C150 Engine Upgrade

[WDD]

If only that were always true...it would have saved me a lot of time chasing down a 10" CG discrepancy between two almost identical airplanes.

Nauga,
shifted

I hope the ARMs and W&B were accurate in the POH for the respective aircraft! Why would they change the Datum Point? Some engineer probably. They like to change things…..

Yeah - I’m finding out that a simple thing like two Skyhawks both being 172Ms mean less than I thought. Parts are can be completely different for same model M - comes down to the serial number.

 

[MBishop48]

THANK YOU WDD! I appreciate you taking the time to try to answer the question as opposed to the previous comments.

If the takeoff weight changed, the envelope would have changed

If you have an accurate weight and balance but weren't provided the correct envelope or limitations then it's not as simple as you state.


If the new allowable takeoff weight exceeded the max weight on the original envelope then the envelope would change, if it were to be 'legal'
There should be a new envelope or limitations as a result of the STC or whatever vehicle you used for the weight increase.

Your question seems reasonable to me...maybe I'm not ready for a checkride either.

Nauga,
flying off the runway, not the handle

Thank you Nauga! Can't say I'd really feel welcomed again to ask any kind of question here. That's unfortunate.

 

[MBishop48]

Again, I would research the STC for the new engine. That surely must include a new higher weight W&B envelope for you showing a higher take off weight.

Ask the STC creator. Maybe also contact the A&P who did the work for direction in where to get that documentation.

That official W&B documentation combined with your recent official unfueled and empty weight and balance by your A&P confined with the ARMs in the POH for fuel, pilot/copilot, and baggage will be what you need to do your W&B calculations before flight.

This is what I was looking for! Thank you again, that's what I thought but was unable to locate that and that is why I was looking to find out what other owners had done in that situation. The STC was from Aircraft Conversion Technologies, not sure they are still around. The A&P who did the work passed away. This was all done in 1997

 

[dmspilot]

Looking for the CG envelope change from standard

An engine mod STC wouldn't be expected to change the CG envelope. Some might come with a gross weight increase due to the higher power-to-weight ratio and better performance, if performance was the limiting factor of GW during original certification. The allowable center of gravity range is established for aerodynamic reasons and I don't see how improved performance would allow a greater range.

 

[WDD]

Agree - except that a higher HP engine I hope would give higher gross weight. Thus, the envelope wouldn’t change left or right, but could stretch upwards.

There would not be a greater range forward or aft, left or right on the chart.

That new chart made “taller” by higher allowable gross weight is needed.

 

[WDD]

The STC was from Aircraft Conversion Technologies, not sure they are still around.

I would dig as much as possible to find them or their successors. I would also think that STC paperwork has to be filed away with the the nice people at the FAA somewhere.

Have you asked your current A&P what he/she thinks is a good way to track down that power work?

 

[Hang 4]

Might try this.

https://www.cessnaflyer.org/media/kunena/attachments/2700/AircraftConversionTechnologies.pdf

 

[Cap'n Jack]

and the solution is to ask the internet?

That's only part of the solution.

Your answer covered only part of the changes caused by the engine change. Later replies in this thread mentioned envelope changes. Those replies made me think of how the plane might fly differently. A gross weight increase would alter things like stall speed, wouldn't it? Yet you didn't mention that at all. How do you think the stall speed would change on this plane if the gross weight were increased? Why?
Do you think takeoff and landing distances would likely change as well?

What I learned from someone asking the internet is to check not only the W&B, but also the envelope and limitations on a plane new-to-me, even if it is a type I've flown many times. If a plane I've flown before has had major alterations, I should review this information as well. One FBO I used had a form where we filled in this information prior to renting a plane, but the planes were all the same so the numbers were all the same and I filled it in from memory. It would have been better that I actually looked it up.

 

[Capt. Geoffrey Thorpe]

Perhaps, the OP could post what he does have. That would make it easier to fill in the blanks.
There should be W&B paperwork that was done when the engine was installed. Perhaps it does not have those PITA graphs like the POH - perhaps only specific numbers that changed (e.g. gross weight, empty weight, empty moment), but that's what you need to do the calculations and that's what you would be expected to show yea olde examiner.

 

[geezer]

The FAA issued that STC after approving a well documented application

Search the FAA for that STC, and download the entire document. It will include the envelope for the modified airplane, and exactly that is the only valid envelope for your airplane.

An envelope for an STC from a different version is not useable for your plane, even if it is the same engine. Oher details make each STC unique.

