[Charles]

Charles on January 30, 2016 at 5:02 am #18034

I had the exact thing happen to me. It turns out that my muffler was clogged due to blockage of the exhaust pipes. Get a long screw driver and lay on your back under the exhaust pipes. Gently insert the driver up the exhaust pipe while looking up there with a flashlight. If its obstructed you will know. Had a new muffler installed on mine and it solved the problem.

[Francis Mcclernon Jr]

Francis Mcclernon Jr on August 21, 2015 at 6:43 am #17814

I would (and I’ve never discussed it with them) but I have the feeling it would have to be milk or orange juice.

This is a very unique situation. The primary purpose of the airport I am at (m17) is to train aviation mechanics and pilots for overseas mission flying. Most of the mechanics (usually 3-4) are in training with one really well qualified mechanic that supervises the trainees. A really nice bunch of guys. . .and very conscientious. The shop is small enough that they will get me involved in the trouble shooting and can take the time to explain issues to me so I understand them.

I am anxious to see what Steve has to offer.

Frank

[Anonymous]

Anonymous on August 21, 2015 at 6:22 am #17812

Hi and I’m very pleased to hear of your progress. It sounds like you have a very thorough and high-quality mechanic. When you get this problem finally resolved you should consider buying him a drink! Please let us know the final resolution.

I’ll send a copy of your posting to Steve Ells so he can follow along.

Best,
Scott Sherer
N344TB

[Francis Mcclernon Jr]

Francis Mcclernon Jr on August 21, 2015 at 5:46 am #17811

Finally had a chance yesterday to address the problems I am having with getting full power on my 1967 180 h.p. Arrow with the constant speed prop.

1. My mechanic borrowed an optical tachometer. We ran the engine from 1000 RPM up to full power (about 2600 RPM) in 200 RPM increments. The optical tach consistently indicated 25-40 RPM more than the tach on my airplane.

2. We performed a standard run-up at 2000 RPM. Magneto drop on each magneto was normal and cycling the prop control show a consistent and normal reduction in RPM.

3. We took the cowl off and checked the compression. Compression was in the upper 70’s on all the cylinders.

4. We checked the propeller governor connection. It seemed to be correct and tight.

5. Then we started looking at the throttle cable connections. I noticed when I pushed the throttle forward, it advanced smoothly until it was almost to the full throttle position. . .then with an extra little push it would go on up to the full throttle position. While I was doing this my mechanic was studying the “throttle body” (?) connections. Evidently, the lever the cable connects to has slipped in its position on the round rod that connects the lever to the butterfly valve. When I had to exert the extra push to get to the full throttle position this lever was going over the center position of the lever, which it’s not supposed to do. Though there is a set screw to connect the lever to the rod it is, apparently, a very critical adjustment that requires special tools/equipment to adjust accurately, which my shop doesn’t have. So they have removed the throttle body and sent it off for adjustment/overhaul.

So, that’s where we are. Evidently, I was only pushing the throttle control up to the point of the resistance, which was not full throttle. Hopefully, adjustment/overhaul of the throttle body will correct the situation.

Sound reasonable?

Thanks for your input.

Frank

[Anonymous]

Anonymous on August 20, 2015 at 7:41 am #17810

Scott;

A slightly amended response:

A normally aspirated engine develops rated power at sea level in standard day conditions (59 deg F).

At higher density altitudes engine power falls off. For instance, the 180 HP engine in this airplane generates 180 hp at sea level pressure and temperature.

At 3,000 feet density altitude it develops (all other things being equal) approximately 164 hp; at 2200 DA approximately 168 HP. This is indicated by a reduction in manifold pressure but the prop should still turn 2700.

If our member still has a mechanical tachometer it could be the culprit; they do lose accuracy but it is usually a gradual process.

Are the pre takeoff mag check rpm drops within limits?? If so, and if the compression readings are above 70 in each cylinder and with a max to min spread of no more than 5 rpm, I doubt there’s a mechanical problem with the engine.

So let’s look at some other possible causes.

1. Was any work on the engine done prior to the low rpm readings? Magnetos re timed or new mags installed? Any adjustments to the prop governor high rpm set screw??

2. A constant speed propeller is driven to flat pitch (high rpm) by a force called centrifugal twisting moment—this force is naturally generated during prop rotation. It’s similar to the lift vector generated by wings. Oil pressure from the governor acts on a piston in the prop hub to increase the pitch of the prop blades, thereby reducing rpm. Check the prop governor high rpm screw to make sure it hasn’t moved.

3. If everything looks good, back out the governor high rpm set screw one turn and see if it affects the full power rpm.

Let me know what your find.

Thanks

Steve

[Anonymous]

Anonymous on August 19, 2015 at 2:40 pm #17809

Hi,

Thanks for the clarification. I’ll get your information back to Steve Ells asap and get his reply.

Best,

Scott Sherer
N344TB

[Michael Scott]

Michael Scott on August 19, 2015 at 11:26 am #17808

“This member’s airplane has a fixed pitch prop.” NO it does NOT….

[Anonymous]

Anonymous on August 15, 2015 at 2:23 pm #17807

Hi Frank,

Here’s the response from the Piper Flyer Assn A&P, Steve Ells:
Scott Sherer
N344TB

This member’s airplane has a fixed pitch prop. The rpm will be maintained at 2700 if he had a constant speed prop but not with a fixed pitch.
A normally aspirated engine develops rated power at sea level in standard day conditions (59 deg F).
At higher density altitudes engine power falls off. For instance, the 180 HP engine in this airplane generates 180 hp at sea level pressure and temperature.
At 3,000 feet density altitude it develops (all other things being equal) approximately 164 hp; at 2200 DA approximately 168 HP.
A 200 rpm drop (2500 instead of 2700) seems excessive for this small loss in power.
If our member still has a mechanical tachometer it could be the culprit; they do lose accuracy but it usually a gradual process.
Check the carburetor heat door for security and proper operation and to see if the door closes all the way in the cold air position. A little carb heat will reduce engine power and rpm.
It woudn’t hurt to do a differential compression test just to make sure the top end of the engine is completely healthy.
Are the pre takeoff mag check rpm drops within limits?? If so, and if the compression readings are above 70 in each cylinder and with a max to min spread of no more than 5 psi, I doubt there’s a mechanical problem.
Best,
Steve

[Anonymous]

Anonymous on August 15, 2015 at 12:40 pm #17806

Hi Frank,

I sent your question to our A&P mechanic, Steve Ells. I’m waiting for a response and as soon as I get one I’ll post it for you.

Thanks so much for your patience,

Scott Sherer
N344TB

[Anonymous]

Anonymous on August 14, 2015 at 8:18 pm #17805

Stand by Francis,

Scott Sherer
N344TB