cowl bumps

[callisontx]

I saw this pic today and thought I'd ask about these cowl bumps.
The craft is listed as having O-300D
What are these bumps for? There is one on each side.
I've never seen any that low.

170bump.jpg

Thanks

[Brad Brady]

From my recollection, if it has an O-300D there is no need for the bumps. Unless there is a later style exhaust system installed, and they needed more room.....Brad

[GAHorn]

That's it, Brad! They've got the Cessna 172 Hanlon Wilson exhausts installed (and may not have the correct approvals.)
They may not have the engine and particularly that 172 spinner approval basis correct, either. (Not trying to criticize the airplane, just pointing out matters of interest.)

[Brad Brady]

That's it, Brad! They've got the Cessna 172 Hanlon Wilson exhausts installed (and may not have the correct approvals.)
They may not have the engine and particularly that 172 spinner approval basis correct, either. (Not trying to criticize the airplane, just pointing out matters of interest.)

Yea, I wasn't going into legalities, since Clay, apparently wasn't the owner ...Brad

[GAHorn]

...Yea, I wasn't going into legalities, since Clay, apparently wasn't the owner ...Brad

That's why I DID mention it,...in case Clay had an interest in it.

[Brad Brady]

That's why I DID mention it,...in case Clay had an interest in it.

Point well taken....I'll try to be more specific on later posts.

[Bruce Fenstermacher]

Every time I've seen those bumps it was because the larger 172 Hanlon Wilson mufflers were installed.

[ron74887]

the Spinner is approved on the latest version of the STC. S7441-SW. I listed the pionted one also, even if it doesn't fit the look. Also, on the bump, actually you only need it on one side if memory doesn't fail me. (which happen more often than I care to admit). Ron

[GAHorn]

Here's the issue with installing Hanlon Wilsons on a Cessna 170 (and may be an issue on the airplane pictured):
The Type Certificate Data Sheet, Item 110 APPROVES Hanlon-Wilson exhaust manifolds and carburetor air heater ...IN ACCORDANCE WITH (Cessna dwg. 0550157).

That drawing specifies which part numbers may be utilized and the manner in which they may be installed. The drawing refers to the same parts as indicated in the IPC for the varous C-170's.

It does not refer to the part numbers which are installed in later Cessna 172 aircraft which used larger muffs and needed larger cowls. The bumps in the depicted 170 are undoubtedly there because someone once installed the UN-approved Hanlon-Wilsons intended as C-172 muffs. The question now, regarding the pictured airplane, is which muffs are PRESENTLY installed? ... and how are they documented as far as approval basis goes.

To some of our participants it won't make a meaningful difference. For most, who care about legality, it will make a BIG difference. In case of an accident or incident, involving carbon monoxide, exhaust leaks, exhaust or engine compartment fire, or loss of power due to carbueretor ice and the associated carb heat system.... it will be of considerable interest to accident investigators and insurance underwriters. (I am not saying an improperly approved system is unairworthy. Airworthiness of an otherwise healthy system is not the issue. My own airplane flew for 20 years with an unapproved engine installation and the purchase of the STC which made it legal did not make any real change to the airworthiness of the airplane. But it makes a big difference as to my risks and liabilities to myself, my passengers, the public, and my pilot certificates.)

[Bruce Fenstermacher]

Hey Ron if I was going to put a bump on one side I'd put it on the other whether I needed it or not. You could be correct thought that only one side truely needs it.

[Bruce Fenstermacher]

While I could be wrong I don't think these sort of things like using the wrong Hanlon Wilsons are being done much today because A&Ps, IAs and lastly owners are more aware of part numbers and legality issues. It seems 25 to 30 years and more ago people weren't as interested in part numbers as much as function and common sense. If it worked on a 172 why wouldn't it work on a 170 as long as we ad the bumps was more the attitude.

So mods were done and considered legal enough but times have changed and there are many many airworthy illegal airplanes out there. I speak from first hand experience.

[GAHorn]

While I could be wrong I don't think these sort of things like using the wrong Hanlon Wilsons are being done much today because A&Ps, IAs and lastly owners are more aware of part numbers and legality issues. It seems 25 to 30 years and more ago people weren't as interested in part numbers as much as function and common sense. If it worked on a 172 why wouldn't it work on a 170 as long as we ad the bumps was more the attitude.

So mods were done and considered legal enough but times have changed and there are many many airworthy illegal airplanes out there. I speak from first hand experience.

That attitude, claiming "function and common sense" was/is a problem and that is why FAA has worked so hard to educate folks to know better. It looks like a common AN4 bolt that ties Baron elevators together but "function and common sense" would be wrong. It's a specially NDT (tested) bolt that only resembles an AN4 bolt.

[callisontx]

I appreciate the replies. I don't know which mufflers are currently installed.

just curious-
Why wouldn't the mufflers be a part of the engine; and if approved for an O-300D, then approved for anything an O-300D is approved for?

[blueldr]

The mufflers are usually airplane type specific. All airplanes using a specific engine do not have the same airframe configuration. A good example of serious differences would be the Cessna 337. The front engine installation is nothing at all like the rear engine. Even the mount is a different type. However, both engines are the same model and sub model.

[hilltop170]

I'm surprised no one mentioned the exhaust stacks in the picture.