shredder111

Need help with the configuration of electronics for a foam glider. This is my first model ever and I have lots of foam sheets which I already elmered to the right thickness. Now all I gotta do is slice out and modify the certain areas so that electronics can fit in and I can prep it to fly. I haven't bought any yet, but I intend to get some very soon. Please let me know how or where I need to cut/ leave spaces open for everything including pushrods. I realize this is hard for you guys to predict because you don't know the sizing/ shape of the plane/ etc. Should I build the plane first post pics and than modify, or can you guys roughly tell me what I need to do? My wingspan will be around 40-50 inches and fuselage about 25-30 inches long including horizontal/vertical stabilizer.


I gotta go sleep

Thanks, Shredder111[>:]

P.S. Don't worry about my knowledge on lift/ aerodynamics. I did my studying. Now its time to get hands on !

BMatthews

Keep as much as possible up in the nose. Gliders typcially need nose weight and it's far better to use the radio gear as much as possible for this and only add enough lead or other nose weight as needed.

Battery pack right in the nose as it's the heaviest part of the radio gear. Receiver is next just behind the battery pack. Then the servos. If it's a skinny fuselage then put them inline. If it's fatter and the servos smaller then side by side. Pushrods need to run in as straight a line as practical from the hole in the output wheel to the hole in the control horns on the surfaces. This assumes the tube in tube style or flex wire in tube style. If you make up rigid pushrods then they need to be made up from wire ends and wood or other stiff rods so they don't flex instead of pushing. Also rigid style pushrods need to have enough room to move without rubbing on parts of the model. If they rub you are robbing servo power.

shredder111

I got a lot of work done today on my glider and roughly prepped it for covering. That newspaper thing is a great idea! I will definately try that. Here are my work pics, let me know what you guys think. Some pics are from the block starting to get carved, than smoothed, holes filled with polystyrene foam, and final prep. I used a 23 inch dowel for the second piece of the fuselage. Do you guys think it is too heavy? It seems to be o.k. on weight considering I make the wings with a 3 inch chord and 40 inch length. The fuselage w/ stick is 35 1/2 inches long. Is the wing length sufficient enough for this? Isn't it a rule of thumb to make the wings slightly longer than the fuselage? Here are the specs for the foam fuselage piece so you guys know roughly which electronics I should get and how big to cut holes.

Styrofoam fuselage length:

Length: 13 1/2 inches to tip

Width: 2 inches

Height: 2 inches


Dowel fuselage length:

Length: 22 inches

Width: 1/4 of an inch

Enjoy and let me know watcha think

shredder111

Here are some:

shredder111

P.S. I still have to add on a piece to the styrofoam fuselage (as you see)

shredder111

Here is some more rough work I did tonight on the vertical/horizontal stabilizer!!!!!!! Enjoy! More is coming soon.


Shredder111[>:]

BMatthews

That's going to be an interesting design. But I hope you realize that with only a 3 x 40 inch wing that you have VERY little wing area and what you have is going to be limited in efficiency by the short chord. It'll fly but to thermal it will need to be kept down to only about a 4 to 5 oz weight.

Also the dowel is going to break for sure. Dowel wood is typcially rather brittle and shatters easily when flexed. It seldom has the grain running very straight either and that just increases the problems. You'd be far better off getting a carbon fiber arrow shaft or one of the carbon fiber tube style pushrods for larger models and using that for the boom.

There's lots of nice little hand launched RC gliders in the 36 to 40 inch range but you need to increase the chord to more like 6 to 7 inches to get enough area and make the chord wide enough to raise the Reynolds number. The Reynolds number is sort of a value of "efficiency" in how well an airfoil will perform and can be more or less thought of as the scale effect. And at 3 inches you've got the scale effect stacked against you.

You mentioned about radio gear. For anything this size you want to buy the very small and very light stuff.

shredder111

O.K. I will make the wing chord 5 inches and the wing 50 inches long. What are some general rules of thumb to go by when building wings? I made a forum for this and people just said guess and that there are no calculations to perform before buidling, so I didn't know where to start. I will keep you posted on progress. I will be making the wings out of foam sheets that are about 1 cm thick so I have to glue them together to make them thicker. How should I make the wings to be strong out of foam? Also, on gliders where are the control flaps? The wings or the rear stabilizer?


