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

[skunkwurk]

hi guys,

wrapping up assembly of a new model, the manual calls for epoxy on the top plate of the motor box. 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. I was thinking a minimum of three wood screws on each side of the panel, one in the middle and one on each end. What are your thoughts?

35% cap with DA-120.

 

[thurmma]

You may be able to make an access whole in the top plate large enough to get to the electronics and still maintain the structural support the top plate provides for the motor box. A picture of the motor box and the top plate would help with an answer for you

 

[Terryscustom]

Glue or epoxy the top on but cut a hole and make an access door in the top. Make sure that your access hole has no corners!! Just make sure you have about 1.25-1.75" around the edges. Make a door and screw the door on top of that by pre-drilling the holes, tap and harden them with CA.

 

[Jedijody]

If the top of the box is lock tabbed, I put tri stock around the perimeter, harden the tri stock and the motor box lid with CA, then use four screws per edge. If the lid isn't lock tabbed, I epoxy and pin it to the tri stock around the perimeter and cut the access hole pictured above.

 

[Terryscustom]

If the top of the box is lock tabbed, I put tri stock around the perimeter, harden the tri stock and the motor box lid with CA, then use four screws per edge. If the lid isn't lock tabbed, I epoxy and pin it to the tri stock around the perimeter and cut the access hole pictured above.

Good plan, I was too lazy to draw the tabs but I like your method as well.

 

[tylerzx9r]

Agree with the prior two, Make an access door or whole, and still epoxy the top plate on for structural purposes.

 

[skunkwurk]

Hi guys,

Pics of the motor box, there is aluminum reinforcement in place. This is part and partial a reason why I thought I would be able to get away with screws to secure the top plate. Let me know your thoughts. Thanks in advance.

sc

 

[Terryscustom]

Ahhh, yea, that 120 will make a mess out of that firewall after time being unsupported at the top. Screws won't even slow it down. Unfortunately the engine bolts are so close to the top......have to ponder on this a bit.

 

[stangflyer]

Glue or epoxy the top on but cut a hole and make an access door in the top. Make sure that your access hole has no corners!! Just make sure you have about 1.25-1.75" around the edges. Make a door and screw the door on top of that by pre-drilling the holes, tap and harden them with CA.View attachment 4163

Terry is 100% correct on this. The motor weight alone with no reinforcement will more than likely fracture the motor box where the smaller bolts go through the aluminum angle pieces. Even on a 50cc size plane, there is enough pull force on the firewall to break a firewall in time if it is not supported correctly. A DLE 55 develops around 5.5 @ 7500 rpm in the ponies department. DA 120 is going to be better than double that. Besides the "PULL" factor on the firewall, you will also have weight hanging from it as well. Screws will not support the weight over time. If it were me, I would tri stock the bottom of the firewall to the bottom motor box plate. I would also tri stock the four contact points of the top plate. Both sides inside, firewall and F-1 inside. (May have to cut sections of tri stock for the inside of the firewall due to the engine bolts) Epoxy the top plate on as manual or directions say, But... an access hole will work great. An access hole is not going to reduce the structural integrity of the top plate and what you are trying to do is give it "PULL" force strength. Engine vibrations and harmonics play a major factor in fractured components.

 

[Terryscustom]

Is there anything attaching the firewall at the bottom? Looks like the bottom angles away so just wanted to ask before I post what I would do.