Really, REALLY, basic engine queries

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wingandprop

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Aug 15, 2014
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Location
Waco, Texas
rv6ejguy had mentioned use of the Chevy 90 degree V-6. In my earlier response to that post, I noted that someone on this site had made a negative comment about that engine but did not explain. I have since found other comments to the following effect: "I would not consider an odd-firing V6 configuration, like the GM 90 degree V6. This engine produces a complex mixture of torque excitations, and from a torsional standpoint, this engine is a terrible choice as an aircraft engine."--JumpinJan. I now remember seeing that same general comment, here and elsewhere, as well as some further explanations detailing the issues presented by that engine, though I had totally forgotten them when rv6ejguy mentioned the Chevy V-6. I do not know, but I would assume GM's new 90 degree V6 would have the same issues.

Matt
 

rv6ejguy

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rv6ejguy had mentioned use of the Chevy 90 degree V-6. In my earlier response to that post, I noted that someone on this site had made a negative comment about that engine but did not explain. I have since found other comments to the following effect: "I would not consider an odd-firing V6 configuration, like the GM 90 degree V6. This engine produces a complex mixture of torque excitations, and from a torsional standpoint, this engine is a terrible choice as an aircraft engine."--JumpinJan. I now remember seeing that same general comment, here and elsewhere, as well as some further explanations detailing the issues presented by that engine, though I had totally forgotten them when rv6ejguy mentioned the Chevy V-6. I do not know, but I would assume GM's new 90 degree V6 would have the same issues.

Matt
Modern V6s have offset crankpins so are all even fire now. The drive would bolt up and these engines have many thousands of flight hours on them already.
 
E

ekimneirbo

What are your plans for getting the thrust line in or near the correct location ? Mount the engine so that the prop is in essentially the same location(s) as was the original. That will actually be pretty easy as the centerline was moved up and down in the course of gearing and ungearing the engine during the war. They were not as picky about those sorts of things as some of us are today. But just look at the nose! It has the nose of a 1990 Mack truck! Line of thrust for its own sake wasn't nearly as big a concern as keeping the engine high enough that the prop would keep clear of the sod on the bottom end (without raising the underbuilt landing gear any higher) and maintaining clearance of the Lewis gun's line of fire over the top of the propeller arc on the top end.

Are you planning to run a reduction drive in order to achieve the rpms you are talking about? If you run a reduction drive what will the combined weight of the set up be?Yes, as I set out, the re-drive would be the hellical Ballistic Gear Reduction unit Ballistic Gear Drives Gear Reduction Units for Airboat Applications. It is 66 pounds, including dampener. The engine is 366 pounds (earlier I said 340 lbs., from memory, but I have checked it again and it is 366 pounds) for a total of 432 pounds.

What was the weight of the original engine in an SE ? The original Hispano was 445 pounds (it was regarded as a very light engine), not including its reduction gear (or its exhaust or radiator: the SE has very long exhaust pipes for an airplane).

What hp are you wanting to attain? I would limit it to 200 hp WOT. The Ford engine does that hp at approximately 4300 rpm. That number is based upon private dyno tests on various stock 2011 Duratech 37 powered POVs, both F 150 and Mustang. Obviously there are variations between those results, but they are surprisingly close to one another. Incidentally, none show the 305 bhp claimed by Ford. A 2.5 reduction gear, one of the standard reduction gears available through Ballistic Gear, would reduce that to 1750 rpm. That is exactly the 200 hp WOT rpm on the original engine. Cruise was 1,500 rpm.

By the way, thanks for being a good sport about my use of your initial post in a (vague) attempt at humor. Obviously you did not tell me I was not allowed to touch anything, but I would not have blamed you if you had. I started to report that one of the folks did say my dogs were ugly and that I didn't know how to dress, but that was just a little too close to the truth for me.


