Humble Pie

[W.J.Langholz]

It is always good every once in awhile to have a piece of "Humble Pie" and admit that you may need to ask something that will seem like a stupid question to most.

So here it goes cause I know nothing when it comes to this subject.

What really happens if you put your 170/172 in the "Experimental" catagory?

Does the insurance go sky high?
Are you limitted to where you can fly it?
Does the value go down?

If you really like your plane and you plan on keeping it for a long time what would it matter?

Thanks

W.

[Bruce Fenstermacher]

Well you just can't "put" your airplane in the experimental category. There would have to be a reason. There are 9 different types of experimental aircraft. The one we are most familiar with is armature built aircraft and that category of aircraft has most of the freedoms of regulation that we would like to enjoy. One of the limitations of armature built experimentals is that an armature must build 51% of the aircraft. In order for a 170 to be an armature build experimental you would have to prove that your or some other armature built more than 51%. Probably not happening any time soon.

There are two categories of experimental aircraft that you could place your 170 in and that is exhibition only and research and development. In both of these cases there are restrictions as to how and where you can fly your aircraft.

Most of the time you name a home airport and you must remain within 300 nm of the airport and you may not be able to land or depart any other airport. You might also have to give prior notice to your local FSDO of everywhere you want to fly before you go and I don't mean like filing a flight plane minutes before departure, I mean several days notice. Some aircraft have very strict restrictions others don't seem to have many. You also are not free to maintain your aircraft as you wish with any parts you wish either.

FAR 21.191 and 21.193 covers the experimental category.

What is your airplane worth as an experimental. Not as much in my mind as if it had a Standard Category airworthiness certificate. How much would insurance cost? Probably not any less if not more.

[blueldr]

Any certified aircraft that is changed to an experimental catagory will have restrictions on its operations. it may be for "Exhibition", Or development (of an STC for a different engine, for example). It cannot be in the catagory of an experimental home built which would allow operation,for all practical purposes, just like a certified airplane. If it could be operated in the manner of a home built, you can bet there would be a ton of them changed.

[W.J.Langholz]

Any certified aircraft that is changed to an experimental catagory will have restrictions on its operations. it may be for "Exhibition", Or development (of an STC for a different engine, for example). It cannot be in the catagory of an experimental home built which would allow operation,for all practical purposes, just like a certified airplane. If it could be operated in the manner of a home built, you can bet there would be a ton of them changed.

Blueldr, as my son says, you're picking up what I'm laying down. I realize you just don't "PUT" anything anywhere,except my reading glasses that I can never find, but now that I have had this o-300 apart it sure reminds me of a VW Bug engine. There are somthings that you could do to this engine that would jazz it up alittle,make it more efficient so to speak. It is 50+years old and if you mess with it too much then it's not a classic it becomes a 'hotrod" which for some is what they're after and that's fine also. I'd just like to tighten things up alittle maybe just alittle more compression etc. How else do things get better if someone isn't out there messing with things. I'll see if I can't fine someone that has a R&D experimental or maybe there is someone on this site also that could add some thoughts. If it's 300nm from home........how many times do you get that far from home anyway?

[Bruce Fenstermacher]

W you don't get the benefits of the armature home built category. You still need to be a mechanic. You still need to follow 43.13. You still need inspections, though while in the category it might only be a condition inspection.

Did you miss the possible restriction of not being able to operate out of any other airport but your own. No more flying somewhere for breakfast. You may not be able to carry passengers as well. I've also been told that for in the R&D category of experimental the airplane can not be operated indefinitely.

Believe me and BL that if this was a good deal I would have done it years ago and I would have been years behind BL and we wouldn't be alone.

[GAHorn]

In addition to what's already been said,... there's no quick and easy "hotrod" fix for this engine or the mfr'r and lots of owners would have already done it. One of the reasons that certification standards are what they are is to protect the rest of us from unauthorized modifications that may not be readily apparent, yet may carry significant risk. A simple "polish" job on the exhaust ports of your cylinders might look very promising to you if you've done it many many times on your super-modified dirt-track racer. But doing that on an aircraft cylinder might lead to head cracking that could kill you on a nighttime takeoff.
And the subsequent owner wouldn't know about it when he bought/flew it because it was never documented because the guy who did it knew it was illegal and didn't write it in the logbooks.
(This is not to start an argument about porting/polishing...it's to give a simple example of how simple things can go seriously wrong. Not long ago a simple tool-mark on crankshafts was the impetus for a large re-call of aircraft engine crankshafts because of cracking. A cracked cranshaft on your VW bug engine is no big deal. But let that happen in a 170B over the Texas Hill Country late at night and I can tell you it's a BIG DEAL.)

You want more horsepower? Install a bigger aircraft engine and either get it approved or fly it in experimental category while you attempt to get it approved. But like Bruce said, expect some restrictions in your life-style.

Worse, try to return the aircraft to standard category and see the can-of-worms you opened. Ol'Gar knows of a very nice 172 he'd like to own except some fool converted it to experimental category for unknown reasons and no inspector or FAA-type wants to deal with it, so this beautiful airplane is sitting in the piney-woods rotting at the tie-downs.

[blueldr]

Bill Langholz,
If you think you might enjoy an extra ten or fifteen horsepower and feel "Bootleggerish", like I sometimes do, threre are always Continental C-85 pistons available. They will boost the compression enough to give you a little bump, and they're pretty difficult to detect once the engine is assembled. The necessary machining is minimal and can be done by almost anyone with a lathe. At least, that's what the big boys tell me.

