Backwards engine runs

Not much to add to what Ken said, I will say that it's not the prop coming off that would concern me, but the lack of cooling.

Ron

Sig Skyray wrote:Another newb question...

Should backwards test stand runs be aborted?  

Thanks!  Greg

IMHO, yes. Part of the cooling comes from the prop throwing air across the cooling fins. When running backwards in a moving situation like an airplane in a pusher configuration, some of the airflow is supplied by the movement...but not on a test stand.

George

Cribbs74 wrote:Not much to add to what Ken said, I will say that it's not the prop coming off that would concern me, but the lack of cooling.

Ron

The prop is still moving quite a lot of air over the cylinder, so cooling is taking place.  It is less than with the prop blowing directly on the cylinder, since air is drawn in from a larger area than the prop disk, while air is blown in a nice column of the prop disk.  The prop is also not operating in the efficient direction.  I will agree cooling is much reduced, but a cowl may impact cooling even more.

If it is the first start of the day I let it run some, but not usually a full tank.  Restarts are typically much easier, and more consistent in starting forwards. So I would say yes, but not with any urgency.

Phil

I put hex drive plates and cam-ring starters on every Cox engine I assemble. Except for the Reed Speed and Tach race engines.

If it's an engine with a dependable needle, I notice the obvious when running backwards; you have to set it richer when it fully warms up in a reverse run. I noticed that when I was running my Reed speed engine and wasn't alert enough to realize it was running the wrong way. I was already on the lines when my son gave me the cut-throat. I tried to argue so he let it go and laughed when it rolled in reverse.
Rusty

RknRusty wrote:I put hex drive plates and cam-ring starters on  every Cox engine I assemble. Except for the Reed Speed and Tach race engines.

If it's an engine with a dependable needle, I notice the obvious when running backwards; you have to set it richer when it fully warms up in a reverse run. I noticed that when I was running my Reed speed engine and wasn't alert enough to realize it was running the wrong way. I was already on the lines when my son gave me the cut-throat. I tried to argue so he let it go and laughed when it rolled in reverse.
Rusty

On the subject of wrong way runs, I Recall a funny story from back when I was a kid, I had one of the limited edition PT-19's that were white with the air race decals on it, I flew the snot out of that plane btw anyway it had the older zero drag spring starter and you had to be careful with the launch or it would bump the prop upon release and it was off to the races chasing it as it scooted backwards. that thing would bump backwards with seemingly a puff of wind. Anyway several years later, i was around 17 and was out with a couple of my friends flying the now rather beat up PT and got brave and tried a couple of touch n go's, I pulled off the first one fine which bolstered my confidence so I tried it again and touched a little too hard and bump, tipped the prop and bounced back into the air then it quickly hit the air breaks and did this crazy tumble backwards and went tail first into the pavement and the hysterics ensued at my expense of course. Yup it popped backwards and broke quite a few plastic parts on that one how ever it was funny at the time. The engine had a lot of time on it and I'm pretty sure the ball/socket was quite loose. At that time I Didn't know of the reset tool back then. The engine still ran great though Wish I still had it so there is my little funny! (Bandit)

Sig Skyray wrote:Another newb question...

Should backwards test stand runs be aborted?  The concern is the prop loosening as I see it, which happened on my first golden bee test run a few weeks back but I didn't know if it was a loose prop screw to start with.

Thanks!  Greg

i dont like it when they run backwards it stops the air flow from the prop cooling the engine so she runs hot! bit like a vw beetle stuck in a traffic jam

Good info, thanks all.  Back flipping does work well for me and I do have a few brass hex drive plates, cams and springs so I'll do that.  I'd like to find a few no drag springs, I have none of those, oddly.
Greg