Engine angle

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Wagflier

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Nov 14, 2021
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Why do you want to go to the 0-0? There are other ways to get the desired output but why redesign. Do you have an opposite rotation engine?

Quick answer is you can go 0-0 but it will not fly as nice unless you correct for engine torque with other methods. Depends on how big the engine is. On a 65 hp Cub it's not a big deal. With 2,000 hp up front it is a big deal.

If you are going to switch engines CW to CCW 0 is better than the wrong way. The advantage of engine offset is an engine change is no big deal to redesign the engine mount for the opposite rotation. If the correction is built into the airframe, it is a big deal to change engine rotation.
I don't necessarily want to go to 0-0, but I don't know what the factory settings were, and I can't seem to find out, so I'm trying to get input to make a decision in how to fab my engine mount.
 

Wagflier

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This.
Also not an engineer, here, but consider when you need the most rudder input; takeoff, correct? Slow speed, higher angle of attack, wide open throttle. And higher power/weight ratio a/c require more rudder. I've flown Swifts with 160hp, 200hp, and Continental 210hp (with a really big prop). The C210hp took a *lot* more rudder on takeoff. The faster you're moving, the less rudder input you need to correct for propeller effects. The rotary powered RV guys I know that set up their mounts at 0-0 did it for max cruise efficiency; accepting the extra rudder needed on takeoff.

The only thing that gives me pause in the original post is the '2 degrees up'. I've never heard of a tractor-configured a/c wanting 'up' in the thrust line; all I've ever heard was right only, or down/right, for USA-typical clockwise turning props, as seen from the cockpit. Does the airframe in question have a high-mounted pusher engine? If so, the 'up' part might become important.
No, I just threw out some numbers for discussion purposes. I'm building a Wagabond, and I don't know what the factory numbers were, so I'm trying to decide how to build my engine mount.
 

challenger_II

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Unless you are building your Wag with an A65, you will most likely be happier with some right thrust, and down thrust. For an O-235 installation, reference the Piper Pa-16 Clipper, and the PA-22-108 Colt. For an O-290/O320, reference the PA-20-135 Pacer.

For reference, the WAG Aero STC for installing the O-290/O-320 in the PA-22 Colt requires the use of the PA-22-135/150 engine mount. From experience, making the engine upgrade using the PA-22-108 mount will give you a sore right leg, holding rudder to keep the bird straight. The PA-22 series uses different P/N motor mounts, and the difference is in right-, and down-, thrust angles.



No, I just threw out some numbers for discussion purposes. I'm building a Wagabond, and I don't know what the factory numbers were, so I'm trying to decide how to build my engine mount.
 

BJC

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No, I just threw out some numbers for discussion purposes. I'm building a Wagabond, and I don't know what the factory numbers were, so I'm trying to decide how to build my engine mount.
Just for reference, the Glasair II has a straight vertical and cants the engine to the right (viewed from the cockpit) 1.5 degreed, with the centerline of the propeller on the centerline of the fuselage. It also is tilted down. IIRC, also at 1.5 degrees.


BJC
 

Dan Thomas

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Just for reference, the Glasair II has a straight vertical and cants the engine to the right (viewed from the cockpit) 1.5 degreed, with the centerline of the propeller on the centerline of the fuselage. It also is tilted down. IIRC, also at 1.5 degrees.


BJC
I adapted a Subaru 2.2L with an RAF redrive to a Glastar. Had to design and build the engine mount, too. No offset in any direction, and it flew well. 130 HP. The thrust line was in the designed location, with the engine low in the cowling. Took some doing, that. More than 20 years ago, now. Late '90s.
 

tallank

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Sep 22, 2020
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Why do you want to go to the 0-0? There are other ways to get the desired output but why redesign. Do you have an opposite rotation engine?

Quick answer is you can go 0-0 but it will not fly as nice unless you correct for engine torque with other methods. Depends on how big the engine is. On a 65 hp Cub it's not a big deal. With 2,000 hp up front it is a big deal.

If you are going to switch engines CW to CCW 0 is better than the wrong way. The advantage of engine offset is an engine change is no big deal to redesign the engine mount for the opposite rotation. If the correction is built into the airframe, it is a big deal to change engine rotation.
With freeflight, RC, and control line model aircraft we always had some down and right thrust. I owned a T28B for over 20 years. It had a 5 degree down thrust. It is very obvious to the eye. This resulted in an amazing handling aircraft. There was no change in pitch / trim when changing power settings. It has over 1400 HP. I do not understand why aircraft are not designed this way. Every powered aircraft I have flown, if you add power the aircraft pitches up and slows down. Constant corrections. The T28 did not do this. Basically hands off on final approach while changing power. The handling during an overhead approach was amazing. 200+ kts overhead, sharp left break with about a 60 degree bank, reduce power, when you start needing back pressure you use the speed brake which does cause a pitch up so no trim changes. The aircraft slows to gear and flap speed which allows the aircraft to continue slowing down. Basically it is hands of all the way to landing.
 

