Found a legal 74 inch diameter prop for a C-85

Re: Found a legal 74 inch diameter prop for a C-85

Dave, I think you missed the point they were trying to make. Since the Taylorcraft airframe with a A-65 is already approved for a 74" propeller, then the same airframe with a C-85 would not have an issue with ground clearance.

Ahhh...

Thanks Tom.

I was not aware of what airframe they were discussing.

In that context it makes sense now.

Dave

[3Dreaming]

Re: Found a legal 74 inch diameter prop for a C-85

Dave, I think you missed the point they were trying to make. Since the Taylorcraft airframe with a A-65 is already approved for a 74" propeller, then the same airframe with a C-85 would not have an issue with ground clearance.

Re: Found a legal 74 inch diameter prop for a C-85

Here it is.

CAR 6.11

04a.611 Propeller clearance.
Propellers shall have a minimum ground clearance of 9 inches when the airplane is in a horizontal position with the landing gear deflected as it would be under the maximum authorized weight of the airplane. Propellers on seaplanes shall clear the water by at least 18 inches when the seaplane is at rest under the maximum authorized load condition. A clearance of at least 1 inch shall be provided between the tips of propellers and any part of the structure.

The "modern" version (FAR23.925) also requires 9" but allows 7" for nose gear planes.

link=> http://specialcollection.dotlibrary....y=(select+100)

Those pesky facts

Dave

[d.grimm]

Re: Found a legal 74 inch diameter prop for a C-85

Not to muddy the waters but I put a 76 in Wood Sensenich
On my C85 powered Fleet Canuck.
Dave

Re: Found a legal 74 inch diameter prop for a C-85

Not for ground clearance.

Why? Please explain. I don't understand why you say that.

Dave

[akndrifter]

Re: Found a legal 74 inch diameter prop for a C-85

Of course it can be an issue.

Ground clearance is an airframe dependent item.

Not for ground clearance.

Re: Found a legal 74 inch diameter prop for a C-85

The 74" is already approved with the A-65, so not an issue

Of course it can be an issue.

Ground clearance is an airframe dependent item.

[PA1195]

Re: Found a legal 74 inch diameter prop for a C-85

Good discussion here...confirm that Aeronca's TCDS for the S7DC is correct and not in conflict with McCauley's data, and then send on the prop proposal to experts for evaluation. Might be worth a try.

Gary

[astjp2]

Re: Found a legal 74 inch diameter prop for a C-85

The 74" is already approved with the A-65, so not an issue

Re: Found a legal 74 inch diameter prop for a C-85

Check your prop to ground clearance with the a/c in level position. That is something the FAA checked when I got an approval.

There is a spec for it bot I forgot where it is, in CAR4 someehere.

Dave

[astjp2]

Re: Found a legal 74 inch diameter prop for a C-85

Maybe McCauley didn't approve it but American Champinion did and that should be good enough to get engineering approval? oh and the A-65 has the same stroke as the 85 and it allows for a 74" prop, the tcds also only shows what's been tested, not what has not, that's why there is no rpm restriction like many Lycomings have.

[PA1195]

Re: Found a legal 74 inch diameter prop for a C-85

My O-200 deluxe was certified with a 74" prop. Mine was done when gilberti still owned the stc. NC53500

From McCauley's TCDS P-842 "The maximum and minimum propeller diameters that can be used from a vibration standpoint are shown below. No reduction below the minimum diameter listed is permissible since this figure includes the diameter reduction allowable for repair purposes."

The O-200 apparently had different vibration characteristics than the C-85 they tested, so a longer prop was certified. The F-19 w/O-200 also had a 74" prop.

"5. Propeller (with Continental O-200-A engine) - McCauley 1B90/CM7443, fixed pitch metal
with the following limitations:
Diameter - not over 74 ins., not under 71 ins. Static rpm at the maximum permissible
throttle setting, not over 2400, not under 2300. No additional tolerance permitted.
20.9 lb. (-50)"

However see TCDS P-842 Item 9 above for the C-85. I really don't care what prop has been installed...just the substantiation in case it matters.

Gary

[Ragwing nut]

Re: Found a legal 74 inch diameter prop for a C-85

Happened to discover an airplane with both a C-85 and a 74" prop in a seaplane configuration! That is a possible justification to get it approved on a Taylorcraft with Terry's STC.

My O-200 deluxe was certified with a 74" prop. Mine was done when gilberti still owned the stc. NC53500

[PA1195]

Re: Found a legal 74 inch diameter prop for a C-85

See McCauley TCDS P-842, Note 9 for C-85/1A90 combinations: http://ohio.shortwingpiperclub.org/M...TCDS/P-842.pdf

See Sensenich TCDS 1P2 1A2, Note 9 for C-85/76AK-2 combinations: http://www.sensenich.com/files/docum...1263321627.pdf

See McCauley fixed pitch propeller applications for the S7DC. I don't see any over 71" approved on sheet J-4: http://www.mccauley.textron.com/MAG.pdf unless it's an STC.

Edit: However...from American Champion TCDS A-759 (http://hangar9aeroworks.com/AeroncaTechInfo/A-759.pdf) for the 1A90, p.16:

(d) (S7DC only)
Static r.p.m. at maximum permissible throttle setting:
Not over 2440, not under 2290. No additional tolerance permitted. Diameter: not over 74 in., not under 69.5 in.

Might be a typo give it contradicts McCauley's TCDS and application sheet above?

Gary

[astjp2]

Re: Found a legal 74 inch diameter prop for a C-85

S7DC, 1A90 not more than 74, not less than 69