Author Topic: Qustions for Larry on the ET-1 (Read 2598 times)

Tim Wescott · « **on:** December 04, 2012, 07:03:09 PM »

Assuming he answers:

I'm building three of these. One each for nephews, and one for me (and maybe one of my kids, if they show any interest). Hopefully I'll be done in time to ship Oregon to Hawaii -- we'll see.

The plans are a bit sparse on details. There's nothing there that I can't figure out, but I was wondering what you did in a few points:

Elevator hinge: I'm thinking of using 3M hinge tape (sold for foamies) or just plain ol' Scotch tape. I was given one Coreplast model ages ago where the builder tried to use the Coreplast for a hinge -- that did not work. So something more mainstream is definitely indicated.

Bellcrank: I've got two Sig 1/2-A bellcranks on order. I'm planning on mounting the bellcrank on a piece of plywood epoxied to the wing -- or maybe one each top & bottom. I'm not quite sure of the best way to mount the horn -- maybe more plywood pads?

Landing gear: You mention that it's all shock mounted, stuck in tubes sewn onto the wing. Do you have any detail pictures of them?

Motor: You call out a 2205 motor in your original thread, and that's what I ordered -- but the cutout for the motor seems to be much bigger than that. ?? (I think what I have will work -- they're listed as 100W motors, and I'm thinking the all up weight will be in the neighborhood of 10 ounces. So, maybe too heavy for CLPA, but good enough for training).

Thanks for the design.

Larry Renger · « **Reply #1 on:** December 04, 2012, 10:17:49 PM »

Here is some more info on the model. Eric Rule is now kitting it.

Scotch tape will work fine for the hinge as there is no fuel to eat its adhesive.

The bellcrank and nose gear are mounted to ply plates on both sides of the coroplast. The control horn as provided with the bellcrank will work fine as is.

The model is definitely only intended as a trainer.

Larry Renger · « **Reply #2 on:** December 04, 2012, 10:22:52 PM »

Oh, and here is the current set of plans.

Larry Renger · « **Reply #3 on:** December 11, 2012, 05:30:27 PM »

I see I neglected to post the sheet with the landing gear. Sorry, gang.

Tim Wescott · « **Reply #4 on:** December 11, 2012, 05:35:39 PM »

Thanks Larry. I somehow missed your December 4 responses until you responded to my PM -- my slowness, to be sure.

This is very helpful.

This needs to get published in something like Model Aviation, but it also needs to get published in something like Make. Normal model airplanes are too old-school for the normal Make vibe, but this goes right down their ally, straight and center.

Why Make you ask? Because Model Aviation gets the word out to folks who have already made up their minds. Make gets it out to a completely new set of people who may just like the idea of flying control line.

Larry Renger · « **Reply #5 on:** December 11, 2012, 11:54:47 PM »

I plan to talk to the Model Aviation guys at the AMA Expo in Ontario, CA next month. Since the model is already a kit, I want to suggest a kit review by some real "newbie".

We will be doing some UC training with this design there, but on 15 ft lines! Gaaah! I am going to experiment with add-on flaps to cut the required flight speed.

Tim Wescott · « **Reply #6 on:** December 14, 2012, 12:27:23 PM »

Quote from: Larry Renger on December 11, 2012, 11:54:47 PM

I plan to talk to the Model Aviation guys at the AMA Expo in Ontario, CA next month. Since the model is already a kit, I want to suggest a kit review by some real "newbie".

I thought it was a short kit? Or is there a complete kit available? Are there instructions that assume that the builder has no knowledge of modeling?

It'd be very cool if you could make it all work that way. It'd be very cool I could just point my brother the scoutmaster at the kit, and have airplanes happen...

(My all-up price on just parts is somewhere between $60 and $70 per plane, by the way. That's including a charger and car radio so I can give each nephew a complete "plug and play" package with charger ($12), radio ($20), and an extra battery ($7) all ready to go in a box. It's _not_ including the coreplast, which comes to me courtesy of my sister in law's failed bid for mayor of her small town: those 4-8 foot signs mean I don't need no stinkin' spars).

Larry Renger · « **Reply #7 on:** December 14, 2012, 10:21:19 PM »

Coroplast is awfully flexible. I would recommend at least installing the main spars, though with 1-piece wings, the little short ones would be hard to install. Or, try it without spars and let us know if the wings fold in the middle.

There is no complete kit available at present, and Eric is out of town on a cruise through the Panama Canal. I'll chat with him when he returns.

Tim Wescott · « **Reply #8 on:** December 15, 2012, 10:25:45 AM »

This first one is to make sure that I've got my head on straight anyway: if it does scary things but doesn't buckle I'll stuff some CF or spruce in there.

News Flash:

I'm far enough along to know that my airframe weight is going to be between nine and ten ounces. Ten g's would mean an airframe weight of 100 ounces, or a bit over six pounds. With six pounds of weight on the center of a wing blank, I can pick the thing up by the tips and nothing breaks. Granted, the tips are flexed over six inches above the center section, but nothing breaks. Given that the test puts a lot more bending moment on the wing than an actual 10-g loop would (because the lift is distributed along the wing, and because part of the airframe weight is the wing itself), and given that I don't think you're going to achieve close to a 10-g pullout with this thing, I think I'm safe.

Larry Renger · « **Reply #9 on:** December 16, 2012, 12:37:54 AM »

I think the only time this bird would see 10gs is hitting the cement.

Tim Wescott · « **Reply #10 on:** December 16, 2012, 03:46:50 PM »

Being me, I couldn't just follow the directions. The most significant deviation is the front landing gear mount: the (800mAh) battery wanted to be far enough forward that it interferes with the mount, and I wanted to mount the battery on the outside of the plane so it wouldn't be visible from the circle. So instead of using the "wire through two disks" I used a 1/4" wooden post through the two disks, and a formed circle on the end of the front LG struct. Here's pictures.

