DR-1 (Sands): Builders Group - Page 183

Tim Plunkett · 26 August 2007, 10:13 AM

The lack of a vertical stab along with the full moving rudder give the plane a great yaw rate. There of course is no load feed back through the rudder. The faster you go does not increase the load of the rudder bar. As you know there have been crashes due to a failure in the rudder. You must be careful when applying rudder forces as it is easy to put a large force on the rudder without knowing it. The short fuselage does not offer much resistance to yaw. The pitch stability is soft. The horizontal stab may be too large for the elevator to overcome. But again due to the short fuselage it will do the tightest loop with the smallest g force of any aircraft I have flown. It the Pitts a loop is a 4g maneuver, in the DR1 it is about 2 because it flies itself right around the loop. I suppose because the wings generate such high lift at low speeds and the location of the center of rotation in the pitch axis .Because the airfoil shape does not lend itself to inverted flight rolls must be of the barrel roll type. You can fly upside down but not inverted.

gipsymoth236k · 26 August 2007, 10:36 AM

Regarding AUTHENTIC design of the Dr.I affecting aerodynamics and handling, I wonder if anyone has yet built a reproduction Triplane with a +4.7 degree horizontal stab incidence, and lighter-built tail tubing wall thicknesses, as is given in the original documents?

Anyone?

Regards, Gary Sewall

crankcase · 26 August 2007, 12:12 PM

Quote:

Originally Posted by Tim Plunkett

You can fly upside down but not inverted.

Tim,
Not being a pilot or an engineer, I don't quite get your last sentence: does the difference between flying "upside down" and "inverted" have to do with the angle of attack?
CC

Tim Plunkett · 26 August 2007, 01:09 PM

I am an Aeronautical Engineer. When I taught Aerodynamics at Embry-Riddle some of my students had trouble with this concept. When I flew with the Airlines some of my Co-pilots did not get it either. It is really quite simple. When you are inverted you are flying on the bottom side of the wing. If the airfoil is not symmetrical( as in the DR1 ) it with fly different because of the difference in lift being generated for the same angle of attach. Maneuvers such as inverted level flight, outside loops, slow rolls, 4 pt rolls require flying on the bottom side. At the top of a loop for example you are not inverted, you are up-side down as in a Barrel roll where you are still flying of the top side of the wing. The DR1 airfoil is concave on the bottom and I doubt that you could fly inverted very well because you would need a very high angle of attack with resultant very high inducted drag. However with it's high lift wing it is quite happy to be up side down. If you are up side down in level flight and indicating 1 negative g then you are inverted. If you are up side down and indicating 1 positive g then you are not inverted. To most pilots this distinction means little, but if you are flying aerobatic are trying to pass my aerodynamics course it is a need to know item. I hope this helped instead of confused.

Sgt Pepper · 26 August 2007, 09:22 PM

Finally got the cowl back from the dry cleaners.

crankcase · 27 August 2007, 03:21 AM

thanks tim,
that was very clear. i think i'll stick to the "straight and level", tho i did enjoy the one time, years ago, when i was taken up in a zlin by the chief pilot gheorghe militaru (at that time senior pilot of the romanian aero club) and was treated to rolls and looping. (sadly, gheorghe died in a flying accident some time after while ferrying a plane from germany -- a great loss).
CC

Jim Bruton · 27 August 2007, 10:23 AM

I appreciate the information Tim. I know I plan to do aerobatics in my DR-1. Establishing the boundaries is key.

Jim

Tim Plunkett · 28 August 2007, 07:08 PM

I believe that my tail incidence is about 5 deg by eye balling it.

gipsymoth236k · 28 August 2007, 11:31 PM

Tim,

What set of plans did you use for the approximate 5 degrees of horizontal tail incidence?

Regards, Gary Sewall

Jeff Brooks · 29 August 2007, 04:22 AM

Quote:

Originally Posted by gipsymoth236k

Regarding AUTHENTIC design of the Dr.I affecting aerodynamics and handling, I wonder if anyone has yet built a reproduction Triplane with a +4.7 degree horizontal stab incidence, and lighter-built tail tubing wall thicknesses, as is given in the original documents?

Anyone?

Regards, Gary Sewall

Gary,
I have often seen washers stacked under the front of the horizontal stab to accomidate some adjustment to the flying charactoristics. Why wouldn't they have built their plane to the original 4.7 deg and adjust from there? I understand the lighter wall tubing part.. it's hard to find!