Speed Brake Holes

[rmaddy]

This was brought up in another thread.

 

There was a discussion of this topic on the Canard Aviators forum back in August of 2003. Follow this link to read it:

 

http://groups.yahoo.com/group/canard-aviators/messagesearch/11797?query=speed%20brake%20holes

 

Enjoy

[cncdoc]

Thanks Rick! (may I call you Rick? or MR Maddy?)

 

I read the posts there with interest, but I didn't really find a consensus of opinion.

 

I noted two themes:

A. Whether or not holes induced drag.

B. Whether or not speed reduction was the intent of design.

 

My thoughts:

(Digging out Aerodynamic Engineering Studies handbook circa 1975 Purdue University)

A.

1. Holes induce as much drag if not more than flat plate design depending on size, placement and quantity. (Designed to create turbulence in a fluid)

2. Structural integrity of design also depends on size, placement and quantity. (the holes are not the weak area nor are the area between the holes)

3. Plans design "Landing Brake" places maximum stress during steep angle deployment at or near hinge area at extreme outward ends of hinge.

4. Maximum estimated drag advantage over flat plate: 12 - 15 %

5. Worth the trouble of making aerodynamically efficient during retraction: Doubtful.

 

B.

1. Power=airflow=air over wings= lift = nose higher (speed = power x AOA)

Drag=less airflow=less air over wings=less lift= nose lower (attitude= AOA +Drag x power)

 

2. Almost anyway you look at it, to get the nose lower (for landing) you have to lower the airspeed (increase drag/reduce power). The Landing Brake being forward of CG but aft of the canard, allows it to increase the overturning moment and increases the need for control pressure on the canard to maintain a consistent approach slope while slowing the airspeed and decreasing lift.

In an acceleration (powered) descent, or an excessive speed deployment, a "flat plate" landing brake extended with not much less than 60% angle of deflection could theoretically cause more lift than drag, whereas the "holy brake" would still cause more drag than lift.

So holes would help if you wanted to slow down when you are going faster, but won't slow you down faster or make you slower.

So, if Burt wanted the nose low for landings, it took more than an after-thought "landing-brake", to do the trick. The landing brake is integral to the Rutan design that Nat carried through in the Cozy.

 

So in the end, everyone was right..sort of. And wrong, partly.

 

I am glad I didn't throw away my textbooks....

 

Once again an exercise in frugality....

 

Hole? nope.

[LargePrime]

Great job. One point tho...

 

cncdoc said

"The landing brake is integral to the Rutan design that Nat carried through in the Cozy."

 

I belive the Long did not have a belly board to start. I belive it was a plans mod.

 

I was not there but I did read that in the news letters. If so that makes it not integral to the design, right? Also many EZ flyers dont use it after getting some time in the plane, so it does not seem nessary.

[Marc Zeitlin]

I belive the Long did not have a belly board to start. I belive it was a plans mod.

The landing brake was a very early modification to the Vari-Eze - it's mentioned as early as CP #11 in 1977 as a test modification to the V.E.

 

I was not there but I did read that in the news letters. If so that makes it not integral to the design, right?

AFAICT, the Long-EZE always had the landing brake in the design, as did the COZY. CP24 was the earliest mention (I could find) of the L.E., and it discusses the Landing Brake as an integral part of the design.

 

Also many EZ flyers dont use it after getting some time in the plane, so it does not seem nessary.

That's true, although I find it to be very useful in controlling glide path. The only time I won't use it is if I've got a long runway (more than 4000 ft or so) and a stiff headwind. It allows me to land with a much steeper glidepath than without it.

 

In CP11, Burt mentions that the landing brake should reduce the minimum field length for the V.E. from 2400 ft. to 1800 ft., indicating steeper approaches and better spotting of landing points.