Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

2nd DD test flight

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Old 10-14-2002, 02:59 AM
  #1  
FlooredCOBRA
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Default 2nd DD test flight

Well today I finally got my DD complete. Got the engine broken in and went out for a test fight. I ended up using a 8.75 x 7.5 prop with my GRRT 40. All I can say is the engine hated it. That was the smallest prop I had for now, the others 7.2 and 7.5 should be in this week.

It was hard to get the engine set right with this prop. I never seemed to get on the pipe, matter fact it never did. The engine just had that tone to it where you can tell it wasn't up in rpms. I used a 9 x 7 on my OS 46 FX and it sound alot better than this one. Idid not have a tac so I have no idea what RPM's I was turning. But I could tell it wasn't correct at all, total let down.

In the air it flew great and I did not have to trim it. I enclosed all the servos and fuel tank to keep i streamlined as possible. I really couldn't tell a difference in speed because the engine wasn't running right. It looked like about 80 to 90 or so. Not very impressive at all. My other DD flew alot faster with my OS 46 FX on it than this one. I am hoping that after I get my new props in I can get it running alot better than it did.

I put up some new pics of my finished DD in my pic gallery.
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Old 10-14-2002, 10:57 AM
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Default prop size

Im running a 7.4x8 on my qm40 nelson. It doesnt have enough thrust to go fast. Turns 21,300 on the ground an only goes 163 mph in the air. Thats on a whiplash. Maybe the dust would go faster. Need a larger diameter to get the thrust I need for speed.
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Old 10-14-2002, 09:47 PM
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Default 2nd DD test flight

I think my problem is that my engine does not create its power until a certain rpm. And they way it is set up now it is running right under the power and not allowing the pipe to kick in it's use. The engine has alot of power but if not at the right rpm it wont perform correctly. I guess kind of like a 2 stroke dirt bike and having it geared to where it never hit the powerband. Hopefully I will have it worked out by weekend.
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Old 10-15-2002, 12:28 AM
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Default Engines, props, and rpm

Floored,

I wish I knew the secret. Glow engines and pipes are funny. I remember when I first got my Jett FIRE 50 it would turn a 9X10 at 16K on the ground and unload some unwordly amount in the air, my Dust was incredibly fast and would rip through the air with a jet-like roar, would cover 500' in somewhere around a second and a half. I sure wish I could have gotten a radar gun on it back then. After a while it just wouldn't unload any more, couldn't figure out why, nor could anyone at Jett.

Have shortened up my header and pipe and am now turning an 8.75NN X 8 cut down to about 7.5 diameter at around 20,600 on the ground but the unload in the air is tremendous once again. Hope to get a radar gun on it some time around the beginning of November when I have some time off.

Meanwhile I have a new Whiplash just about ready to go. Am debating whether to put my present Jett in it or just buy a new one. Based on what Dan Gill has said the Whiplash seems to do better with a 9" prop. If I can get a 9X10 to unload to 20K I will have at the very least a 190mph airplane, based on the rpm X pitch in inches X .000947 formula. An 8 pitch prop would have to unload to about 25K Am guessing the Whiplash will be faster than a Dust because of the thinner, more rigid airfoil.

Hope to have some good data to pass on soon.
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Old 10-15-2002, 12:50 AM
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Default whiplash launch

It takes alot more to get the whiplash up than the dust. Weights are comming in about 4lb 8oz give or take an ounce. With my nelson 7.4x8 @21300 im only getting just over 4 lbs of thrust on launch. Very sluggish and sinks alot. Running a 9x10 @16,000 your barely up to 5 lbs of thrust. Should be ok for takeoff but not great. I am thinking about an 8.5x10 on my jett fire 50 to crank the rpms up on takeoff with my new whiplash. I'm not saying the DD is better than the whiplash...just lighter.
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Old 10-15-2002, 12:38 PM
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Default Thrust

I would have never guessed I was only getting 4 lb thrust with a 9X10 turning 16K, felt like way more than that.

I figure for a 190 mph + airplane you will need a 10 pitch prop to unload to around 20K or an 8 pitch to 25K. The best I ever saw with 10 pitch on the Jett FIRE 50 was 16.5 peak on the ground, and so far the best I have done with the 8 pitch was 20.6.

The 9X10 seemed to have a lot more pull with those big sport blades. To get the 20.6K on the 8 pitch I've had to cut the NN prop way down to around 7.5 inches diameter and thrust has really suffered.

When the engine was new it certainly seemed to unload the 3.5K in the air with the 9X10 but something happened where I couldn't get it to unload any more.

Turning the 8 pitch now, judging from the enormous increase in pitch (sound) it sure sounds like is unloading at least 3 or 4 thousand in the air.

Considering that I've had to cut a 8.75 X 8NN all the way down to 7.5 inches I'm not sure if you can turn a sport APC 9X8 at enough rpm with a Jett 50 to get close to 200.

It really sounds like your Nelson is doing what my Jett was doing, failing to unload. If you are turning 21.3 on the ground I would think the Nelson would unload several thousand minimum and put you into the 200 mph zone.

