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First build Sig LT-40

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First build Sig LT-40

Old 07-23-2020, 01:05 PM
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JayAreJr
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Default First build Sig LT-40

Hello All,

I have started to build my first RC airplane, thanks in large part to this community. So I first want to thank all the great builders and contributors to this forum.
Once I get closer to a finish plane, I will call a local club to see about joining and getting flying lessons.

Just a little background , I have admired the building aspect of this hobby most of all for a long time.
I would love to one day build a giant scale F-14, after seeing the cost in them I will settle with a Corsair F4U, which is my second favorite airplane.
So that is what I am working towards. Building my skills as a pilot and a builder to be able to build and fly the Corsair F4U.
So for my first build I am starting with the ig Kadet LT-40.
While I am a complete newbie in this I do plan to add dual aileron servos. Everything else will build built to plan. I have decided to go with electric for this build.
The Eflite 46 will be my motor for this build. My thought process is that anything I build under .46 power will be electric , and anything above will be gas.
Please follow along with my journey as I have many questions and will need all the help I can get. If I can accomplish this, then I can guarantee anyone can.
Thanks to all that join along!
Old 07-23-2020, 01:22 PM
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JayAreJr
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So the first thing I had to do is get some building supplies starting with a table and a hollow core door from lowes.
Next comes the unboxing of the plane. There is a lot of wood in here. Next comes a small unboxing of items.
Love the fact that it comes with rolled plans, along with many accessories like the wheels, nose cone and a gas tank(which I won't need for this build).

unboxing

First look


Many pieces, I can;t wait!

Old 07-23-2020, 02:13 PM
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JayAreJr
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So now we get to building. When I first opened the box and saw of the sticks included, I thought how I am ever going to figure out what stick goes where.
After putting all the sticks together I found that it was easy to see the differences and was able to check them off the inventory list.
So I have my sticks separated in the first pic. I have glued my front spars and spar doublers together.
Next you will see I have pinned down the left wing panel plan.

Next I have glued my balsa doublers to the hardwood spars. First two were a little off, but by the 3rd and 4th I had them pretty straight.

I have pinned down my spars and glued some sheeting to them along with the trailing edge. I am ready to start installing my ribs, but I need to drill my holes for my two servo wires.

My first question is how far out should I put my servo's? I am thinking around the middle. So that would be about bay six from the inside of the wing. That gives me five bays on either side of the servo.

Sticks Seperated

Spar doublers glued on

Plans pinned

spar doubler mishap

Skin and doublers glued

Old 07-24-2020, 03:42 AM
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I will be picking up my servo's this weekend and have a question on which to buy. My LHS has 2 in stock.
The hitech hs 311 is the cheapest, what do I gain by stepping up to the hs425bb?

So the first problem I have run into is that ribs 3 & 4 have some issues.

After further investigation, I found that one w3 rib and one w4 rib were cross labeled. Check out the pictures.

Next I split 2 w5 ribs while drilling a whole in them, I happen to have some 3/32 balsa on hand. So I created 2 new ribs.
For some reasons I didn't create any pictures of this.
However the next issue I had was w2 was off. I attempted to try and correct this with filing, but I felt like I was doing more damage than good.
So created 2 new W2 ribs.

Here you can see the 2 w4's don't line up.

Hopefully a better pic of the issue.

the light shows where the problem with the rib.


Tracing the original W2

First cut

Sanding ribs to size


My First rib installed.

Old 07-25-2020, 09:03 AM
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daveopam
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You could not have picked a better air frame. The LT-40 is a great trainer assuming you have someone to buddy box with you. I notice a gap where the rib in your next to last picture fits around the spar. This should be a tight fit.

david
Old 07-25-2020, 03:37 PM
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Originally Posted by daveopam View Post
You could not have picked a better air frame. The LT-40 is a great trainer assuming you have someone to buddy box with you. I notice a gap where the rib in your next to last picture fits around the spar. This should be a tight fit.

david

Hi David, Thanks for the response and for checking out the thread!. Which spar are you speaking of the front or rear or both? Also yes will be flying this hopefully with a buddy box and/or getting a trainer at a local flying club. This most likely won't be until the beginning of next year, but the plane will not see the sky without training first, something else I learned from this great site!
Old 07-26-2020, 12:21 PM
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Next you can see I have installed rib 4, which is technically rib 3. Its now time to add some shear webs, so the next pic shows me labeling the shear webs.
Following that I have now continue to add ribs and shear webs.

Looks like I drilled one rib too many. I plan to have the wing servo in the bay that shows the word Left in the pic.

Ribs went in without event so am getting closer to finishing the left panel.

The rest of pics show the rest of progress up to the wing tip. I will be holding off on installing rib W1, until I complete the second wing panel.
I will be starting on it shortly.














