RVM

I'm getting ready to buy the wood (if I cut my own parts - if I don't I'll get the parts cut by Precision Cut Kits) for my Hostetler 300XS. I'm researching balsa and the best way to cut balsa. Is contest-grade balsa worth the extra cost? I know it is about 50%-75% the weight of AAA balsa, but wouldn't the softness and lighter weight translate into lower strength? I was thinking of using contest-grade for sheeting, ribs, and other parts that don't have to take a lot of stress. I would use heavier (and stronger?) AAA for the framework, trusses etc. Does this seem logical? Should I use it everywhere, or not at all? I have found some contest-grade, but I haven't really been able to figure out exactly how much more it costs than other balsa with equivalent dimensions.

I think I have balsa selection down. For instance, I would use balsa where the grain runs lengthwise (forgot the name for it), for ribs yes? Anything I should keep in mind here?

This plane is built very light; not designed to take abuse at all. I read the one thread I could find (and I checked all the RC sites I know of) which specifically concerned this plane, and the builder (shag555) said he thought a bit of reinforcement might be in order if one plans on really pushing the plane hard, especially with a gasser. Since I'm going to use a gasser, and I'll eventually put it through some high-G, 3d type maneuvers, would it be advisable to add a bit of carbon fiber reinforcement? For instance, get some of the thin CF strips and glue them to the spars, stuff like that.

Finally, what's the best method for cutting parts? The formers and ribs seem to be the parts with the more difficult shapes to cut. I'm guessing a scroll saw/band saw and a disc sander, based on advice from another thread. Is there a good way to do it by hand? I guess I should use a very, very light grit on the sander, if I use one, so it doesn't make a meal out of my balsa. Would 600 grit be too smooth? Should I cut to match the template inside or outside the outline? When building kits I always cut parts and make everything fit along the inside of the outline.

Now I need to figure out just how much wood I need. I guess I'll go start measuring parts.

I've tried to get my plans copied at various copy places. They are all off by a fair margin. Is this acceptable? Is there any way to have the plans copied with 99.99% accuracy that won't cost me $50 per sheet?[&:]

This is a lot of questions, and I am sure I'll have more later. I know they might seem a bit silly, but I am a noob to plan-building, and I want to make sure I do it right.

Thanks!

PatternPilot

My Feedback: (58)

RVM,

Since I'm looking at the same plane, I have built pattern planes in the past using all contest grade balsa with out a problem...
If I do my extra I'm going to use some honeycomb nomex and HCN with carbon is spots... Also a carbon fiber landing gear.. I might get the cowl and other parts and use a a plug and make new molds so can be done in carbon unless the maker will do it for me..

here is my direct email [email protected]

keep in touch..

scott

BMatthews

Beefing up the spars is never a bad idea but it needs to be done properly. Just adding carbon willy nilly may not have the desired effect. I'm guessing that the spars are set up much like sailplanes use with top and bottom caps and full depth and full span webbing between. If so then first of all I'd go for spruce for the spar caps. And then add carbon caps to the outer faces of the spars.

Webbing is best if it is precision fitted to go between the spar caps to form an I when looked at in section. But may foks just glue then so it forms a [ sort of shape with extras in the center one half to form a full box shape. For this sort of shape the webbing wood should be very hard stock for the center section out to about 2/3 span and medium for the rest of the wing. This is due to the high stresses of these parts and the need for a higher shear strength at the glue joint which only the stronger wood will provide. In fact with the center 1/3 span it would not be innapropriate to use even 1/16 ply for the webbing of a gassie stunt model. The main spar is not the place to be shaving grams.

A gassie engine often has a lot more vibration. For this reason it's worth making the mount and first part of the longerons carrying the mount a bit stronger through using carbon or kevlar or some other method and material.

RVM

I was either going to completely box the 4 main spars (1/4"x1/4", running full length of the wing for the forward two and about 70% of the length of the wing for the rear two) or put two strips of .0007" carbon fiber vertically on them (I guess that's what you mean by capping the spar on the front and back with carbon?). Also, the plans (if I remember correctly) call for the shear webs to be placed on the front of the spars and just glued in. I was going to put them between the spars, full length between ribs and spars, as I think you are describing. It seems like a much more effective I-beam than just gluing them on the front. I suppose I should use a heavier grade balsa for webs?

I had intended to use spruce spars. Stronger than basswood and the same weight.

I was going to run carbon fiber strips along the length of the longerons. The strips I'm talking about will only add a few grams, including glue, so I'm not worried about them adding excess weight.

How would I go about reinforcing the firewall area with carbon or kevlar? I guess with the kevlar I could just use it as if I were glassing the joints.


