Geared engines and inflight operation?

RyanB

RyanB

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Can someone explain how geared engines work? (ie. On the C421) Ive heard they are not as reliable as other types of engines? I know some of the basics, but have little understanding of how they work.
Thanks
 
Ryanb said:
Can someone explain how geared engines work? (ie. On the C421) Ive heard they are not as reliable as other types of engines? I know some of the basics, but have little understanding of how they work.
Thanks
Click to expand...

Two types, the Continentals use a Bull Gear system rather than planetary. The main issue is to prevent chattering of the gear set and also driving the engine with the prop in 'zero thrust' situations like descent. Also you want to avoid ham fisting and jamming the throttles around. Example, in a 421 I can count to five as I advance the throttles on takeoff and move them at a similar rate to reduce power.
 
Well they work by using gears
 
You hear a lot of things at the airport. Most of it is nonsense.

The point behind gear reduction is that propellers work better when they spin slowly, and engines provide more power when they spin faster. Gears let you do both. I run my engine at about 5000 to 5500 rpm, but the prop spins at about 2000 to 2300 rpm.
 
The gears are used to increase the engine RPM while leaving the propeller at a speed that is subsonic. For an example the Rotax 912 runs 5500 rpm all day long. If the engine was direct drive the blade speed would be supersonic. The 2.43 - 1 gear box reduces the prop speed to subsonic speeds. Not many issues with this set up, the Rotax 912 series engine is fairly bullet proof.
 
Ryanb said:
Can someone explain how geared engines work? (ie. On the C421) Ive heard they are not as reliable as other types of engines? I know some of the basics, but have little understanding of how they work.
Thanks
Click to expand...

Henning put his finger on it. Be sure that the engine is driving the prop at all times...never pull the throttle back to the stops but keep at least 11" MAP. The operator I flew for had three 421s, two A's and a C, and while they did go into the shop more than other twins of my acquaintance it was never because of an engine failure.

Full disclosure: The one and only time I had to feather a prop in flight was in a 421...but the cause was turbocharger plumbing external to the engine itself. Can't blame the airplane for that.

Bob Gardner
 
There was a 4:3 geared engine in the Cessna 175 Skylark that got a really bad reputation because pilots trained in 150's and 172's just couldn't bring themselves to push the power to 3200 engine RPM in cruise. Either the engine loaded up at the low power settings, or they didn't get the expected performance. If properly operated, it was a perfectly good engine/airplane. Bottom line (outside of don't let the prop drive te engine) is you should get proper type-specific training on any unusual system like this, as the best practices for one geared engine may vary from another one.
 
Thanks, the info helps. Ive just heared about these types of engines and never fully understood how they worked vs. a non geared engine. Thanks for the replies!
 
I flew for years behind the GO-435-C2 geared Lycoming. It has a gear box that spins the prop at a ration of 77:120 of the engine speed. I had ZERO problems as a result of the gear box. Most of the problems revolve upon the reprehensible TEXTRON lack of support of the engine. The gearing, as pointed out, allows a longer and more efficient bladed prop. In the long run, it's usually a zero sum game. The weight of the gear box counter acts any benefits in the increased efficiency.

\
 
Mine is a geared... (well belted) engine.... ;)

It works perfectly..

Motor turns 4400 rpm's on take off... Prop is spinning 3045 rpm's.. Tip speed is .92 mach.....
 
All any one needs to understand about a geared engine is you must keep tension on the gear teeth in either direction. It does not harm the gears when the prop is driving the engine as long as the tension is there.

It is only bad when there is no load, and the gear teeth are allowed to chatter against each other. most damage occurs at idle when there is no load on the gears. the power pulses between each cylinder are like hammers on the gear teeth.
 
N801BH said:
Mine is a geared... (well belted) engine.... ;)

It works perfectly..

Motor turns 4400 rpm's on take off... Prop is spinning 3045 rpm's.. Tip speed is .92 mach.....
Click to expand...

Belting is not like two steel surfaces banging together.
 
