Cessna 180 Seaplane prop question

[a3holerman]

In another thread I have posted about my looking for a Cessna 180 and received a wealth of helpful insight and tips.
I ran across one in Canada that is pretty much what I am looking for but have a question.

It has a new 88" prop on it now. My previous 58 had 88 incher also and I liked the added thrust on takeoff. The one I am looking at is a landplane as was mine.
As I understand it a 88" prop is not authorized for a C180 as a landplane vs seaplane. Many people do it all the time. I will need a DAR to go over the plane and paperwork to recertify it and get a US Airworthiness Certificate.

What are the thoughts on having an issue with that prop?


Tom

 

[stewartb]

Where did you read a limitation linking an 88" prop to floats? I've seen seaplane prop limitations on Cessna nose draggers but not on Skywagons.

 

[OLDCROWE]

Blame it on the internet, meanwhile I'll keep running my noise maker...

 

[a3holerman]

The limitation is on the McCauley Blackmack 88" prop on the C-180 for seaplane or anfibs only.
http://www.rockyprop.com/mccauley\m-c180-88-2.html

 

[stewartb]

In another thread I have posted about my looking for a Cessna 180 and received a wealth of helpful insight and tips.
I ran across one in Canada that is pretty much what I am looking for but have a question.

It has a new 88" prop on it now. My previous 58 had 88 incher also and I liked the added thrust on takeoff. The one I am looking at is a landplane as was mine.
As I understand it a 88" prop is not authorized for a C180 as a landplane vs seaplane. Many people do it all the time. I will need a DAR to go over the plane and paperwork to recertify it and get a US Airworthiness Certificate.

What are the thoughts on having an issue with that prop?


Tom

You made me look. TCDS 5A6 lists 88" props for all models. For G and H models some prop models were tied to engine models but lengths weren't limited. The later models do specify 82" props as approved for land and ski planes and 88" (90-2) for land, ski, float, and amphibious planes. The K model (slow turning U motor) is approved with the 90" (90-0) prop in all gear configurations or the shorter prop for wheels and skis. So the correct answer is there is a limitation for some models that requires the 88 or 90" props for floats but no restriction for wheels or skis.

http://rgl.faa.gov/Regulatory_and_G...8e1e465986257810004f5a7e/$FILE/5A6 Rev 67.pdf

 

[hotrod180]

As Stewartb pointed out, the TCDS lists several 88" props. But not all 88" props are approved on all models --for example, I put a McCauley 2A34C201/90DA-2 (aka 88" C201) on mine. This prop is approved on the TCDS for the C180G and later with R engine, but not for a 180 with a K engine like mine. But it is approved under STC SA388NW held by North Sound Aviation.

Hopefully there's some sort of approval paperwork for the one you're looking at, which will pass muster on the conformity inspection. Which model 180 (180, 180A, etc) is it,and which prop does it have?

 

[skywagon8a]

Tom, You have not said which model or year the 180 in Canada is. Read the TCDS via stewartb's link. The 88" prop is approved by Cessna on the "J" models for all configurations. You would need to know the entire model number of the prop. My question is "Why does that 180 have a NEW prop?". That sometimes indicates that the airplane has had an accident. Sudden engine stoppage, gear box replacement, etc. Were the repairs done correctly? ALL of the damage fixed? To your satisfaction? There had better be some really good reasons for the new prop or I would run very quickly away. Is the prop really new or just "newly" overhauled? "New Prop" really perks up my ears and raises many questions in my mind.

Another clue is that as far as I am aware Cessna never issued a ferry permit for a 180/185 when it had a seaplane prop on it. They did do this for 172s and I think 206s when they had long seaplane props. This was for the purpose of getting the new airplanes from the factory to the location for the float installation.

Another question for you to consider is "What will the neighbors at Marston Mills think of a 180 with a long prop doing TO and landings?". This can become a problem in our neck of the woods. The neighbors at Plymouth complain regularly. If this 180 has the slow turning (2400 rpm) engine it is less of a problem.

