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

Hi Reyn,

Thank you for the feedback, I appreciate it. I'll leave it to the experts to answer your question, definitely a good one.

Regarding the resin and CF, once I get everything mocked up I intend to coat everything in a 50/50 or perhaps 70/30 mix of resin/alcohol to seal it all with a brush to add some strength before final install and then complete with a final/final CG check. Part of the choices I want to get right in finding the tradeoff based sweetspot I mentioned earlier is that I want to build it so it lasts but not overbuild it. I don't need it to survive the rest of the plane or components. In other words, I could build a motor box out of steel, but this would be impractical as it adds no value, as the entire airframe would not be as rigid. I certainly understand I need to do something as the DA120 is much more powerful than the originally intended motor.

Regarding the standoffs, I'm getting more attention on these than I thought I would. I think I'm going to perform my initial ground runs with them and evaluate if I want to maiden with them or toss them. I understand the value of a laminated mount, and it is probably what I will replace the standoffs with if I decide to go down that route. Or perhaps a Hyde mount, I know i know, soft mounts are an other religious concept. I just want to take it one step at a time, test and re-check things before I make too many changes etc...

sc
 

Robotech

70cc twin V2
I had the H9 Sukhoi and the Edge 540 with a DA1oo. If my memory serves me, and it doesn't like it used to, I didn't need stand offs at all and the DA120, according to DA's website is only a 1/4" shorter. So why the long standoffs?
 

jaybird

70cc twin V2
I had the Cap and the Edge with a ZDZ 80rv and had to use standoffs. Seems like I remember my buddy's H9 planes using oak blocks to mount DA 100's.
 

reyn3545

100cc
Let us know how much the motor twists around when you get it started. And keep in mind that if motorr mounts fail, it's usually over time, and usually happens in a snap or other maneuver that just puts the forces beyond the strength of the weakened frame..... and the results are not pretty or inexpensive.
 

camss69

70cc twin V2
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?

You mention that the plane isn't tied down but it is still pulling through the resistance of the air isn't it? Last time out I was flying on a calm day and did a high speed fly-by and chopped the throttle and the noise of the air coming off the plane was really loud, it's displacing A LOT of air! I doubt it adds any additional wear on the firewall, I'm not an expert but that's what I thought of after reading your post.
 

reyn3545

100cc
Hey, camss69, I think you have my dog.....

Reggie.jpg
 

reyn3545

100cc
This is our second one also.. He's just over 2 now, only about 65 pounds, so he should stay fairly trim, but he only has 2 speeds... asleep, and WIRED! They usually settle down around 3 or so, so we're getting close.
 
OK guys,

I got some time tonight to work on the motor box. I feel better about it, I tried to put to use a lot of your advice, I feel better about it lasting past the maiden . Hope you agree.

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