Dorrance Lance

In 1949, when Cruisair production [and other light plane production] cooled off, I think GMB looked at something a little more poopy for his next rendition, the 14-19. The 'E' series Continental existed, putting out 185HP, and maybe 205HP for a minute after T/O. I think that N/A,. Ryan and Beech soaked up much of the production. Thousands of these airplanes were produced. Therefore, we have more spare parts. I think GMB's choice of the Lycoming engine 0-435A was an end run around the competition. It was available. Lycoming only produced the engines for the 99 14-19s, a handful of Johnson Rockets, few experimental A/C and about 200 Fokker trainers in The Netherlands. BTW, I have several friends that have 'E' series Continentals and they are worried about parts. Go figure.
 
Yes, Jonathan, I love the smiley face of the 14-19. However, The cooling path did nothing to enhance the O-435A installation. Dan
 
All the technology that Lycoming ever learned in the the six cylinder, horizontally opposed series, came from the basic O-435 engine. All the operators of the O/VO GO/IVO/IGSOseries 480 and 540 series engines owe a debt of gratitude. Lets give a round for the enlisted and comisioned pilots who proof tested this engine in WW2
 
Weren't O-435 engines also used on the Stinson L-5 spotter planes during WW II?

I thought they were also on one of the early Navion models, but after a little digging, it turns out that it was a GO-435-C3 pumping out 260 HP.

Dave York
 
That was a different version of the O-435 that was used on the Stinson L5. The one used for the 14-19 was the O-435-A, and it has a different accessory case...which, as I discovered to my utter dismay, makes a huge difference, alas.

Jonathan
 
Lycoming made an impressive list of O-435 derived engines, in the '40s and '50s. It started with -1 engine for the Stinson L5. Some engines were used in light armored vehicles. The -2 was one of, if not the first, geared aircraft engine produced by Lycoming for use with the Interstate TDR-1 flying bomb. Now, if you really want some fun, fly behind an -A2. I have. It delivers 225HP at 3000rpm-direct drive. All your airport neighbors will invite you to leave as you make at least as much noise as any T-6!
 
I have the high compression pistons in my -A that would make 225hp if I were to move the timing from 20 degrees to 25 (not smart when you're already doing just about everything to keep the hottest CHT down to 400 degrees) and redline my Hartzell HC 12x208D (again, none too smart). The pistons are pretty much the only major difference between the two. What makes using the higher (not high....just higher) compression pistons a good idea is that they should be a tad more efficient and help just a bit with lead fouling...or so I'm told.

And let's not forget the VO-435 used to power the Bell 47 helicopter.

Jonathan
 
Dan Cullman,

I wonder if you would contact me offline. I'm curious as to whether you knew my Uncle, who lived East of Kent, WA for 40+ years. He was interested in all things aeronautical, so I figure that you two might have met.

york40@bellsouth.net

Dave York
 
All the VO,GO, GSO,IGSO and IGO series have their roots with the basic O-435. BTW........I do have the manual for the -A2. Besides slightly higher compression that calls for brown avgas.........does anyone remember that stuff?.......an upgraded valve train was required to prevent valve float I flew Fred Egli's N500A with the -A2. It would easily turn 3000rpm for T/O. However, it seemed that everything above 2800 converted gasoline into noise------not performance. He had a hard time keeping guides. Rocker rollers seemed to help.
 
I looked at 500A when it was for sale but backed off when I realized that the 225 HP was at 3000 RPM. Didn't notice at the time, but what size prop does one use to keep the dang tips from going supersonic on takeoff (I recall it was a Hartzel "rebuild often"special-Yshank)
 
As the 14-19 was never certified with the -A2, no reduction in prop size, from the 78 inch limit for the -A1, was ever specified.

And, as usual, Dan is spot on regarding using the original length prop at higher RPM. I was climbing out at 2900 RPM once, and found that my climb rate actually improved when I reduced it to 2800. You don't hear the prop going supersonic from inside the cockpit. No...I did not mean to let the RPM get that high; I was simply not used to the controllable, vs. constant speed prop, and I allowed it to creep up before I noticed it. It feels smooth at that speed and thus it gets away from you easily until you learn - and I learned QUICKLY - to add the tach to my scan shortly after the wheels leave the runway.

Jonathan
 
Oh-oh, the uber-Geek engineer inside me just kicked in. (Sorry, it's genetic - my Dad was the same way, as is my Son)

The speed of sound at the sea level standard atmosphere is generally listed as 761 mph.

761 mph = 4,018,080 ft/hr (761 x 5280 ft per mile) = 48,216,960 in/hr (4,018,080 x 12 in per ft) = 803,616 in/min (48,216,960 / 60 min per hr).