Ron Levy said:
That puts you in the same boat as a lot of people who bought and then bad-mouthed the Skylarks. :D
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The only guys bad mouth-ing the G0-300 were the owners who were buying cylinders.
 
Ron Levy said:
There was a 4:3 geared engine in the Cessna 175 Skylark that got a really bad reputation because pilots trained in 150's and 172's just couldn't bring themselves to push the power to 3200 engine RPM in cruise. Either the engine loaded up at the low power settings, or they didn't get the expected performance. If properly operated, it was a perfectly good engine/airplane. Bottom line (outside of don't let the prop drive te engine) is you should get proper type-specific training on any unusual system like this, as the best practices for one geared engine may vary from another one.
Click to expand...
The biggest offenders of harming the GO-300-D were the old Radial pilots that were trained that no engine could be operated at any RPM above 2200. Thus when they saw a red line on the tach that was 3200, thought well, anything under red line is good. ----> well no.
 
Ryanb said:
Thanks, the info helps. Ive just heared about these types of engines and never fully understood how they worked vs. a non geared engine. Thanks for the replies!
Click to expand...

As said before, it's a simple gear reduction set so the engine can turn faster than the prop.

There is real advantage to be had due to the physics of the fuel burn rate, with a 5" piston you really want to be able to turn around 3400 RPM to maximize the HP output while operating at 'comfortable' combustion pressures.

Also the gear reduction allows for longer, more efficient, quieter, propeller blades. The slower a prop turns, the more efficient it is, and when tip speeds start exceeding .92 Mach, the drag, and noise, increase dramatically. ROP tip speed is why direct drive engines are limited in RPM to levels that require extreme combustion chamber pressures to produce more than .5HP/Cubic Inch, basically maxing out at .65HP/CI before you start running through cylinders every few hundred hours. With a gear reduction, you don't have this limitation and match a more efficient power plant to couple to a more efficient prop.
 
Tom-D said:
All any one needs to understand about a geared engine is you must keep tension on the gear teeth in either direction.
Click to expand...
That understanding is necessary, but not sufficient. There's more to operating these engines than just that.
 
Ron Levy said:
...because they weren't running their engines right.
Click to expand...

No argument there :)

Many pilots do not know there are many teeth in a planetary gear assembly pulling torque all the time, (no problem in the old radials) not so the spur gear type where there only 2.
 
N801BH said:
Exactly why I went the belt route.... There are several gear redrives out there though......
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If I ever need to use a PSRU, I'll use a Lenco pack to get a 2 speed drive. I know a Lenco will hold whatever I throw it on and throw at it. It's about the only thing I haven't managed to break.:lol:
 
In the case of the C175, the powerplant is the same as the non-geared O-300 which produces 145 HP @ about 2400 rpm max. If you increase the maximum RPM, you get more horsepower, in this case, the engine RPM is bumped up to 3200 RPM max and you get 175 HP. So you've satisfied the need for more HP, but there's a problem. Now the engine is spinning too fast for a prop to safely operate. So the engine has a gear box (gear reducer) that allows the prop to spin at a safe and efficient speed of 2400 rpm while the engine is churning along at a faster, more powerful 2900-3200 RPM. Now, you might ask what the advantage of the extra horsepower is if the prop is still spinning the same RPM as the non-geard engine. The answer is that with the higher HP, you can swing a longer prop, which translates to more thrust. Bada bing! The penalty for this is a little higher fuel burn, and ultimately parts wear out a little faster because of the extra 600-800 revolutions per minute. As others have mentioned, you have to be a little more gentle with the throttle changes to keep from being too hard on the gears. IMO, this is really only a problem at start-up, during taxi, and on approach when there's little thrust demand. The resto of the time the prop should be loaded and the pressure on one side of gear teeth.
 
A much longer prop. IIRC, the 175 swings an 84" long prop.


Jim R
Collierville, TN

N7155H--1946 Piper J-3 Cub
N3368K--1946 Globe GC-1B Swift
N4WJ--1994 Van's RV-4
 
Henning said:
Two types, the Continentals use a Bull Gear system rather than planetary.
Click to expand...

get your terminology correct. Continental used a "SPUR TYPE" no bull gear in the assembly, you simply have the drive and driven gears. The drive is attached to the crankshaft, the driven is attached to the propshaft.

both are conical cut gears that have the next tooth engaging prior to the last tooth disengaging, makes a lot less noise and vibration. but as in any gear setup, you must have running clearance, to allow oiling.
 
