Lost thrust thru glow plug hole.. how much?
 

I was running the new engine on my Yellow F-18 DF and noticed something for the first time. There is quite a bit of air volume that comes out of the glow plug hole on top of the fiberglass thrust tube. I've never really paid attention to this but is seemed like it could be something that would cause a slight decrease in thrust...

Has anyone ever done any modifcations to see what would happen if that hole was covered, ie a sliding cover or something..

Just wondering..

Cowdog

Lost thrust thru glow plug hole.. how much?
 

When my wingman, Ghost Rider, was still flying DF he used to take a plastic bottle (Shampoo I think) and cut the top off, then Goop it over the glo plug hole. He then unsrewed the lid, attached the glo driver. When it started he put the bottle cap back on, thus plugging up the hole. No thrust loss there. :cool:

BV also sold a small teardrop shaped thingie held on with two "O" rings and two of the half moon deals he uses on the engine covers. Looked a bit neater than Ben's but cost a lot more too. ;)

Glow plug hole
 

I usually glue a piece of foam to the underside of the fuse hatch so that it just touches the engine cover when the hatch is installed. I then glue a piece of thin plastic or 1/64 ply to the bottom of the foam. This way you don't have to fool around with an extra little cover, when the main hatch is off, you have access to the plug. Just be careful you don't crush the top of the engine cover. You don't realize how much the engine needs that air flow over the top of the cylinder head until you restrict it. It only took 2 flights to destroy an OS .91 cylinder head and piston.

Lost thrust thru glow plug hole.. how much?
 

Like the idea Gary.

Did you notice any change in flight characteristics by covering the hole (besides the blown engine!).

I've still got plenty of clearance around and above the cylinder head within the engine cover, so I'm not TOO worried about overheating...

Cowdog


BTW Mike, looks like the replacement engine is going to do fine. It's one of the old ones I replaced the piston/liner with. No change needed in idle either, got a good 70 second idle with smooth transition to full power.. no hesitation..

Thrust loss
 

I could not tell a difference in thrust after I sealed the glow plug access hole, but it did make me feel better.