heliothiszea

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Thought I would share my latest sport speed project with the group. I've been a quiet reader for a while. Thought I would finally post something . . . hope you find the story of the "power squirrle" interesting.

I purchased a Lanier Predator when the local hobby shop was closing about two years ago. Got a good deal on the plane. I assembled the plane and flew it, but I really did not enjoy flying it. I put the plane up for several months. One day I had a brilliant idea . . . I decided to clip the wings. I cut the main wing down to 32 inches. After the first couple of flights I realized I also needed to clip the tail proportionally the same as the wing (thanks Electric Delta) . Clipping the tail is a must if you clip the wings.

I'm powering this bird with an OS 46 FX with a performance specialties (PS) muffler. I've added an extra head shim to keep the motor from eating plugs. As suggested by PS I swapped the OEM main bearing for PS high speed bearing. I'm running Sig Syn Plus 15% nitro fuel and using a tettra bubbleless tank. So far I think I'm getting the get performance with an APC 8.8 x 7.75 Q-500 prop.

I've put about 20 flights on the clipped wing Q-500, now called the !QUOT!Power Squirrel!QUOT! thanks again to Electric Delta. Electric Delta & Vicman witnessed the maiden flight and a few of the subsequent flights.

I'm measuring speed & in-flight rpm's using waveOscope. I'm in the 130 range turning 18,300 rpms in the air. This seems to correlate nicely with the formula e mph = prop pitch inches X rpms / 1056. In my example: a 7.75 pitch prop, 18,300 rpms give a speed of 134 mph. So I feel this is probably a realistic speed.

The plane is now a blast to fly. It goes fast and is a little twitchy. When flying it I have to really concentrate. I'm calling it my speed trainer.

I'm interested to know if anyone elshas tried this modification?

I'm also interested to know what the speed gain is compared to an unclipped q-500 . . . if any.

Thanks

Rudeboy

What muffler are you using? The "sport" or the "racing" type?

If you are using the sport ultrathrust, you may gain some more by running a little more pitch, as 18000+ is at the very top end of the tuned range for that muffler.

130 is not unreasonable, but I think you got more from the muffler swap then from cutting the wing down. With a half decent racing engine, Q500 planes are doing like 160+ (maybe not the Predator though)... and that's with a full size wing.

Kmot

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Yeah, it looks very cool with the clipped wing and tail!!! [sm=thumbup.gif]

heliothiszea

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I'm running performance specialties short pylon pipe. I understand it is good in the 16 - 20 K range. I'm really pleased with the OS 46's performance . . . for right now. I am still going to experiment with some steeper pitched props. Right now I'm using 8.8 x 7.75 . . . I've purchased a 8.8 x 8.0 and 8.8 x 8.5. See how they do on the plane.

Eventually I'm going to step up the speed with an OS 50 SX. I've picked up one from a friend. It has had a few tanks of fuel through it so I'll finish breaking it in. Be interesting to see what / if there will be an improvement. I realize this is still not a super high performance engine, but I want my flying skill to progress as the speed quickens. Thanks for the comments Rudeboy & Kmot.

buzzingb

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More engine and add a cowl.

daven

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Try the 8.8" x 9 or 8.8" x 9.25

Those were about the best for straight line speed with the .46 FX, but took a while to get up to speed.

vicman

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Daven's prop suggestions are right on as you have plenty of takeoff omph right now. (like 3' [sm=bananahead.gif]) The steeper prop will make you use a little more finesse and runway on takeoff but will give you a bunch of straight line speed when the plane unloads.

His biggest issue with full wing was the roll rate, well, he's got plenty of that now![8D]

Nice job on the graphics plant boy. I got the motor and servos mounted in mine, maybe with the short week I can get mine out there this weekend.[>:]

Electric Delta

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Hi, nice to see the Power Squirrel posted now. It definitely flew nicer after the Fun Fly Saturday, than it
did on the maiden!

Using the Performance Specialties bearing in conjunction with the Ultrathrust muffler is a good idea, as
I can now attest. The OS .46 SF that was on my Predator II is now FUBAR. I wanted to fly it after the
Fun Fly too, and it was locked up. I took the engine apart Saturday night, and the bearing cage had
come apart, sending bits of metal through the engine. A new piston and sleeve are $85 from Tower,
so this OS .46 SF is going to be retired. It's a shame, the engine WAS running really great! I guess I
will put my MVVS SHO .40 Quickie engine on the Predator II. I have a Jett .40, but not too confident
the ARF airframe is up to it...

daven

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I've seen some predator wings hold up to a Nelson or Jett .40, and others that didn't.