I'm going to use softmounts of some kind on the engine. Save the servos, save battery power, keep the airframe longer - can't go wrong.

Thanks for the advice!

BMatthews

Good for you for going with the webs between the spars. Webbing is not optional on this sort of model if you want light weight. Also when I said cap the spars I meant on the top side of the upper spar and the lower side of the lower spar. The spar then provides the support to the carbon so it can do it's job in the most effective manner. But that's best for the thin wings of most sailplanes where it's critical to get the most separation of the carbons strips as possible. With a thicker stunt model wing adding carbon to the front and rear of each spar would not be a bad option. But definetly use the webbing as well.

For the webbing do not be afraid to use 1/4 hard for the first 1/3 of each panel then switch to 3/16 hard for the center third and then 1/8 medium for the outer third. The webbing takes a LOT of loading and if it can't support the spar caps then it's of no worth at all.

I'd have to see the plans but stringers that only shape and support the covering can be just hard balsa unless they are generously sized and then medium is fine. For the main load supporting longerons adding carbon over the first portion from the firewall back to the wing center isn't a bad idea. Even the shaping stringers could be bass or spruce back to the same region and then splice into balsa for the tail. This would go a long way to avoiding handling issues and it would also help to spread and damp out the vibrations.

RVM

I'm not changing anything to spruce or basswood unless the plans call for it. I'm using carbon fiber for reinforcement because it's strong and the weight gain is negligible (<1oz for me to reinforce everything I want to). Also, I like the added rigidity - this should add a touch of precision to the handling, and, of even more importance, consistency.

Lots of great information. Thank you for your time!

intruderdave

I'm looking into the same sort if project, and just today bought a small bacndsaw for cutting my own parts. I'm running into a problem: working in soft pine just for practice (cheaper than balsa) I used the new bandsaw to cut an airfoil shape about a foot chord, about 1.5 inches thick, and total width of around 3 inches. Intending to section it in 1/16 or 1/18 inch slices for ribs, I cannot accurately and repeatedly get good even cuts. I thought that is what bandsaws were good for. Any advice for me?

RVM

I thought the appropriate method was to buy the balsa in the thickness you need, then cut the ribs one by one like that. I think you sandwich the balsa between a tougher wood though, to prevent it from ripping/tearing the edges.

Of course, I don't know for sure. That just seems like a logical way to do it anyway. You can sandwich as many ribs of the same size as you need.

mmattockx

This is pretty much it. To cut a bunch of ribs the same, rough cut pieces of balsa from your desired thickness sheet, then sandwich all of them between two pieces of 1/4" plywood. Use bolts through the stack to solidly clamp the balsa tight. Then glue a rib template to the top of the stack and bandsaw/scrollsaw the stack to rough shape. Finish the stack to the edge of the template with a disc sander and you have a stack of ribs ready to go. The only things to really note are that your saw and sander must be tuned and cutting at as close to a perfect 90 degree angle as possible to keep the ribs all the same and your stack must be clamped TIGHT, using close fitting holes on the clamp bolts to prevent things shifting while cutting/sanding.

If you are doing a bunch of one-off ribs (tapered wing), then glue a template to each piece of balsa and cut them with the scroll or band saw and finish them with a disc sander. Not as easy as above, but you have no choice when doing lots of different size ribs.


Mark

RVM

What is the best way to cut the notches?

I'm still thinking of simply buying the plane in laser cut form. I might be moving overseas and carrying a plane is bad enough without bring a scroll saw, disc sander etc. with me. I'll be over there for quite awhile I think.

intruderdave

I guess I'm going at this backwards (my normal apprach to everything!), but it looks to me as if a decent bandsaw should be capable of accurate enough cuts to slice off 1/16th or 1/8 thick sheets from a larger piece. That is likely the way sheet balsa is created in the first place. That way, I can buy large bulk balsa and make my own sheet balsa. Basically it is an attempt to cut cost. My table saw will do this up to a point, but the blade thickness means I'm throwing away a lot of balsa dust to get a thin sheet. So far, I haven't been able to get my bandsaw to cooperate, even though the book shows resawing of 6 inch thick wood against a rip-fence to create two thinner boards from one thick one. Maybe I'm in need of a better saw? Better blade? Has anyone done this succesfully? [sm=50_50.gif]

RVM

You need one of the tiny tablesaws like a Microlux to do what you are talking about.

BMatthews

Dave, there's some tricks to resawing accuratley. First you want a nice blade that uses a skip tooth pattern to allow room for the dust over the length of the long cut. And don't push too fast or it'll clog and push the blade anyway.

