MTK

Bob,

The minimum thickness for the balsa spacer is about 1/2". That's the thickness spec we built Ed's mount to. Mine was built to 0.6" and after all the smoothing and leveling of the surfaces, the thickness reduces to about 0.56 or so. The practical maximum is around 0.7" or so, because thicker than that means a much softer set-up which doesn't work as well in my opinion. A little too floppy at least of a four stroke.

Anyway, you control the softness with the rubber thickness you use. I don't like anything thicker than 1 mm and 1/32" is even better at least on my set-ups. Others swear otherwise so it's probably a matter of experience. The point is that it isn't all that critical as long as you don't go nuts on any one dimension either to the large side or to the small side.

The ply discs can be cut with a band saw...that's how I cut the first set for the first prototype I made 7 or 8 years ago. But I found that a hole cutter works more accurately and is much faster.

The balsa spacer for the SAP mounts were just balsa...no glass between the layers. The end grain that results is hardened with thin ca. Thin epoxy also works fine with slight heating (monokote heat gun) to wick it in. The thin plywood facings aren't really necessary because I use rubber bumper stock to keep the faces from slapping together. But they add very little weight and add some strength so I use them.

Tried something a little different on my latter mounts regarding the stand off mount bolts. Rather than use a blind nut on the front face, I simply install a maple block on the back side and drill and tap the 8-32 threads into that. The threads are hardened with thin ca and chased with the tap. I then use countersunk 8-32 screws epoxied in place and that's it. Simpler and lighter. Must countersink the maple blocks to make the head of the screw flush. I suspect that 8-32 aluminum bolts will work fine but I have only used steel bolts so far. Removing the blind nuts reduces weight considerably and makes a neater seat on the front of the ply ring.

All up weight of the mount alone is less that 2 ozs and the stand offs add about 1 more ozs.

Regarding stiffness, the second layer of rubber adds some. I have used the design without a nose ring before and it works fine. Very little shake and nothing I could notice in flight. But, being a purist, I have resorted to using the nose ring nevertheless. I am not sure where Todd Syssa is with the retrofit design we came up with a couple months ago for nose ring applications.

Please let me know if you need further clarity

Matt

cmoulder

Matt, thanks so much again for your patient explanations, and for filling me in on your subsequent "upgrades". I love to tinker with stuff and am always looking for ways to make things simpler, which almost always means better as well.

OK, I think I now have a complete understanding of the design, materials and process.

The only wrinkle with the Syssa - as you know from doing your and Ed's mounts - is that the engine uses 3 stand-offs and one of them, the "top" one in the inverted mounting standard, is not the same distance from the crankshaft center. By my measurement that odd one is 31.5mm and the other are 42mm.

So I am just going to make a little "ear" extending inward on the engine-side ply plate so that the crankshaft and soft mount centers are in alignment, and maybe beef it up a little at that spot on the ring. No biggie.

More later when I get underway... probably a couple of days.

MTK

Bob,

That's exactly what I did on the new mounts. The stand offs are on the circumference of a 4" circle...however that circle and the mount ply ring circle are not concentric. The maple blocks behind the ply ring provide plenty of support. The blocks are approximately 1/4" thick and extend to the surface of the balsa spacer. I make the blocks and just slice down the balsa spacer using the block as guide with the Xacto knife to make a snug fit. I used maple but other hard woods will work fine. The maple is ca'd in

Oh BTW, on Ed's and my second mount that I have in the new plane (first one is in the test bed), I shaved the top of the mount as Merle Hyde does with his, to make it even with the top of the firewall. It shaves some weight too Let me take a snap and post it

Matt

MTK

Bob,

Let's see if I can download a large photo file

Matt

MTK

And BTW. the simplest way to cut the squares on the stand off bases is with a belt sander since I don't have access to an end mill

Matt

cmoulder

Ha! I live in a condo and have no shop tools, but I figure out a way to do stuff with a DeWalt drill, a couple of Dremels and the little Dremel drill press, sanding blocks, razor saws, and... um... that's about it! Already I have figured out a work-around for making the ply discs and a clean, level cut of the balsa dount using the hand drill, a bolt and 2 nuts and a razor saw. The order of construction will have to be modified a bit, but it will absolutely work.

Your photo depicts what I had in mind, so I'm on the right track. Seems you have about 2.5 deg right thrust?

Hmm... looks as if your new design has a canalizer. Craftsmanship looks excellent. I hope to see the final product in person next season!