Good luck

There is also a 8.8" x 9.5, not sure if you will be able to get the heavier prop on the pipe at 16k though... It would be close, depends on the motor.

Electric Delta

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I'd rather not risk airframe, radio and Jett engine on the ARF quality. I've got a Doddger on the workbench,
that I sheeted and glassed myself; I'm a lot more confident about my own work than any ARF, and the Doddger
will make a nicer home for the Jett .40. The Predator II is not bad though. With the OS .46 SF, PS Ultrathrust
muffler and APC 9x7, according to the WaveOsScope software, it was turning 18100 rpm in the air and
flying in the 135-140 mph range. I guess they run best right before they blow up, LOL. The wing held up just fine
in hard turns.

heliothiszea

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Sounds like the consensus is the motor can handle a prop with a bigger bite . . . I'll test that this weekend and see what the waveOscope tells me.

Electric Delta sorry to hear your SF decommissioned itself.

heliothiszea

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Vicman are you going to be around this weekend? Want to help me experiment with different props?

bob27s

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Sounds like its been a fun project.

I'm surprised more of the speed folks do not take this approach. Taking a P-2 or Viper and clipping the wings gives you a serious speed machine. Lord knows the Q-500 at 3.5 lbs does not need all of the wing area to stay in the air I modified an old damaged scat-cat years ago - clipped the wing tip out of necessity - made for a fun toy

Only issue Ive found on the last 4 Preditor II builds (stock birds) is the firewall/hatch area. I add triangle stock, and glue the hatch on to make the front end a bit more solid. One flying with my old SS.40 - haven't run into an failures. My only other desire is to see Bubba add some useful v-tail pushrods to the kit - carbon, fiberglass, something along those lines.

heliothiszea

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Bob - Thanks for the comments. I've really enjoyed the plane.

I also just posted a video clip. I used my digital camera so the quality is marginal. [link=http://www.rcuvideos.com/view_video.php?viewkey=c241134dae6cd3fb8c18]http://www.rcuvideos.com/view_video.php?viewkey=c241134dae6cd3fb8c18[/link]

vicman

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Yep, the vid shows a typical flyby from this guy.
I just got the tank and cowel issues squared away on Miss LA. The tank is in the Pred, TT .46 hung off the nose, servos and rods connected for the V-tail (my first). I will try to start working on covering the wing tonight and maybe tomorrow.

To answer, yes I will try to make it out this weekend. Friday looks like an option too. Even if I don't get the Pred square I got other stuff to come out with. Should I bring my prop balancer?

Vic

heliothiszea

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great vic . . . I'll be out of town Friday, but Sat I'll be at the field about 9:00am. Hope you get the pred ready, but atleast Ms LA will be ready. Don't eat too much turkey, see you this weekend.

heliothiszea

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Just posted a second video . . . this one has a landing sequence

[link=http://www.rcuvideos.com/view_video.php?viewkey=5ae3eaa2c291eebb46e6]www.rcuvideos.com/view_video.php?viewkey=5ae3eaa2c291eebb46e6[/link]

vicman

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I am busy in the am on Sat, maybe in the afternoon.
Does the w/scope work with just that short of footage? Is that Jack at the camera?

Mike Connor

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Here is what I got on the 4th pass on the second video. Seems long enough.

Electric Delta

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Ideally, what you want for WaveOsScope is just one fly-by pass. The files are smaller, and there is less clutter on the WaveOsScope screen. So it is easier to pick out the approach and departure of the aircraft, which yields the Doppler shift and hence the speed. I usually film the whole flight at the field, and use the PC to edit the video down to a single fly-by pass of interest. It's a lot easier to work with the video, since you can see what's going on. I then save that short video clip as an .mpg file, and then move on to the next fly-by pass of interest, save that as an .mpg and so on. WaveOsScope needs a .wav file to work on though, so the next step is to extract or record just the audio from the video. I use my Soundblaster soundcard's recording feature to just record "what you hear" as the source selection, while my short video clip plays. The Creative Media Organizer (the software that came with the Soundblaster Audigy 2 ZS soundcard) will even synchronously start and stop video playback with the recording, which is real convenient and easy. So, I make a short .wav file out of each of the short .mpg files I recorded with the camera.

vicman

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Man, you guys need some kids.
I will just scare the poo out of Seth and his camera when I really need to know.
I would like to get a good idea on the Miss LA. I'm guessing about 90.

