Another Waco Taperwing Repaint

[attaway]

Hi guys.

The Question Mark, built as a one-off 'Special' by Waco in 1932. She is quite a handful, with a 500 hp R975 Wright Whirlwind modified for racing. She now lives at Creve Cour Airport.



I took her for a spin around the Cleveland race course in GW. Quite an experience cranking her round the pylons at 100 ft with the throttle firewalled. Managed to get one good screenshot and survived the lap.



My hats are off to the Golden Age Simulations team for their realistic flight model and to the daring aviators who actually raced these things.

She is up at avsim and flightsim: waco280w.zip

You can find more about the actual plane at www.airandspacemagazine.com/ASM/Mag/Index/2005/JJ/ppcc.html and see some photos of the actual Question Mark at www.nationalwacoclub.com/memberalbum/slides/1929%20Waco%20CTO%20NC280W.html

Stephen

[jimslost]

Beautiful repaint! I guess that means this week's project is to write an aircraft.cfg file for the big engine!

[attaway]

Jimslost:

turbocharged=1 //Is it turbocharged? 0=FALSE, 1=TRUE
max_design_mp=36.5 //Max design manifold pressure, (inHg)
min_design_mp=5 //Min design manifold pressur x x xH{)
critical_altitude=1400

Keep everything else the same and that gives you a Wright R-975 E3 Whirlwind set up for racing.

Hope this helps,

Stephen

[jimslost]

Helps a lot, Stephen, thanks.

[spad54]

Well done, very well done!

[jimslost]

I took things a step farther, Stephen, or even possibly a step too far. Bored out the cylinders to 108.3 cu" (to make 975) and brought the compression ratio to 6.3:1. Then I threw on a 99" Ground Adjustable Hamilton Standard. The result (as well as I can measure it) is 170 true at METO power at 1400'. (With a power to weight ratio of 1.73hp/#, it climbs well too.) The problem is, I don't know how well a 450 hp Taperwing really performed. Does anyone have any authorative numbers? Or a set of cruise charts for a - any - 450 hp Wright R975?

[attaway]

Jim:

You can find the dimensions on the Wright 975 online at www.oldengine.org/members/diesel/Duxford/usaero16.htm

You are in the ballpark.

The 'box stock' cfg file for the Waco gives you a 975E-1, unsupercharged, from the late 30s.

36.5" is probably as high as you could go with manifold pressure on the Wright. That and the 1400 ft 'rated altitude' are from the 1943 Wilkenson's datasheet for the Wright 975-E3. Your CR agrees with oldengine.org.

The rated rpm for the E3 was 420@2200, max take off 450hp@2250, so the 2400 rpm in the aircraft.cfg is already 'full race', and should be about 500 hp.

I think you should leave the prop at 9.0 ft (108"). See if that makes a difference in your speed. I bet 2400 rpm with a 9 ft prop beats whatever you are getting with 99".

The article on the CTO Taperwing in the US Civil Aircraft Series says the full race versions could do nearly 180 mph at sea level. Anything more and you are too hot.

Stephen

[jimslost]

Thanks for the link, Stephen, it adds another page to my data base. I've got about the similar data for the 330 hp 975 A,B,C,D,E, the 400 hp GR 975 C and the 420 hp 975E-2 from an old FAA source. Unfortunately it's all "late" (1960ish) data; your 1943 datasheet is probably more topical.

At full throttle, I ended up with 174 @ 2250 rpm; I'm confident that I could break 180 by pushing it to 2400 rpm, even with the short club. I'm just wondering if the rib-stitching will hold (LOL).

For anyone interested, the aforementioned FAA book says the J-5 was 788 c" (87.55/ cylinder), compression ratio of 5.1:1, and put out 220 (to 223) hp @ 2000 rpm on 50 (!) octane fuel. But once again, we're dealing with information put out 30+ years after the fact.

I hope my kids appreciate the fact that I'm holding on to every airplane and engine manual that comes my way.
jim