thunderjet

My Feedback: (1)

I just got back from flying my first DD. First I must say I was disapointed. Those 140 and 160mphs That I have heard about is either B.S. Or I am doing something wrong..

My first flight was with a 9-6 master airscrew at 17600 on the ground. The gun showed only 96mph out of a slight dive. It sounded fast but it felt like it hit a wall on speed.

Second flight. APC 9-8 turned 15600 on the ground. In the air it was faster and more sensitive. The gun showed 136 mph.

Now I don't have a lot $ I save that for my Turbine Planes. But I need more speed. What can I do to go faster...

By the way. Powered by a Sport Jet 46 on 10% wild cat.

Prop selection, change to a real tuned pipe, fuel change or what ever...

Would a Nelson Quickie motor be faster?

Thanks

Thunderjet

ChuckAuger

My Feedback: (12)

I'd say 15600 on an APC 9X8 sounds pretty low, but other than that I'd say your speeds sound about right.

bob27s

My Feedback: (19)

A 9x6 on the SJ46 is way too small of a prop for the engine..... ok for breakin as long as you keep it rich and in the RPM band.

(our sport racing thunder tiger pro .40 engines turn over 16K with an APC 9x6)

first off....don't run a Master Airscrew. Use a APC props.....they are rated for higher RPM and loading. Plus I have a load of data on different sizes.

The rpm for the 9x8 on the ground sounds ok. The blade on that prop is a bit on the thick side. Its a bit low in the power band for the SJ46, but the DD will let it unload in flight. You would rather keep the engine above 16,500 rpm peak on the ground, and back off 500-800 rpm before launch. Try a APC 9x7 or better yet go with one of the APC q-500 props..... 8.8x8 and 8.8x8.5 work well.

If the engine is new, give it some time. It will take about 1 gallon before you are up to full tilt. After you get some time on the engine, you can go up in pitch a bit.

Fuel you are using is ok. I typically run 15%, but its only about a 300-400 rpm difference. That might get you a bit more performance. No real benifit to using much higher nitro though.

The speed you noted sounds about right. 140 range is about on target. Getting above that requires some work, and usually a rear exhaust set up to cut down on frontal area a bit. Your best best it to experiment a bit with props, keeping in mind that the engine should peak above 16,000 on the ground to really jump on the muffler. I tend to use the q-500 props (mainly since I have all sorts of differnt sizes lying around). Chuck and some of the guys on here have a lot of experience with the same engine/plane set up.

Which muffler do you have on the SJ46? The standard jettstream, or the 'racing' muffler ? That will help with prop selection. The racing muffler is tuned to run up in the 17K-18K rpm range, which allows different prop selection.

The Q-500 racing engines (nelson or jett) will present basically the same prop issues. the SJ46 is essentially the Q-500 engine. The muffler is the RPM limiter. If you want the Q-500 RPM performance (18K and up), installed the Jett SS .40 muffler.

Bob

SWICK

My Feedback: (4)

I had a DDUST with a 46fx and a tuned pipe running a 9x8 prop at 17700 my buddy has a computer program that measures the sound and figures the speed. first run was 137.6 tweaked it with some more nitro and last run was at 149.8.

Good Luck