Replies to This Discussion

Assistant AdminPermalink Reply by Joshua Johnson on May 12, 2011 at 9:58pm

I want a strong brushless motor because I plan on adding extra electronics to it. I'm thinking off adding a camera and an auto pilot last. I need 3 servos and a 40A brushless ESC a a brushless motor. Also a 11.1V Li-Po Battery and a 4 channel rc.

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Permalink Reply by arashi on May 13, 2011 at 10:47am

What fun is a UAV with a 3 min flight time?   Those inefficient ducted fan models have short flight times to begin with.  It will be worse after adding more weight.

 

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Permalink Reply by Gerry Lichter on May 13, 2011 at 12:07am

It's been said before, but you're also going to want to buy a cheap durable RTF trainer like the Easy Star to get you in the air. If you already have a TX/RX then an ARF would also work.

 

Imagine trying to learn to drive on a car which flips over if you go slower than 60 miles an hour.

 

I don't know how familiar you are with the F-117 but you should read about what a nightmare the real thing is to fly even with fly by wire assist.

 

http://en.wikipedia.org/wiki/Lockheed_F-117_Nighthawk

 

How much modification has been made to the kit design I couldn't tell you, so it's impossible to know if the kit you have will have a similar level of difficulty. When you start adding weight to a airframe, you change it's center of gravity, so you'll have to be careful about where you put the increased payload to counteract the increased weight of the larger motor(these size/weight increases can easily snowball.

 

A plane with dihedral and a center of gravity below the wings will be easy to fly and stable. If you want a UAV for photography, you want something that moves relatively slowly, which is bad news when your airframe has a high stall speed.

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Assistant AdminPermalink Reply by Joshua Johnson on May 13, 2011 at 9:12am

The c.g is right exactly where the motor sits. Adding a stronger and heavier motor wouldn't affect flying correct?

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Permalink Reply by Gerry Lichter on May 13, 2011 at 10:20am

Honestly I couldn't tell you. I don't know that much about any of this stuff. Some reading which may or may not be relevent:

http://en.wikipedia.org/wiki/Center_of_pressure
http://en.wikipedia.org/wiki/Aerodynamic_center

I can picture the vertical stabalizer(V tail fins) location being a compromise determined by the center of pressure for the intended operational speed. If you modify the speed by increasing wing loading, the center of pressure may no longer be ideal?

I have no idea how big of a concern this should be. I generally have a "try it and see what happens" attitude to the concerns of worry warts(the role I'm playing for once).

The only reason I reason I bring it up at all is that with airplanes, stealth geometry generally comes at the expense of aerodynamic performance. What, if any, changes have been made to the model to increase it's stability from the real thing IDK, but if it didn't come with an autopilot for stabalization, it stands to reason that it must be possible to fly without one.

Once again though, the general consensus is that you should always learn to fly on a cheap durable trainer plane like the EasyStar and only then after you've put in the flight time risk crashing your expensive dream plane. Fewer tears that way. Same reason your first motorcycle shouldn't be a new supersport.

If this type of stuff is interesting to you, I'll share with you something I heard: that is that someone strapped an airframe to the roof of their car as a makeshift wind tunnel. Cool trick IMHO.

Regards,
-Gerry

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Assistant AdminPermalink Reply by Joshua Johnson on May 13, 2011 at 11:10am

It's made out of the same styrofoam type material the easy star is made out of. I'm researching more on the aerodynamics on it.

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Assistant AdminPermalink Reply by Joshua Johnson on May 13, 2011 at 11:20am

If I upgrade the motor and the fan my flight time will be roughly around 8-10 min.

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Permalink Reply by Gerry Lichter on May 13, 2011 at 11:25am

This is probably a dumb question but did you account for the drag of the airframe with that estimate? It sounds like you've got this covered, but it never hurts to ask.

 

If the cost and durability is the same as the EasyStar, the learning curve would be steep but all other things being equal: sometimes the tool you have available right now is better than the ideal tool which you don't. Time is money and all that.

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Assistant AdminPermalink Reply by Joshua Johnson on May 13, 2011 at 1:30pm

Yep I accounted that to. The airframe itself is very light weight but still offers lots of protection. One thing I'm gonna have to do is cut a section off the top and make some sort removable piece so I'll have access to all the electronics. Idk if I should use magnets like I have on the door underneath the motor and fan area.

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Assistant AdminPermalink Reply by Joshua Johnson on May 13, 2011 at 1:35pm

I also want to reenforce the V tail wings and the front wings. Got any suggestions on this?

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ModeratorPermalink Reply by Gary Mortimer on May 13, 2011 at 2:57pm

Keep adding more weight and you be able to fly with a much higher  V_S 

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Permalink Reply by Ritchie on May 13, 2011 at 3:34pm

Link the kit

Put the in kit specifications into the spreadsheet here to check viability. Everything is explained within it.

If everything stays green then it will be possible to do what you ask (although it might not be easy).

If you see yellows you are in for a fight but it is possible.

If you see red then the components pass the flight limit of 0.15 Oz/in (67g/dm).

 

Personally I wouldn't recommend using your F117 straight away as a FPV setup or a UAV as its your goal so crashing it won't be fun. Get a simple safe plane to practice flying while you build the F117 that way you might actually have a chance to control it when it goes south.

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