[ron74887]

BL, I was going to say what you stated except I didn't want to start something. the race (reno) boys do this to the 0200 and talking to shop in CA., they do it quite often. Need to 45 the top of the piston to keep it from touching(hitting). Only thing is if the cylinder could hold compression factor for how long? With the low compression of the design with higher compression would cracking happen quickly?
From what they said doing this can make you about 165-180 Hp. without changing anything. may have to alter the prop? Probably have to get the AI from AZ to sign it off but no one would ever know till it was pull apart. (after the accident ) I thought about this while talking to the guys never did. Ron

[jrenwick]

You can get a slight increase in compression by milling the case halves down to the manufacturer's limit. That's a small improvement, but it's legal.

John

[GAHorn]

You can get a slight increase in compression by milling the case halves down to the manufacturer's limit. That's a small improvement, but it's legal.

John

Yes. A humid day completely negates it.

[jrenwick]

You can get a slight increase in compression by milling the case halves down to the manufacturer's limit. That's a small improvement, but it's legal.

John

Yes. A humid day completely negates it.

We have fewer of those in Minnesota than in some other places I can think of!

John

[Joe Moilanen]

A friend of mine put the C-85 pistons in his 170, and I have to admit, the difference did impress me somewhat. He has even more power now that he installed a 0-360 A1A in it. He was forced to install another engine, something about a total engine failure on the previous one...something about some type of top end failure in flight... can't remember all the details...

Joe 4518C

[Bruce Fenstermacher]

The difference in the piston pin position between the C-85 pistons and the 0-200/C-145/0-300 pistons is .25". or maybe it was .125" with the 0200 connecting rods being .125" shorter I can't remember. Let me explain.

Under STC I have a 0-200 crank in my C-85 on my Cub. The throw on the 0-200 crank is .25" longer but using the 0-200 connecting rods and 0-200 piston brings that back to nearly the same height at TDC as a C-85 so no clearance problems. In this case the C-85 ends up being stroked but that is not recognized by the Feds because it is within their allowable tolerance. It is said but never measured that this combination yields at least 100 HP if not a bit more out of the C-85 not all because of the stroking but because in part the stock C-85 cam works better than the 0-200 cam. I believe it.

So again while I don't remember the exact number if you swap a C-85 piston for a 0-200/C-145/0-300 and do nothing else you are increasing piston travel measured at the top of the piston at TDC at a minimum .125" and maybe as much as .25". That is one heck of an increase in compression either way.

[cessna170bdriver]

So again while I don't remember the exact number if you swap a C-85 piston for a 0-200/C-145/0-300 and do nothing else you are increasing piston travel measured at the top of the piston at TDC at a minimum .125" and maybe as much as .25". That is one heck of an increase in compression either way.

The standard compression ratio on C-145/O-300 engines is 7.0:1. The bore is 4.06" and the stroke is 3.875". If I did the math right (I'd welcome anyone to check me), a 0.125" taller piston would increase the C.R. to 8.44:1. A 0.250" taller piston would raise it to 10.79:1. This is just geometry; I'll leave the debate of the desirability of such a modification to others.

Miles

Note: I found an error in my original calcs, and modified my original post accordingly.

[johneeb]

So again while I don't remember the exact number if you swap a C-85 piston for a 0-200/C-145/0-300 and do nothing else you are increasing piston travel measured at the top of the piston at TDC at a minimum .125" and maybe as much as .25". That is one heck of an increase in compression either way.

The standard compression ratio on C-145/O-300 engines is 7.0:1. The bore is 4.06" and the stroke is 3.875". If I did the math right (I'd welcome anyone to check me), a 0.125" taller piston would increase the C.R. to 7.2:1. A 0.250" taller piston would raise it to 9.16:1. This is just geometry; I'll leave the debate of the desirability of such a modification to others.

Miles

Miles I get C.R.s 8.44:1 using a piston that is .125 inches taller and 10.79:1 using a piston that is .25 inches taller. Here is my math please check and see if it makes sense.

The bore 4.06" gives us a piston top circle whose area is 12.95 square inches (Pie x R squared), this circles area times the stoke 3.875" gives us a swept volume of 50.17 cubic inches (12.95 sq.ins. x 3.875"=50.17 cubic inches) add the swept volume plus the stock Combustion Chamber volume (8.36 cubic inches) and divide by the stock Combustion Chamber volume (8.36 cubic inches) to find the Combustion Ratio ((50.17+8.36)/8.36=7:1). Now if piston moves up the bore .25" further we have to reduce the Combustion Chamber volume by the piston top area (12.95 square inches) time .25" yielding a reduction in Combustion Chamber volume of 3.24 cubic inches (12.95 sq. ins. x .25" = 3.24 cubic inches) so the stock Combustion Chamber Volume (8.36 cubic inches) minus the 3.24 cubic inch reduction gives us a new Combustion Chamber volume of 5.12 cubic inches (8.35 - 3.24 = 5.12 cubic inches). Back to Swept area (50.17 cubic inches) plus new Combustion Chamber Volume (5.12 cubic inches) divided by new Combustion Chamber Volume (5.12 cubic inches) equals new Compression ratio (10.79:1) ((50.17+5.12)/5.12=10.79:1)

Why didn't we have Excel when I was in grade school?