Hi Bob,
I have noticed a few people wanting to try the composite Quickie 500 and Q 40 planes for sport use, myself included. The engine most of us are choosing is the Jett 50 with the racing muffler. I was wondering how much performance difference there will be in both types of airframe with the Jett 50 as compared to the all-out racing engines from Nelson and Jett.

Thanks,

Dave

Hi Dave,

Thanks for writing.

Yes, the more competitive Q40 and Q-500 planes have become pretty popular for sport use. Its hard to find something much faster

By rules, the racing engines are 6.5cc .40cui displacement. For sport, there are no such rules.

The racing engines are indeed extremely powerful. But, they are tweeked to the very edge of stability. They are very rpm dependant. It takes some experience with them to set the needles, and to deterimine which prop is best for a given set of weather/location conditions. Plus, neither the 428 Q-500 or Q-40 engine have a throttle.

You can use them for sport use. Many do. As long as you do not mind not having the throttle (or you can add a jett carb), and you choose to go with a conservative prop size (8.8x8.5 is ideal), the engines operate quite well, and will be user friendly. And as you gain experience - you can experiment with heavier props. The bounus here - is you actually have a 'legal' plane that you can race if you wish. And you gain the experience of setting up the engine and aircraft for race conditions. The 428 engines are mainly AAC these days, and are an ounce lighter than the ABC sport engines, and sometimes this makes balancing the airplanes easier. Often enough, you can find older generation Nelson and Jett QM40 and Q500 engines, well cared for, just tired and maybe a few rpms down on power, for some bargan prices. Just beware the source when purchasing a used engine like this.

The reason many folks use the higher output SJ-50 with the racing muffler (or a SJ-60LX engine with a black racing muffler) for sport racer applications is that these engines produce basically the same power as the Q-500 engine, the muffler tunes for the same rpm, they turn the same Q-500 racing props at the same rpm - and do that effortlessly. Here we have a powerful engine, user friendly, no critical needle, AND a fully functioning throttle And most folks choose to stick with the standard glow plugs (The nelson plug head is available, but the nelson plugs do not idle or transition all that well). Added bonus here, is later on, you can install a standard jett-stream muffler, and put a 10x6 on that same engine.

For the Q-500 application, you can aquire a SJ-50 race configuration with the backplate mount - bolts right on to the plane as the racing engine would. Use the 8.75x9W, 8.8x8.5, 8.8x8.75 or 8.8x9 props. Set any of these down 600 rpm off of peak rpm, and go. For some, getting use to the speed is a challenge - in this case, throttle back

For the QM40, a few of these have some ground clearance issues with 9" props, but most will actually accomdate a 9" prop quite well. So for most, you use the same props above. Also, you can take one of the 8.8x9 or 8.8x9.25 props, and clip it down to 8.25" diameter - the engines love this, and the QM40 will go like he|| with that setup. The bonus here, is with the larger blades, yeah, you give up 5-10 mph on the top speed, but the low speed pull is there ALL of the time - take off is effortless - just a bit of right rudder as usual. On landing, you can idle and approach as usual. The spinning prop actually helps you slow down. I do recommend killing the engine on final though - save the prop.

Ive attached a couple of examples of what was discussed here.

I hope this is helpful

Bob

Bob, thanks again for taking the time to share your knowledge with us less experienced fliers. You've been more help than you can imagine. I may link to this in the extreme speed forum, since I think such information would be viewed by more people that may make use of it there.

Nice fleet you have there too.

I already have the SJ 50 with the race muffler. Just gotta decide which plane to buy myself for Christmas to put it on.

Again, thanks !

Dave

Bob,

Was curious. I took delivery of a 60LX a few weeks ago. It was accompanied by a red muffler, not a black muffler as you indicate above. I compared the length to my black muffler that I got with my Jett 50 and the red one is about 3/4" longer. Probably an unrelated part to the story: the engine came engraved as a 60L not 60LX. I called Dubb and he said it was an oversight and that it was the only 60 he produced on that run, even recalled running the beast up on the bench, I believe the descriptive word was 'animal.' He assured me it was an LX. Anyway, I'm puzzled by the muffler length issue. Can you shed any light?

Jonathan

Hey Bob,

Where can I find these smaller racing props with those odd sizes. I would like to try some of them on my Jett 50 and see if I can get better rpm performance. Thanks, Ken

Tower has them. You can order from APC directly, or you can also go to www.darrolcady.com

Fairly common props.

Keep in mind, the racing props will only work on a plane that will easily get up to speed, and allow them to work properly.

What prop/rpm/aircraft are you working with now ?

Bob

Bob, one more thing here, and I almost hate to ask this one. Both you and a friend of mine have mentioned putting carbs on the race engines. Would this by any chance include the FAI motors ? Just curious.[>:]

We often put the red 2-needle carbs on the 428 Q-500 engines. Those work fine. Costs about 500 rpm off the top end, or a drop in one prop size.