Propeller tip speed (inches/minute) = Pi * propeller diameter (inches) * RPM or
RPM = Propeller tip speed / (Pi * diameter) or
diameter = Propeller tip speed / (Pi * RPM)

So, for the original question "what prop diameter is needed to keep from going supersonic at 3000 RPM", we get:
diameter = 803,616 (speed of sound in inches per minute) / (3.1416 x 3000 RPM) = 85 inches. At this RPM, the tip would *just* be at Mach 1.

For a 78 in diameter prop:
RPM = 803,616 / (3.1416 x 78) = 3279 RPM. Again, at this RPM, the prop tip would "just" be at Mach 1.

This is pure theoretical rotational math and does not take into effect any local airflow effects across the propeller.

Also, at the end of WWII, the faster fighters discovered compressibility effects as the airfoil approached the speed of sound which created much more drag than expected and therefore required much more power (or rate of descent) to maintain the speed.

I suspect that this may have been what Johathan observed in his case, even though, mathematically, his prop tips seem to be only about 90% of the speed of sound.

Dave York

DISCLAIMER: Any of my math may be wrong and should be considered suspect until verified. Do not use for navigational purposes.

Trivia side note: A side effect of the compressibility factor noted by the WWII planes was that there was often a control reversal or total loss of control as the planes approached the speed of sound. In Microsoft's Combat Flight Simulator 3, the P-38 aircraft will show this behavior, just like the original plane. If you dive on your opponent and allow your speed to exceed about 500 MPH, pitch control gradually goes away and leaves you in a terminal velocity, vertical dive with no way to pull out. This dive continues until you finally create a smoking crater in the ground. I got nailed several times before I realized what was actually happening.
 
alabamaflyboy said:
If you dive on your opponent and allow your speed to exceed about 500 MPH, pitch control gradually goes away and leaves you in a terminal velocity, vertical dive with no way to pull out. This dive continues until you finally create a smoking crater in the ground. I got nailed several times before I realized what was actually happening.
Click to expand...
In this case, would pulling power off slow you to elevator effectiveness?
 
This situation set up a shockwave that blocked airflow over the elevator in a dive - by definition a very high speed dive. The solution was a hinged flap-like device on the inboard underside of the wing's trailing edge that deflected the shockwave so that the elevator became effective. Pulling power would not have saved you from becoming a lawn dart.
 
It was described in Kelly Johnson's book, More Than My Share Of It All.
Although these parts were shipped to Europe to retro-fit on the serving P-38s, the ship carrying them was torpedoed and sank.
 
The prop tip is moving only at Mach.90 but at 76 MPH the plane is going Mach .10 Add the two together and you get a supersonic prop tip. The prop is not just describing a circle but a spriral through the air which is more distance.
 
The spiral idea is correct, and I missed that (good catch), but the forward movement is at right angles to the movement of the blades, so forward speed can't be directly added to the rotational speed of the prop tip.

It's like computing wind drift with a right angle wind and doing no wind correction. Your ground speed is higher than the forward speed, pushing you off at an angle, but the ground speed is not the sum of the forward speed and the wind speed.

The forward speed does add to the total prop tip speed, but only partially. Using vector math, at a forward speed of Mach 0.1 at right angles to the prop rotational tip speed of Mach .9, the propeller actually sees a spiral tip speed of Mach 0.91. For the spiral tip speed to reach Mach 1.0, the forward speed must be about Mach 0.44 when the prop tip rotational speed is Mach 0.9, which means an airspeed of about 330 MPH. (Don't we all wish the Triple Tails would do that speed!!!)

I also wonder if Jonathan's engine had passed its peak HP region at the higher RPM and changing the pitch of his prop pulled the engine back into the peak power range? I don't have access to my Lyc. O-435 manual to check out the curves.

Maybe an engine expert can comment on this?

At any rate, a prop speed in excess of 0.9+ is very likely to be running into the compressibility factors which take energy away from thrust and waste it as drag.

Dave York
 
I have the performance curves for my engine, Dave. Given the age of my 'Master I consider myself fortunate that I have the Ops manual that the CAA created for it, not just the exercise in marketing that passed for a POH during that era. Thus I have real climb rates matched with real ambient temperature ranges based on actual test fights performed by neutral party pilots.

The curve remains steady and travels past the 250 hp range. As you know, this engine - with some changes to aid reliability and longevity as Dan noted - had a geared version used on the Navion that made 260hp.

One thing I'd forgotten was that my prop at the time exceeded the certified length due to the previous owner who replaced the blades and could not bring himself to cut them from 80-81 inches to the legal 78. This alone, however, does not match your numbers. I've not run the engine up to 2900 with the current and legal prop, nor do I plan to. The previous owner did that all too regularly and ended up turning the round mounting holes for the prop bladder into ovals. Some pilots are never quite satisfied with the inherent limits of their aircraft, and I inherited an aircraft that had been owned for 29 years by just such a pilot.

Jonathan
 
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