Old 07-26-2020, 04:07 PM
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Something that may not be in the instructions is that die cut parts are never perfect. First think you should do is put a straight edge on all edges that should be straight. If they are off, sand them lightly with a straight sanding block. When you have multiples, like the wing ribs, put pieces of stick stock in the spar slots to keep them even, tape the edges that won't be sanded to keep the parts together and sand the straight edge. This will eliminate the gaps that show up. If you can find them, Great Planes had an 11 and 20+ inch aluminum sanding blocks that used adhesive sand paper. They work great for this kind of touch up as well as smoothing the outside of the fuse and wings before covering.
As for the servos and where to locate them, the middle of the aileron is going to be your best bet. Word of caution, don't skimp on your radio gear. This is one area that you are better with a bit of overkill than having "just enough". Personally, I use all Futaba as it's always worked well for me. What brand you use is up to you but don't go with an radio and servos because they are "cheap". I'm sure you've heard the saying, "You get what you pay for". Last thing you want, when flying your plane, is to have a cheap, off brand servo to fail. There's nothing worse than watching your model crash due to losing control due to a cheap servo.
Something else you may want to consider is using heavy duty servo extensions rather than standard ones. Not sure how much you know about electricity and wiring but a heavy duty extension uses larger wires. A larger wire can handle more power and has less resistance than a smaller one making it a better for carrying the power and control signals to the servos over a longer distance due to less loss from the resistance of the wires. I know some will say it doesn't matter but, to me anyway, piece of mind is worth the extra cost.
Old 07-27-2020, 07:53 AM
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The pic I was talking about you labeled "my first rib installed". It may just be the photo. Your work looks really good.

David
Old 07-28-2020, 11:55 AM
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Hey Hydro, Thanks for the response I have seen you in quite a few threads that I have looked at. I did a small amount of sanding on the ribs to smooth them out. I probably could have done more, but I got a little nervous sanding so much. I do see now I should have done the same things with the bottom sheeting, but it seemed like i would have had to take off too much to make it actually square. I actually did look for some of the great planes sanding blocks but found they were discontinued. So I made some of my my own out of a piece of 1x4, but they are not as long as the gp's. I currently have a 1st gen spektrum dx7 radio , that i am hoping to use with this. I do still have to decide on the receiver. I have decided to go with the Hi Tech 322hd for servo's, if anyone has any info on those I would love to hear, as there is a wide field of servos to choose from. Thanks again for the extension info as I had not even thought of that yet, so I will not do research on those. Thanks again for the response.
Old 07-28-2020, 12:41 PM
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Hey David, Thanks again for checking in on the build. I think the gap in front and rear of the spar are for the 2 madb's that are added when the wing is joined. Here is a close up pic, Let me know what you think and please keep the advice coming.
Old 07-28-2020, 02:58 PM
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The LT-40 is a great airplane to build and a great airplane to fly! I built mine in 2004 and it has been my favorite flier ever since.

Mike
Old 07-28-2020, 03:19 PM
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I found other options for sanding blocks:Unlike the Great Planes version, the Fiberglast aren't as long but, in their favor is you don't have to periodically change sand paperThere are others on the market as well, just a matter of finding one you like and works for you

Last edited by Hydro Junkie; 07-28-2020 at 03:22 PM.
Old 07-28-2020, 03:19 PM
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The 322HD is a solid choice for servos. I would not use them on a glow or gas model but for electric power they are fine. When choosing the RX for your DX7 I strongly recommend you stick with a genuine Spektrum product. There are a few 3rd party offerings that have given issues. You will also want to use a 5cell nickel metal battery or a 6.6V LiFe battery. A 4.8V battery with Spektrum has led to issues as well. The Spektrum receivers like to shut down at 3.5V. Looks like you are off to a great start.
Old 07-28-2020, 04:46 PM
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Originally Posted by speedracerntrixie View Post
The 322HD is a solid choice for servos. I would not use them on a glow or gas model but for electric power they are fine. When choosing the RX for your DX7 I strongly recommend you stick with a genuine Spektrum product. There are a few 3rd party offerings that have given issues. You will also want to use a 5cell nickel metal battery or a 6.6V LiFe battery. A 4.8V battery with Spektrum has led to issues as well. The Spektrum receivers like to shut down at 3.5V. Looks like you are off to a great start.
Speed and I don't often agree, but on this one we do, to a point. Stick with one brand when buying radio gear for the reasons he gave. A couple words of caution on servos. Not all servos will work with all radios. I personally prefer digital servos however some radios are not compatible with them. I THINK the radio you have is compatible so it shouldn't be an issue. You also need to look at the voltage requirements of the servos and receiver. I THINK most receivers will handle the 6.6 volts Speed recommended. Some servos, however, won't and are very specific to use only 4.8 volt packs. With my boats, I use 4.8 volts nicad packs and have never had an issue with Futaba equipment. That said, many servos can handle 7.2 volts though, with your plane, that would be overkill. Again, that said, you could probably use any servo that has 50 to 100 inoz of torque and be fine. I'd be looking at using analog S3004s in my Kadets since I use Futaba. They are bearing supported analog servos with around 50 inoz and are made to work at 4.8 volts, of which I have many packs. My larger planes will all be higher powered digitals, when built, as they will be dealing with larger loads and higher speeds than the Kadets