Usually the QM40 can use the carb - slightly - the minute they fall off of the pipe, they tend to go rich and shut off. It has some effect, but with the port timing and critical short muffler, its not much good.

Most of the current FAI engines are Rear Intake . The rear induction engines can not use a carb - the intake and port timing is insain. The intake for the most part is a huge hole. You are fortinate if they run in the first place

Thanks again Bob. I wouldn't really expect one of the thoroughbred race engines to slow down much, maybe just enough to catch my breath for a moment. Been looking around at the Jett site and noticed how inexpensive ( comparatively ) the Jett FAI motor was. Bad idea I guess.

Bob,

I have a Jett 50 on my Patriot 40. I'm using a 9x7.5 APC prop on it now. Its turning around 17,900 on the ground. I'm just looking for the best prop for speed for my Patriot. Everyone always says rpm's means speed. I was thinking about your suggestion of using an 8.75x9 prop to see if I can get just a little more speed. Can the Jett 50 take more rpm's without hurting it?

Also, is there a difference in a racing muffler and the standard red muffler that comes with the Jett 50? If there is, I want to buy one.

Thanks for your expertise!

Ken

Hi Ken,

thanks for writing....

First - the muffler question...... go here
http://www.rcuniverse.com/forum/fb.asp?m=3495337
(thread regarding the 60LX, but its the same sorta info)

You will not break that engine unless you break a prop and have a full throttle shaft run. Worry not.

The Patriot is a quick plane, but it is also a big plane - lots of surface area - it does not fly at 140-160 mph like the Q-500 planes (and a few others). Some of the q-500 props end up spinning their wheels so to speak - they do not work all that well on an aircraft like this.

Turning 17,900 is actually about where you want to be - maybe a little bit on the high side for the standard jett-stream muffler. Prop selection anywhere from 17,000 to about 17,500 is ideal. Launch it about 500 rpm down from there.

On the patriot you need more prop than you are running now. Load the engine down a bit more.

The 8.8x9 or 8.8x9.25 is a good place to start with the D-1 props.

The standard blade APC 9x8 and 9x9 are also popular choices for the Patriot. Many folks fly those.

Bob

Bob,

Thanks for all the helpful information. Is the black muffler you were describing the same thing as your lite-mufflers? I tried looking up some info on them in your Jett Engineering Web page but the lite muffler web page would never come up. I'm thinking about trying one for my Jett 50 and do some expermenting with different props. Can you give me the part number for that particular muffler and price. I'll call Dub and order one.

Thanks, Ken

No, the lite-muffler is the untuned muffler used on the 3D/profile, some scale, and the control line engines. (shown on BSE-76L below)

The black muffler refered to is the muffler supplied with the AMA 428 Q-500 engine - just like the red jett-stream muffler - just shorter, and well...... black Slightly lighter, and tuned for over 19,000 rpm.

No specific part number on this (although I should add it.. ) Just tell Dub you want the Q-500 black muffler to try on your SJ-50 engine.

Bob,
The nelson and Jett FAI engines are front intake, I can't imagine ever putting a carb on one anyway, but they're certainly not rear intake. I remember the old F1 engines, they were a big hole in the backplate, not really even a port, the old Nelson's were just a big hole in kind of a triangle shaped cut out :P But the current FAI engines are definitely front intake

Jeremy, point taken.

Dont go by what is on the Jett website with the FAI engine though. That front intake jett version was 5 years ago, and although it was going to be competitive, it never was fully developed. There was another much more radical front intake version Dub played with too. Its hard to get enough intake air/fuel through the crankshaft while permitting the correct timing. You have to cut too much crankshaft away.... and you reach a limit that is unacceptable from a performance standpoint and a structural standpoint.

Dub's last design of an FAI engine returned to rear intake... but it was not built. The R&D and time required for development, racing and testing is just out of any reasonable rhelm these days. Maybe one day....

The Nelson FAI engine Grunk flew this year at the Worlds was a real piece of work. Outstanding powerplant. Craig and Henry worked on that engine for nearly 3 years to get it where it needed to be. I know they had considered a RI version for a while. Im not sure which one they actually took to France (im a bit too far out of the loop)

Bob

Hey Bob, well, all I can really comment on is what is currently a production FAI engine, ie: what I can actually buy as your average joe speed freak. That is the Nelson, and the JETT, and even the BSE JETT is front intake. So is this MB Profi FAI engine.


I have no clue what JETT or Nelson have in the works, I know Nelson used to have a rear intake FAI engine in the early 90's but it evolved into the front intake engine. The Profi went from front intake to rear and back to front again. I wonder if the rear intake makes it to hard to get the required amount of air into the engine? So anyway, I only pointed out the intake location since you mentioned current FAI engines, and from what I can see, all the current and available FAI engines are front intake