P.S. I just did a weigh up on the kitchen scale and I weighed in 1.1 ounces for the styrofoam fuselage + dowel shaft




Thanks, Shredder111[>:]

shredder111

Anyone?

BMatthews

You're obviously very new to this design stuff. How much flying have you done? I'd suggest a larger amount of dihedral in the wing combined with rudder and elevator control. Also you need to add a spar to the wing to resist the bending loads from towing it up or highstarting it. Something like 1.8 x 3.4 spruce up on edge and at the 35% point of the wing. Foam in front and behind, carbe to something that looks like a thick Clark Y airfoil and then use the newsprint and WBPU for a covering that will add strength and torsional stiffness.

I'd make the wing in three panels. For a 50 inch wing go for a 26 inch wide center section with 12 inch tip panels. The center panel being flat and the outer panels raised up by 3 inches at the tips.

5 inches is stil pretty narrow. I'd suggest increase that up to 7 or even 8 inches. THis will add wing area and extra volume to the wing that will both fly better and build stronger due to the extra size. For a 50 inch wing the fuselage should be about a total of 30 to 35 inches long. Horizontal stabilizer should be 20% of the wing area and the fin and rudder should be 12 to 14% of the wing area.

shredder111

This is actually my first RC airplane. I have built a P-51 kit completely before, but because I was younger at the time I could never afford any electronics or components for it, so I ended up selling it. I got into planes through my natural interest/ paper airplanes and aside from that those are my only flying experiences. That is why I am asking so many noob questions I really appreciate the help and with your guidance this project seems to be going very well for my first one. More pics and questions coming later today!


Thank you, Shredder111[>:]

shredder111

I got the sheets cut out, so now the wings are with an 8 inch chord and 50 inches long. Here are some reference pics. Do you think the rear stabilizer is too small? I will use the Clark Y airfoil and start shaping tonight.

BMatthews

The second pic looks great other than for the tail surfaces. They would have been about the right size for the 3 or maybe even 5 inch wide wings but they are far too small for the new (and much better looking) 8 inch wing. I'd say double them or perhaps even 2.5 times them. Better too large than not large enough.

Also I see you're still using the dowel. Ditch the dowel in favour of a carbon fiber arrow shaft or similar. The dowel will shatter on any sort of hard or semi hard landing when the tail whips it around at all.

Otherwise it looks great. If you don't have the radio equipment bought yet I'd suggest you stick with some typical parkflyer style radio gear with the smaller servos. The 8 gram ones like the Hitec HS55 or 10 gram ones like the Hitec HS81's would suit this size of model nicely. You'll also need to get a lighter battery pack.

Assuming that you'll be using a high start or handlaunch for this model don't forget the full depth spruce spar I suggested for the center section. The newsprint and WBPU will provide the strength you need for the tips but the center section is where all the stress from the rest of the wing gets concentrated and it needs the extra help.

For the fuselage pod you can use the WBPU and some 2 oz fiberglas cloth to provide a nice ding resistant skin. Or if you want to stick with the paper mache bit then narrow strips of the newprint soaked in water and then brushed on with WBPU in random diagonals that overlap every which way until you have about 3 layers of thickness overall and 5 or 6 around the nose and belly will work too. The strips will need to be cut so they are only about 1/2 inch wide. It'll take a lot of 'em too...

For shaping the wing I suggest you cut the foam in angled facets by marking felt pen lines on the blank. Cut or sand until the lines are just touched and then add more lines. Finally just a little smoothing and you're done and the airfoil should be nicely consistent and decently accurate. Consistent from end to end is more important than accurate. If it changes from one side to the other by much the model won't fly well.

BMatthews

Here's something that may help. It's a drawing of the measured bevels that I was talking about above. If you use this to shape the wing it'll come out as accurate as you could possibly require and it'll be more consistent. Don't worry about the decimals in the sketch. I did it quick but the CAD program doesn't know that so it gives you numbers that look a lot more fussy than they need to be Just round them off to within the thickness of a fine to medium tipped felt marker.