I also changed to an adjustable LO guide. A cheap, easy adjustable LO guide, and boy I hope that it won't wear through...

John Cralley · « **Reply #11 on:** December 16, 2012, 04:00:58 PM »

Hum Tim,

Those look like music wire leadouts. If so, I'm not sure how you are going to adjust them. Will they bend enough to slip in and out of the guide or do you remove the bell crank to pull the leadouts out of the guide???

Tim Wescott · « **Reply #12 on:** December 16, 2012, 04:10:57 PM »

They're 008 wire, and they easily bend to come out of the guide without permanently deforming.

Not that I think they'll need adjustment -- that guide came about more because I could make a nifty looking thing out of a scrap of coreplast than from any necessity.

Larry Renger · « **Reply #13 on:** December 16, 2012, 05:51:14 PM »

Great stuff! Keep us posted. Are you going to test fly them before shipping?

Tim Wescott · « **Reply #14 on:** December 16, 2012, 05:58:08 PM »

Larry, Larry, Larry. You designed these -- why should I need to test?

But, as a matter of fact, I am going to test before shipping. In fact, this one is my test pig so that I can learn all (well, some) of the ways that I can screw up the build, and to make sure that it flies right.

BTW: right now it has a 7-6 GWS prop on it. With a two-cell pack it draws 5-1/2 amps and will lift the plane straight up. With a three-cell pack it draws almost 10A, and I don't want to think about the thrust/weight ratio. I need to see what the LHS has in 6-inch props, or cut something down, or something.

Larry Renger · « **Reply #15 on:** December 16, 2012, 11:27:51 PM »

APC 7x5 cut to 6" is what we use. That keeps the amps down and the duration up.

Tim Wescott · « **Reply #16 on:** December 20, 2012, 01:49:56 PM »

Rain wind, wind rain. These may not arrive until August at this rate, or I'll just have to trust you.

Larry, do you realize that you've gone and invented a system of control line flying where one can arrive at the flying field only to realize that one has forgotten one's @#$% transmitter?!?

Larry Renger · « **Reply #17 on:** December 20, 2012, 09:38:08 PM »

Been there, done that. With my boss at Cox with me. Not good!

Tim Wescott · « **Reply #18 on:** December 22, 2012, 01:50:14 PM »

Lesson from Friday:

Testing is good (as a design engineer I knew this).

Listening to Larry when he says to use bolt-on prop adapters and not rubber-band prop savers is good.

Rubber-band prop savers, high motor RPM, and tests to see how tightly you can turn a plane is bad.

Larry's basic design tends to break at the glue joints, making for easy repairs after crashes -- even when the plane explodes in mid air.

Rebuilding is good.

Lesson from today:

Rebuilding Friday night, before the wind kicks up would have been better.

(But the ham dinner was good, so that's OK).

Hopefully the wind will be down on Christmas Eve morning, because I've got to ring bells in church tomorrow and the weather pattern at the moment seems to be good flying weather until about 11:00, then things go downhill.

And my nephews are going to get some New year's presents, 'cause this sure ain't getting shipped until it flies successfully!

Larry Renger · « **Reply #19 on:** December 23, 2012, 10:06:18 AM »

In the current version, I do use rubber-band on prop savers. No hard maneuvers, though!

Tim Wescott · « **Reply #20 on:** December 30, 2012, 06:18:32 PM »

Whew! Two ET-1's complete, and my personal one that's just missing the electrical system (it was the prototype: I'm giving the nephews the ones that don't have all the screwups and crash damage -- I just need to shift the stuff over from another plane, and I'm in the air).

Here's a link to a set of directions that I'm going to send off with the planes. I'm sure I've left out something important, so comments are welcome. (It's a 500kB file, which is why I'm linking to it instead of posting it. If you have dialup, beware!)

https://docs.google.com/open?id=0B5lSHlBBxGvjY2pZZ2p0b0RJR1U

Larry Renger · « **Reply #21 on:** December 31, 2012, 09:41:53 AM »

Wow! That is a great set of instructions. I think you should write them up with a review of your experiences with the model for one of the magazines. Model Aviation has already expressed an net rest in the design. Drop an e-mail to Jay Smith.

Tim Wescott · « **Reply #22 on:** December 31, 2012, 11:38:19 AM »

Isn't there already a review of the kit lined up? It would seem kind of odd to call a review of my slightly loose interpretation of your preliminary plans as a "kit review".

As a companion article, particularly if I got some flying pictures, it may be good, though.

Larry Renger · « **Reply #23 on:** December 31, 2012, 06:56:13 PM »

Nothing formal has been arranged. At last report, Jay was interested in a construction article, but since it is already a kit, that seems a moot point. I expect to see Jay at the AMA expo in a couple of weeks and will discuss possibilities with him. May I reprint your instructions in order to show it to him?

Next up, the progress on a short line indoor conversion. I added some beer-can aluminum (actually, printers' offset sheets) flaps and an elevator kicker to the model. The flaps are 1" x 4.5" folded at the 1/2" line and double stick taped to the bottom of the wings outboard of the booms. The exposed 1/2" is bent down at 30 deg. A similar piece is adhered to the top of the elevator, bent up. 15 deg bend seems to have worked out to trim the model at 1/2 power.

I switched from the 850 pack to a 450 pack taking 1 ounce off the nose. Viola! An indoor trainer.

(Yes, I know it should be voila' )

Tim Wescott · « **Reply #24 on:** December 31, 2012, 10:41:01 PM »

Larry, you're welcome to show that off to Jay.