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Yet another DDUST take II - 6/21/2005 9:14 AM   
Jbolt


 

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Status: offline 		I couldn’t stand it so I robbed a receiver from another plane and built another ddust. This time I was able to get 4 flights in AND take it home! Woo Hoo!

This one sports an old ST G34H I bought in 1990 to go in a heli but never used it. About all I can coax out of it is 16,4k on the ground with an APC 8x8. It’s fast enough but it doesn’t have that shrill sound like the OS32 had. Still gets the adrenalin going.



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RE: Yet another DDUST take II - 6/21/2005 3:37 PM   
ChrisSpad



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Status: offline 		i'm glad it worked better this time around. They really are a handfull until you get it dialed in. I bet it screams. 16,400 with an 8x8 is really fast!

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RE: Yet another DDUST take II - 6/22/2005 6:22 AM   
Jbolt


 

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Status: offline 		The handling is not too bad but I did make some changes from the first one. I used 4mm coro on the elevons and reduced the cord of the elevon to 1-1/8”. The throws are the same but I added more expo.

You are right about moving pretty fast. It does get tiny in a hurry. Its weird how this engine is so different from the OS. The OS would really unload in the air and get on the pipe where this engine never seems to “get on” The OS sounded really cool when it wound up.


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RE: Yet another DDUST take II - 6/22/2005 6:33 AM   
ChrisSpad



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Status: offline 		you might want to try an 8x7 if its not getting on the pipe. Sometimes, less is more.

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RE: Yet another DDUST take II - 6/22/2005 10:39 AM   
Jbolt


 

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Status: offline 		Ha ha well all I had was an 8x8 or a 9x6. The only 8x7 I had is hidding in the brush somewhere.

I've been running it on crappy recycled fuel so I might try some 20 or 30%. The specs rate the engine to 17k. I'm not sure how far I should push it.

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RE: Yet another DDUST take II - 6/22/2005 8:57 PM   
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Status: offline 		Jay, just an observation. The pipe length on your D Dust looks awfully long. The reason the engine never seems to be "ON" may be due to the pipe length. I race boats as well as fly and we are constantly aware of the pipe length on our boats. It is very obvious when the engine gets "on" the pipe. For instance, my racing 21 marine engine pipe length is 9" from the end of the divergent cone to the glow plug. It turns near 30K RPM. Of course my engine is timed for a pipe so don't expect that from yours, but you should hear it respond. I'd guess that you want to be around 9 1/2". With your setup, that length is measured down the center of the pipe and exhaust header to the plug. Actually, the distance the exhaust flow has to travel to the fat part of the pipe. If you are up to experimenting, start cutting back the header in 1/4" increments till you hear the engine respond. You'll know it when you're there.

< Message edited by John Palica -- 6/22/2005 9:06 PM >

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RE: Yet another DDUST take II - 6/23/2005 12:42 AM   
ChrisSpad



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Status: offline 		i still think an 8x8 is too much prop for a 34 sized engine. My 36 currently has a 9x6 on it, and for a speed plane, thats a good deal of prop. I think 8x7.75 is a typical 40 size pylon prop - and, while the engine is fairly stout, its not going to keep up with a 40 size pylon engine. Therefore, i'd think that the 8x8 is just a bit much for max power. The other consideration versus a boat engine and an airplane engine is the difference in the rpms- the lower the rpm, the longer the total pipe length will be.
Cutting the pipe for max rpms is a good idea, doing so while overpropped will probably result in a header thats just too short.
You can always try it with the factory mufferl and see what your turning, and decide from there if the pipe is close to being tuned properly.
I'd think you'd pick up at least 1000 rpm with the pipe over the stock exhaust.

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RE: Yet another DDUST take II - 6/23/2005 3:33 AM   
Jbolt


 

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Status: offline 		John- you could be right. I pretty much followed Macs pipe tuning info. The length from the plug to the fat part of the pipe is 10.75” The last two 1/4” cuts off the header resulted in no rpm gain so I stopped. Maybe I should cut until the rpms drop? The OS32 I had on the other plane I lost got “on” the pipe nicely. IIRC the header was ½” shorter than I’m running on the ST now.

Chris- I did the break-in and initial needle settings with a 9x6 & muffler. Peak rpm was 15,4. Open exhaust it was 15,8. I put on the 8x8 and still got 15,8 with open exhaust so I figured the props has similar loading. So if I assume the 8x8 would also run around 15,4 with the muffler I do have a gain of 1000 rpms at 16,4

Without getting into all the intricacies of prop efficiency, induced drag etc. etc. (it is a spad after all) an 8 pitch prop turning 16,4 has a theoretical speed of 124mph. A 7 pitch prop would have to turn 18,7. Now if I could get the 8 pitch prop to turn 18,7 we might be getting somewhere.