 

[a3holerman]

I have asked the owner which model prop is on the plane and hope to hear in a day or so. It is a 1966H model with an R engine.

The reason for the new prop is simply the owner bought it 3 years ago without floats and a standard prop. He then bought floats and put on a NEW "Mac" as he referred to it, and it has some 110 hours on it now. You are right about the noise and Ill have to get the RPM back asap We do have a Turbo 210 on anfibs there now.
My concern is bringing a Canadian registry A/C to the US and then getting a US AW certificate. Read all I can find on the internet including AOPA's articles on the process. It seems if I want to fly it back myself I will need to get a temp Canadian pilots authorization. Upon arrival at home will need a DAR to go over all the paperwork and A/C to issue a AW cert.

 

[stewartb]

A 180 with an 88" prop is a pussycat compared to a 185 spinning an 86" prop at 2850 rpm. Still, rolling back the revs to 2500 once wheels up is pretty simple to help keep the neighbors happy. When visiting a short strip with tall trees is when you need everything that prop can give you and on those days your safety is more important than the neighbor's quiet time. In cool climates there aren't many days that we need to spin full rated RPMs with 180s or 185s. Guys need to be familiar with temperature and prop speeds for their planes and adjust the rpm as needed. And they need to check their mechanical tachs occasionally to verify accuracy.

 

[a3holerman]

Its a 1966 H model and the prop on it is the proper one per the STC 2A34C203/90DCA-2.

 

[hotrod180]

.... My question is "Why does that 180 have a NEW prop?". That sometimes indicates that the airplane has had an accident. Sudden engine stoppage, gear box replacement, etc. Were the repairs done correctly? ALL of the damage fixed? To your satisfaction? There had better be some really good reasons for the new prop or I would run very quickly away.
....

My C180 has a freshly overhauled 88" C201 Mac, which I installed a few months ago. The reason being that I wanted to to maximize performance, and the old 82" prop was actually down to minimum length at about 80-1/2". So a new prop doesn't always mean some nefarious scheme to conceal damage from a mishap.

I agree with stewart that sometimes max performance & safety is more important than the someone's quiet time. I generally start dialling back the prop as soon as I'm in the air, when possible, but it's nice to have the max power there when you need it. And as stewart also points out, an 88" prop at 2600 isn't anywhere close to an 86" at 2850 in the noise department.

 

[180Marty]

I'm curious, in 1999, I installed a brand new 2A34C203/90 DCA-x 88 inch on my 1954 with "K" engine. Was it legal since I wasn't float equipped? It's not on there now but as I remember it said it was good for A,J,K, R and S engines.

 

[stewartb]

TCDS Rev 67 lists that prop as approved for early model K engine land planes but it requires service kit SK180-46. Anyone know anything about that service kit?

 

[CamTom12]

On a side note, all that noise that a long prop at high RPM generates requires energy to make. Energy that's coming from your engine. I'd be interested to see someone do some back-to-back testing, taking off at max RPM and taking off at the highest RPM that's still "quiet."

Higher RPM means more engine horsepower, but transonics create a lot of drag for your engine to push through and reduce propeller thrust. Prop thrust is the only thing that matters in take-off and climb-out performance, but we don't have a way to directly measure that so we deal with RPM and MP instead.

There's a balancing act of increasing power produced by the engine at higher RPMs vs. the increasing power required to spin the prop through higher RPMs. And the reduction in prop thrust as more of the tip goes transonic. The normal shock wave (what makes that noise) causes airflow separation from the prop airfoil and also causes a TON of drag.

Here's an example with some made-up numbers:
Say you generate an extra 50 hp between 2500 and 2700 RPM. Also say at 2700 RPM your prop requires an additional 75 hp to spin as compared to 2500 RPM due to increased drag. In this example, we have an additional 25 hp available to generate prop thrust at 2500 RPM vs. what we have available at 2700 RPM (and airflow separation might further reduce the amount of thrust you could generate at 2700 RPM).


