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This thread is privately moderated by A Useless Geek, who may elect to delete unwanted replies. |
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Thread OP
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Question
How do I go 300 KPH with foam?
So, I'm thinking about a stupidly fast foam plane for the summer. I've seen folks going pretty fast with Multiplex Funjets and such, but my target is 300 KPH, about 186 MPH. I'm not interested in any kind of hotliner, since those things just look too ugly to me. I want to build -- or at least assemble -- something jettery with a single motor and a single prop. Not an EDF, not a turbine. A prop.
It's fairly easy to get small stuff to go relatively fast. I built a perversion of a Pinkstar with a Blue Wonder 3000kV motor that does in the 60 MPH range (haven't instrumented it yet), and that's not even trying very hard. (60 MPH doesn't seem very fast outside, but in the golf dome it's at the limit of my abilities.) Lots of folks have pushed scratch Funjet clones of various types to the 200-250 KPH range. What does it take to get over the cliff and hit 300? Suggestions welcome. |
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Thread OP
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Well, that's what I did. Start with insanity, add a generous helping of LiPo, stir in maximum motor, and sprinkle with EPS. Flavor with WBPU and nylon sheer. I still don't know how to go about this.
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Get a 100 amp ESC, a big wattage motor, high KV, small prop (6 x 4 or 7 x 4 or so) and at least 6 cells. You should break 300 kph with that combination.
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Latest blog entry: Viper + Draco 4K FPV
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300 kph Foam Objective
There are some very fast planes in various threads. The speed freaks tend to take the foam ARF and put helicopter motors in them. Sometimes the fit is prefect and sometimes heavy modifications are needed. They tend to be testing the ability of the foam planes to keep their wings on during a high speed pass. The flights are often around 4 minutes maximum and more than a few batteries get puffed. I wonder about the sanity of flying an RC model with original cost of less than $100, spend another $150 to gear it up, and then risk the whole mess hitting the ground at 100 mph or faster. If you want, I will hunt down one of the threads that seemed to be focused on "more speed" desired and post the link. Very popular planes with plenty of variety in the line. I am sure the same parts can be used for your objective if you don't want to speed demon a Rare Bear, Mig-15, or one of the other popular choices.
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Last edited by Tsavah; Feb 12, 2013 at 04:30 PM.
Reason: Spelling ...
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Thread OP
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Yeah, the Skyartec Skyfun (sold by Hobby King as the "EPO Park Jet") is a favorite target of this kind of abuse. Guys take a $15 airframe and add $300 worth of junk, not to mention many hours of labor, to try making a hypersonic aircraft. I'd kinda like to start with something with the insane speed capability to start and move up from there.
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My brother built a funjet with the setup proposed by www.dauch.fr (french guy).
It is a monster. We even hit 400 kph once ( downwind on a windy day ), it is well over 350 without wind:
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Funjet - Too Fast
I suspect at least a few speed freaks know there are a lot of Funjet video on Youtube and most of those are about Funjet modifications for excessive speed. Needless to say, more than a few of those video include some crashes and damaged 4 to 6 cell Lipo battery packs. The other damages are discussed also.
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Thread OP
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Wahoo! Pretty stupid fast, I'd say. Perhaps I'll start with a Funjet all 'glassed up and everything. A couple of guys I fly with have done fully 'glassed Funjets, but they haven't gotten close to the kinds of speeds I'm looking for.
Oh, and at that speed a crash equals total destruction of the plane and all its complement of equipment, not just the batteries. You wouldn't be able to recover anything after impacting the turf at that rate of speed. |
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Our funjet is a standard funjet ultra airframe without glass or anything. You do not need to reinforce it. It is far more important to have good servos and linkages.
The plane tracks very well and in spite of the weight of the 6s lipo, it is not critical to land. But it is important to launch with half power, otherwise you get a half roll to the left because of the torque. Because of the high speed and the small size, i need some time to relax after each flight and you need high visibility scheme (and weather). You can get a really fast and more docile plane on a 4s lipo. |
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Thread OP
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"Docile" is not part of the vocabulary I am using for the 300 KPH project. <cough>
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You are right. You can`t go 300 plus and keep calm and relaxed. Forget docile.
Theoretically, you need a 7``(pitch) prop running at around 28000rpm in flight to exceed 300kph. Here is a chart for calculating speed out of rpm and pitch: http://www.acteurope.de/Steigung_Drehzahl.pdf Steigung means pitch and Drehzahl is rpm, Vortrieb is speed. Maybe the increase in rpm in flight equals the drag of the airframe ( if it is not too draggy). |
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Last edited by Thomas B.; Jul 01, 2013 at 02:54 PM.
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Thread OP
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What I need to do is look at APC's best high speed props and calculate max RPM based on prop diameter, then select for best pitch speed. I still keep hearing from people saying they're doing 300 KPH and better, but the motor/battery/prop numbers don't seem to come out right.
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Thread OP
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Yeah, I'm not married to APC nor Windsor. Graupner has some carbon fiber stuff that might be more suitable than anything APC has, don't they?
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