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Posted by lincoln | Feb 16, 2016 @ 06:00 PM | 39,087 Views
This is a reference for this post:

This is just about wing skin stiffness in bending, without the core material.

I remember that, after some time, I couldn't interpret my old notes for experiments I did on this stuff. So I'll do a reality check on this stuff with other people's data. Unfortunately, I didn't find data on epoxy/paper, so I'm using data for phenolic and paper, which ought to be comparable. It's my understanding that the basic grade of phenolic/paper uses kraft paper, which is the paper I'm talking about. Can't be sure of it. Anyway, there's enough uncertainty here that we can't say anything except we may be in the ballpark, or we're not in the ballpark.

Here are the material properties I'm using:
Style 1581 glass cloth with epoxy:
(this cloth is much heavier than you'd use on a wing, but I'd expect that the bulk properties are similar.)
Elastic modulus, flexural: 3.6 mpsi (this seems much higher than other sources but is what the paper says, and may be explained by a higher than usual fiber volume) Seeing as it's nearly as stiff at 280F, the epoxy must be some special stuff
2.0mpsi is what I've usually heard
Flexural strength: the paper only gives ultimate strength, I've usually heard about about 30kpsi yield. This stuff is about 68 kpsi ultimate, but I don't know what it is in yield.
Resin by weight: 33 percent I think usually this number is closer to 40 or 50 percent! Long ago, in MAN...Continue Reading
Posted by lincoln | Jan 18, 2016 @ 09:44 PM | 40,085 Views
Dave Stott did a plan for this. On another forum, I can't figure out how to attach files, so I'm uploading a picture of the model here.

As of 2014, Paul Stott was handling the Airdevil plans, and perhaps the Joy's Racer as well:
Paul Stott, 175 Thoreau Drive, Shelton CT 06484
Posted by lincoln | Jan 15, 2016 @ 09:05 PM | 38,726 Views
January 15, 2016

I understand that comments to the FAA on the registration rule are allowed up until midnight, though I don't know which time zone. I just managed to put mine in. In case you're in a hurry and you want to borrow some of the information I dug up, I've attached a copy of what I sent to the FAA. (It didn't fit on the form, so I sent it as an attachment.) Please don't copy the wording or structure of my note, but feel free to cite the sources and use other information. Make it your own letter, just without as much research required. It's probably not a surprise, but be aware I'm not perfect and I may have made a few mistakes. So check if you have the energy.


P.S. The following links may be helpful:!submitC...2015-7396-0001!documen...2015-7396-0001
Posted by lincoln | Nov 03, 2015 @ 02:20 PM | 39,786 Views
The following is a bit of nonsense inspired by a thread about converting stick and tissue rubber scale to electric power.
I really should have been doing other things. Keep in mind that I haven't tried the motors and other items mentioned below. I HAVE used the IPS motors and a Potensky 01 (I think), which is what I'd recommend if I could find one. If you can find one, I can check to be sure I got the name right.

I think that RC-Dymond, some years back sold the Potensky 01 under the name Max 01, or maybe 001, or 150?

An answer to a question about GWS LPS motors:
A, B, and C appear to refer to gear ratios. The higher the number, the larger the prop you can swing, but the lower the rpm. Fast models probably need a lower gear ratio, slow ones need a higher ratio.

If I'm interpreting the information correctly, the RLC is a much "hotter"wind than the RLX, aka a higher KV*. That means it pulls more amps for a given gear ratio, prop, and voltage than the RLX. So it might be suited for lower voltages. For example, a 1S lipo instead of a 2S. Another way to put it is that the motor itself has a higher KV. (try poking around at and I bet you find an explanation of that, though the site is mostly for larger models)

