Buil a mini F3A / practice machine. Need input from scratch builders. (Full Version)

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dolanosa -> Buil a mini F3A / practice machine. Need input from scratch builders. (10/13/2009 8:24 PM)

Hello everyone,

    As winter is coming upon us early this year (Chicago is freezing right now), I'm thinking of building my own Mini F3A pattern plane to build along with my full on pattern aircraft.  I have scratch built airplanes a long time ago and I'm planning to get back into the hobby.  There are several planes out there right noe that meet the criteria for mini-F3A but I want to build my own for several reasons.

    I currently have the plane in 3D CAD format, the way I want it to look as well as the technical, aerodynamic aspects.  Unfortunately, the end product actually looks like a smaller version of the new F3A designs out there, wide body, deep fuselage, thick trailing edges, etc.  I'll post some pictures later as I go.  So let's say the actual fuse, wings, stabs, etc are all planned out.  I want to build it out of wood as light as possible and possibly getting the second "kit" laser cut once the first one is flight tested and deemed neutral in all aspects of flight.  Here is my dilema and I have to balance weight, strength (not meant to survive a crash but able to withstand snaps), and budget.

    As you guys well know, there are several ways to make built up planes.  There is the 'normal' pattern plane method of building a box and gluing formers where needed, then sheeting the plane with 1/16" balsa.   I have built planes this way before and it has served me.  I believe this is an evolution to the old pattern 'slab' method where 1/4" slabs of balsa were used to make the sides and carved blocks to make the irregular shapes such as the nose or the leading edges of the vertical stab.

    There is also the tried and true stringer and former (bulkhead) method that is an older technique but make make for a heavier plane.  I think that this may be cheaper too since I don't have to buy a ton of thin balsa sheets but thicker sheets that I can make stringers.

    Now, as you guys also know, with the advent of 3D (flying) design, many things have changed.  I have seen several models that have a very open box structure without sheeting.  I was looking at my buddy's 40% and it was very open barely any sheeting except to make the upper deck shape.  Other than that and the part in front of the cockpit, no sheeting.  I have also seen examples of this in the smaller 3D aircraft.  This looks promising as it will help by having less weight, I guess.

Ok.  This is where you guys can help me a lot as many of you are avid builders.  What are the pros and cons for each design?  Please note that this plane will not be designed for 3D or very high G maneuvers like blenders and such.  It's meant to perform its best in pattern maneuvers so lighter will be better and will help in downline maneuvers as well.
  1. I want to keep the weight as light as possible to maximize the available engine power. 
  2. I also want to embrace the latest building techniques to advance my knowledge. 
  3. Most of all, I want to save money since that's the resource that's very limited right now. 
  4. What about built up wing vs foam with balsa sheet?
  5. What about a 1 or 2 piece wing?
Here are some design specs:  Screen shots by tonight.
Motor to use:  Non-piped Rossi 40
Span:  56"
Length:  58"
Width:  4 - 4.5"
Total height:  12"  (canopy height is around 8")
Weight:  As low as I can get.

Thank you very much for your help.  I really appreciate this.

butch



dolanosa -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/14/2009 7:43 AM)

ok, I have the initial drawings.  I don't see upload image at all.



da Rock -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/14/2009 1:20 PM)

The Fast Reply box doesn't have upload image.

You get that when you click the Reply or Quote buttons that're top-right of any existing post. Do that and the box presented has the upload buttons in the lower-left.



dolanosa -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/23/2009 11:58 PM)

Here is the basic plane.  It's a solid so I can cut it up to make the parts.




combatpigg -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/24/2009 1:05 AM)

I just finished a fuselage for a Jett .46 powered speed plane made almost entirely out of 1/16" contest grade balsa sheet......[:D]

The "catch" is there is a layer of 1.5 oz cloth on the outside and 1-2 [maybe 3 in some spots] layers of 4 oz cloth on the inside laid in before I sheeted the top.