Not to say I don't think it sounds cool :smile:

 

[stewartb]

I can offer that an 86" prop spinning at 2900 rpm on a 70* day out-pulls 2700 rpm with the same prop/same temp. Anyone with Skywagon experience knows the acceleration/pull diminishes with rolling back the rpm. Clearly there's no thrust improvement.

 

[OLDCROWE]

With my 180 (IO520 and a 88X3 Mac.), One cool morning I tested take off at 2500 (took maybe an extra 250 feet) and then established a stable climb at about 1400fpm and 80 knots then pushed full prop (only rated for 3 minutes) and within 15-20 seconds while holding airspeed I was climbing at 1700fpm and then pulled it back to 2550 (sustained, top of the green) and the climb reduced to 1500fpm. If you do the same at 100 in the climb you do slow down as you go up.

All in max. climb produces crazy deck angles with truly impressive climb rates that come in handy when climbing through a hole but not for every day for me.

I usually back back the prop out 8-10 half turns on take off then tune to 2500-2525 rpm after lift off and climb at 90 (so I can see over the nose in our crowded home airspace). If I need to get off short or am really loaded I'll go full but it makes uber noise so on those special occasions at home I always request a SE departure (takes me right over Eaton's house).

 

[CamTom12]

Interesting to know! Thanks for sharing!

Sent from my LG-D850 using Tapatalk

 

[a3holerman]

Can anyone from experience say how much speed you loose in cruise going from a standard prop to a 88 inch.


Another question which is more general.

I am looking at a 68 model next week that has lost its logs. The current owner bought it from the widow of the original owner after many years of sitting around and had no idea where or what even logs were.
He thinks it has around 3500 hours and has been flying the past several years with no issues after a, in his words,full inspection and recertification. In reality how much does that decrease the actual value of the plane?

Again thank you all for the help and advice. Its amazing how much info and help is here on the supercub forum and the 180 forum won't even let one join if they don't own a 180.

 

[Barnstormer]

I can offer that an 86" prop spinning at 2900 rpm on a 70* day out-pulls 2700 rpm with the same prop/same temp. Anyone with Skywagon experience knows the acceleration/pull diminishes with rolling back the rpm. Clearly there's no thrust improvement.

Stewart is right on. Scientific theory is nice, but it's just that, theory. And static tests are nice, but they are static and don't account for the propellor moving forward through the air.

As far as cruise speed difference if going to an 88" prop, that depends entirely on too many variables, including propellor blade design to what you are comparing it to, and the density altitude and/or altitude in which you are flying, as well as the load of the aircraft (and probably more variables). Go high and the 88" blade will cruise faster because the air is thiner and the extra blade length bite will surpass the length drag. For the same reason it will climb to a higher altitude.

When taking off I leave the prop setting alone until I'm either high enough to turn back to the runway, or high enough to safely execute a forced landing. Only then will I change the engine rpm. If an engine is in the process of disintegrating itself it will hold together longer if the power setting, whatever it may be, is not disturbed.

 

[Gordon Misch]

Scientific theory is nice, but it's just that, theory.

. Maybe not so much that, as being sure to include all the pieces of the theory. The counterpoint to that is anecdotal evidence which does not necessarily constitute data.

I'm not quarreling with the evidence Stewart or Kirby have presented; I'm sure it's valid. But it just irks me when people denounce theory as immaterial or unrealistic. Sometimes it is, but often it ain't. What CamTom was saying wasn't "wrong", it was just incomplete - which is to be expected in off-the-cuff musings.

Not tossing mud at ya Phil, just offering a slightly different perspective.

 

[stewartb]

I don't think anyone disputes the decline in prop efficiency at high rpms. Apparently for the rpm ranges we use the addition of horsepower more than makes up for it. That's easy to demonstrate. If lower rpms offered an advantage we'd turn our props down to utilize it. It doesn't work that way in my plane.

 

[Barnstormer]

. Maybe not so much that, as being sure to include all the pieces of the theory. The counterpoint to that is anecdotal evidence which does not necessarily constitute data..

Well said.