Anyway, for a given application and prop, the RLC will need a lower gear ratio (i.e. higher number in the chart) than the...Continue Reading
Posted by lincoln | Sep 10, 2014 @ 01:22 AM | 41,139 Views
Have just been setting up a 6 servo sailplane with a motor in it. Ugh! Servos were buried in the tail when I got it. Since I can't see how to get at them without grave trauma, I have to adjust them electronically, with one of them using almost all the available adjustment. Would have been nice if installed to use the center of the travel. Sigh. Lots of other back and forth fiddling. Had to shorten the elevator pushrod, not sure how previous owner dealt with that, change hole in horn, etc. etc. etc. Not done yet, and it's been a few hours. I miss RES, or in this case REST. Hmmm...
This model is pretty old and has an Aveox LMR motor in it. Gobs of current! 14 inch carbon prop. Was set up for 7 cells, planning on switching to 2 A123 cells, except maybe on windy days. The tail is a bit heavier than I'd like, especially for a t-tail. Maybe I can make a lighter tail and use a smaller motor for balance.
Posted by lincoln | Jul 05, 2014 @ 09:04 PM | 41,921 Views
A while back, I asserted that kraft paper rolled up with glue makes a convenient and durable blast tube. I encountered a lot of scepticism, although no one really said why it couldn't work except that it wasn't strong enough. Or something like that. Anyway, I thought it might be good to do a reality test. So I rolled up a tube around a 1 1/4 inch (32mm) dowel. I used enough layers so the wall thickness was around 0.040" (1mm) or maybe 0.050" (1.3mm). I used Titebond 3 for the glue. I meant to test it after only a few hours, but I ended up leaving it in the car for weeks. The workmanship is lousy and it's ugly, but it works fine. I made up a 32 strand motor from old 1/8" FAI Tan (or Tan II? box doesn't say). Batch was June 00 2001. I've tried to take care of it over the years. The whole thing was pretty short because I didn't want to waste rubber. No damage was apparent. After, I tried supporting a cinder block with the tube. The ends of the tube weren't square, so it did to some damage to the very end of the tube. Unfortunately, I seem to have deleted the picture.
The rest of the pictures should be attached to this post.
Posted by lincoln | Jan 31, 2014 @ 11:15 PM | 41,206 Views
One of my favorite cover pictures from the FAC News, from the Sep/Oct 1990 issue. It's done by Bob Rogers, creator of many hilarious pictures for the FAC News over the years. This one shows Captain Downthrust's nightmare, harking back to his struggles with the now disbanded Bad Guy Squadron. I find many of the old covers a bit bloodthirsty, but not this one.

For those of you who are not familiar with the Flying Aces Club, it's a group of people who indulge in vicarious (by now) nostalgia. Not so many of those guys left who used to complain that mom tossed out their model stuff while they were fighting WWII, though I can think of at least one. Anyway, we all mess around with stick and tissue model planes.

Those who are susceptible can find out more at
Posted by lincoln | Jul 24, 2013 @ 02:16 PM | 42,162 Views
I have a new flying student who is making pretty good progress. He's flown weird little toy airplanes before. (I think they're usually harder to fy than regular ones.) He showed up with a Flyzone Sensei with the radio that comes with it. Although it's an electric foamy, it seems to follow in the tradition of the old, lighter glo powered trainers like the PT 40, Midwest Aerostar, etc. I think it might be a bit lighter, and it seems to have very good manners. Not sure about ground handling because we fly on town athletic fields and it has small wheels which don't do well in grass. So far, my only beef is that, as supplied, the ailerons had reverse differential. This is easily remedied by fiddling with the linkage. My student did this on his own after I mentioned it. It flies ok with the original reverse differential but I have the impression it doesn't need the rudder as much after he fixed it. This is good for students as using two controls for turns is plenty confusing at first. We're using the radio that came with the model, which has a wireless buddy box system that is very convenient, except for holding over that annoying little switch all the time. Not a problem if your student screws up often enough. An odd feature is the bomb bay that can be opened by a 5th channel. We haven't tried that yet. I can't say how easy it is to set up as my student did that before he showed up. He seems to have done a decent job of it, but I don't know how much needs to be done.

Anyway, it's only been a few lessons and my student is getting close to soloing. He's done an entire flight now with just my advice for external guidance. If we didn't have so many trees I'd probably just tell him to go for it sometime when there weren't many people around.
Posted by lincoln | Jul 04, 2013 @ 07:50 PM | 41,593 Views
We had a flight demo for the holiday today. Dewpoint was at or above 70F and temp was above 90. Fortunately, we did have a bit of wind. Still, after a while I found myself moving slowly, and it's taken a long while to get my energy back since I got home, even though I must have had close to a gallon of water out there. Should probably have been 5 quarts. Without wind and shade canopies, it would have been unbearable. The hat with a fan in it helped too. (Fan can't easily be seen and is very quiet, too. ) As is, fun but eventually exhausting.

