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

How Fast is it going?

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Old 09-21-2003, 10:33 PM
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RSands
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Default How Fast is it going?

Can one of you tell me how fast this plane is going? It was approx 100 ft out & 30 ft in the air. Vid is 2.5 meg. Thanks!

http://f1.pg.briefcase.yahoo.com/bc/.../video&.view=l

Almost forgot, the mpg is the vid, the mp2 is just sound!
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Old 09-22-2003, 06:27 AM
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Default RE: How Fast is it going?

download the program from my site www.philsrcworld.fsnet.co.uk
however, thats a long way out for accutate speeds.
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Old 09-22-2003, 06:57 AM
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Default RE: How Fast is it going?

Is that a DD? hard to tell in the dim lighting.

The interesting thing was the rushing air sound, almost like a jet. If that is a DD, I have long thought the exposed engine was casuing alot of turbulance. I would think fairing the engine would give quite a speed increase at the speeds they go.

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Old 09-22-2003, 11:24 AM
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Default RE: How Fast is it going?

OK, I'll bite..

Simply running the audio thru the doppler analyzer gives a reading of 125-129 mph @ approx 15,000 rpm. To be accurate, you need the air temperature on the field that day (I assumed 25 deg C) and the plane should be approaching the microphone (camera) at an angle as direct as possible (don't hit the cameraman!), otherwise you have to figure in a cosine error factor (I used 10).

When I try to measure speed with this method, I always try to record 3 or 4 passes and take the average. A single pass is not very representative.

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Old 09-22-2003, 11:46 AM
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Default RE: How Fast is it going?

Yes, it's a DD. K&B 48 with tuned pipe, turning a 9x10 APC. Max RPM on the ground is 16,400, but I richen it up, seems to actually be quicker in the air with a rich setting. My guess is the air noise is that big square head on the motor I'm guessing it's in the 140 neighborhood. Think swaping the motor for a Webra 50 would make it much quicker?
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Old 09-22-2003, 11:54 AM
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Default RE: How Fast is it going?

thanks Darwin. Your RPM readings may be low, but the speed is about where I thought.
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Old 09-22-2003, 01:24 PM
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Default RE: How Fast is it going?

I think you would get some more speed but not as much as you would by cowling/fairing the engine in. The parasite drag getting quite high at those speeds, since it goes up with the square of the speed (ie. 4 times the drag at 150mph as you would have at 75mph.)

It is odd that a machine built for speed like that would not cowl/fairing in the engine. Seems like a no brainer to me.

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Old 09-22-2003, 01:42 PM
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Default RE: How Fast is it going?

Glad to help.

I'd be curious to see what numbers someone else gets with the doppler on your video. Like Phillybaby said, the program is a free download, and it's pretty easy to use.

By the way, a couple of weeks ago I was using a regular radar gun (not audio doppler) and taking measurements on a clipped-wing Diamond Dust that was running a modified Jett FIRE 50 turning an APC 7.2 x 8.6 prop @ 23,700 rpm on the ground. The pilot is very experienced and gives exhibition demos at RC events with this thing. He was bringing it by the gun about 15 feet away and 6 feet off the deck so I could get the most accurate reading! We had to stand out on the runway, unprotected. Well, I was standing behind the pilot, so at least I was somewhat protected!

("Warning...Do NOT try this at home!!! This stunt performed by a professional on a close course")

Oh yes, top speed was 170, my heart rate was 120 and I even managed to keep my pants dry..

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Old 09-22-2003, 05:25 PM
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Default RE: How Fast is it going?

Shmleff, I'd be concerned it'd add a fair amount of weight or be blown off, or that if it adds any significantly different aerodynamic forces to the nose, it could be bad. Any other opinions on this?

Darwin, Thanks again. Can you tell me what settings to use on this spectrogram thing, and if it's not too much trouble, could you explain the temp and cosine error correction? I'd love to hear the dust you checked, would make a great "you've got mail" greeting for at work
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Old 09-22-2003, 05:35 PM
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Default RE: How Fast is it going?

ORIGINAL: schmleff

It is odd that a machine built for speed like that would not cowl/fairing in the engine. Seems like a no brainer to me.

Schmleff
I don't think Dusts and the like are really built for speed, they are just "cool-fast" planes that guys can slap a good sport engine in (like the K&B .48!! great to see one in a Dust!) and go at a pretty good clip.
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Old 09-22-2003, 07:51 PM
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Default RE: How Fast is it going?