I don't think anyone disputes the decline in prop efficiency at high rpms. Apparently for the rpm ranges we use the addition of horsepower more than makes up for it. That's easy to demonstrate. If lower rpms offered an advantage we'd turn our props down to utilize it. It doesn't work that way in my plane.

Yes we would. Nor mine. And also well said.

 

[skywagon8a]

I have asked the owner which model prop is on the plane and hope to hear in a day or so. It is a 1966H model with an R engine.

The reason for the new prop is simply the owner bought it 3 years ago without floats and a standard prop. He then bought floats and put on a NEW "Mac" as he referred to it, and it has some 110 hours on it now. You are right about the noise and Ill have to get the RPM back asap We do have a Turbo 210 on anfibs there now.
My concern is bringing a Canadian registry A/C to the US and then getting a US AW certificate. Read all I can find on the internet including AOPA's articles on the process. It seems if I want to fly it back myself I will need to get a temp Canadian pilots authorization. Upon arrival at home will need a DAR to go over all the paperwork and A/C to issue a AW cert.

For your DAR questions contact Pete Connor at Yankee Aviation in Plymouth. five O eight 746 5511 He is the local DAR. You may tell him that I sent you.

Can anyone from experience say how much speed you loose in cruise going from a standard prop to a 88 inch.

Another question which is more general.

I am looking at a 68 model next week that has lost its logs. The current owner bought it from the widow of the original owner after many years of sitting around and had no idea where or what even logs were.
He thinks it has around 3500 hours and has been flying the past several years with no issues after a, in his words,full inspection and recertification. In reality how much does that decrease the actual value of the plane?

Again thank you all for the help and advice. Its amazing how much info and help is here on the supercub forum and the 180 forum won't even let one join if they don't own a 180.

I think that you will find that there are likely more 180/185 owners here than at the 180 club. The 180/185 owners have Cubs for a second airplane or is it the other way around?

For the "no log" airplane you need to get the CD from the FAA with all of the records which have been filed. This will show if there has ever been any major (337) work done. With that you will know what you are getting. If your purchase is to keep for a while, the missing logs would be a personal thing which you figure in with your price.

Having flown both a land plane prop and a seaplane prop 185, I'll take the seaplane propped airplane if given a choice. If not given a choice, I would change the prop, without any consideration to the top end speed.

 

[skywagon8a]

My C180 has a freshly overhauled 88" C201 Mac, which I installed a few months ago. The reason being that I wanted to to maximize performance, and the old 82" prop was actually down to minimum length at about 80-1/2". So a new prop doesn't always mean some nefarious scheme to conceal damage from a mishap.....

That is a legitimate reason for the prop change. During my years of messing around airplanes I have found that "new Prop" often relates to an "oops", not always.

 

[skywagon8a]

A 180 with an 88" prop is a pussycat compared to a 185 spinning an 86" prop at 2850 rpm. Still, rolling back the revs to 2500 once wheels up is pretty simple to help keep the neighbors happy. When visiting a short strip with tall trees is when you need everything that prop can give you and on those days your safety is more important than the neighbor's quiet time. In cool climates there aren't many days that we need to spin full rated RPMs with 180s or 185s. Guys need to be familiar with temperature and prop speeds for their planes and adjust the rpm as needed. And they need to check their mechanical tachs occasionally to verify accuracy.

You are absolutely correct stewartb. However you live in the aviation community of Anchorage in the state of Alaska. Airplane Country! a3holerman lives on the right coast in the middle of a large contingent of lefties. It is an entirely different mind set and we always have to watch our 6! We do need to take preemptive actions in order to be able to slide under "their" radar. We do prevail then. When we do collectively cover our six we can get away with "mur...". :smile: Many members here are neighbors and do understand.

 

[stewartb]

Back to the prop tip efficiency question....

If the tips of an 88" prop are causing excess drag at high RPMs it would favor using a shorter prop, yet Cessna requires a longer prop for float ops. Another clue that supports long props pull better even with the tips making noise.

