Sessholvlaru

I had mentioned this combo here before, but found a guy here on RCU selling a NIB Magnum locally and finally made it happen. Built pretty much per the manual, but moved the recommended CG (120mm to 130mm) back to about 170mm after hearing that the stated CG was really nose heavy, i.e., the whole "glides like a brick" thing. Battery ended up behind the elevator servo. Used the stock tank and mount for the Q40 Nelson. Used a mini HS-225 on the ailerons, HS-525MG on elevator. All up weight of 3 pounds, 6 ounces less fuel. Manual states 5.5 pounds!!!???

Nelson was tuned with a 7.4X7.8 APC Q40 carbon pylon prop (all I had) and hand launched. Plenty of pull, flew right off. Flew it three times today, awesome sound, great speed. Glide was very good with the CG at or around this point, landings just plop down on the ground at next to no forward speed. Slide on grass was maybe two feet. Going to try a 7.4X8.1 APC prop for some more speed.

My friend took some video so that hopefully someone here can give me some speed numbers with that Doppler audio program. Is anyone here capable and willing to do so? My guess would be around 160, but I would love to see how wrong I am. Attached are two pics.

Links to videos, would love to see how fast some of these passes were:

http://www.youtube.com/watch?v=UustKvPFUis
http://www.youtube.com/watch?v=nqLANiiRTJI

The pass at around 40 seconds on the second clip may be the fastest?

MJD

My Feedback: (1)

If you send me the video file via email I can export the audio and analyze it for you. Only takes a few minutes. I'll pm you the address.

MJD

Sessholvlaru

Files away! Thanks Mike. Anyone have any prop suggestions? The pitchiest APC pylon Q40 prop is the 7.4X8.1 and I'm not too sure what other props can be safely run on this engine.

combatpigg

My Feedback: (3)

Nice looking Speed Plane! The list of props is pretty narrow, those pylon racers have it down to a science.
Eliminator Props has a wide selection of possible props.

If you are willing to experiment with what you have, the APC chopped carbon props are pretty easy to modify. Shaving the top of the blades can bring up RPM, same goes with trimming some diameter. I cut the blades down to a high aspect ratio, instead of the "butter knife" shaped stock blades. When I'm done, the blades look like they belong in a switchblade instead of at the dinner table.

Sessholvlaru

Thanks combatpigg. I ordered a 7.4X8.1 from APC to replace the 7.4X7.8 on the plane now (prop says 7.8X7.4 but I assume that is backwards) and will see what it does. Not sure I feel comfortable altering these props, if only because of my lack of experience with prop modding. Can I run regular gray APC pylon props on the Q40? Or just carbon Q40 props?

combatpigg

My Feedback: (3)

APC has had problems with the long stroke Nelsons, but any good engine can blow a prop. The $4 props with the hefty hubs are pretty tough. 190,000 divided by the diameter is the red line, so a 7 inch prop is theoretically OK at 27,000. 24,000 on the ground, in other words.
No one ever showed me how to modify a prop, but over the years I've competed with guys who all ran modified props. It's not brain surgery, but it does take practice. The goal for all out speed is simple. If the model is clean and the engine has good RPM potential, the blades can be real skinny.

combatpigg

My Feedback: (3)

This is one of those 7.4 x 8.2 props. The prop is now 7 inches and the blades are narrowed on a band sand / scroll saw over the wood pattern, then rough sanded with a drum to a thinner airfoil. After that, the blades are block sanded starting with 40 grit and brought to a balance after graduating to 80 grit. The prop is balanced before graduating to the next finer grit. I call it good at 320 grit.

Sessholvlaru

Real nice. Exactly what kind of advantage does this give you? Also, I have a basic idea of what it means when an engine "unloads" in flight, but maybe you can clarify for me? Also, the Magnum is draggier than your 202 mph Screamin' Demon (very nice, fyi). I listened to your audio, sounds good. Sounds similar to mine, but I know I am no where near that mark (hoping to hear around 160).

combatpigg

My Feedback: (3)

The smaller blades allow the engine to rev up high, less load, less critical needle, less wear and tear. The amount of drag dictates what you can get away with. Just like with a drag racer, it doesn't pay to lug any more tire down the track than you need until you run into traction problems. Same idea here. You might find that your present combo is already 98% there already, but the fun of the "speed" hobby is the hunt.
Unloading is when the on rush of air is matched with the thrust of the prop. The stored energy of the plane is converted to horsepower [during the dive] and helps push the prop faster, the sleekness of the airframe limits the unloading, as well as the prop's diameter and mass. The engine itself is being revved beyond any rpm it could achieve otherwise. When the plane levels out, the load is gradually transferred back to the engine but the lighter prop will delay the transfer.

Mike Connor

My Feedback: (5)

I came up with 176 mph at the 40 second mark on #2.
Let me see if I can get a rpm for you.

Mike Connor

My Feedback: (5)

rpm was 24,219

Sessholvlaru

176!!!!! Wow, Better than I had hoped for!!!!! Thank you very much Mike, I appreciate all the effort. I would love to know the R's....

combatpigg

My Feedback: (3)

Congratulations Sess! That's pretty Extreme and you still want more!

Sessholvlaru

Sweet!

Mike Connor

My Feedback: (5)

You still want more, don't you cp?

Sessholvlaru

Thanks CP! Certainly the fastest I have gone to date with my clipped wing Q500 pulling in a close second. You're right, need to go faster! Time to mess with props!

Mike Connor

My Feedback: (5)

We will see what MJD comes up with. We should be close.

Sessholvlaru

Does that rpm sound about right for a Q40 Nelson LS with that prop? I didn't tac it on the ground, just did a quick tune by ear/pinch test deal. Can't wait for that 7.4X8.1!

combatpigg

My Feedback: (3)

Honestly.....just many more of the same is fine without buying a new engine every 6 months

Sess, did you notice if the engine was hot or not? How is the plug?
Dave Norman [daven] is the Q40 guy, he could give you spot on advice.
Dave Shadel at Performance Specialties is also a wealth of knowledge and Your source of parts. No time better than now to introduce yourself to him.

Sessholvlaru

Plug was/is fine, motor was not hot immediately after touch down...but that was after the glide home of course.

MJD

My Feedback: (1)

I analyzed the same pass a few times, all the readings I came up with were 173-178. I'd agree with 176.

Interesting.. it jives with the 165 or thereabouts generally accepted around here as top speed for a West .50 powered Magnum.

MJD

Sessholvlaru

I have dealt with Dave a few times for Nelson parts, always helpful! Bought plugs, mufflers, etc. I will be giving him a buzz this week for some plugs and a 2-inch spinner for the Magnum/Nelson. As you can see in the pics, the 1.5 inch spinner doesn't quite do it.

Sessholvlaru

Thanks MJD, appreciate your help. Doubt this thing can hit the coveted 200mph mark, but how do I calculate approximate speeds via prop pitch? If the 7.4X7.8 gives me 176 at 24k, trying the 7.4X8.1 or 8.25 will give me X? This is assuming the engine can handle it, of course. Fuel is plain 15% Omega. Motor was roughly tuned, could probably get more out just tweeking the needle.

Mike Connor

My Feedback: (5)

You can download ThrustHP at
http://www.hoppenbrouwer-home.nl/ika...rusthpv20d.htm
or just do the math for pitch speed. I just noticed the pitch speed for 7.8 at 24219 is 178.90. Close to pitch speed so you are doing good in the drag department.

Sessholvlaru

Excellent. I see potential here, and between the used LS Nelson, plane, servos, etc, I am into the plane around $300 and that isn't too bad. I am going to post my progress here before it starts snowing...