Nose cowling

[jrenwick]

As a matter of curiousity, on an aircaft using engine intake manifold pressure as an emergency vacuum source,what seems to be the critical altitude at which one can reduce the throttle setting to acquire the necessary differential vacuum to operate the vacuum gyros and still maintain altitude?

That has to be determined by a flight test. The manufacturer discusses it here: http://www.thevacsource.com/faq.php. Their flight manual supplement (http://www.thevacsource.com/pdfs/SVS-mn ... -02-00.pdf) has more info.

[GAHorn]

Just remember Kyle, the more "custom" things you do to your airplane now is just more work to put it back to stock when you decide you want to be "An originality nut for what ever reason". At your age it won't be for a while. This is something that comes later in life. But you've been warned

if I did that, I would have to tak off everything I just did!

Kyle...this is genuinely offered as a helpful comment rather than a critical one:
Maybe it's only my imagination but.... It seems that you have tended to modify your airplane to some level ...and then asked members for advice on how to correct/cure some problem with that modification. I strongly urge you to share your contemplated mods prior to beginning them, and we will be in a better position to perhaps save you a lot of grief.

There once was a Sunday cartoon in the paper ....known as "BC"... in which the prime character was shown to be standing by a large rock with a hole in the middle for accepting an axle. The cast-away prototype lying on the ground was a square-shaped rock...obviously a poor attempt at creating a wheel. The newest model he'd created was a three sided triangle.

His explanation to his companion was that his triangular wheel was a vast improvement over his previous attempt....because it had one less "bump" when rolling!

Despite the considerable ribbing I get from my motto.... my avocation of originality actually stems from the belief that it's usually best not to try to reinvent the wheel. Whenever I modify my airplane (which I admittedly have quite a bit) ...I take much time in contemplating the original design as the model to mimic...making changes in a minimalist way...rather than a huge way.

So, my best advice is to thoroughly familiarize yourself with the original design, and carefully evaluate it's advantages/disadvantages... before creating a new one. Many times the original design addressed most problems quite adequately.

[54170b]

ok thank you

[Bruce Fenstermacher]

BC was the best.

If I could have back the time I've spent reinventing the wheel, well I'd be in my mid twenties again. But I'd would probably know much less about things than I know today. And I'd be stuck with a round wheel someone else designed instead of the one I designed that works nearly as good.

[48RagwingPilot]

All--

I'm going through a pre-buy on a '48 C170 and discovered an early C172 nose bowl. There doesn't appear to be any paperwork on this mod and I'm wondering if anyone here can tell me the basis for getting this approved. Thx.

Dave

[Bruce Fenstermacher]

You didn't specifically say, and you may not even realize that the 170 had an internal pressure box and the 170B '53 and later as well as the 172 had a pressure cowl.

I can only assume that the internal pressure box was removed and the proper internal baffling added for the 172 cowl to make the 172 cowl part of the cooling system. In other words pressurized.

There isn't any cut and dried legal approval basis to do this. But the reasoning one might use to convince an IA and Fed that it is OK to do is that it in fact was done by Cessna on the 170B. The early 172 cowls being nearly identical to the later 170B. So you are simply updating the old cowl and cooling system design to the later design.

[n2582d]

Dave,
Welcome to the forum.

If it's just the nosebowl that has been changed I would consider that a minor alteration. If your IA considers the modification a major alteration have him take a look at AC43-210: Standardized Procedures for Requesting Field Approval of Data, Major Alterations, and Repairs. I've posted it in the Maintenance Library. It's also readily available on the FAA's website. Take a look at paragraph 105 b. (1).

Good luck on your 170 search. Post some pictures of the Good, the Bad and the Ugly ones you find!

[48RagwingPilot]

All--

Thanks for the replies. I'm meeting with my A&P/IA this afternoon to discuss. Hopefully, I'll be a new owner and paid member of the Association by this time next week.

Dave

[blueldr]

How high will a C-170, with an engine intake manifold instrument vacuum back up system, be able to maintain level flight while reducing the throttle setting to produce a 4 inch vacuum differential ?

[ghostflyer]

have a talk with Harry Dellicker at Porterville in Calf. he has nose bowls for sale when you use his stc for the conversion to 180hp.

[48RagwingPilot]

All-

Turns out the only modification was to the nose bowl (i.e., replacing the original '48 C-170 nose bowl with an early C-172 nose bowl). No other changes were made to the cowling, the air box, the baffling or anything else that we could see. Given these new facts, do any of you have thoughts about the nature of this alteration? FYI, my A&P/IA is calling a contact at the FAA to discuss.

On another note, the pre-buy went well (with the exception of the lack of paperwork on the nose bowl). The airplane is mechanically sound and suffers only from a few bothersome cosmetic challenges. Not a show plane, for sure. The purchase is now contingent upon solving the nose bowl paperwork issue. Thx.

Dave

[Bruce Fenstermacher]

Do you have a picture of this. The early cowl bowl is completed on the top by the top cowl which reaches down to the prop. The later cowl doesn't have this. There is really now way to just change the cowl bowl and not sure you could even do it with modifications.

Screen Shot 2012-12-26 at 5.28.16 PM.png

Screen Shot 2012-12-26 at 5.28.38 PM.png

[48RagwingPilot]

Bruce,

I'll try and find a picture. In the meantime, I can tell you that whoever did the mod took an early-model C-172 nose bowl and made a cut-out above the prop to mimic the original nose bowl. The resulting nose bowl is "completed" on the top by the upper cowl reaching down to the prop in the same way it was w/the original (as pictured in the drawing). FWIW, my A&P/IA said the installer did a nice job.

Dave

[48RagwingPilot]

Bruce,

In follow-up to my last post, I have a distant picture of the nose bowl but don't think I can post it because I'm not yet a paid member of the association. I can say, though, that the nose bowl on this airplane does not resemble the one depicted in the lower drawing attached to your post. Instead, it's a single opening with no dividing structure. Thoughts? Thx.

Dave

[bagarre]

Here is the photo Dave was talking about.
I asked him to send it to me so I could post it on his behalf (cropped to make forum requirements)

C170Nose.jpg