Hi chuck! Question I've always wanted to ask, and I'm sure others are curious about to Every time I look at your avatar it gives me the hebejebees. On one hand, I think that with those creepy eyes, and that big forehead and goofy hair it looks like it's one of those puzzles where if you stare at it long enough it'll transform in to something totally different, but then on the other hand it's so damn ugly you can't stare it that long, so it's gotta be real! So who is he, and why's he on your avatar? I agree with you on the Dust. It sounds and looks cool, is far fast enough for most (including me) to be thrilling, and the best part, it's cheap and easy. Speed for the masses!
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Old 09-22-2003, 08:01 PM
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It's a chroma-negative taken from a picture of me on my wedding day. [&:]
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Old 09-22-2003, 08:13 PM
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Whoops! Well lets be thankful you don't walk around in chroma negative!!
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Old 09-22-2003, 08:16 PM
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Default RE: How Fast is it going?

Nah, just had to throw that out there...

You can read more about My Avatar, Bug-Eyed Earl here.
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Old 09-22-2003, 08:31 PM
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Default RE: How Fast is it going?

LOL - I was really hoping you were gonna say that!
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Old 09-22-2003, 08:33 PM
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Default RE: How Fast is it going?

You could make a glass shroud over foam, remove the foam and use screws to fix it to the plane. I would think it would add less than an ounce. I bet it would get you 15+ mph, shooting from the hip. The engine sitting out in the open should account for the majority of parasite drag on one of those things.

if they were not so dang spensive, I would get one one and try it myself

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Old 09-22-2003, 09:08 PM
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Default RE: How Fast is it going?

A little dry & definately twisted, but funny. That is if you call laying unconscious in a garbage can all night funny! Thanks!
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Old 09-23-2003, 08:10 AM
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Default RE: How Fast is it going?

At first I thought how would you measure the speed from a video (please keep in mind I am a n00b to speed and planes) Then my general scientific knowldge kicked in and thought you might be able to determine the speed from the sound, just the way the hubble determines the speed of galaxies, except the hubble uses light. Yes I know Doppler came first, thats where Hubble got his idea.

Where would I get this program.
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Old 09-23-2003, 12:12 PM
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Default RE: How Fast is it going?

Schmlef, I was thinking of something similar, maybe remove the motor and carve up a foam piece that would fit over it, then glass it and melt the foam. It is an interesting idea. I'm still concerned that doing so might create a lifting force on the nose, and cause a serious trim problem or worse. Guess no guts no glory. I'm waiting on a pipe for the Webra, so will have the motor off, and going from the K&B to the Web is gonna require some nose weight anyways, and I do have some matching flourecent yellow epoxy pigment, hmmm.... Anybody else think this is worth trying??
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Old 09-23-2003, 04:34 PM
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Default RE: How Fast is it going?

you can get the program from my site under the speed page. theres some info on how to use it and a link to the site i got it from with ALL you'll ever need to know about it.

having a canopy is a good way to reduce drag, 17mph is the figure i heard for engine + pipe steamlining, my 40 size Magnum can keep pace with its 50 size brothers thanks to it's lower drag.
go for it. another possibliity is the way the Outlaw does things, engines on its side faired into the wing section, perfect for side exhaust engines as the pipes right down the center
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Old 09-23-2003, 06:32 PM
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Default RE: How Fast is it going?

It is definately worth it... something like that is almost always worth the trouble... unless you're flying 3D of course...

Use plenty of wax on the foam... try to fill all the pores: that way you'll get a nice smooth cowl outside and inside. 2 layers of very light cloth should be enough.

When everything is dry you can remove most of the foam by hand usually (when you waxed it thouroughly)... if anything sticks, then just use some solvent to kill the foam...

I've made cowls without waxing the foam, and removed all of the stuck foam with some solvent... that works too, but it's messy: the inside of the cowl is rough and takes some cleaning to get all the sticky goo (molten foam) out...
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Old 09-23-2003, 11:52 PM
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Default RE: How Fast is it going?

Thanks guys, I'll give it a shot. With the Webra and a cowl, maybe this thing will turn in to something halfway respectable in terms of speed. Do you think the cowl should go over the pipe as well? I'm thinking cowl the motor and run it back over the top of the pipe, then blend it back down to the fuse with maybe an inch or two of it sticking out so I've still got good flow over the vertical stabilizers. On the front, since it's side exhaust, there's going to have to be an accomidation for the header pipe to come out and go back in. What about the head - how much will need exposed for cooling? Air intake? Will be some work, but may even turn out looking halfway cool!
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Old 09-24-2003, 04:04 AM
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Default RE: How Fast is it going?

have a look in the pylon section. you can fully enclose the engine if you want if you get the cooling right.
remember one thing...
hold your hand out in front of you.. now blow with your mouth wide open. farily warm yes?
now blow with your lips together.. cold..
concentrated jets are better than gaping great holes when it comes to cooling. no good having the air floating around in a big chamber, better to have it all close fitting and a small amount of air forced close to the engine and pipe.
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