Last edited by Hydro Junkie; 07-28-2020 at 04:53 PM.
Old 07-28-2020, 05:00 PM
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The DX7 is fine with either analog or digital servos. For some reason I can't figure out Futaba still has servos rated at 4.8V. Not that it is an issue as Futaba doesn't have the same low voltage threshold that Spektrum does. All of the Hitec standard size servos will handle 6.6V just fine. The only drawback is having to buy a charger that has adjustable voltage do you can charge them. On the plus side of that is you can monitor the current required to top them off and can easily gauge how many flights you can safely make on a charge.
Old 07-29-2020, 06:27 AM
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Mike , Thanks for stopping by, I hope to enjoy this plane for many years!

Hydro, Thanks for the list of sanding tools. I had actually looked at the perma grit before, but didn't know how they would work for this hobby. Glad to know they are useful here also, so they will be my next building supply purchase.

Speed ,Thanks for the info and good to see you in another of my threads. Looks like I will have to use the 6.6v with the 322's since that's what gets their torque over 50. I am currently looking at spektrum receivers. The spektrum ar620 6 channel sport receiver seems like a good buy. Any thoughts on that one. The only thing I am unsure of is the fact it doesn't have an external antennae, however reviews seem to be good on it.
Old 07-29-2020, 06:47 AM
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For wing building I have a 33" and a 44" Great Planes sanding bars. I know the GP bars aren't available new anymore but you might check a local metal supplier for "T" shaped aluminum extrusions. These can be cut to any length and make great sanding bars, I have some of those too. If the handle is too thin for your liking you can epoxy wood to each side of the center post. The self-adhesive sandpaper can be purchased buy the roll on Amazon or you can use 3M No. 77 spray adhesive with any sandpaper. The 2 1/2" and 2 3/4" are the easiest to find and can be cut to the correct width with a utility knife after applying.
Old 07-29-2020, 07:02 AM
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An external antenna isn't needed nearly as much on an airborne 2.4GHz as it was on the older 72MHz receivers. Same thing can apply to the transmitter antenna, many don't even have an external antenna any more. In fact, out of the entire length of a 2.4GHz receiver antenna, only the stripped end is actually accepting the signal. The rest of the antenna is actually a shielded coax cable, just like what is used on cable TV installations except smaller.
As far as the sanding tools go, you could also stop by an auto body repair supply shop and see what they carry. I found at a local one in my area sanding sponges that are great for sanding curved surfaces. They also are a great source of light weight fillers and solvents, even better than box stores like Lowes, Home Depot or Menards, not to mention less expensive since you can buy once and have for years or, at least until you hit the shelf life limit
Old 07-29-2020, 11:33 AM
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Currently I am using a 1x4 cut up into pieces and I ca'd sandpaper to it. Duh, I didn't even remember I actually have a can of 3m 77, I could have reused the same piece of wood. Here are a couple of pics of what I am currently using.



Since I am having a lot of fun building this, I am sure I will continue at the least building so I will be checking out some more permanent sanding options.
Its good to hear external antenna aren't always needed, seems perfect for what I need.

Thanks All for checking in!
Old 07-29-2020, 11:40 AM
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I have added the top spars and front leading edge.

I will hold up here on the left wing panel and start on the right wing.
Once I am at the same place with the right wing, I would like to start on my fuselage next. So I started to read ahead, and just realized I also need a motor mount for the electric motor.

So I am looking to order the electric motor mount box from Sig, If there are better ones out there please let me know as I am still open to what to use.

I will start next on the tail fins awaiting delivery of a motor mount.







Old 07-29-2020, 02:25 PM
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That RX should work just fine. As always with a new airplane you should do some range checks with the TX in low power mode. As long as you are using the motor in stock configuration with the rear mount you can just space it away from the firewall with some nylon spacers and long screws. If you need to space it out any farther then 1.5" you can easily just trim the cheeks back to clear the prop. Speaking of props, take a look at the APC electric props. Typically they will perform very well but the thrust per amp is better then most. End result is longer flight times.
Old 07-29-2020, 07:52 PM
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Nice building!
Old 08-01-2020, 03:34 AM
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Hydro and Speedracer, Thanks for the info on receivers, looks like I can check one more item off my list.
I must admit , I hadn't thought about props as of yet. The specs for the eflite 46, says it can handle a prop between 12'8 and 14'10. I saw another thread with someone using a 13'8 apc propeller , so I figure thats a good place to start. What determines which one I use?
I went ahead and ordered the electric motor mount from sig, as I may one day put a cowl on it. So just waiting on delivery of the motor mount to start on my fuselage. Thanks for the help! And for dropping by.
Old 08-01-2020, 03:35 AM
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Originally Posted by FlyerInOKC View Post
Nice building!
Thanks Flyer! That means a lot coming from you!

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