I believe the q500 props are 8.75x9 and turning at 19k+


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RE: Yet another DDUST take II - 6/23/2005 4:03 AM   
ChrisSpad



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Status: offline 		the speed of the prop doesn't take into effect the prop's lift, only its pitch. Its actually (theoretically) possible to exceed the pitch speed of a prop for a given rpm - due to the lift the airfoil of the prop makes.
Keep in mind that when a plane unloads in the air, 10% or more rpm gains aren't unusual.
According to thrusthp (which isn't the most accurate thing there ever was, i'll grant you that) at 16,400 with an apc 8x8 prop your producing 1.032 hp. With an 8x7 apc, you would spin 17150 rpm to produce the same hp. Couple that with 10% unloading in the air, and your at 19000 rpm - which gives you a pitch speed of 126 mph.
If the 8x8 isn't unloading in the air, and the 8x7 does, your looking at it being worthwhile to try. But, when it comes right down to it, if you really want to know, the only way for sure is to try it with both, and either time it, shoot it with a radar gun, or doppler effect - and see which one is actually faster.

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RE: Yet another DDUST take II - 6/23/2005 8:07 AM   
Jbolt


 

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Status: offline 		Thats cool- how are you coming up with the numbers?

Unfortunately the only thing I have to shoot the plane with will only reduce its speed........

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RE: Yet another DDUST take II - 6/23/2005 3:29 PM   
ChrisSpad



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Status: offline 		the program is called thrusthp - its free, you can download it here:
http://freespace.virgin.net/barry.hobson/software/thrusthp.html

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RE: Yet another DDUST take II - 6/23/2005 5:42 PM   
Jbolt


 

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Status: offline 		Hmmm....I can't get the program to exicute in my puter

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RE: Yet another DDUST take II - 6/24/2005 1:26 AM   
ChrisSpad



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Status: offline 		i've had it on mine for ages - it runs fine for me on xp, and 98 before that. what system r u running?

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RE: Yet another DDUST take II - 6/24/2005 4:54 AM   
Jbolt


 

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Status: offline 		here is the message I get- winXP pro

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RE: Yet another DDUST take II - 6/24/2005 6:29 AM   
ChrisSpad



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Status: offline 		i've got xp home, and it gave me no problems at all. what happens when you click ignore?


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RE: Yet another DDUST take II - 6/24/2005 7:38 AM   
Jbolt


 

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Status: offline 		Absolutely nothing!

I tried the compatability wizard too and it does the same thing. THANKS BILL!!!!

Maybe I'll try it on my laptop.

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RE: Yet another DDUST take II - 6/24/2005 8:01 AM   
ChrisSpad



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Status: offline 		its such a simple program, i can't beleive it won't run. thats weird. If nothing else works, send me an email, and i'll send you the executable.

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RE: Yet another DDUST take II - 6/25/2005 4:50 AM   
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quote:

Unfortunately the only thing I have to shoot the plane with will only reduce its speed........

LOL!

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RE: Yet another DDUST take II - 6/26/2005 5:51 AM   
jmess73



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Status: offline 		Hi, I was wondering if anyone had plans for a coro dust they could share? I just smoked my Dust, tore the engine mount off on a rough landing, I was thinking about making a spad version and I came across this post. My Dust has a Sport Jett 40 on it, and it really screams, but its just a little fragile for my liking.

Jeremy

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RE: Yet another DDUST take II - 6/26/2005 6:18 AM   
RC-Captain



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Status: offline 		sounds like you had the rapier. I may have to get one.

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RE: Yet another DDUST take II - 6/26/2005 6:22 PM   
jmess73



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Status: offline 		whats a rapier?? Is it a Diamond Dust style plane? Mine is definately a Diamond Dust


This pic has my old engine on it, a Quicke Jett 40 with the black air bleed style carb. This carb is for racing only and it has no throttle, way too sick for me, top speed @ 180mph, with no throttle!!!!!! Landings are, shall we say, difficult! This is what probbally led to my broken engine mount.

Jeremy

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RE: Yet another DDUST take II - 6/26/2005 7:36 PM   
RC-Captain



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Status: offline 		RAPIER delta wing plane

Heres a link to one. I'm not sure of the speed but it looks fast as hiccups. How do you fly yours with out a throttle must be kinda of tough.

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RE: Yet another DDUST take II - 6/26/2005 7:40 PM   
jmess73



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Status: offline 		Thats's why I changed to a Sport Jett, it was too hard for me!! The Sport Jett is awesome, if you get the chance to try one I highly recommed it! They are just a little pricey though, I got mine on Ebay for $75.00 what a deal!

Jeremy

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RE: Yet another DDUST take II - 6/27/2005 7:44 AM   
MrGreenSpeed



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Status: offline 		Designed by ChrisSpad
http://users3.ev1.net/%7Ecdjump/main/mydesigns/ddust/gallery.html

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RE: Yet another DDUST take II - 6/27/2005 1:55 PM   
jmess73



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Status: offline 		Thanks for the info, what is the fuse made from 2mm or 4mm? Also how about the vertical stab is it also just 4mm? How fast will it go before it starts to flutter? Has anyone tried balsa evelons and 1/16 ply vertical stabs?

Jeremy

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