Pops

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Ercoupe has down and right thrust.
On the JMR Special I put in 1.7 degs of right thrust. But its really not worth the extra work of building the cowl to match the right thrust, plus the design of the engine mount. If I was do it again I would go 0/0 and I would rely on a rudder trim tab set for cruise.
 

PacerPlus

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I usually just cruise in here and don't say anything but thot I'd put up a little comment on the "zero thrust line".......... I build/repair mostly Piper rag wing types and similar. Most all the rag wing Pipers have about 3 3/4° down and about 2° right, except the J3 that does have some right thrust but not down. It is widely known if you are after more performance (STOL plus a small amount on the top end) the zero thrust line has more advantage. I like zero down and the 2° right on the stretched Pacers as the Pipers do not have any fin offset. The common way to get a little more "right trim" is to "tweak" or bend the top of the fin to the left.......... which works fine as long as the welds hold! The problem with the higher powered Pipers is, like any other, the faster you go, the more down trim you need............ to the point you run out of trim with the high lift USA35B section. This can be mitigated with larger rear horizontal surfaces which is common practice on the bush types. Some even have a trim system to apply tension to the right rudder cable.

So, the way it was explained to me years ago is the right thrust is to compensate for the torque or P factor and the down thrust acts kinda like an "auto trim". The Maule, which has its roots from the Piper Pacer, incorporates a 0/0 engine mount (which just happens to bolt right up to a stretched Pacer airframe BTW!) has the offset fin and rudder trim. It has the same airfoil as the Pacers but has a little performance advantage if similar weights and HP are compared.

*I did this little edit since it might not be understood that all the references to the "down thrust" are to the HRL or horizontal reference line.
 
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Wagflier

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Nov 14, 2021
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Unless you are building your Wag with an A65, you will most likely be happier with some right thrust, and down thrust. For an O-235 installation, reference the Piper Pa-16 Clipper, and the PA-22-108 Colt. For an O-290/O320, reference the PA-20-135 Pacer.

For reference, the WAG Aero STC for installing the O-290/O-320 in the PA-22 Colt requires the use of the PA-22-135/150 engine mount. From experience, making the engine upgrade using the PA-22-108 mount will give you a sore right leg, holding rudder to keep the bird straight. The PA-22 series uses different P/N motor mounts, and the difference is in right-, and down-, thrust angles.
Some background on the Wagabond: It is a clone of the Vagabond, as far as I can tell from talking with Vagabond owners, and checking dimensions on the factory plans and the Wagabond plans. That being said, the angle of incidence for the horizontal stabilizer on both sets of drawings is 4 degrees leading edge down, which is going to cause a pitch UP condition for the nose. neither set of drawing shows the angles for the engine installation, but if you reference the Datum Line (which is the defacto thrust line) after leveling the fuselage per the drawings, it is 2 degrees down thrust, which is going to cause a pitch DOWN nose condition. Seems to me in my feeble mind this is creating drag to compensate for each other. If there is an aeronautical engineer out there who can explain why this was done, I'd sure like to hear from him/her.
 

TFF

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Why is it different? That is to the whim of the person who built the first and drew the plans. They fixed something they did not like about the original. Is it an across the board wish fix? Probably not. I have never studied the Vagabond. Not a lot have compared to the Cub, my guess is expecting Lycoming on the nose.
 

Dan Thomas

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Some even have a trim system to apply tension to the right rudder cable.
There's an STC'd kit for that rudder trim for the PA2- & 22 series:

Steve's Aircraft Rudder Trim STC

The Cessna taildraggers usually had a spring bungee between the leading edge of the stabilizer (which went up and down with trim control) and the elevator pushrod. It was to pull the elevator down to eliminate the need to push forward in high cruise at full-down trim.

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I've seen the same idea in a TriPacer. It pulls on the lower elevator cable.
 

rv7charlie

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the angle of incidence for the horizontal stabilizer on both sets of drawings is 4 degrees leading edge down
Is that related to the wing's incidence, or to the fuselage longerons? If to the fuselage, what is it related to the wing?
 

OhAnElBirds

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Nov 8, 2021
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I have a set of barely legible PA-15 plans, the horizontal angle is two right, there is no listed vertical angle. This is for the as stock Lycoming O-145 engine.

IIRC in the past somebody made a J-3 virtually impossible to stall by adding a certain significant amount (I don't want to say because I'm not sure) of down angle but it decreased the cruising speed.
 

OhAnElBirds

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Impressive. I had no idea that was possible.

;-)
I should say stall straight ahead, wings level, WITH power-- although power's implied.

Apparently if the engine is "drooping" enough, at high angles of attack, it still pushes enough air over the wing that you simply descend and never break.
 

Wagflier

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Nov 14, 2021
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Is that related to the wing's incidence, or to the fuselage longerons? If to the fuselage, what is it related to the wing?
It is a welded tube fuselage, so there are no "longerons". It is when the fuselage is leveled per the plans, the stab is -4 degrees. In the leveled condition, the wing attach points are level as well.
 
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