The panels should all be shaped before you join them at the dihedral breaks. To join them sand in angles until they fit at the right angle to each other. Just like a big balsa glider. Doing this at the edge of a table and holding the panel down helps keep the joint square and then tip the sanding block to roughly the right angle. Sneak up on it until it fits with the right dihedral and as little a gap as possible.

Note that I've shown a leading edge shaping template. If you're new to this sort of wing shaping using the template to check your progress often and trying to get as nice a fit as practical is a good idea. Make the template out of something like thin plywood or something thin and stiff. Check it every new inches along the span and carefully sneak up on the shape.

Use fresh sandpaper and a light touch for sanding the foam. 50 or 80 grit for rough shaping followed by a finishing with 150 or so to smooth things out. That's pretty much how I did it when I used this same foam and newsprint method for some control line combat models years ago.

Send me a PM with an email address and I'll send you a better copy of this quick sketch. Then you can print it out and get the correct size for the LE template. Or if you can use a CAD version I can send you the DWG or DXF.

shredder111

Great info!!!! I got a bunch of work done today and started pasting the fuselage and shaping the wings. I chose to go with the newspaper on the fuselage because it seems like it was very strong on my test piece. I drew out my Clark Y template and made a couple of copies to paste on the side of the wing so I could carve length wise down the wing. What I did is I literally hacked away according to my eyes along the airfoil shape leaving about 1-2 mm of slack for mistake and once I was done cutting I took my trusty sanding block and got to grinding until the wing panel was perfectly aligned/ shaped from every angle. I appreciate the template info, but I feel that I am pretty well off with shaping. I will use toothpicks to strengthen the dihedral breaks and will add newspaper spars to joining points to decrease stress. I kind of cemented the dowel into place with toothpicks, glue, and newspaper earlier so now it is kind of stuck I will just wait until it breaks and than I will install a carbon shaft I ripped off the old rear stabilizer and will start working on a new one tomm. I have a lot of questions and I will seperate them from my main body so you don't have to go hunting for them

Questions:

What angle should the wings dihedral lift up being viewed from the front?

What angle should the wings be, looking at the plane from the side? Front to back (vise-versa)

Where should I mount the wing on the fuselage and how do I find the planes center of gravity?

How should I design the rear stabilizers considering they will control my plane? Control surfaces and their mechanics are new to me and I am not quite sure how to design them. I know I need to use hinges and some linkages but how about the details? I think I will loose the funky snake tips and go with a flat cut off.

What motor/esc should I get? I will probably go with Li-Po batteries. I need two servos, correct?

My fuselage with the dowel shaft but without the rear stabilizor is 31 1/2 inches long. Is this long enough for this big wing? I realize when I make the rear stabilizers it should increase the length by 5-7 inches.

How should I prepare the newspaper for the final coat/ paint so it looks nice and smooth? You say put 3 layers on? Isn't that too heavy? I already have a quarter of an ounce increase on the first layer with diluted 50/50 elmers glue. It is still slightly wet though I will give a final weigh up in the morning when it is totally dry.

How should I make the wing mount and what will hold my wing in place?

This are mostly all of my questions for now, if I forgot something I will post later. Lol, I hope all of these questions aren't a burden for you


Thank you, Shredder111[>:]

Pics coming up! I will keep you posted

shredder111

Here are some before and after, comparison, and final pictures of my wing work. Also included is the first coat of newspaper onto fuselage pics.

BMatthews

Templates are good. Sounds like you got that part down pat.

Electric power is good too. You won't need the full depth wood spar in that case. But what I would do is make up a strip of wood with some coarse sandpaper on one edge and use it to cut a groove that is 1/8 deep and 1/4 wide for the span of the center section. Into that glue a strip of either very hard balsa or spruce strip to take the compression loads from pullups.

The wings need to angle up about 3 inches at the tips as seen from the front. Also if yoiu sand your tips to bevel up from the bottom from about 2 inches in from the tip on the lower surface the upper shape will give you a nice looking stretched version of the ClarkY as a wing tip outline. That angle will also help the dihedral situation.