Now here's something to think about: a buddy of mine, (the legendary and incomparable Jr. RC Psycho) has a Dust with a YS 45 turning a 9X8 that is brutally fast. It may just be a more powerful engine than the Jett 50.
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Old 10-15-2002, 02:29 PM
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Default ys 45

my ys 45 side exhaust no pipe is nothing compared to the nelson/jett. Its not broken in yet but only getting 115 mph out of it with a 9x7 on a DD. So far it looks like the 90 dollar os46fx at 150 mph is the easiest/cheapest/fastest bang for the buck.
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Old 10-16-2002, 02:14 AM
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Default 2nd DD test flight

I kept my tried to keep my dragg to a minimal. I am looking to get every bit out of my DD and so far it came out fairly light. Seems much lighter than my last DD. Only thing now is if i could figure how to get my engine running right now.

I e-mail MVVS about the engine carb set up. I was thinking i should use a gasket of somsort between my carb and engine. Just doesnt seem to tight a fit without one. But thats the way it came. For those who have the GRRT with rear exhaust and rear intake know what I am talking about. You have to use a speacial braket to get it to mount correctly. Very odd set up.
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Old 10-18-2002, 12:50 AM
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Default 2nd DD test flight

I finally figured out how to change the size of my pics. I added one more
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Old 10-18-2002, 11:29 AM
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Default Dust

Floored,

Nice job!
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Old 10-18-2002, 09:33 PM
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Default 2nd DD test flight

Thanks Dustflyer,

I finally got me a tac so I can see what this engine is turning. I also got some better props in and will be testing them out. Hopefully much better results than last time I flew it.
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Old 10-20-2002, 08:49 PM
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Default GRRT

FlooredCOBRA-

Your right--your GRRT needs a smaller prop! 8x7 is as big as I'll go with mine...I used this when I 1st flew my Dust. I'll also put it on if I haven't flown it for a while, just to get used to it again. Then put on a 7x9. I also have a CF 7.4x8.2 (or so) that I haven't tried yet. That prop is STIFF!! Should work well...

Now tha you have a tach; with the 8x7 or 7x9, tach to about 21.5k or so on the ground...that will save glowplugs. It will be smoking alot, but thats good! It will unload quite a bit in the air. If you REALLY wanna go fast, you can lean it to 22 or 23k on the ground, and will hit a noticably higher exhaust note in the air, but be prepared to change plugs every flight or so! The element inside the plug will be literally SMASHED in as far as it will go!

Carl

PS- You and whoever is helping you better be wearing ear protection while your taching it and launching it if you want to keep your hearing for more than 5 years!
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Old 10-20-2002, 09:14 PM
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Default Hey Carl...

Take a look at the "Can't get RPM readings" thread below..a GRRT guy having some grief...I bet you can get him going!
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Old 10-21-2002, 12:05 AM
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Default 7x9 prop

A 7 inch prop? Thats going to be an exciting launch. Be careful.
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Old 10-21-2002, 12:50 AM
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Default It's a Dust...

The Diamond Dust will launch and fly great on a 7.00" ~ 7.4" Diameter prop. Launches are nothing special, some left torque. You might be confusing this thread with one about the Whiplash.
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Old 10-21-2002, 02:59 AM
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Default 2nd DD test flight

yes I am now using ear plugs now when adjusting it. I noticed after I broke it in my ears rang for 2 days before finally back to normal.
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Old 10-21-2002, 02:07 PM
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Default thrust

My DD is 3 lb 9oz with ys 45 se. A 7 inch prop gives barely 3 pounds thrust at 21000. With this ratio the takeoff will not be that great. With my 4 lb 8 oz whiplash it would be impossible. It takes everything my nelson has to get it up with a 7.4 incher.
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Old 10-21-2002, 03:00 PM
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Default Well, those are numbers...

I had maybe 100 launches of a DDust on a 7.4" prop, and can say from experience that it works fine. I have no idea how much thrust it put out, all I can say is it flew great, had amazing vertical, would fly straight up out of sight in just a couple of seconds while doing rolls. I guess it must have had enough thrust.

And I agree that the same set-up would not work on a Whiplash.
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Old 10-21-2002, 05:29 PM
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Default 7.4 prop

7.4 is a big jump from 7.0. I use a 7.4 on whiplash and it does ok. Nearly 4 lbs thrust at 21000. Once airborn its not an issue at all. But a 7.0 prop even on a diamond dust is going to be a difficult lauch unless you are really light and the CG is near rear of range.
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Old 10-22-2002, 05:27 AM
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Default 2nd DD test flight

I believe my carb may not be the right one. I ordered the Q500 carb but for some reason don't think it is the one I received... But one thing I will do is put back on my stock venturi to see what numbers I get with that compared to my carb set up. Doubt I fly it with that but just out of curiosity.
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Old 10-23-2002, 02:26 AM
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Default 2nd DD test flight

There's an easy way to see if you have the right carb. Measure its bore..ie, the diameter of the hole. Should be right around 9mm as I recall. Just put a ruler w/ mm across the opening and read it.

Also to eliminate any fuel tank/line problems, you should put the engine on a test-stand if you have access to one.

Carl
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Old 10-23-2002, 10:52 PM
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Default 2nd DD test flight

Good idea, I'm going to check to see what I have right now. There has to be a reason why it is not getting the rpm's it should be.
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