Be careful out there. Lots of water, shade, and don't move too fast.
Posted by lincoln | Sep 18, 2012 @ 07:32 PM | 43,124 Views
Went to a dlg contest last weekend. Had been trying to get a used Salonit ready, but wasn't there yet. Flew the Sidewinder II on Saturday. Managed to do a tip strike with the S2, but it was still flyable with some temporary repairs. By Sunday morning, I had the Salonit sort of ready, although I hadn't figured out how to do flaps with the radio I was using. The Salonit seemed to launch much higher and I liked the way it flew. However, I managed to break the tailboom in the first round. Not by a tip strike, though. So I scrambled and repaired a couple of cracks in the S2 that I had noticed, and was back by the third round. I intend to get the Salonit ready soon, because it was a lot of fun, but that's it for the dlg season for me, I think.
Posted by lincoln | Aug 07, 2012 @ 11:35 PM | 43,072 Views
Was helping someone to get a plane out of a tree today. It was high enough that we were using a bow with a bowfishing setup (big spool) to get a string over the branch. Sometimes I use dowels with a slot and a hole. The string acts instead of the fletching. (i.e. feathers) I got curious as to what would happen if I fired one off without the string. Pointed it down range across the field, with no one in sight, at maybe 45 degrees elevation. I expected it to go sideways and slow down very fast. Instead, it pulled up as if it had wings, looped over, and came down BEHIND me. Took a while to do it but was very surprising, I'll admit. I doubt if I'll be doing that again!

Anyway, we only lost one arrow and we got the plane back with only minor damage.
Posted by lincoln | Aug 02, 2012 @ 08:23 PM | 43,034 Views
Was instructing today. My student is learning to land, but I don't have a buddy cable that works for his radio. I have one I thought was SUPPOSED to work, but it doesn't.

He landed his Radian off the field after a moment of confusion. Very gently in some bushes. But the brush in between was very dense and had a muddy little brook in it. Somehow I got across the brook without getting my feet wet. However, a machete might have been very useful. Until I noticed that I'd dropped my cell phone, when I might have been tempted to use the machete on my neck. ;-) My student had also been bushwacking, but I sent him back to call me with his cell phone. Eventually found the phone and heard the servos as I worked the right stick on the tx. Managed to find a clearing with sight of the field and was able to fly the plane out instead of dragging through more bushes. Took the long way out myself. I'm tired!

Hoping it won't happen again, since my student is making good progress, especially since he got a simulator working on his Mac.

We managed to get a couple more flights in after this incident.
Posted by lincoln | Jul 28, 2012 @ 09:37 PM | 43,150 Views
Well, it finally happened. After MANY years, I finally launched a glider with the transmitter off. That was last year. It was quite sad. I managed to pick up another one at our auction in the fall. Have been having fun with it, but today I launched a bit too hard, for another first. I don't think I'd ever unintentionally broken a wood glider on the winch. (I've broken a composite glider with a carbon spar that way, but that's another story.)

I'm used to the wing rod bending before the rest of the structure fails, since it's only 7/32 inch diameter. This one was only barely bent, but the joiner box broke. A post mortem revealed that some of the epoxy was not bonded to wood. So be careful about surface prep and all that stuff when you're doing joiners.

This should teach me to build my own stuff more often, or else at least fly stuff that's newer. Sigh. Meanwhile, it joins the large pile of repairables.

Consoled myself with some dlg flying just in advance of an impressive thunderstorm. Lots of fun for a few minutes. Surrounded by very tall metal lightposts, so not quite as nuts as it sounds. Or at least not as risky for me. One of these days I may hit a lightpost with a model. Not yet, though.
Posted by lincoln | May 11, 2011 @ 11:53 PM | 43,568 Views
Why a Sidewinder II is better than a Cyberdyne. (note the bend) (That's a Cyberdyne in the picture.)
Posted by lincoln | Apr 08, 2011 @ 02:09 PM | 44,479 Views
Lots of fun. Much floatier than my Skeeter was. (don't start!) A good flier, but don't pull down on the launch grip. If you're really strong you might want to make sure the covering is very tight before launching. Mine had a cut down, conventional tail, but the handling was still very good.

This is a javelin launch type so it hurts more and doesn't go as high.
Posted by lincoln | Apr 08, 2011 @ 02:06 PM | 44,226 Views
Not a bad 2M. A bit twitchy, and of course it doesn't have the latest airfoils or a skinny fuselage, so it's not as fast as some. But fun. I don't think they kit this one any more, but the Jester is supposed to be a full fuselage, normal tail version of same.
Posted by lincoln | Apr 08, 2011 @ 02:03 PM | 44,269 Views
I've never built one, but I've owned one for 15 years or so. One of the very best soaring trainers. Better than the GL. A real floater. Can stay up on the slope when no one else can. If it's a big hill, when you can hardly feel the wind. But mostly it's a thermal soarer. I put rocks in it (literally) when the wind blows.