The stabilizer should have about 20% of the wing's area and the fin about 15%. Size your new tail surfaces as per that. Out of those position the elevator hing line so the movable area is about 1/5 and on the fin position the hinge line so the movable area is about 1/2 or even a touch more of the area. Face those edges with balsa wood on both surfaces before doing the newsprint covering. The wood will provide the gluing strength needed for the hinges. The foam won't hold them for long.

The tail as noted is a little longer than you need. That's not a problem but given your whippy dowel it would be better all around if it was about 3 inches shorter. One way to help that poor dowel would be to wrap it with long diagonal wrappings of strands of unwoven fiberglass, kevlar or carbon fiber so the dowel is just a core that holds the fibers.

One item I didn't mention that scares me about the dowel. Being so flexible it can let the tail flex around. When that happens the angle between the wing and the tail can change adn that can lead to lots of problems as the boom alters it's flex due to air drag on the tail as the flying speed changes. I almost lost a pod and boom glider once that way. It was a 2 meter design and the carbon arrowshaft I was using wasn't stiff enough (stiff, not strong. There's a difference) to prevent the drag from the T tail bending the boom down and making the glider tuck into a dive that it could not pull out from. Some quick thinking and lots of altitude to play with let me do a part outside loop, which it did nicely, and then half roll back to upright. A rather nervous SLOW SPEED descent followed and some mods to prevent that happening again. Learn from my mistake and stiffen up that dowel. Or cut your losses now and do the mod to change to the CF arrowshaft before you paper mache the fuselage. After all, for best strength the paper mache shell has to form down over the first part of the boom to provide proper strength at this critical joint.

The wing to tail angle can be pretty much set with the flat portion of the lower surface even with the horizontal tail. The upswept curve at the leading edge provides a build in 2 degrees of positive incidence on the ClarkY airfoil compared to the tail and that should be pretty much all you need. Set the motor so that it points down about 2 degrees negative compared to the lower surface of the flat portion of the wing. By far the easiest place to mount the wing is to cut a flat saddle area on the top of the fuselage pod. It's hard to tell from your pictures but you may need to build up the rear area of the pod a little to allow for that. If you cut in this flat saddle area part way then you can add a little fairing to the center front part of the wing later on so it blends in nicely to the pod. If you didn't make allowances for it I would suggest that you build up this area enough that the wing's lower flat section is raised above the boom but in line with it. This space between the boom and the wing will be needed for the pushrods to come out and run along the top of the boom in any event.

To set the CG you can just balance the model on your fingertips under the wing. Just get it so that it tends to seem like it'll sit level when your fingers are at a point 2 3/8 back from the leading edge. It may not want to balance stabely there but as long as it tends to tip one way as easily as the other that'll be close enough for starters.

For pushrods you won't find anything easier to use than the Dubro plastic in plastic tubes known as Nyrods that you can get from the local hobby shop. Mount the outer jackets so they aim at the proper hole on the servo arm at the front end and run down and along the dowel to the tail and use small wedges of wood to aim them so they run to the inner hole on the rudder's control horn and the outer hole on the elevator control horn. Keep the open space distance from the end of the firmly mounted outer tube to these holes to between 1 3/4 to 2 1/4 inches. You need SOME spacing to allow the inner pushrod tube to flex a little but you don't want too much spacing or it could buckle under the pushing load. 1 3/4 to 2 1/4 is about right. At the ends they give you short lengths of threaded rod and some quicklinks. The outer tubes of the pushrod must be wrapped and bonded to the boom and somehow bonded at the ends as well. The ends are critical the bits inbetween are just to prevent the tubes slapping around.

You see why I'm saying that doing the boom now will be a lot easier than fixing it later?

Another thought is to dump the pod and boom and just make a nice carved foam fuselage that looks like a proper full sized glider. The larger cross section of such a new fuselage will ensure that it is stiff enough with a minimal amount of newsprint paper mache while still being reasonably light. I've added a sketch of a plan I'm sort of working on as some inspiration.