I was part owner of a Cessna 172 with a 215 HP Franklin engine, and we copied the very different envelope from the STC, and kept a copy in the plane at all times. The STC itself was a notebook of many pages, and had much more about various limitation which must be complied with for safe flight. That superseded many parts of the POH.

You need that complete document, read it, and comply with it, in order to safely fly your plane. That document should have come with your plane, if bought already converted, and must be provided by your A/P if you had it done. The job is not done until you have the paperwork.

EDITED to add:

The firewall of our 172 had a limit of 180 HP, we had a chart of density altitude, and manifold pressure limits for cold days or high barometric pressure.

The engine was heavier, and had a constant speed prop, so CG went forward a lot, stall speed data was very different from the POH. In the winter, we often took off at 22 inches of manifold pressure. I hope your plane has a manifold pressure guage.

Those are 2 of the most critical items you seem to be incompletely aware of.

Get the facts from the FAA, they have them.

 

[Salty]

The FAA issued that STC after approving a well documented application

Search the FAA for that STC, and download the entire document. It will include the envelope for the modified airplane, and exactly that is the only valid envelope for your airplane.

An envelope for an STC from a different version is not useable for your plane, even if it is the same engine. Oher details make each STC unique.

I was part owner of a Cessna 172 with a 215 HP Franklin engine, and we copied the very different envelope from the STC, and kept a copy in the plane at all times. The STC itself was a notebook of many pages, and had much more about various limitation which must be complied with for safe flight. That superseded many parts of the POH.

You need that complete document, read it, and comply with it, in order to safely fly your plane. That document should have come with your plane, if bought already converted, and must be provided by your A/P if you had it done. The job is not done until you have the paperwork.

Nah. You can get it from some random dude on the internet man.

 

[Huckster79]

I don't think the O-235 is a good upgrade at all. For one it doesn't make that much more power while being considerably heavier. The perfect marriage would have been a Franklin or O-290 both of which sadly have no support.

In regards to the O-200 HP, idk where this all started. Maybe from people afraid to run it at the higher rpm it's designed for. I hear people saying all the time that the C85 "makes the same power". Well I've flown with enough 140's to know that even the lighter 140 with a C85 is no where near the performer my straight tail 150 was. I think it was a Corvair engine builder that did a static thrust comparison test. Even with the shorter 150 propeller with standard pitch had the same pull as a C85 with a longer prop pitched for climb. So whether or not the 0-200 makes the claimed 100 hp at 2750, idk. But it still has more power than a c85 or c85 hybrid contrary to what many say.

Interesting, My experience was somewhat the opposite, my ol C140 outperformed a 150 in every way. I owned a straight tail 150 for a minute at the same time, the 140 took off shorter, climbed better and cruised faster… both that one and a friend of mines 150 or 152 I forget what his was. Mine did have the “stroker” STC on the c85. Eternal argument if that added unclaimed HP or not. I beleive it minimally added torque if not hp. But my ol 59V outperformed the 150s I flew…interesting your experience was opposite. Shows how subjective some of this is.

My suggestion to OP would be rip off everything that doesn’t help it fly. I stripped my interior and upgraded seat cushion and lost 20lb. I had my 140 light. If I recall right I removed 60 lbs or so overall. Starter, battery, interior removal (which made it no louder or colder and once painted was easy to clean) seat foam replacement alone I lost 8lbs… the old stuff was heavy as all get out. Lighten her up and she’ll thank you. Fly the 0-200 wound right up like lil continentals like and accept her for what she is…

 

[Dan Thomas]

Part of getting such STCs approved includes a mass of POH revisions. But I have found unrevised POHs in modified airplanes. The OP might have a boxful of paperwork that came with the airplane, and the stuff might be buried in it. If the mechanics that did the conversion were doing their job, the paperwork would be up to snuff. Sounds like it's not. Maybe they "borrowed" the STC certificate from someone and just did the installation without all the instructions relevant to that conversion. STCs like this cost money, lots of it, just to cover all the R&D that was necessary to get the STC approved by the FAA.

 

[Magman]

Most engine “ upgrades “ do not necessarily change the envelope

or other limits. Very common a GWI ( gross weight increase ) is a

separate STC. Many Lyc- Hawks are this way. I’ve met 150 hp

150’s n 152’s and agree with performance comments . Particularly with

a STOL Kit. IIRC the envelope was not altered.


A certain 152 was a particular nightmare for me due to owner alterations.

I seem to be a magnet for strange birds. Maybe a separate tale someday.

The late Harry Delaker ( del- air) obtained the STC and helped immensely.