Matt
Glad you have a sense of humor, I'll try to sound less intense in my replies too. I have brain thrashed many of the issues you will encounter, so hope to point you in a logical direction and save you some time. The thing about the crankshaft centerline/thrust line is that as it changes, it affects how the airplane will fly when you apply power. Think of it like a childs swing set. The further away from the lifting point/pivot point (wings) that its located, the more leverage it will apply. Just as with the swing set, the force will cause rotation as well as lift as you move forward. Some of the planes with pylon mounted engines above and behind the wing have lots of this effect to deal with. The closer the thrust line is to the wing, the less pronounced the effect. As you raise the engine to negate the effect of thrust rotationally, you begin to create a problem with your line of sight when landing (or flying) the airplane. Many people use the reduction drives to correct for this problem.
 

wingandprop

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Joined
Aug 15, 2014
Messages
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Location
Waco, Texas
Modern V6s have offset crankpins so are all even fire now. The drive would bolt up and these engines have many thousands of flight hours on them already.
Thanks Ross. Is there a year that they began using the offset crankpins, so we know what years are acceptable and what years are not?

Matt
 

wingandprop

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Joined
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Messages
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Location
Waco, Texas
Some of the planes with pylon mounted engines above and behind the wing have lots of this effect to deal with. The closer the thrust line is to the wing, the less pronounced the effect. As you raise the engine to negate the effect of thrust rotationally, you begin to create a problem with your line of sight when landing (or flying) the airplane. Many people use the reduction drives to correct for this problem.
As a lawyer who used to represent Beech and Lycoming (among others) in accidents down here in Texas, the first case I ever took to trial on my own was a torque roll after a single engine missed approach in a medium twin. You are very right about the potential adverse effects of the thrust line (albeit in a somewhat different context).

torque roll, Junction, TX.jpg


Use of the reduction drive to intentionally change the line of thrust in a reproduction is actually a bit of an irony where the SE is concerned as that is how you can tell, in looking at the old photos, what type of engine was being used in a given aircraft. The 200 hp Hispano was geared while the 150 hp Hispano and the 200 hp Viper were not. The thrust line was significantly different (several inches) between the geared and direct drive engines.

(Figuring out why they crashed is a whole lot easier than building them. Good news: the pilot recognized the roll at its onset, shut down the good engine, and bellied in off field. The fire started pretty quickly after impact when the wings separated, but the pilot and seven passengers, including four kids, all got out pretty much without a scratch. The pilot had some back problems, maybe from hitting the emergency exit so hard, but that was it.)


Matt
 
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ekimneirbo

As a lawyer who used to represent Beech and Lycoming (among others) in accidents down here in Texas, the first case I ever took to trial on my own was a torque roll after a single engine missed approach in a medium twin. You are very right about the potential adverse effects of the thrust line (albeit in a somewhat different context).

View attachment 34453


Use of the reduction drive to intentionally change the line of thrust in a reproduction is actually a bit of an irony where the SE is concerned as that is how you can tell, in looking at the old photos, what type of engine was being used in a given aircraft. The 200 hp Hispano was geared while the 150 hp Hispano and the 200 hp Viper were not. The thrust line was significantly different (several inches) between the geared and direct drive engines.

(Figuring out why they crashed is a whole lot easier than building them. Good news: the pilot recognized the roll at its onset, shut down the good engine, and bellied in off field. The fire started pretty quickly after impact when the wings separated, but the pilot and seven passengers, including four kids, all got out pretty much without a scratch. The pilot had some back problems, maybe from hitting the emergency exit so hard, but that was it.)


Matt
Quite a while back I measured the difference between the centerline of both a Lycoming and an LS1 Chevy to the top of the engine. If memory serves me correctly there was a 9 inch difference. Other engines will be

different, but that meant I would have to raise the LS engine 9 inches to have the same thrust line.......or invert it......or use a redrive. I could also raise it less than 9 inches and change the thrust line somewhat. On some airplanes I

have been told that changing the thrust line a few inches will not have bad effects...........how true or how universal that statement is .........is anybodies guess.
 

wingandprop

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Messages
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Location
Waco, Texas
On some airplanes I have been told that changing the thrust line a few inches will not have bad effects...........how true or how universal that statement is .........is anybodies guess.
I would once again harken back to the original SE and note that shifting the thrust line up or down several inches made no appreciable difference in the flight characteristics at all. The tremendous variety among repros would seem to support the same conclusion, though it might just as easily be said that none of them are truly the "same" airplane. In a modern, cleanly designed, high performance airplane, of course, thrust line might make a huge difference, but an SE is none of those things and there is a lot less precision in the whole design (though I wonder if Robert Baslee at Airdrome Airplanes might beg to differ!)

Matt
 
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