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Old Jul 11, 2004, 07:54 AM
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How fast can a Micro(EDF)jet go? / down and dirty composite construction

Hi All,
After flying the Minx with an auw of 18 oz. and 19+oz. of static measurable thrust I started getting the idea in my head it should go faster… The first setup used older 1500 Tanic batteries and the stock foam tail cone with a 45mm exit. The video showed a Doppler reading of 85 to 90 some mph so; I started tweaking it for more speed at SEFF to see if it could be improved. First was a battery upgrade to the new Tanic 1550 12C’s. That bumped it up some. Then I had a set of tail cone inserts made up to neck down the exit from 45mm to 42mm, 40mm and 38mm. Each one bumped the speed up until I got to the 38mm. That showed a drop in both acceleration and in top speed. When I moved back to the 40mm the Minx really cooked along great. But… always those buts, it was definitely at the limit for the airframe, ducting and power setup.
So what’s a mad man to do……

Build a real Ultra Minx…… One just built for speed. What got in my head was a cross between a Stinger and a Minxish EDF…. so

From the Minx Mk2 I liked the basic profile and the control layout but the rest had to change to increase the speed potential. The frontal area had to be reduced, the ducting although efficient for it’s intended flight envelop would be getting in the way and the wing needed to be cut back and thinned even more than I had on my first Minx… Years ago flying 1/2a pylon taught me speed comes from the smallest, lightest and most powerful planes. Very easy to say…a lot harder to do.

Before I go on with this and show ya what I’ve been working on does anybody out there know what the speed potential is for a 50~55mm EDF?? There must be some chart out there…. I know it depends on how fast it’s being turned…..and then the drag losses, so just figure really really fast on the rpm and hopefully a slippery airframe.

Anybody


joe
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Last edited by wireit; Oct 13, 2004 at 04:12 PM. Reason: me...and not enough coffee
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Old Jul 11, 2004, 09:17 AM
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Wildwood, Florida, United States
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Hi All,
I'd like to make a few things clear from the outset. This is not a Minx and I have no intention of or nor have I copyed the design. The only commonaility (sp) is in the "look" of the profile and that is different in true size and shape. I like ejf and don't want to rock the boat. Just to be clear, I have no intention of kitting this... I'm doing this for fun and to see how fast I can get a micro jet to go... Thats all.

Ok on with the stuff,
This thread will be about two things. First how fast can we make this stuff go and second, a quick basic method for fabing composite components.

The airframe I've come up with is as thin as I can get it and still fit a 3s battery pack and just tall enough to get the fan, wing and controls in.. so as you look this over if you see a way to compack this more toss in the ideas and I'll try to mix it in to the structure. Building a new plug and mold to add in changes is not that great of an expence... I have the stuff, work with it on an off all the time so this could evolve..

The wing is a new thing all together, cut back to about 24" and about a 1/4" thick at max cord.... it's thin. Building it strong enough and keeping it straight will be a trick so I'm thinking it will evolve also.

Here are a few pictures of the plugs. They were built about three weeks ago and have been molded off of allready.

comment.... thoughts??

joe

Robert, if you feel the need after you see all of it pm me.
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Last edited by wireit; Jul 11, 2004 at 09:19 AM. Reason: me....
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Old Jul 11, 2004, 09:20 AM
310mph Kolibri T25 Swist
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uJet does 120km/h @ 150watts. (clocked)
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Old Jul 11, 2004, 09:29 AM
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I have to say that after reading your comment in the contest rules post this did peak my intrest. Where are the pictures?

120km/H=74MPH?

Is that conversion correct?

Ted
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Last edited by TGoodwin; Jul 11, 2004 at 09:31 AM.
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Old Jul 11, 2004, 09:30 AM
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Fuse and wings in raw balsa

Just balsa
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Old Jul 11, 2004, 09:33 AM
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Sealed and surfaced

Just sealed and smoothed
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Old Jul 11, 2004, 09:40 AM
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75 mph is not going to get it.... we can go faster than that allready.

I'm going to use a Vasa 55 for the first one, though the fuse will except a microfan using a block glued to the fan houseing.

I have some numbers for the Vasa 55 if someone can match the thurst level and get a poss efflux speed.

I get 665 grams of thrust right now and gettin above 700 should not be far off.

anybody??

joe
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Old Jul 11, 2004, 10:08 AM
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How do you do doppler video speed checking. I understand about doppler but what software do you use to check the speed of a model on video. I am about to build a go fast micro jet as well. I will convert a small F16 foam pusher but at first look it will not fit a 50mm fan. I think 40mm or maybe 45mm if there is such a thing will be all it will take.
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Last edited by hornant; Jul 11, 2004 at 10:11 AM.
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Old Jul 11, 2004, 10:33 AM
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hornant,
I don't have the software to do it myself.
I posted the video and asked if someone would check it for me. I'm sure you could do the same. Glad to hear your trying to get some real speed out of the micro sized fans too.

Good luck
joe
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Old Jul 11, 2004, 10:49 AM
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With the Vasa55 you should be at about 42kRPM for the 665g of thrust. This would make for about 127MPH velocity. In Henke's example they have about 100MPH. A flight speed of about 70% of exit velocity is typical for a clean model. If it's really clean you can go faster by reducing the exhaust diameter. The above assumes exit area equal to annulus area. My guess is that henkes model had reduced exit area.

Greg
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Old Jul 11, 2004, 10:58 AM
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I found this chart in my files .... I have no idea where it's from.... I collect stuff like this when I find it. Anyway if you check out the line for the micro fan, it seems to track with the doppler info. I'm guessing now the yellow Minx is about 25 mph less than the efflux speed at the thrust level its at. 1.2 lbs of thrust and right around 100 mph. The Vasa 55 shows about 125mph for the 1.5 pounds of thrust I'm getting now. Maybe a smaller, slipery aircraft will better the 20% loss of speed with the old airframe.

joe
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Old Jul 11, 2004, 10:59 AM
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chart

Heres the chart
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Old Jul 11, 2004, 11:08 AM
310mph Kolibri T25 Swist
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question was: How fast can a Micro jet go

MPX uJet 120km/h.... prop foam plane
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Old Jul 11, 2004, 11:16 AM
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Greg,
your very close, I was taching 41400. The minx was using a reduce exit also. But not at 150 watts. I was pushing 280 watts in the minx. If anyone can confirm this chart... it would be good. I don't know if it's based on test data or curve fitted with a few data pints???

joe

BTW, For those that don't know the fan in the pictures is a Vasa 55G same as old V55 with the streamlined shroud. The fuse is setup to fit it perfectly.
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Old Jul 11, 2004, 11:21 AM
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Hi henke,
Thanks for the input. I have a microJet EDF that turns about 160 km/h now and I'm trying to improve on that... But with an EDF not a prop.

joe
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