Doc Austin

My team flies in Florida, which is a beautiful place for about 9 months out of the year, but in the summer the heat is absolutely brutal. It isn't unusual to see us out in 92-95 degree heat hammering on our Mini Ultra Sticks and Ultra Stick 25Es. Since we aren't smart enough to throttle back a bit when conditions dictate a litle restraint, our batteries tend to run a little hotter than we like. I don't think they get so hot that we damage them, but the cooler you keep a Li-po, the better it's going to perform and the longer lifespan it will have.

The Mini Ultra Stick and Ultra Stick 25E have enough holes in the firewall for sufficient cooling under sane conditions, but the Florida wildmen need a little more. We could open up the firewall a little, but that would weaken it. There also isn't another good area to cut an intake hole without sacrificing some strength, so the only place we could look at was the battery hatch. A scoop would work really nice, except the drag could possibly pull the hatch off in flight. After a bit of tinkering we settled on a NACA duct. These produce good airflow with very little drag penalty. Since the hatch angles slightly upwards at the rear, this also adds a little bit of ram effect, but not enough to rip the hatch off.

As you can see in the photos, we plugged the forward lightening hole in the hatch (which actually strengthens the hatch) and cut a nice triangle out for the vent.




Then, we built up some sides for the piece we just cut out, and glued the whole thing to the bottom.




We have tried to cover the finished hatch and ventwork with Ultracote before, and it's too much work, so now we cover the hatch first, paint the ventwork with black dope, and then glue it on the bottom.

On the 25E, there is a lot of stripework, and we were loathe to peel it off just so we could measure and cut all the pieces out and then have to line them all up while recovering. It was a fairly simple matter to remove the red Ultrakote from the front of the hatch, do the work, and then put it back on. This way, the scheme remains unchanged, we saved a lot of work, and the finished effect looks almost like E Flite built it that way.



Again, there was no need to out think ourselves here. This is a simple, effective solution. The batteries don't come out of the plane with icesickles hanging off them, but they do run noticably cooler than before. We haven't put a temperature guage on them, but before they were uncomfortable to hold, and now they are just warm. I'm guessing 10 degrees difference or so, but we'll get some readings next time out.

Richard D Bahmann aka/Wrongway

My Feedback: (42)

I love it Doc. That looks like it has the angles of a NACA scoop. The NACA inlet uses aerodynamic principals to creat a low pressure to draw air in more than just a hole. Did you free hand it or use a method?

Richard

Doc Austin

That's what we were going for, so at least it looks right.

Used a straight edge ruler and eyeballed it. We gotta do things exact. We're a high tech operation here.

Richard D Bahmann aka/Wrongway

My Feedback: (42)

If interested here are the numbers.. I want to look at making some as air inlets for the cabin on giant scale. I just never thought of balsa, was always thinking fiberglass.

http://www.wisil.recumbents.com/wisi.../naca-duct.htm