Warbird Information Exchange

This was sent to me via e-mail for you guys to peek at.

Paul; (I guess)
My name is Steve Anderson and I have a question on the BT-13. We are putting a Travel Air Speedwing together and on it is a R-985 with a 2 position propeller such was used on the BT-13 I believe. What should I look for on take-off - 2300 RPM and 36 inches MP at sea level and what will be the cruise RPM say at about 28 in. MP?
Thanks,
Steve Anderson

Paul-

Steve is correct that TO should be 2300/36.5, that will be full throttle if it is a SL rated engine from a BT, part throttle if it is an altitude rated engine such as installed in a Beech 18.

He is attempting to work the cruise problem backward since the RPM is somewhat fixed by the prop pitch. On a two-position equipped BT-13 cruise was at 2000 RPM with MP as required to acheive 300 HP (65%). Under average conditions that would require 29-31" of MP depending on temperature and altitude.

From personal experience I would suggest removing the two-position control and adding a govenor.

Tom-

I had a BT-13 and agree the hot setup would be to install a governor... be sure the arm and counterweight assemblies used on the prop are the correct ones for the governor setup... ours was initially set up with the incorrect arms/wts and it didn't hold rpm well in dives and climbs.....once set up correctly the thing worked beautifully. We'd cruise it at 26"/1850 rpm, climb at 30"/2000 and t/o at 36/2300..... Tom

_________________
Tom N

Can you guys just reply to Steve for me? Thanks!



From: Steve Anderson [mailto:sanderson@syix.com]
Sent: Tuesday, September 20, 2005 11:33 PM
To: 'Paul'
Subject: RE: Bt-13 Vultee Website Information

Tom;
I am the one who has been volunteered to fly the beast and a mechanic friend came into the picture late also. He thought the propeller was a constant speed propeller but we couldn't get it up to RPM before the manifold pressure. He worked on the governor and controls. The governor had been overhauled along time ago (the project has been in the works for years with several different mechanics and an owner not up to speed with regards to what should be best) anyway, the governor went in for another overhaul because we thought it had sat around for such a long time something was sticking. Still the same problem. The prop is the same story, overhauled along time ago also. Well the prop went back in to be looked at and the mechanic was told that the counterweights, blades and the adjustments were for a two-position prop. The cost to bring the prop to a constant speed was something like $4000 or some figure so the owner said to get rid of the governor and put a two-position valve on the engine and run it that way to get the plane flying. The owner is in his late 70's, I imagine, and has had this dream of seeing the airplane fly since about 1956 or so. To make a long story short, that is where we are. The plane is a Travel Air Speedwing built in 1931. From what I am told it is the only one in existence of this model. Originally it had a 440 Wright on it, with a two-position prop I think. The owner wanted to keep the original brakes, cable, and it doesn't have a locking tail wheel. Somewhat steer able but if it flew like that 50 years ago it will fly that again.
Where are you guys located?
Thanks,
Steve

Tom N-

Using those numbers for RPM/MP at average temps, altitudes, you were climbing at 65% and cruising at less than 50% power, that certainly made the BT perform like a dog.........................

For anyone interested I still have the Plumly R-985 Power Computer from my Beech 18 days and can quickly verify power settings.

TomB-