N3368K said:
A much longer prop. IIRC, the 175 swings an 84" long prop.


Jim R
Collierville, TN

N7155H--1946 Piper J-3 Cub
N3368K--1946 Globe GC-1B Swift
N4WJ--1994 Van's RV-4
Click to expand...
depends upon what version you have. there are three versions of the C-175. one isn't even called a 175.
 
OkieFlyer said:
In the case of the C175, the powerplant is the same as the non-geared O-300 which produces 145 HP @ 2700 rpm max. If you increase the maximum RPM, you get more horsepower, in this case, the engine RPM is bumped up to 3200 RPM max and you get 175 HP. So you've satisfied the need for more HP, but there's a problem. Now the engine is spinning too fast for a prop to safely operate. So the engine has a gear box (gear reducer) that allows the prop to spin at a safe and efficient speed of 2400 rpm while the engine is churning along at a faster, more powerful 2900-3200 RPM. Now, you might ask what the advantage of the extra horsepower is if the prop is still spinning the same RPM as the non-geard engine. The answer is that with the higher HP, you can swing a longer prop, which translates to more thrust. Bada bing! The penalty for this is a little higher fuel burn, and ultimately parts wear out a little faster because of the extra 600-800 revolutions per minute. As others have mentioned, you have to be a little more gentle with the throttle changes to keep from being too hard on the gears. IMO, this is really only a problem at start-up, during taxi, and on approach when there's little thrust demand. The resto of the time the prop should be loaded and the pressure on one side of gear teeth.
Click to expand...

FTFY.

but not all 175s swing the long prop, there is a version that has a constant speed prop.
 
Tom-D said:
get your terminology correct. Continental used a "SPUR TYPE" no bull gear in the assembly, you simply have the drive and driven gears. The drive is attached to the crankshaft, the driven is attached to the propshaft.

both are conical cut gears that have the next tooth engaging prior to the last tooth disengaging, makes a lot less noise and vibration. but as in any gear setup, you must have running clearance, to allow oiling.
Click to expand...

No conical gears in a GTSIO 520 prop drive, this is the shaft. I don't know what you call it, I have always heard of this refered to as bull gears.

image.jpg
 
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flyingron said:
I flew for years behind the GO-435-C2 geared Lycoming. It has a gear box that spins the prop at a ration of 77:120 of the engine speed. I had ZERO problems as a result of the gear box. Most of the problems revolve upon the reprehensible TEXTRON lack of support of the engine. The gearing, as pointed out, allows a longer and more efficient bladed prop. In the long run, it's usually a zero sum game. The weight of the gear box counter acts any benefits in the increased efficiency.

\
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Same here. Put 350hrs on my GO-435 powered Commander 520 with zero problems. Great engines, and because they're so torquey and accelerate so fast, they produce great short field and climb performance. In this video you can see me lift off in 600ft (that's the distance to the displaced threshold at KEMT). Unheard of in other twins.

https://www.youtube.com/watch?v=0zEhHJkUERE
 
Henning said:
The first sentence of the thread?



Best of my recollection a 421 has a GTSIO-520.:dunno:
Click to expand...

Oh Well I missed that.. when we were deverted to the GO-300-D. by guess who?
 
flyingron said:
I flew for years behind the GO-435-C2 geared Lycoming. It has a gear box that spins the prop at a ration of 77:120 of the engine speed. I had ZERO problems as a result of the gear box. Most of the problems revolve upon the reprehensible TEXTRON lack of support of the engine. The gearing, as pointed out, allows a longer and more efficient bladed prop. In the long run, it's usually a zero sum game. The weight of the gear box counter acts any benefits in the increased efficiency.
Click to expand...