For a traditional box that will be up to your standards for strength and low weight, go with Q-500 designs. If you see any deficiencies as you wring the plane out, they won't be catastrophic failures and nothing that a patch of FG can't correct.
Ever seen how hard a Q500 gets yanked around by a hot Nelson .40?



dolanosa -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/24/2009 3:32 AM)

combatpigg,


    Interesting...I'll take a look at a couple of my Q500 planes lurking around the basement.  That kind of construction is very easy.  I will just have to add the top and bottom formers to make the other shapes.  I'm out of town at the moment and I should be back next week to work on the design again.  I was already doing something like that with a doubler from the firewall to the wing TE.  I'll upload a pic once I get back.  Thanks.


Butch



combatpigg -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/24/2009 7:56 AM)

Butch, I don't think you can use the latest techniques without spending lots of money....no way. The cheapest way will be the old standby methods, balsa and carpenter's glue. Design the plane to have more air than wood. Refrain from drilling a bunch of GD lightening holes, though! They are great for weakening airframes with very little weight saved in return. If they ARE saving much weight, then the choice of wood or design is poor.
It takes a lot of good quality medium grade balsa to add up to a substantial amount of weight, but "doll house grade" balsa will add up quickly.
The biggest poundage comes from your choices of onboard equipment, hardware, rigging, finishing techniques, etc.



dolanosa -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/24/2009 8:59 PM)

Well put, combatpigg.  I will go with tried and true techniques and think you're right about the latest techniques.  I was pricing some wood and the waste after all the cutting and the lightening holes will be quite a lot.  Maybe once the plane is flight tested and found to be true, I can invest more into making a lighter aircraft.  Right now, I'm thinking 1/8" sheet sides with 1/4" triangle sticks for the main box with 1/8" sheets for the formers.  That sounds about right.



BMatthews -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/25/2009 8:09 PM)

I'm no pattern model designer but to me it seems like you need to raise that wing a little or add just a hair of dihedral. As it sits with no dihedral and that super low position I think you'll find that it will have a slight tendency to adverse roll when you yaw with the rudder. With any luck Dick Hanson will be around to either refute me or back me up on this. If not try PM'ing him. Also your nose looks very short even by today's standards. Again this will depend on how lightly you think you can make the fuselage and tail surfaces.

CP's post gives me an idea for molding thin and light balsa and glass shells as an option for a cheap composite shell style model. This would involve 1/2 oz cloth over the entire outside AND inside with a second layer over the nose and wing area on the outside where you'll be gripping it the most. On the inside patches of 4 oz would act as doublers in higher stress areas followed by the overall layer of 1/2 oz cloth. Skinning the entire inside and outside would form a sort of molded honeycomb shell with balsa as the core. Ideally you'd vacuum bag such shell segments to ensure a good bond with minimal resin. But a less fussy way is to pressure mold them using sponge rubber and tightly wrapped tensor or similar outer wrapping. I'd suggest in this case that the fuselage could be formed in two or three segments with a split along the vertical center or perhaps the top could be formed as a "taco shell" and the bottom a second part. Or using this system it wouldn't be hard to mold a cover for a tuned pipe or mini pip tunnel if you wanted. On a model of your size I'd consider using 2.5 mm sheet for the core layer and preforming it using a soak in household ammonia to pre-mold the shells to make life easier prior to the layup process. The difference being that for the molding step the wrap that holds it in shape has to be able to breath so the ammonia can evaporate. This is going to stink to high heaven of course so it'll need to be done outside and allowed to dry outside. You'll also need to wear latex or nitrile gloves to protect your skin.



combatpigg -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/25/2009 8:55 PM)

Bruce, I laid in light, but generously sized [1/2"?] tri-stock inside the fuselage to give the cloth large radius support in the corners. The cloth has enough tension inside the box to keep it where it belongs until the resin kicks. 1/2 -3/4 oz cloth on the outside is just cosmetic for even a 1/2A model, so that is why I bumped it up to 1.5 oz cloth and now that I think of it, 3/4 oz cloth went over the top in the same process.
When all is said and done, this method did not save any significant weight over traditional balsa construction, but it is pretty rugged and it's ready for paint instead of being stuck with using iron on covering.



dolanosa -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/25/2009 10:29 PM)

Bruce and CP. 

