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May 20, 2019, 02:38 PM
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Build Log

CRAZY JET: Ultra light trust vectoring jet


Hello Everybody
The "indoor jet" thread (https://www.rcgroups.com/forums/show...404-Indoor-Jet) incited me to build a slow flying jet with vectoring thrust.

The differences with the original jet are:

Civilian model
Full fuse
wing span of 50 cm
1S equipment
Vector foam
Vectoring thrust

I've modified a little bit the original shape and made a fuse, although i know that it adds weight( but i prefer full fuse airplanes).

The original model has a wing span of 63 cm and weighs around 95g, which brings to a very low wing area.

I've calculated that to get a similar scale speed with a wing span of 50cm, my plane should weigh 47.5g (half the weight), which is quite difficult to obtain with vector foam (heavier than depron, but much more resistant) and a full fuse.

The first thing is to cut out the foam and cover with waterslide decals.

Thus, by adding a 300mA.h battery, 3 x 1.7g servos, a deltang RX and the motors and props + linkages and glue, i hope to stay under 60g: the equivalent original plane would then weigh 120g and the speed would increase of around 12.5% which should not be noticeable.

Here's a picture of what i've done so far. I have to cut the elevons and the top of the fuse, then cover with colored decals.
The wing and the elevons are consolidated with light carbon spars.

Stay tuned.
Last edited by indoor_fr; May 25, 2019 at 05:35 AM.
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May 20, 2019, 02:42 PM
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coriolan's Avatar
Quote:
Here's a picture of what i've done so far. I have to cut the elevons and the top of the fuse, then cover with colored decals.
The picture is a bit fuzzy......................
May 20, 2019, 03:57 PM
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Quote:
Originally Posted by coriolan
The picture is a bit fuzzy......................
Sorry. Now it should be clearer!
Last edited by indoor_fr; May 20, 2019 at 04:07 PM.
May 20, 2019, 04:32 PM
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coriolan's Avatar
Looking good Frank
May 22, 2019, 01:22 PM
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indoor_fr's Avatar
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Thank you!
I've cut the top of the fuselage (holes) and will finish the cutting + covering by the end of the week, i think.

About the motorization, i have abunch of 7mm motors and props (normal and reverse) used for drones:

https://www.banggood.com/fr/7mm-Holl...r_warehouse=CN

A motor gives around 25g of thrust with this propeller:

https://www.banggood.com/fr/Hubsan-F...r_warehouse=CN.

For the rudder, i will use a 6 mm motor wich gives 15g of thrust.
So the overall thrust should be around 50+15 =65g.

Otherwise, i'll use a third 7mm motor. This would give 75g of thrust. I have to measure the current which will probabily be over the 2A output current of the Deltang RX.
I think i have somewhere a small 1S brushed ESC to supply the current, in case of need. But every gram counts!
Last edited by indoor_fr; May 25, 2019 at 05:32 AM.
May 24, 2019, 01:00 PM
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cutting done


Ok. Here's the final result before covering.
The weight is 29.1g. Not too bad.

I don't know what the added weight will be with decals. I expect at least 5 or 6g.

Cutting out and covering the foam will save more than 7g on the initial weight of the plane, and allows at the same time to achieve the decoration.

I have to buy ink for my printer. The colors choosen are blue for the wing, the elevons and the top of the fuse and yellow for the edges of the wing and additional decoration.
Last edited by indoor_fr; Jun 02, 2019 at 03:28 PM.
May 27, 2019, 04:19 PM
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thrust measurements


I've been a little to optimistic about the thrust deliverd by my motors.

I've finally found that the 7 mm motors delivers around 21.5g of thrust at [email protected] and that the 6mm motor gives around 13.5g of thrust at [email protected]

To be able to fly the plane vertically, i need a thust/weight ratio greater than 1. This means that i must:
keep the AUW under 64g
use three 7mm motors
use an external 3-4A ESC

I've seen that Microaces sells a 3.5g brick with an integrated 3A esc :

https://microaces.myshopify.com/coll...rum-compatible This could be the solution to replace the DT RX, the external ESC and two 1.7g servos but i'm not sure that linear servos are suitable for thrust vectoring.

Any thougts?
Last edited by indoor_fr; May 27, 2019 at 05:01 PM.
May 31, 2019, 11:26 AM
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A bit of covering


I've started to cover the frame but i'm out of glue (UHU stick ).
The method is described here:

https://www.rcgroups.com/forums/show...12&postcount=1

I think it will be longer than expected....
May 31, 2019, 12:07 PM
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coriolan's Avatar
Quote:
Originally Posted by indoor_fr
I've started to cover the frame but i'm out of glue (UHU stick ).
The method is described here:

https://www.rcgroups.com/forums/show...12&postcount=1

I think it will be longer than expected....
Just read the thread linked above, that GeeBee build was awesome
Jun 01, 2019, 08:22 AM
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Hi Corolian
Thanks for your interest.

Yes, the geeBee was a nice looking plane, thanks to Fiddlersgreen, but if i had to make it again, i would enlarge the wingspan and modify the wing and elevator incidence to make it more stable.
Cheers.
Jun 08, 2019, 04:48 AM
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Sorry for the delay. I've covered half the wing but was not satisfied with the result as i used 2 pieces of decals. The overlapping was not good .
So i've removed the covering and applied an other.
The added weight is reasonable. That's a good point.
I hope to show you more tomorrw or monday.
Jun 10, 2019, 12:30 PM
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I hope to finish tomorow, and begin to install the motors.
Jun 10, 2019, 02:57 PM
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RX and servos


I think i'm going to buy the DT RX 35 with 2 built in 2A brushed ESC:

http://www.micronradiocontrol.co.uk/...t_rx35_120.jpg

plus 3 x 1.7g servos:

http://www.micronradiocontrol.co.uk/...-molex_120.jpg

The RX should be able to handle the current i need for the three motors.
Jun 23, 2019, 03:38 PM
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Too busy for building these last days.
Covering is finished except for the top of the fuse that i'll do when electronics will be installed.
Actual weight is 34.1g without electronics, of course.

I expect 1g more or so for the top, so it should weigh around 35-35.5g.

I've received the servos and the Deltang RX 34d with two brushed outputs. It weighs 1.5g with the additional connectors for battery and the motors.

I have to install the 3 motors and decide where i must put the servos, the RX and the battery to balance the plane.
Last edited by indoor_fr; Jun 24, 2019 at 04:14 AM.
Jul 08, 2019, 01:12 PM
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Some progress


At last, i got a few hours to continue the build.
The three motors are inserted in small pieces of plastic (3D) cut in two as they where heavy. Note that i have not reversed the propellers yet.
The propellers mounted on the elevons are contra rotating ones, of course.
I've mounted the rudder servo and installed the RX.
I've made gliding tests in order to determine where to put the battery and the 2 others servos.

As i'm in holidays now, i will have more time to go on.
Last edited by indoor_fr; Jul 08, 2019 at 03:51 PM.


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