CAD_Flyer_321

So this is my first scratch design and build. Going with a 1/2a, 30" built up wing with 2" taper. i have attached a 3D mock up. let me know what you think or what you would add

kyle

icerinkdad

I like it!   One potential problem is the bent trailing edge as that requires a glue joint and creates a potential weak point.   If I were set on doing that I think I would do a long tapered joint to maximize the gluing area or consider extending the center sheeting out far enough to go a rib bay out beyond the bend.    Also I do not know what you are using for power but that is a pretty big wing for a sport 1/2a like a Cox or Brodak 049.   It might be okay for a Norvel or other 061 engine.     If I am seeing correctly your wing is the same thickness out to the tips.   That actually is a good thing as it helps avoid tip stalls as the thick airfoil at the tips would stall later than the center section.     I have had some very interesting problems with airplanes flown in overhead manuvers falling in on me due to tip stalls.
Bob

jayseas

When you all speak of 1/2A.How is that determined, plane size or is it just engine size?If engine size is the determining factor what is the largest engine size useable in the 1/2A class.
Jim

icerinkdad

The answer to that goes back many years.When free flight was the only way you could fly a model there were classes established A, B,C and I think D with engine size from smallest to largest... Class A was .09to .18 Ithink. Well technology caught up with the engine sizes and sometime in the late 40's after the invention of the glow plug folks started making these little engines that were called 1/2A.Currently that is any engine of .049 displacement and smaller by the AMA rule book. That said many modelers lump in anything smaller than a 09 or maybe even 15 into a general small engine class. So maybe more correctly your design looks great for a small engine but maybe just a bit big for an 049. Take a look at the wing spans and area on the www.brodak.com website for some general ideas about what size works for what engine.
Bob

Jim Thomerson

We need to know what engine you plan to use.  You need a really good reed valve Cox 049 for an airplane that size.  Might make the nose an inch longer.  1/2A's tend to come out tail heavy.  you can always cut the nose back if too long.

CAD_Flyer_321

i have a real nice running cox 049 texaco, and as far as the size, i redesigned it to have a 28" wing and took your advise and make the nose longer, measure once cut twice right. but if the motor im using doesnt work i might throw a .10 onto it

icerinkdad

The Texaco engine was designed to turn a larger prop at slower RPMs than other Cox motors for an RC event that rewarded maximizing the engine run time.    If the plane is very light it may have enough power but I suspect you will be happier with a larger motor.   It just depends on what you want the plane to do.  If you are still learning and happy with mostly going around in circles then it may be just fine.    If you want performance that allows much in the way of aerobatics then a very strong running black widow might be much better.
Bob

CAD_Flyer_321

i have a black widow sitting around here thats itching to go on something, but i think ill start out with the texaco. since its my first build i dont want to crash her on the first flight, but as i get more comftorable ill probably switch them out. i know i need to sheet the center ribs of the wing, but how thick should the sheeting be and how far out would you recommend i go?

icerinkdad

It is a small plane. 1/16 is probably more than enough.... if you have a source for 1/20 (Sig used to sell it... I do not know if they still do) that would save a bit of weight. Usually only a couple of bays are sheeted in the center mostly to give ou something to glue the fuselage to. With the bent trailing edge you may want to extend at least the rear sheeting out beyond the bend to add strength there. The other option would be to join the trailing edge piecesusing long scarf joints to spread the load there. Otherwise you risk breaking the wing on anything but a perfect landing.
Bob

CAD_Flyer_321

ok great, i have tons of 1/16. ill try weighing everything first then see if i need to go lighter.  but i was definitely going to sheet the rear of the wing by the taper, but i think ill put at leas one full sheet on it before i switch to rear only 

build light

The Texaco engine is definitly a great engine but this is the wrong application. I would not say it would make the plane more likely to crash, just that it would be a rather tame choice. The Black Widow on the other hand would be a great choice to try on this one.
You could go with the Texaco engine first and the later try the Black Widow for comparison.

The design looks really nice and I think you are on the right thack for success with it But I would like to suggest the trailing edge looks like it will be too blunt at the rear. I think you would be more satisfied if you were to extend the TE farther back as shown in this example.

Robert

CAD_Flyer_321

yea i believe i will go the route of doing a flight or two with the texaco then switching to the black widow, and at the time of the design i did not know how i wanted to go with the TE design so i just put in 1/4" square stock to complete the wing, however i have started building as of tonight and have a TE on it more like the one in your example

Jim Thomerson

Light 1/16 is fine.  I use 1/32 and then cover the sheet with silkspan which stiffens and strengthens it considerably and is probably heavier than really light 1/16. 

T.L.A.R. eng

Back in the eighties I scratch built a 29" plane with the appearance of a Baby Ringmaster.  Then I made the mistake of using Monokote covering which made it heavier,
It flew ok on an .049 Cox, but it wasn't no Ringmaster!
My then brother in law scratched a bigger plane with allmost 40 inches wing span and it was HEAVY. The Cox .049 struggled to keep it aloft, like having a glider on the end of the lines.
Think small and light when scratch designing for 1/2 a.
Build them, fly them, find out what works, that is the great fun of modeling.

CAD_Flyer_321

what would you recommend i cover the wings with that is lighter than monokote

Jim Thomerson

I do tissue and dope.  Monocoat should be OK, not that much heavier. 

CAD_Flyer_321

do any of you guys know of any good links on instructions for covering a wing with tissue?

build light

Stay away from Monokote. It is not as good as it used to be and even then it was too heavy for 1/2A models to fly well. Each and every step you take to save weight on this rascal will result in a better flying machine. Every step you ignore or do not take will take you in the wrong direction and will result in a heavier. plane that will only want to fly well.

To help answer your question:

http://www.instructables.com/id/Cove..._medium=footer

http://www.instructables.com/id/Cove..._medium=footer

http://www.easybuiltmodels.com/Notes_on_tissuing.pdf

Dumas has a DVD for sale showing how to cover with tissue.
http://www.dumasestore.com/catalog/p...roducts_id=685
__________________________________________________ _____________
You might want to take a closer look at the Aeromaniacs site as they really have a lot of questions answered for you there. It will only help your experiance.
http://www.aeromaniacs.com/Tips.html

You can also find more here including those above:
http://www.altavista.com/web/results...ssue%22&stq=10

Robert

P.S. It really makes it harder trying to learn it all at one time.

scott17

http://www3.towerhobbies.com/cgi-bin...?&I=LXGDW3&P=7

509boatman55

I have had good luck covering smaller models with 21st Century Microlite-an excellent and easy to use iron on. Also, Merlin Glowplugs makes a drop in high compression glow head and clamp ring that when used with a timing shim between the crankcase and cylinder give considerably more poop to your Cox .049. They are almost identical to the old Glo-Bee after market glow heads-I am lucky enough to own a couple of those. One is on an earlier Baby Bee with the double ports and open exhaust and it is a SCREAMER!