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Mini Learjet 23 twin 30mm EDF

Dr. Looping Looie

Well-known member
#1
Its been a looong time, but here we go again! In the past, I experimented a little with super tiny EDF units, with very limited success. The planes were too small and issues with thrust tube and motor cutoff due to ESC overheating made me stop working with EDFs for a long time. But now I wanted to have a plane for the small units that Just works and doesnt make any problems. So I searched a long time for the right plane to recreate. It should be pretty conventional and stable in the air and also look good and it should be a twin engine, because i wanted to put both EDF units into one plane to go up with the size. I choose the Learjet 23, because it looks super cool with its wingtip tanks and features exposed engines, which do not only provide good thrust, but are also mounted in the middle of the plane, so theres no need for thrust angle.
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My model is not build to scale, because I only used the pictures for reference, so its a no-plan-build. I focused mainly on keeping it simple and light.

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It also features a removable landing gear using Lego Technic. Its super easy to Install and features suspension. I already used it with great success on my Viggen. Right now, Im working on a steerable nose wheel.

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Theres a lot of space inside and the ESCs are mounted under the engine mounts, where they are not so easily seen, but recieve great air cooling.
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The plane has a wingspan of about 65cm and a weight of 500 gramms when loaded up with a 3s 1200 mAh battery.
Theres no need for a thrust tube, because im running 3S and that way, theres more power. The speed is also good.
I already maidened it and it crashed two times because the hatch opened mid-air, causing a stall. One time, it landed upside down, and I was super impressed with the durability, because nothing broke or bendet. Once trimmed out, it flyes super straight and rolls perfectly. It also glides better than expected. Im going to record a video today and hopefully get it posted.


Who's interested in building one?

If its successful in long time testing and you guys want to build one, too, plans may be ready next week! So get your materials in order and get two small EDF units or a twin A-pack!
 

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Vimana89

Well-known member
#2
Looks very nice. I noticed you are using no thrust tubes on your fans. You will probably have more than enough thrust anyway and the way you did it is easier to build, but I've heard even a short thrust tube is better than none. I expected to see the fans more in the center of the engines than at the very back giving them some length of tube. The way you did it should give you very good static thrust and enough thrust to fly, but if it feels underpowered, maybe try with some thrust tube length behind the fans(y). Can't wait to see more and see how this one flies!
 

Grifflyer

WWII fanatic
#3
That looks really, really good!!!
You might benefit from larger intakes.

Looks very nice. I noticed you are using no thrust tubes on your fans. You will probably have more than enough thrust anyway and the way you did it is easier to build but I've heard even a short thrust tube is better than none. I expected to see the fans more in the center of the engines than at the very back giving them some length of tube. The way you did it should give you very good static thrust and enough thrust to fly, but if it feels underpowered, maybe try with some thrust tube length behind the fans(y). Can't wait to see more and see how this one flies!
Correct, a thrust tube of the right size and diameter will give you more power. FT did an article on thrust tubes a while back https://www.flitetest.com/articles/edf-thrust-tubes-flite-tip
 

Dr. Looping Looie

Well-known member
#4
Looks very nice. I noticed you are using no thrust tubes on your fans. You will probably have more than enough thrust anyway and the way you did it is easier to build, but I've heard even a short thrust tube is better than none. I expected to see the fans more in the center of the engines than at the very back giving them some length of tube. The way you did it should give you very good static thrust and enough thrust to fly, but if it feels underpowered, maybe try with some thrust tube length behind the fans(y). Can't wait to see more and see how this one flies!
The reason I went with no thrust tubes is that the EDFs are rated for 2s, but Im running it on 3s, so the Speed of the air pushed out of the EDF is higher anyway, and I like it to have plenty of static thrust. In the air, It felt just right but Im No EDF expert.
 

Vimana89

Well-known member
#5
The reason I went with no thrust tubes is that the EDFs are rated for 2s, but Im running it on 3s, so the Speed of the air pushed out of the EDF is higher anyway, and I like it to have plenty of static thrust. In the air, It felt just right but Im No EDF expert.
I figured as much, that you already had more than enough power and went with that setup for better static thrust and ease of build. As long as it flies well and you are happy with the performance including the power, then I think it was a good move(y)
 

Vimana89

Well-known member
#7
Few and filmed once again, now with steerable nose wheel and it flyes very good. Battery went hot, so I'll add some cooling holes in the fuselage. And yes, I absolutely felt No need for a thrust tube. I'll cut the video and then upload it today.
Sounds awesome, man! Glad to hear it flew so well. It will be cool to check out the video when you have it ready.
 
#12
Flight video is done!
If you build this, I highly recommend using at least a 50c battery!
The battery got pretty hot and the flighttime is just 2 minutes. Im going to try a bigger battery this weekend.
 

L Edge

Well-known member
#14
A rule to remember for EDF's, if you reduce the exhaust area, (yes the exit velecity is increased) but the other half is the overall thrust is reduced. You choke it area, it increases the pressure inside the unit which cause leakage out the front area.

So, what is the overall gain? more thrust or a slightly higher speed?
 
#15
A rule to remember for EDF's, if you reduce the exhaust area, (yes the exit velecity is increased) but the other half is the overall thrust is reduced. You choke it area, it increases the pressure inside the unit which cause leakage out the front area.

So, what is the overall gain? more thrust or a slightly higher speed?
Sorry I dont understand what you mean. I didnt add a thrust tube, so its clearly more power but less speed. But in flight, this thing is clearly fast enought. I placed the EDF units right at the end of the pods, you can see the motors sticking out. The inlets are also bigger than the EDF units, so theres enouth air going in.
 

L Edge

Well-known member
#17
Sorry I dont understand what you mean. I didnt add a thrust tube, so its clearly more power but less speed. But in flight, this thing is clearly fast enought. I placed the EDF units right at the end of the pods, you can see the motors sticking out. The inlets are also bigger than the EDF units, so theres enouth air going in.
I agree with your approach on what you did leaving off the exhaust tube. These are ducted fans(low exit speed), not jet engines(high speeds) so things have to be looked from a different perspective if you want to analize the whole picture. I have projects where carbon tubes go thru the exhaust nozzle and also located directly behind the blades and with a exhaust tube with TV, doesn't bother it.

Dr LL, just keep doing what you are doing. I even have a transport with 64's and it works fine without choking the exit.(with or without an exhaust tube)
I prefer to have the max thust(how about spooling up time) to overcome all of the frontal drag of a plane rather than a higher exhaust speed. There are many factors to intergrate this issue in a simple staement..