If you're on a budget with all this the commonly available GWS 350 geared motors would work nicely along with a 2 cell 800 to 1000 mah Lipo pack and the motor and speed controls are cheap for these since they are brushed and no one seems to want them anymore. But I would plan on useing an APC parkflyer prop cut apart and modified to make it into a nice little folding prop for this. The fixed blade ones tend to get caught on landing and just break. The folder greatly helps prevent that.

Remember that you need some way to get at the radio gear inside the fuselage and something to mount the servos to as well as some hard points to prevent the wing crushing the foam and paper locally due to stresses and some way to mount the wing. All this will require a little more work on the pod than you have done so far. Typically this is done by building up a skeleton of keels and formers to provide hard points for mounting the wing, motor, boom in this case and servos. Then for this style of building you lightly glue in the foam blocks to fill in the spaces and then carve it all way so it blends to the keels and formers. From there you can cut out what you're using for a hatch to access the gear and battery pack and hollow out the foam inside for room for the stuff. These keels or stringers would also provide a more solid way to hold the boom and transfer the forces into the pod. If your existing pod is going to need to many mods to work given all this new info then perhaps it would be wise to cut your losses now and make up a new one.

As for the radio yes you'll need two servos and a speed control or ESC (Electronic Speed Control). The motor and ESC need to be matched so that the motor can't draw more current than the speed control can provide without burning up. Also the motor, prop and battery voltage need to be tailored to avoid drawing more power than the motor can deal with or it'll burn up as well. The proper prop to use is available through the GWS website as well as some other online shops that sell the GWS gear motors. For a glider you'll be wanting the 6.0:1 gear ratio and that means a 9x6 or 10x5 prop as I recall.

shredder111

That darn tootin pesky dowel! No matter, I have enough foam to build a house I will bite the bullet and leave the dowel fuselage for another project and build a new one without a shaft as a whole piece. Any tips on starting a whole new fuselage? I will draw my plan out and post it as soon as I am done.


Thanks, Shredder111[>:]

slopemeno

My Feedback: (2)

Something you might consider is checking out a plane thats similar in approach to your project. "Mountain Models" makes a glider called the DL-50 that shares some similarities. Matbe you could buy one, study it, and either build or sell the kit once youre done with it. They used blue foam for the wings and cover them with 3/4oz fiberglass cloth and polyurethane.

Also, it doesnt hurt to study other peoples designs. I'm not saying that you would be ripping off someone elses ideas, or that yours are any less worthy, but studying/building a proven design will answer a lot of questions for you.

shredder111

I appreciate the advice, but the whole purpose of this project is to learn about rc planes, how they work, and their mechanics through limited supplies other than electronics. By designing my own parts with people's assistance I can learn a lot and when I move up to a real kit I will be more educated I don't just want to go and buy a kit, I want to fabricate the parts on my own and call it mine/ learn about it. Don't worry about comparison, thats what I have Tower Hobbies for


Thanks, Shredder111[>:]

More progress pics coming soon!

shredder111

Sorry for not writing so long, I have been really busy and haven't had any time to work on my glider. Now, lets pick up where we stopped. I thought about not using newspaper to cote my wings, but epoxy. How does it work and how do I apply it? I have all my wings roughly carved and will get ready to sand during the next few days, possibly tommorow if I have time. Pics coming soon!


Thanks, Shredder111[>:]

BMatthews

Epoxy is only a glue. You don't get your strength just from epoxy. For the skin to add strength you need fibers of some form in the mix. These fibers can come from fiberglass, paper fibers, fiber strapping tape, wood fibers (as in wing sheeting) or probably other options. But the glue, be it epoxy or the water based polyurethane, is only there to provide the stickum. Epoxy is also heavy so it's wise to only use as little as possible.

A while back I found a very tough and fibrous material at a sewing store that is used to trace and cut out patterns that are intended to be kept for a long time. This stuff is quite tough and it may well be that it would be a good choice as a skin material. It doesn't have much if any ability to conform to compound curves though.

shredder111

O.K. That sounds good. I will use the newspaper technique. It turned out pretty good/strong on my other fuselage. I finished some rough work on the fuselage today and am waiting for the glue to dry before I start carving. I will let you guys more info later.



Peace, Shredder111[>:]