MTK

Bob,

I understand. I don't have much either but do find the small band saw from Craftsman pretty valuable. Also have a small drill press from Harbor Freight. The rest are hand tools. After you cut the balsa spacer in half you may want to sand the faces flat first. The simple way to do that is placing sandpaper on a small piece of glass, say 1 foot square, and just run the balsa onto the glass. But it isn't terribly critical to get the faces perfectly. I just do that as a matter of course

Not a canalizer as much as SASSI (spiral air stream straightening initiator) ....a lot to say. The canards surfaces are right behind the prop. Simply put, it's designed to initiate straightening the prop blast. My theory is that a straighter air stream right off will require minimal off set of thrust. Forget about P-factor and all that nonsense about why we need right thrust on out planes. It is the spiralling slip stream that causes all kinds of havoc with the flying quality of the model. I built in about 1 degree of right and zero down

It was a revelation to me when I calculated the amount of air mass that gets thrown back in seconds of running. Air weighs a ton. The reactive force that gets generated from all that mass hitting the fuse side at an oblique angle is what causes the veering off tract. Also the difference in roll left and right. Also the pitching at knife edge.

It's another experiment that showed promise in foamies so I decided to try a larger platform. It's only 20 square inches but it is located at a difficult place for other maneuvers such as snap rolls, spins etc. So I made the canards removable just in case. I could have made them work in conjunction with elevator but these are fixed for now. I may change my mind after flying the crate for the first time and make them movable.

Matt

cmoulder

Very interesting!![8D]

I hope it disrupts the spiral effect and performs as you expect. Probably see them on CPLR's planes a few weeks into next season!

MTK

CPLR...Hmmmmm! Great flier of pattern and IMAC planes and probably racers and other stuff also. That's about it. As a designer, well, he could use some help. I've flown a few of his stuff and they are more compromised than they should be. Just wish that we wouldn't see every change he comes up with commercially available. The masses will gravitate to the latest change because it is the latest and it is his.

The guy whose stuff I respect the most is probably Bryan Hebert. Bryan takes time to work out the kinks before he offers it to the market. That is a great thing for the average flier who has little experience and doesn't know where to start to beat the model into submission. But I am on my soap box, pontificating, and I have to get off...My apologies

Matt

cmoulder

Sorry, Matt, but that's what I meant about CPLR... he seems to be the first to, uh, "adopt" ideas as soon as they appear on the scene. People gotta have the latest and greatest, so they buy more planes.

But I understand what you're saying about Bryan Hebert. His triangulation trimming method makes the most sense to me, and his explanation of CG effect on KE performance makes me think I understand it, even if my skill set does not yet permit me to appreciate such subtle differences.

cmoulder

Matt, I have made some progress and am pretty close to finishing the mount. It is not nearly as neat and refined as yours, but it is after all my first attempt. Since I am at a lack for tooling to cut and tap the maple blocks accurately, I decided to simply use the blind nuts as you did in your first unit in the thread.

I found an inner tube that fits as you described earlier in the thread - snug but not tight.

My only remaining questions are 1) do you give the mount some overall coating of epoxy or something for fuel proofing a bit and 2) what is the "rubber bumper stock" that you mentioned above (just a donut from the inner tube??) and is it glued in at all, or glued in on one side of the inner faces of the donut spacer?

Thanks much! The finish line is in sight!

cmoulder

PS... As you see it in the photos it weighs 1.9 oz according to my digital postal scale. With the rubber and whatever coating you suggest it will still be way under 3 oz, without stand-offs.

MTK

Bob,

The bumpers are just 4-6 pieces 3/8" square of flat rubber glued onto the inside face of the balsa ring. When the mount is working with the engine idling, often the faces slap together and it makes a strange noise. Merle's mounts do this all the time. The rubber facings if you will, serve to stop the faces of the two ply-balsa assemblies from slapping one another.

I seal the mount with epoxy paint usually but regular epoxy works great. Just try not to coat the areas where the rubber will attach. If you get some on the surfaces, no biggie, just sand to expose fresh wood. The wood to rubber bond when using ca as the adhesive, is rubber tearing bond or around 900psi of tensile strength. That's huge and is the reason the mount works so well. No engine we are using can produce that kind of pull.

Excellent, great job.

Matt

cmoulder

Thanks much! More work than I thought, but I had to figure out some of the tool workarounds as I went.

I cut the balsa ring down the middle by using double-sided scotch tape and some balsa sheet to secure my razor saw to a block of balsa, with the saw blade exposed to the side. Got a dead straight cut, and after hardening with thin CA and sanding a couple of times, the faces are perfectly flat and slide silky smooth past each other.