Second, setting up for the blade is important. This is the job that is so often overlooked. Here's a point form of what you need to do in order to resaw.

[ul][*] Back off all guide blocks and bearings on the top guide and the one under the table. Mount the new blade and tension to a nice sort of middle C tone when plucked for a 1/4 wide blade or an octive lower C for a 3/8 wide and a nice base note for a 1/2 inch blade. Turn the wheels by hand while adjusting the tracking to center the blade on the wheels. Spin the motor on for a short spurt to test. When it's running in center with a longer spurt then button up the covers.[*] Now bring the upper and lower guide side blocks in on the blade until they are just scuffing very lightly for metal ones and just a hair harder for the phenolic ones. DO NOT allow them to push the blade to the side at all. Then bring up the rear edge bearing wheels until they are sort of touching but you can easily reach in and spin them. If these bearings are wobbly by much then they need to be replaced first. Wiggle them, If you can only feel a little click and do not see ANY movement then they are OK. IF you can see the wobble when you wiggle them then replace.[*] You're almost there. Every blade cuts on a bias. I have no idea at all why some bandsaws come with rip fences because they are useless. Make a new rip fence out of plywood or other material that you can clamp to the table on a bias angle of up to 4 to 5 degrees. A simple long L shape is fine. Place this clamp down fence and clamps close in reach. Set the upper guide so it's down within an 1/8 inch of the top of the block for maximum support. [*]Mark off a line on the block that matches the thickness you want and start a resaw cut on this line. Support and push the block from the other end with a single pushing finger in line with the cut line and adjust the cut tracking by swinging this back end side to side until the blade is tracking right on the line and you've cut a good 2 inches worth right on this line. DO NOT push or guide the block up by the blade. The downward cutting force will hold the block in place.[*] Once it's cutting along this line hold the block in place with our other hand pushing down on the table to clamp it down and shut off the saw. DO NOT LET THE BLOCK MOVE DURING ALL THIS! The block is set on the sweet line for this setup and you need to hold it there during the next step. [*] While carefully holding the block place your clamp down rip fence up against the cut sheet side of the block. Now transfer your holding hand to the rip fence and use your free hand to clamp it at each end to the table.[*]Let go and sigh in delight. The clampon fence is set now so that you can slice off consistent sheets until the cows come home or you run out of block.
[/ul]

Using the above method I've cut 5/32 thick by 8 inch wide spruce, mahogany, black walnut and rosewood boards up for making music instruments back when I was in a phase of that sort. It worked like a charm.

And no, there just is no way to simplify this setup. Every time you mount the blade the bias angle will change as it is totally determined by the placement of the blade on the wheels. Those wheels are crowned and this means that the blade is never going to sit in the same spot twice other than by sheer accident. And you do not dare force the blade into a track with the blocks or rear guides since that will deform the blade and cause it to curl and that'll cause all sorts of odd blade paths.

Good luck if you try it. Some sanding will be required as no bandsaw cuts smoothly. But a thickness sander is a whole other deal....

scratchonly

Find American Woodworker bandsaw resawing on the web. It will tell you how to set up your saw for this.

intruderdave

Much thanks for the bandsaw setup advice. I will apply it to the fullest, but I'm not convinced the saw is properly made from the factory. I already figured out that I would have to find the natural tracking angle of the blade for each setup, and have tried a skip tooth blade. What gripes me is that there is no mention of any of this in the book. And, this is not a no-name saw, it is from an old line tool company. When I contacted them, they had a 'technician' call me back, and he didn't even offer the advice I've now gotten on-line. Why pack the saw with a miter gauge, or sell a rip fence at all? And how about another adjustment for matching the table to the natural cut line of the blade? I am resisting the urge to mention the brand, but thumbs down to the manufacturer, and thumbs up to all you helpful folks on the net![sm=thumbup.gif]

intruderdave

In case anyone is interested, I just cut a few decent wing ribs from an airfoil shaped pine block! They aren't quite good enough, yet, but I'm getting there (with a little help from my friends!).[sm=thumbs_up.gif][sm=thumbup.gif][sm=teeth_smile.gif] The finished ribs will probably be from balsa, but pine is a lot cheaper to waste.

By the way, for those who may wonder why I'm doing this, I have always wanted to build a plane from scratch, as in NO prefab pieces of any type (including sheet or precut of any type), and as much as possible to use wood available from the local lumberyard. I even asked if they could get balsa boards for me, but they have no supplier. If it were feasible, I'd even try building the radio, and may build the electric motor from a kit if I can find the right one. Will this be sucessful? Won't know till I try, and these are the first steps. Any and all advice is welcome. Thanks much!

RVM

It will be an adventure, I can promise you that!