before it breaks. Poplar/aspen usually breaks with out much notice though it isn't much of an issue for some parts. I haven't seen or worked with paulownia so am kinda curious about the grain structure and flexibility.

It's going to be hot this weekend so I hope to get some work done on the Cloud Ranger I'm building.

Jack

[Nitro Blast]

@ Jack M- DI water works as a perfect accelerator, with no smell, and a crazy good low cost.

[road king 97]

Dave i have built heavy planes all my life till now and i found ivans site for all electrict planes . I just finished his short solent sea plane withh a 99 inch wing span and fuse 6 ft long it weighs a little over 8 pounds with the 4 motors and batteries in it. He is known for his scale looking airplanes and his very light construction. When i first started it i thought it would not be strong enough but once you sheet a couple sections and the front of the wing it is very strong. I realy know how to build light now and here is ivans site. If you want plans you have to email him and he takes a bit to get back some times but he always does. http://ivansplans.com/ My solent is 3/16 sticks and all 1/16 sheating,he calls for a 3/32 balsa main spar with 1/8 x 1/8 bass wood strips top and bottom and it is very strong . joe