Triplane flat turns

[baldeagle]

Not to beat a dead horse, but having been presented with the opportunity to fly a Fokker Triplane this past weekend, I decided enroute to time the rate of turn banked and flat. A 360 degree turn in level flight without banking took about 35 seconds, and with maximum bank (maybe 70 degrees) it took just under 20 seconds. If I let the nose drop for some extra speed the numbers were about 30 and 15.

[greenknight]

Thanks very much for carrying out these measurements and posting the results. *Topics *involving the handling characteristics of the old planes are very interesting to me.

A couple of questions:

(1) Approximately what entry speeds did you use?

(2) For the banked turns (or at least the first scenario you mention that took about 20 seconds to complete the turn) did you maintain altitude and hold a pretty much constant bank angle?

I'm curious to see how this performance compares to the turn rate for a typical lightplane "steep turn" such as flown on the FAA exams, using recommended entry speeds from the POH. *

I will NOT be attempting any flat turns in the club C-172 however.

Thank you

[CptRoyce]

BE- Interestingly enough, several months ago I did some analysis on the turning circles and turning times of these old machines, based on their wing loading factors and speeds.
At 40mph( I don't know if that is a real world possibility, I made an assumption) the Dr1 would turn 360 degrees in 19.19 seconds. Apparently that has held true by your very fortunate opportunity to fly a "Dr1".

[baldeagle]

Entry speeds were at cruise, about 87 mph. Timing was from wings level straight ahead flight back to same. 40 mph would be too slow, I did pull until nibbling on the stall, but in a steep bank pulling Gs that would be a bit higher.

[CodyPaul]

What engine was in the Dr I you flew? Was wondering if it was a rotary engine or a modern one and how that might affect the results you obtained.

My question exactly Cody. The Rotatary had a load of torque in one direction. So much so that a cadet would often ground loop.

[stephen]

Two of the three DrI's at the Dayton Rendevouz were powered by authentic 110 hp Le Rhone's... did you get into one of those, BE?

Also, were you at low altitude during your tests? You said you entered the maneuvers at cruise speed... would combat speed have been much higher than 87? The DrI could only do around 90-95, couldn't it?

[Alan]

This is great info, BE, thanks for sharing it.

Also, given the quirky nature we've all read about, did you attempt a snap-360 turn as is alleged by several accounts? *I understand that might be pushing things a bit....

Also, as MvR has said, did it climb really well?

[baldeagle]

I haven't flown a rotary-engined Tripe, Brian's airplane has a 125hp Warner radial, rated hp is at 2050 rpm. The 110 LeRhone is rated at about 1250 rpm I believe, and obviously turns a much bigger prop. The Warner is about 440 cubic inches, the 110 LeRhone about 800+ cubic inches. The rotary-engined Triplanes at Dayton could easily run away from me, and outclimb me, though Brian's airplane was no slouch in climb. Never timed it though.
Brian's plane does have an airspeed indicator in it, which seemed to be pretty accurate. At full throttle it would show over 100 mph. I think slow is a relative term-- when I used to fly the Warner Triplane at Rhinebeck back in the '80s I had heard all that stuff about how slow it was and hard to run away from a fight. So one day I went up high, pulled the throttle back, and nosed over into a vertical dive. That one had a good airspeed indicator on it also, and it was accelerating through 150 mph so fast I couldn't believe it, maybe a few seconds, with the throttle back! I immediatly pulled out so didn't go much over 150. That seemed awfully fast to me for a "slow" airplane, but I think you have to consider how fast they dove in other airplanes. I believe I read somewhere that the SE-5 pilots would hit 200 mph in dives, so in comparison the Triplane would indeed have been slow, and that's what the pilots would have been concerned with, not how fast but "am I faster?"
As far as torque and the rotary engine, this is somewhat misunderstood. A "normal" airplane, Stearman, AT-6, P-51 requires right rudder on take-off and climb, it wants to turn left, because of torque and p-factor, and swirling slipstream. The rotary engined aircraft have the reputation of turning more quickly to the right, but that isn't quite accurate entirely. The spinning mass of the engine imparts gyroscopic force to the equation, which reacts at 90 degrees to the force applied to it, so that in a level right hand turn the nose tries to drop, and in a level left hand turn the nose tries to rise. It doesn't actually pull you into a right hand turn as many believe, but makes it easier to make the right turn since you don't have to fight the nose coming up and bleeding off airspeed. If you read page 10 of the Osprey Camel Aces book Raymond Collishaw talks about this some.
As far as snap 360s, there really is no such thing, and as I've said before the Triplane has to obey the laws of aerodynamics just like everything else. It will yaw rapidly about 20-30 degrees, but the rate of turn without banking is quite slow. I think the flat turn stories came from the recollections of young RFC pilots in the heat of battle who saw German pilots (Voss) making wildly uncoordinated turns, because the Triplane rudder is more powerful and fast than the ailerons, so it would yaw faster than it would bank. To them in the heat of battle it seemed like flat turns, but I guarantee that he had aileron in and as much bank as fast as he could get it, for maximum turn rate. There's been plenty of debate on how accurate such recollections are, and that's my educated theory on the flat turn stuff. As far as rate of turn in combat, diving would increase the rate of turn, which is one of the reasons they were always losing height in battle.

[Lufbery]

Thanks for the excellent post, BE. You explained things very clearly.

Regards,