climb prop question

[Bill_Green]

Have you contacted the owner of the STC for putting the 8042 prop on a 170? I think that is where I would start. Perhaps they can add a converted 172 such as yours, to their Approved Models List?

[cessnut]

Different TCs, unlikely it would be that easy.

[n2582d]

-You write, “the plane has the original 6 bolt flange O-300.” But then, in your next entry, say you have an O-300-A (which has an 8-bolt flange). Your ‘56 originally came with an 8 bolt O-300A or O-300B. Our Association has SA7441SW which authorizes the use of the O-300C or O-300D on your plane.

While I don’t think the juice is worth the squeeze, you might look into installing an electric variable pitch MT prop. One of their DERs would have to approve the installation. Here John Nielsen, an MT prop dealer, writes,

… 2: The electric MT constant speed prop STC used for the 172 planes with solid crankshaft is just under $20K all in delivered in 2024. Not enough demand to support a $100K STC development investment for the O-300/C145 market. But we can do one at at time with a Field Approval done by our in-house DER for an added fee. …

If price is no object, their DER may be able to approve a MT fixed-pitch prop for your plane as well.

Both the Wick Air and Kenmore C-170 STC's are for the 8-bolt flange.

I think you're correct when you reason that the STC's for an 80" prop are available for the C-170 but not the C-172 is because of "clearance issues". It's interesting that Hartzell's STC SA02186AK is for an 80" constant speed propeller on a C-172. Their instructions for this STC specify that the original 5" nosewheel and strut must be replaced with a heavy-duty strut and nosewheel tire no smaller than 6.00 X 6.

The only private strip I see on sectional charts with field a field elevation of around 9500’ is True Grit South which is a 4000’ strip at 9580’ just northwest of Telluride, CO. Here’s a snapshot of Telluride’s average temperatures since 1970 - so, with current trends, probably cooler than what has been experienced in the last decade.

So, if the temperature is 50°F, the density altitude will be around 11,200’. The performance charts for the C-170 stop at a pressure altitude of 7000’ but 100°F at 7000’ is a density altitude of around 11,200’. T.O. Distance over a 50’ obstacle at that DA is 4040’ — 40 feet longer than the airstrip length. Ground run is estimated to be 40% of that or 1616’. Those operating with bush wheels might chime in on how they affect takeoff performance. Operating on skis? The 170 Owner’s Manual says, “Under the most favorable conditions of smooth packed snow at temperatures of approximately 30°F., the ski plane take-off distance is approximately 10% greater than that shown for the landplane. NOTE: In estimating take-off distances for other conditions, caution should be exercised because lower temperatures or other snow conditions will usually increase these distances.”

My suggestion would be to look into Airworx modification of your O-300 or a Del-Air or Stoots Lycoming upgrade. Also, taking a look at the first page of this thread, you might contact Mark directly. He has/had a taildragger 172 with an 80" prop.

[GAHorn]

Responding to your earlier post…. The “original” was an 8-bolt prop and crankshaft.

[Lhorn]

Okay, #1, sorry for the lapse in communication. I didn't realize my last post was the end of the page, and all replies were accumulating on the next page. I finally figured it out. Doh. After doing a bit of homework with the replies provided, I think I have what I need to proceed, so thank you for the help!

After the posts on the engine flange, an inspection of the log books was in order. The engine was swapped for an O 300 C engine, so that explains the flange. It was approved through a 337 filed back in the eighties.

As for density altitude at those elevations, more ponies couldn't hurt! Just called David and had a conversation, thanks for the suggestion. We'll try the prop first. My runway is downhill by a lot, and there's a cliff that drops off at the far end, so the treetops are below runway elevation, and beyond the lip the elevation drops away, so there's no climb out. Temps are near freezing most all summer in the mornings. We're north of Telluride..

Called the office so I could get copies of the STC #SA7441SW If the 8040 prop was approved for the 300 C, we should be able to get a field approval showing both the CS 80" prop, and the seaplane approved 80" prop on the C engine. Here's hoping.