MB-33X 50mm EDF

[davidk]

Here is a sport version of the Aermacchi MB-339 that Lorenzo Sardo calls the MB-33X.  https://cults3d.com/en/3d-model/game/3d-printed-mb33x-sport-jet

Lorenzo's company is called LSPlanes and he's done a great job of designing some really interesting jets.

LSPlanes ticks all the boxes that I inspect before deciding to buy and print a plane.

1.  It's got to be designed with infill which creates a very solid, but lightweight, structure.
2.  Part weights must be included.  It's really easy to make a mistake in a single setting that would double or half the weight of a part.  The Slicer predicts the weight and a quick check with the manual tells you all is ok.
3.  The design must incorporate some kind of alignment system that ensures parts fit perfectly together.
4.  There must be some test parts available to print.  Usually, if they're not readily available, every designer will send through a few parts.  This ensures that what you're looking at online translates to a good print.  The exception to this is Planeprint.  Rene produces excellence... so if I like a design I just get it because I know the quality that goes into his planes.  It looks like Lorenzo is going to join that club.

This is a 4S 50mm EDF Jet, 770mm long with a wingspan of 729mm.  It's hand launch which is why I'm building it.  I want to test the new Spektrum Hand Launch Assist (HLA) in the latest firmware updates.  I've got an AR637TA from something... can't remember... that I've updated to the latest firmware and set up AS3X, SAFE, and HLA.  HLA allows you to set, through the transmitter, a number of really interesting parameters:

Threshold G's: the number of G's it takes to activate HLA.
Threshold Throttle: the amount of throttle it takes to activate HLA.
Duration: the number of seconds HLA is active.
Pitch Offset:  the Pitch Up angle in degrees that is applied when HLA is activated.

Essentially, you throw the plane, HLA detects that you've launched and goes into SAFE mode with an up angle of ascent for a certain period of time.  Once HLA has elapsed, AS3X+ will kick in, and the plane should (should) level out and allow full control.

I'm trying to figure out a way to test this without actually throwing the plane.  I think setting the throttle and the G's to low settings and setting the timer really high may do it.  I can simulate a launch and see what the control surfaces are doing... ensuring that the elevator is up and that SAFE is on.  Wait for the timer to expire and confirm I return to AS3X+ mode.

[davidk]

The MB-33X is complete and tested and ready for a maiden flight.  She weighs in at 785g with a 4S 1800mAh battery.  Would someone please, please order a bit of temperate weather and clear the snow off the ground so I can launch this little beauty, get her in the air, and back on the ground without ingesting ounces of melted snow water.

For testing, I set the HLA Threshold G's to .5, set the HLA Throttle to 10%, and set the Pitch Offset to 45 degrees, and set the timer to 10 seconds.  I started up the throttle and moved the plane quickly forward and watched as the elevator added a 45 degree angle.  As I counted down the 10 seconds I rolled the plane and watched the ailerons correcting in SAFE mode.  The timer elapsed and I watched the elevator slowly return to a neutral state and the plane went into AS3X+ mode.  This is very cool.

I set up SAFE, AS3X+ and HLA on a 3 way switch so that position 0 is SAFE, position 1, is "everything off", and position 2 is AS3X+.  HLA is applied to any position where SAFE is available.  So, I can launch on the SAFE only position so that when HLA expires, the plane goes into SAFE mode.  I can also launch on AS3X+ mode so that when HLA expires the plane goes into AS3X+ mode.  This is the setting I'll use.

I'm not sure how much Pitch Offset to use.  How much is enough, how much is too much?  I've set it at 15 degrees for now, but it doesn't look like much.

[GuyOReilly]

Nice weather has been ordered.  It should arrive somewhere around April 1, 2026.