Kmot

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Is there anyone who can give a quick tutorial in English on how to get and use WaveOScope? [sm=thumbup.gif]

Mike Connor

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Electric Delta,
The Windows sound recorder will record while playing a video. I just lay the mic by the speaker and manually start and stop the recording. The wav file used in the above calculation was only 2 seconds long and gave decent lines. Checking the speed only takes a couple of minutes for each pass.

Kmot,
You can download the program here
http://www.sprut.de/electronic/soft/scope.htm
and maybe translate the page here. It errors out sometimes and you may need to try more then once.
http://babelfish.altavista.com/tr
Open the wave file with the program and the curved lines will appear. Using the left mouse button you can place a line on the left vertical portion of one of the curved lines. The right mouse button will place a line on the right vertical part of the same curved line as seen above.

Edit - I can right click on the German site and have a translate option. It is a Google function and may be available because of my Google tool bar.

vicman

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This would be right up your alley Tom You can also get a decent idea of what your F-20 was doing at RLII.

Electric Delta

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Mike, you are right about that with the Windows sound recorder, that's something everyone (with a Windows PC) will have too. Many roads lead to Rome, I was just relating my method. Not using the mic has the advantage of not picking up noise from the room, plus losses from the digital-to-analog conversion of playback, and the analog-to-digital conversion of recording. Of course, WaveOsScope is not that picky about the sound quality, and in fact I usually record in Mono with the 4000 Hz frequency cap (telephone quality sound). That saves on file size / hard drive space.

A lot of people may not know what WaveOsScope is doing, and what they are looking at. WaveOsScope analyzes a .wav sound file over the time of the recording and displays it graphically. The analysis is called spectrum analysis, and basically it determines the "prominent" frequencies in the overall sound. The horizontal axis of the graph shows the frequency range being looked at, the vertical axis is the time axis. The prominent frequencies that show up are generally related to the prime noisemakers of our aircraft. The exhaust note will be at one frequency, a two-bladed prop will produce double that frequency, there will also be some harmonics or multiples of these frequencies showing up on the graph. Other parts of the aircraft, like wheels and control surfaces, may resonate at their natural frequencies. And there will always be some unrelated background noise, which usually shows up as random specks on the WaveOsScope display. As the aircraft passes by, the prominent frequencies will all be shifted due to the Doppler effect, and this is what produces the S-shaped curves on the graph. It doesn't matter which of these curves you pick, just as Mike stated, you click on the one end of the S-Curve with the left mouse button, and click on the other end of the same S-Curve with the right mouse button. The speed it computed based on how large the frequency shift is. Sound travels faster at lower temperatures, and WaveOsScope has a provision to compensate for this. "Lufttemperatur" means the ambient air temperature, which defaults to 15° C, which is the equivalent of 59°F. You will get more accurate results by adjusting the temperature.

A couple of useful formulas for those in the US:
°C = (°F-32)*(5/9) for inputting the correct °C
mph = kmh / 1.609 to find your speed in miles per hour

Another use for WaveOsScope is to find out your rpm in the air, as its interesting to know how much a prop unloads vs. static rpm on the ground. Pick a distinct S-Curve towards the left side of the graph, and mark it just as you would to look at the speed. WaveOsScope shows the two frequencies at the bottom of the graph. Add these two numbers together, and divide by two. This gives you the average frequency of that S-curve, and basically cancels out the Doppler shift up or down; this is the point where the aircraft is directly in front of you, there is no Doppler shift because it is neither approaching nor departing at that moment. Now multiply the average frequency by 60. Hz is cycles per second, and we want to know cycles per minute. Depending on which curve you picked, you might get an astronomical number, that you know is wrong, but is generally a multiple of the engine rpm. For example, if you get 36,000 cycles per minute (36,0000 rpm), then you can be confident that is wrong, but you may have picked up the S-Curve that shows the frequencies generated by the propeller. If it's a two-blade prop, divide by two, and you get 18,000 rpm. If you know your ground rpm is 16,500, for example, the 18,000 in the air is realistic, and probably right. If you at first get something like 72,000 rpm, you probably picked up a harmonic, and will need to divide by 4 to get the true rpm. You at least have to have an inkling of what range the rpm is going to be, to figure this out with WaveOsScope... i.e. a ground-based measurement using a tachometer as a reference.