    I can't wait to get back to the workstation to keep at this model.  The way I was thinking about this since it's getting colder in Chicago was to follow the construction techniques of several of the 2M planes like the Black Magic series or my old Typhoon 2000.  It's basically a box with the top and bottom shape either built up or a foam shell.  The main box will have a doubler up to the wing's trailing edge, traditional construction so far.  If I do the foam top and bottom, I may just make the wings foam as well.  That may not lower the weight but at least it will be done relatively quickly.

    As for the design of the model, I have moved the wing about 3/4" up and will most likely create a "false" dihedral by making a flat top and a dihedral bottom, kinda like the Ultra Sports series.  Also, I'm really thinking about adding an anhedral to the horizontal stab.  (Maybe that will also help with the low wing or maybe because I think anhedrals just look especially cool.)  As for the nose being short, I followed the very simple 1/3 rule for building the plane.  The CG is 1/3 distance from the tip of the nose and 2/3 distance between the horizontal stab MAC.  Actually, the distance between the CG and the stab MAC is a little longer to have more moment.  I wanted to keep the nose moment short enough so there is "less" torque acting on the plane but still within reasonable limits.  It also looks short because the canopy is closer than the wing.

   Back to construction.  I do have a lot of 2.7oz glass cloth since I making some molded parts a while back.   If I use that as the outside skin, do you guys think that I will still need reinforcement inside the fuse around the less stressed areas of the fuse?  Maybe an outside skin and internal reinforcement around the high stress areas such as the firewall or and the landing gear?  I do like the idea of just painting the model and not applying covering unless necessary.  I don't have any covering material and they can get expensive...plus I'm not really great at applying them.  I also have some CF that I can use for the LG plate and will be making a CF-1/8"ply-CF sandwich for the firewall as well.

    Anyway, this winter will be very busy for me with these planes since I'm planning to build three pattern planes to compete in sportsman next year.  I will have this plane as a winter practice plane and two primary planes, a Silent ST that I never finished building and a Hydeout, (if that's the name of the 120 sized plane.  If not, it's the Hydeaway.)  I still need to buy decent servos, rebuild the YS 120 for the SIlent, get an OS 160 for the Hydeout, make some Hyde mounts, etc.  It's gonna be a lot of time spent in the basement during midnight hours, but I really hope to compete in some local events.  I just hope I get some good deals at some swap meets and such.  I will also need to get another vacuum pump as my old one finally bit the dust.  

    Thanks for your input, guys.  I really appreciate this little round table.

Butch

   




combatpigg -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/25/2009 11:26 PM)

2.7 oz will leave a coarse texture that will need lots of heavy filler...a layer of 3/4 oz on top of the 2.7 will be lighter [with the tighter weave] than a ton of primer on the coarse cloth. I can't comment on other glass/balsa/glass ideas than the only one I've tried. The important thing is to work within a weight budget and always be in total control over what you allow your ideas to end up weighing.



dolanosa -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/29/2009 11:52 PM)

So here's the first of the second set of pics. In this one, I have cut the fuse lengthwise and made some formers. These are actually the formers I used to create the fuse in the firset place.  It starts at the firewall and goes to the tail. You should be able to see the canopy section as well as the doubler that runs from the firewall to the wing trailing edge.

There are more formers than needed so please tell me what I need to delete.  I friend of mine says to take out the three that are in front of the vertical stab which is what I'm planning to do. 

As far as the verticaln stab is concerned, I will change the leading edge of the rudder to be correct and have a bevel.  I will also add some wood to go around the horizontal stab.  Of course, if the vertical stab will be made from foam, I can change that as easily enough I think.  

Speaking of foam, I can just take out most of the top formers and make templates for a foam-based top.  In which case, I might as well do the bottom formers in foam as well.

I'll upload more detailed pics in a few minutes.

Thanks for the help.




dolanosa -> RE: Buil a mini F3A / practice machine. Need input from scratch builders. (10/30/2009 12:09 AM)

Here are more detailed pics.



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