S

Stewie

Well Known Member
Patron
Hi all-
Had an EAA tech inspector come over for a midway inspection recently. He is an old-timer, ex-racer, and has built a couple of RV4s. He had put together a list of RV4 lightening mods including drilling holes in the disc brakes as is typically seen on motorbikes, etc. Just curious if anyone has any experience or informed opinion on this.

Eric
 
Holes

Check out the new Carbon Cub from Cub Crafters , it has holes in the disc . Maybe Randy L can give some input on this.
 
I think I'd be concerned that if you wore the brake lining down to a rivet head and it caught one of the holes, it could break/rip/tear the pad and then... no brake at all. Food for thought.....
 
With pants on I would say that any gain in cooling would be minimal. Then you would need more pressure to be applied to get the same braking action. That would generate more heat. Heat that could not be carried away. If I had rotors in the free airflow then I would go for it.
 
saving weight

I have drilled rotors on my car and I think they are pretty good and help in the mountains keeping the brakes cooler. On a plane looking to cut weight, I think I would just not drink a soda or eat a sandwich before the flight.
 
Clarification

Hi all, thanks for your comments. To clarify, these holes are for lightening not braking performance. By my calculations (16 evenly spaced 7/16" holes) at 8gm/cm3 density steel weight, savings would be 2 ounces per wheel. Not bad...
 
You would be removing approx 2.40 sq in of braking surface area X 2 rotors. Aircraft brakes are pushed to the limits. There have been many brake/wheelpant fires to prove it. My rotors gray paint turned brown 1-2" from contact area after 10 hrs and all of my flights to that point were at <50F, no pants and no hard braking. Imagine what it will look like this summer with pants on now.

I would consider cloth seats vs leather or painted interior vs leather/plastic for lightening. That is just me though. That is the nice thing about building your own experimental.
 
My experience with automotive brakes says that, it will not change your brake performance, including cooling. In other words, the brakes will not run cooler. It will not help with disipating gases because modern brakes pads don't need the gas paths. It will, however, introduce stress concentrations in the disk, so if you do it, I would look carefully at the brakes often. Not enough of a riskto say don't do it, but something to think about.

In my opinion, it is not worth the weight benefit, but that is just me.

Tim
 
Two ounces? Consider eating one less taco for lunch. ;)

I have always been amazed at just how small and light the brake rotors are on our airplanes, considering how much energy they have to take to get us stopped. I'd be hesitant to simply start drilling holes without some real engineering study. If you read the daily accident reports from the FAA, more mishaps occur during landing roll out than in any other phase of flight - brakes are a primary control dung that phase - I wouldn't skimp on them.

Paul
 
Diet?

Two OZ... why don't you remove the passenger seat cushion that weighs at least two POUNDS!
If you try it we would all love to hear how it works out though! It is EXPERIMENTAL after all... have fun!
 
I know little about brakes... However, we are looking at alternative brakes (from Cleveland) to save weight on the RV-3, and 99% likely to use Beringer - who not only do aircraft brakes, but also motor sport.

Firstly, their aircraft discs do not have holes.

Secondly, they were keen for us to use the "high energy" brakes for an RV. We will not, since it negates the weight savings, so might as well use Cleveland. What is of interest is that their standard brakes have Energy Absorbtion significantly better than the Cleveland (144K ftlb v 117.5K). Now look at FAR 23.735 and my calcs show all OK for an RV-3. But for the 2 seat RVs, I reckon the standard Cleveland brakes do not meet FAR 23.735.

This is not an issue for those who use brakes sparingly. Those who post videos on here ;) showing "short landing runs" that are really an exercise in how hard one can press the brake pedals (rather than showing a decent approach and landing technique) might be in for a nasty surprise :eek:

So then drilling holes on the discs just reduces this energy abosrbtion (KE) value further, as well as the torque available :mad:

My suggesiton would be, if you want light brakes, do it properly and get a lighter set than the Cleveland, but use as designed. I suspect when you see the price, you might decide to stick with Cleveland though :D
 
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