Tim most of the crashes we encounter are pancake like crashes. A Bob Hunt type motor mount should work perfect, so if you copy that mount in 1/8 aluminium in either 2024 6062 7075 or just laminate two of Bobs mounts plates should be pretty good for pancake crashes. You will end up with a broken prop and stuff like that. For a nose in crash you loose the whole plane anyways so I will not even bother building for that.

That’s an interesting problem. You need a mount that breaks sacrificially to save the motor, but which won’t have any bad resonances. How about glass: not glass-reinforced plastic, but actual glass.

You should also use a Combat TUT, so power gets cut immediately in a crash.

Does anyone have pictures of how you mount your motors to your planes in a way that it'll survive crashes?  I'm mostly looking for mounting motors on profiles, and for pics from people who've actually crashed and had the motor survive.

Happy to oblige.
Two versions have been tested: crash-prone beginner mount for smaller profile planes (0.10 - 0.15 glow equivalent, up to 30 oz, tested on Twister and similar) and an occasional crash mount for .40-.46 size planes (tested on profile Cardinal, 48 oz).

The first version is bent out of soft-ish 1 mm aluminum sheet using a bending brake from Harbor Freight.  My friend who is teaching his junior to fly used aluminum from an old discarded awning; similar material is used by roofers to make flashing. Pictures make it self-explanatory. The mount bends upon impact and absorbs crash energy.  I bend the inboard bracket to 95 degrees and the outboard bracket to 85 degrees,  which results in a 5 degree outboard engine thrust offset.  Really helps with line tension.  Don't want the offset?  Bend both brackets to 90 degrees.


 

Isn't there a step 4 in there, to bend the "wings" back?

Thanks Mike -- this looks simple to do and maybe it'll do the job.  By "tested" I assume you've put it into the hands of a beginner who obliged you by crashing?

Step 5.  Attach motor to the mount.  Using Robart incidence meter, set 0 degrees of up/down thrust, mark and drill flange mount holes in the fuselage.  Attach mount to the fuselage using 4-40 screws and nylon insert nuts.  You can add washers for outboard thrust.

Mike, this is really cool.  My wife is learning to fly (although she's busy getting a degree at the moment), and is just not happy with the noise or fuss of engines (she has not yet met the fuss of electrics).  Having something she can crash and not damage would be way cool.

I've watched electrics fail at contests, sometimes causing crashes.

Come to think of it, that's true.  We had a Castle Edge Lite 50 intermittently go blank during flight, and almost lost a plane several times.  I've heard that Paul's anteater had intermittent contact problem during qualifying at Nats. 

Still, compared to the combustion systems, these incidents are few and far in between.  I've seen more cases of engines quitting overhead (not counting bad engine runs) during this Nats than electrics having problems, and there was about an equal number of both.

One year into electric full time and I have had 2 times that the motor quit before the timer stopped it.  Once was my failure to make a tight battery connection and the other was a timer going bad in flight.  Stuff happens.  Compare that to the crap shoot that is IC.

I have had two nose first crashes with IC and the motor(s) survived both and are still in use.  We don't have the vibration issue with electric that we do with IC so we don't need as strong a nose.  Mine are "collapsible" and it worked both times.  The motor needs a secure mount that won't twist when it powers up and cannot pull out forward.  That is about it.  If it encounters a force from the front the motor mounts need to collapse and the nose break away.

If you can see behind the mount, there is noting there.  All of the reinforcing is in front.  When this mount hit the asphalt straight in motor running this is all of the damage to the plane.

However, the best protection is to NOT CRASH!

Ken