This topic is a little simpler than the perpetual discussion of 2-blade vs 3-blade performance. ;-)

 

[a3holerman]

Barnstormer,

Your theory about an 88" being faster at altitude I have not heard before.
Are you saying that at, lets say 7500', all else being the same a 88" will cruise faster than a standard prop?
The use of the plane will be to travel 250 miles to some remote strips. no seaplane operation, for camping and fishing in Maine.
When I bought my 58 180 landplane many years ago I talked with Max Folsom in Greenville and he said by all means get the 88". He said it was a bit slower in cruise but had more T/O performance.
I do not plan to go into any marginally short strips but the help would be nice. With a 500+ mile round trip speed is important.


Skywagon8a,

Thank you for the heads up on the DAR on Plymouth I will call him after I see the Canadian 180.

The CD was ordered 5 days ago. I just received another one previously ordered for another airplane. There were no stc's included which may be the case as I recall they are not required to be submitted to the FAA only a log nook entry. The 337's are there with registration and bill of sales. The problem is that none of these forms have A/C time or engine time recorded so I guess tach time is all one had to go on and that is not a very reliable indication.

 

[hotrod180]

.....
Higher RPM means more engine horsepower, but transonics create a lot of drag for your engine to push through and reduce propeller thrust. Prop thrust is the only thing that matters in take-off and climb-out performance, but we don't have a way to directly measure that so we deal with RPM and MP instead. There's a balancing act of increasing power produced by the engine at higher RPMs vs. the increasing power required to spin the prop through higher RPMs. And the reduction in prop thrust as more of the tip goes transonic. The normal shock wave (what makes that noise) causes airflow separation from the prop airfoil and also causes a TON of drag.....

Pponk has a tip speed calculator on his website, they say "to produce maximum thrust at full power, your tip speed should fall etween .88 and .92 mach".
http://www.pponk.com/HTML PAGES/propcalc.html
if their tip speed calculator doesn't work on your computer, here's the formula for figgering it out yourself
http://www.pponk.com/HTML PAGES/propellers.html
Tip speed on my 88" prop at 2600 rpm is 680 mph, or .89 mach-- right in the sweet spot.
Tip speed of an 86" prop at 2850 is 728 mph, or .96 mach-- too high for max efficiency.
Tip speed of an 84" prop at 2850 is 712 mph, or .93 mach-- still too high.
On paper, seems like both the 2850 rpm examples above would do better dialing the rpm back a little, but in real life...maybe not so much. Per Stewart's last comment, apparently more horsepower outrules less efficiency.

 

[Barnstormer]

Barnstormer,

Your theory about an 88" being faster at altitude I have not heard before.
Are you saying that at, lets say 7500', all else being the same a 88" will cruise faster than a standard prop?
The use of the plane will be to travel 250 miles to some remote strips. no seaplane operation, for camping and fishing in Maine.
When I bought my 58 180 landplane many years ago I talked with Max Folsom in Greenville and he said by all means get the 88". He said it was a bit slower in cruise but had more T/O performance.
I do not plan to go into any marginally short strips but the help would be nice. With a 500+ mile round trip speed is important...

7500 feet? I wouldn't expect the 88" to be faster, but I wouldn't think slower either.

I was speaking more of 10,500' to like 16,500' to get over the big rocks in the west and/or get favorable (200mph+ ground speeds) winds on long trips. Forgot your mountains are a bit shorter. Heck, 7,500'+ is the altitude of a number of runways I use.

Skywagon8a had an excellent point about you needing to fly amongst the lefties. If that's where 90%+ of your flying is going to be, and you aren't working out of short strips (or going to altitudes) where you need the performance of the 88, you might want to consider a little shorter prop to keep the anti's happy. That would obviously be your call based on your mission parameters.

[Okay everyone go ahead and make fun of the fact that I carry oxygen, and head for the flight levels, in my big tire 185 on long trips.]

 

[Barnstormer]

Me, I have a character flaw when it comes to being PC or giving a **** what the anti's think, which is no doubt why I live where I live. I mean, what's not to like about this? ;-)