Ah, okay the last pieces of the puzzle. All I need now is some 1/64 ply. I have the bike tube.

Thanks again. Would not have been possible without your explanations.[sm=thumbup.gif][sm=thumbup.gif]

NJRCFLYER2

My Feedback: (42)

Nice work Bob!

cmoulder

Almost there!

cmoulder

I don't have any 1/64" ply and could not find any locally. So - since you mentioned the ply faces aren't really necessary anyway - I am going to use a thin layer of FG cloth epoxied to the faces and really squeezed out thoroughly, so it won't add more than a gram or 2. Just seems it wouldn't hurt to give those balsa rings something to integrate them a bit, and then put in the bumpers. I cleaned up the outer edges of the rings (some epoxy had squeegeed out when I clamped the dount together) with a file, and have got good, clean wood all way around for the rubber bands.

I made some boo-boos here and there, but the unit will be solid.

cmoulder

I posted this over on the SAP 180 thread, but am posting the same photo here just to wrap it up.

In short, overall it was a great learning experience, and the next one I make will be much easier since I now have 100% understanding of the construction and how it works.

Although it is not as polished as Matt's work, it is a very solid little unit and I am surprised at how secure it feels. I am a lot more confident now that it will work than when I first started out with the project. Never ran an engine on a test stand before, but I will take Matt's suggestion and run the engine (on the new mount) on a test stand and get familiar with it and get it tweaked.

MTK

It's been so long, I forgot I took snaps of my canard outfitted Aesthesis (post 55 above). The model has a slight bit more than 1 degree right thrust.

With canards on, the model veers off to the right quite readily following its thrust vector. With them off, it doesn't have quite enough right thrust, veering left slightly, following the tail force vector which pushes the tail right.

Canard surfaces right behind the prop are very effective in straightening spiralling air stream but the engine should be set at zero for best flying. One of these days I will get Aesthesis flying again with zero engine offset and canards

tggilkey

Matt --

I have an electric soft mount that doesn't seem to be made any longer but from its behavior would benefit from a reinforcing of the rubber ring. The OD where the rubber would go is 2.3" What would you recommend for the diameter of the inner tube to use?

Thanks,
Tom

MTK

Tom, for an electric mount you should not need much. A bicycle inner tube should have the right thickness.

A diameter of 2.3" means circumference of about 7 1/4". An inner tube with flat width of 3 1/2" should work, except I doubt you will find anything that's just right.

You can make your own. Here's how I do oddballs....I cut a strip about 1/4" longer than the circumference, with the correct width and thickness, wash it well and degrease it with alcohol or acetone, and prep the ends to be glued together. I grind about 1/2" of the rubber ends with a dremmel drum sander into a tapered section and simply glue the ends with rubber containing ca. You may use any ca, such as that for foam, as long as it stays a little flexible. Regular ca probably will work in an electric app since vibes are less.

You want the rubber band to actually stretch slightly when fitted. My early stuff required too much stretching and the mounts tended to be stiff. Now the stretch is minimal and mounts are better, absorbing vibes better.

Hope that helps. And btw, the last couple mounts I made for gas engines were done this way, and still holding strong. The trick is to expose fresh rubber. It sticks to itself with ca great.

MTK

I went up and read the last few posts. Let me update it a bit. I found that rubber bumpers are not the best answer to keep the faces separated. The better solution is using small pieces of Velcro, either the hook side or loop side, doesn't matter. I have used both the sticky back Velcro and the glued back Velcro, set down with ca. The Velcro separates the donut facings about 1/16" which is fine. When installing the rubber band I squeeze the facings and Velcro separator firmly. Works great....

tggilkey

All good information, Matt! Thanks much!
Tom

MTK

Tom, my pleasure. It's kinda Kool to go back and re- read some of these older posting and compare notes so to speak to my current practice. It's good to have the record......

flybyjohn

My Feedback: (2)

I recently made a couple small versions of the hyde mount for a twin engine scratch build that was just vibrating to holy heck. The engines were small (.36 asp 2 strokes) but the high speed vibration felt like it burned your hands just holding on to the airplane. After a couple throttle servo failures and bolts from the landing gear dropping out in flight, I looked into soft mounts.

I did use a piece of rubber between the front and rear halves because that is what I saw in some other diy threads. Is there a specific reason that you changed your practice?

My mount used the rear of the round hayes motor mount for the front disk and a piece of 3/16 birch ply with a 1/4" balsa glued to it for the rear half. The mounts reduced airframe vibration by at least 90%. I just was curious why you are using Velcro. Should I be concerned and looking for something to go wrong if I used a disk of rubber instead?