Magnus Lord

Hi all,

I am going to fly the new Super-Q500 class in Sweden, which is roughly 428, but with unlimited size venturi, any propeller and 20% castor, 0% nitro fuel.

I guess that you have experimented with different prop sizes. Which prop do you think would be fastest, with a Nelson Q500 engine and an FAI-venturi, if you could pick any size, manufacturer and material?

Magnus

daven

My Feedback: (1)

I would stick with the following APC props.

8.8x8.75
8.8x9
8.8x9.25
8.8x9.5

Those should be the only 4 that you will need.

Magnus Lord

Thanks, Dave!

Would you gain anything by decreasing the diameter? 8x9, 8x9.5?

Cheers,

Magnus

daven

My Feedback: (1)

I don't think so.

Also, the props I listed have the D-1 hub, and are designed to withstand the high RPMs this engine will deliver. Most Sport props are not really designed for these RPMs and may fail.

After Break in, I would prop the engine to peak a minimum of 19,000 Rpm and not any higher than 19,500. Change props until you are within that range, run the engine 300-500 rpm richer (300 with the smaller pitches, and 500 with the higher pitches) than peak, and you should be good.

I normally break my Q500 nelsons in with a 8 3/4" x 8.5 W prop at just over 20,000 rpm.

Per_N

Daven
Do you break in your engines by flying or in the bench?

Per

Ed Smith

The Nelson 428 engine that we run in North America has a 9mm venturi. We also have to use a min prop dia 8 1/2 wood or 8 3/4 molded. Even though we use 15% nitro the engine is not using the full potential of the tuned muffler.

In the Q40 event there is no prop restriction but still the 9mm venturi. We can use what prop we like. So the Q40 engine is timed differently to enable the use of a smaller propeller to get the rpm up higher to fully utilise the tuned muffler.

Therefore why not use the Q40 engine (Same price as the 428)with the large venturi. Then try a prop somewhere close to 7.5dia x 8.0 pitch. The timing of the Q40 engine is the same as the Timing of the F3D engine. What you describe is basicly an F3d setup, agreed without the full tuned pipe. However the Q40 engine revs at about 24k with our restricted setup. In the never ending quest for speed it is worth a try.

Ed S

daven

My Feedback: (1)

I'll typically only run the engine once (on the plane), slightly rich with a smaller prop, and then fly..

Lots of secrets out there, but my engines seem to be competitive, I just need to fly a little better.

Magnus Lord

That is an interesting point, Ed.

I discussed this with both Jett and Nelson before deciding which engine to buy. They believed that with such a big model (with lots of drag) the Q500 engine would still be faster (with an FAI venturi).

Both engines are used in the Swedish class, and it seems that the Q40 engine produces a higher top speed, but the Q500 engine compensates this by being faster out of the curves (so I'm told).

We will just have to see...

Thanks,

Magnus

Magnus Lord

Wow!

First test-fly today. It flew great and I have never experienced such speed before. A fantastic feeling!

I was surprised it was so easy to fly. I ended up with the CG at 2 7/8, which felt perfect. It was very silent in the air, which I guess may indicate that the aerodynamic design is not a total disaster.

Rough timing showed 6.8 second laps, with a Nelson running rich and a low pitch prop.

Thanks for all your advice, guys!

Best regards,

Magnus

midgetmustang

Hello Magnus,
we use an APC 8.75X7.5N with the Q500 Nelson engine. RPM ~19200 with FAI Fuel.

mm

daven

My Feedback: (1)

I missed the FAI fuel part in your first email. I'm glad the props mentioned worked for you, but may not be the optimum prop on FAI fuel (They work best on 15% nitro). Keep experimenting, their are lots of Pylon props to play with. A few others worth trying are:

8 3/4" x 8.5 W
8 3/4" x 8.75 W
8 3/4" x 9 W
8 3/4 x 8.25 N

I would still try to keep the engine between 19 - and 19.5 k RPM.

DHG

My Feedback: (7)

Magnus,

If you haven't tried it yet, consider using the Nelson FAI head with about 0.020" to 0.024" head spacing. (Sorry, I don't know the metric conversion offhand.) Also, the flat-wound GloBee plugs seem to work better with FAI fuel. I don't know if either of these features would help as much at 19,000 rpm as they do at 27,000, but it's worth a try.

Gee, I feel like I'm corrupting the young here ... didn't Socrates get in trouble for that?

Mr. Cough Syrup