Well, not quite 'zero sum', you still end up with a quieter plane and lower ICPs.;)
 
flyingron said:
In the long run, it's usually a zero sum game. The weight of the gear box counter acts any benefits in the increased efficiency.

\
Click to expand...

I have to respectfully disagree with this. From the specs on early 172B, vs 175A(similar year ~1960)

Cessna 172 B - Performance Data

Horsepower: 145 Gross Weight: 2200 lbs
Top Speed: 122 kts Empty Weight: 1325 lbs
Cruise Speed: 114 kts Fuel Capacity: 42 gal
Stall Speed (dirty): 51 kts Range: 515 nm

Takeoff Landing
Ground Roll: 875 ft Ground Roll 600 ft
Over 50 ft obstacle: 1370 ft Over 50 ft obstacle: 1115 ft

Rate Of Climb: 730 fpm
Ceiling: 15100 ft

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Cessna 175,-A,-B - Performance Data

Horsepower: 175 Gross Weight: 2350 lbs
Top Speed: 128 kts Empty Weight: 1312 lbs
Cruise Speed: 121 kts Fuel Capacity: 52 gal
Stall Speed (dirty): 54 kts Range: 593 nm

Takeoff Landing
Ground Roll: 735 ft Ground Roll 590 ft
Over 50 ft obstacle: 1340 ft Over 50 ft obstacle: 1115 ft

Rate Of Climb: 850 fpm
Ceiling: 15900 ft

~~~~~~~~~~~~~~~~~~~~~~~~~
175 performance wins in every category except stall speed. I have to assume the 175 used a bit more gas than the 172 as it's 30HP more on the same displacement, but there's no free lunch.

The only downside that I'm aware of on the 175 is the atrocious SMOH rating, although if the engine had continued in production it would have likely increased to maybe 1500-1600 hours. Possibly, but one is turning more revs for the distance traveled so maybe not... :wink2:
 
docmirror said:
I have to respectfully disagree with this. From the specs on early 172B, vs 175A(similar year ~1960)

Cessna 172 B - Performance Data

Horsepower: 145 Gross Weight: 2200 lbs
Top Speed: 122 kts Empty Weight: 1325 lbs
Cruise Speed: 114 kts Fuel Capacity: 42 gal
Stall Speed (dirty): 51 kts Range: 515 nm

Takeoff Landing
Ground Roll: 875 ft Ground Roll 600 ft
Over 50 ft obstacle: 1370 ft Over 50 ft obstacle: 1115 ft

Rate Of Climb: 730 fpm
Ceiling: 15100 ft

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Cessna 175,-A,-B - Performance Data

Horsepower: 175 Gross Weight: 2350 lbs
Top Speed: 128 kts Empty Weight: 1312 lbs
Cruise Speed: 121 kts Fuel Capacity: 52 gal
Stall Speed (dirty): 54 kts Range: 593 nm

Takeoff Landing
Ground Roll: 735 ft Ground Roll 590 ft
Over 50 ft obstacle: 1340 ft Over 50 ft obstacle: 1115 ft

Rate Of Climb: 850 fpm
Ceiling: 15900 ft

~~~~~~~~~~~~~~~~~~~~~~~~~
175 performance wins in every category except stall speed. I have to assume the 175 used a bit more gas than the 172 as it's 30HP more on the same displacement, but there's no free lunch.

The only downside that I'm aware of on the 175 is the atrocious SMOH rating, although if the engine had continued in production it would have likely increased to maybe 1500-1600 hours. Possibly, but one is turning more revs for the distance traveled so maybe not... :wink2:
Click to expand...

I have flown a couple different 175s, (one tail dragger, and one nose dragger) and most of my few hours are in a 150 hp Lycoming powered 172. The difference in performance is VERY noticeable. Some say the 175 was a flop, and the geared engine got a bad rap, somewhat deservedly, but Cessna succeeded in making an airplane that is way more fun to fly than a 172. I can attest to the 175 being able to climb at 900 fpm with two rather fat guys in the front seats on a hot day. With a little extra power and Johnson bar powered barn door flaps, it's a real hoot to fly. If the bank would have loaned me the money, I would have bought one a few months ago.
 
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