IRLJR

My Feedback: (37)

Hello
Could you please suggest a prop size for breaking in the NMPRA/SEMPRA q-500 engine. What RPM range should the engine be running while on the test stand?
Also, could you offer suggestions for what prop size and RPM range to run during racing. I'm not finding info on your web site about this engine.
Thanks in advance.
IRL

bob27s

My Feedback: (19)

Thanks for writing.....

The new spec engine Dub is working on is not in the website yet. Still being fully defined, but I will get information up shortly.

The original sport SS-40 SEMPRA engines can run with a few different props.

My selection for breakin prop would be the 8.5x7 APC D1 prop. Target 19,000 or more rpm. Should get there while slightly rich. You will recognize how it runs fairly quickly.
Use it on the bench, and for the initial flights.

Alternate, any 8.8 D1 prop you have (I use a 8.8x8.5) cut down to 7.75" diameter. Bench run only. Target 19,500 rpm slightly rich.

For racing/flying, depends on who you are racing with, and what rules.

If allowed, move toward the 8.5x7.25, 8.5x7.5. For standard rules requiring 8.75 min diameter, the 8.75x8W is a good place to start.

With the 8.75" prop you are looking for "over" 17,500 peak ground rpm. Nothing less.

With the 8.5 prop, the muffler hits a new tune point, and you are looking for 19,500 or better.

IRLJR

My Feedback: (37)

Bob
Thanks for the info, one other question please.
I have read that the use of prop inserts, placed in the rear molded center of APC props, will insure proper centering of the prop on the shaft. Have you had any experience with inserts, and if so, do you know of a source?
Thanks in advance.
IRL

bob27s

My Feedback: (19)

I use the inserts on the QM props, and usually on the Q-500 props.

APC has them, I think Darrol Cady does too.

I have a handful I had made up at work a while ago from some tube stock.

They are not 100% essential. We did without them for a long time. A bit more important for the QM40 setup.