motor box top plate - ok to use screws or is epoxy a must

[Bill Vargas]

>>> I'd prefer to make it removable, it will make it much easier to maintain the plane as the batteries, ignition and IBEC will all be located in the motor box.<<<

Before you install batteries ignition ibec permanently, temporarily install your gear and do a CG check. The point here is, you may find out that the batteries and the ibec may have to be place further back and out of the motor box. As for the iginiton box itself, it is what it is and there's absolutely nothing wrong with mounting it on the outside of the motor box.

 

[Robotech]

>>> The point here is, you may find out that the batteries and the ibec may have to be place further back and out of the motor box. As for the iginiton box itself, it is what it is and there's absolutely nothing wrong with mounting it on the outside of the motor box.

The H9 33% series balanced pretty well with a DA100 on the nose. Given he has chosen a DA120, he will be loosing a couple of pounds of nose weight right off the bat. I would use that as an opportunity to beef up everything up front including tossing the long standoffs in favor of a laminated ply standoff.

 

[stangflyer]

The H9 33% series balanced pretty well with a DA100 on the nose. Given he has chosen a DA120, he will be loosing a couple of pounds of nose weight right off the bat. I would use that as an opportunity to beef up everything up front including tossing the long standoffs in favor of a laminated ply standoff.

 

[49dimes]

Just as Terry and jaybird are recommending.....the torque and power these class engines develop is HUGE.
Ever try to fight the force of a spinning gyro??? like when I was a kid you could go to the dime store and get a gyro top.
Spinning at moderate speed I could NEVER get to hold it still. That engine is constantly trying to twist itself loose like da gator in the death spiral!


Boy I am slow...too much turkey!

 

[49dimes]

Just thought of somtin?!?!? H-9 Cap DA_120.....That is going to be SICK!! 25?26 pounds and 60 plus pounds of thrust!!!

 

[skunkwurk]

Hi guys,

Thanks for the feedback, I think I just woke up from a Turkey comma. The rationale behind placing the batteries, ignition and ibec in the motor box is the well known fact stated above. The model was originally designed with a heavier motor in mind, the use of the DA100 has proven it's capability to take abuse and balance well with a 100cc motor. I've selected HV servos for the elevator and rudder, that's (4) in the tail. That and the DA120 being lighter than a DA100 leads me to expect to have to accommodate by keeping components forward. Nevertheless, the model is mostly complete, I have not permanently installed these items in the motor box as I'm still waiting for my spinner. I intend to mock everything in place and test the CG. I'm hoping things work out as planned.

sc

 

[skunkwurk]

one more data point, the new ignitions from DA are pretty small, the ibec is a small circuit board and the batteries are (2) 2c Lipos 2800mah. they are very light and compact.

 

[reyn3545]

I would also toss the standoffs in favor of a plywood ring that makes up at least half of that space. Hollow out the middle to save some weight of you want to. Just build out layers of ply until you get the thickness that you need, then laminate them together with some West Systems epoxy and clamps. When dry, drill it out and mount it.

While you're at it, take some of that same epoxy and some CF cloth strips and stiffen up ALL of the inside and outside corners of the motor box and where the motor box hits the fuse. I do this to most of my planes anyway. I had a 91" Extra with a DA85 on it, made a mistake down low and it went nose in at a pretty high rate of speed. The motor was ruined, the plane was trash, but every joint where I added epoxy and CF cloth was still holding firm. That made me a believer.

 

[reyn3545]

While we're on the subject, I do have a question for everyone.....

I've always assumed that the additional "pull" from an oversized motor would have little if any impact on wear of the firewall. If a DA100 had 30 pounds of pull, and a 120 has 40, since the plane weighs probably 28 and isn't tied down, it would just accelerate. Now, the additional torque of a larger motor would certainly have an impact on the motor box, and that's why I've always added some stiffening, but I never considered the additional pull from a larger motor and prop to present any problems... your thoughts?

 

[Jedijody]

You are 100% correct. Torque and vibration are the forces we need to build and counter for.