new member, new project...

[N171Q]

Greetings to all from balmy Anchorage. I just joined up and wanted to say hi.

I currently fly a little PA-22, but just bought a '56 172 tailwheel that needs to be put together after 10 years of disassembly. It looks complete and came with a shiny 0 SMOH Avcon O-360 conversion, but no prop, so I'll be shopping for one of those...

I've already been searching through the old threads and have picked up tons of useful info on some of the things I'm dealing with (float kit, cargo door, etc). Man, that gahorn can type! Seriously, this place is a great resource.

A couple of questions I needed some advice/input on as I get going on this project:

1. On the engine mounts at the firewall; Do I go with rubber or aluminum bushings? The plane came with new-looking rubbers in the mount holes that I think came with the Avcon conversion, but my mechanic thought aluminum would be better, and the drawings look like aluminum... anyone with the Avcon setup have an opinion?

2. Float kit; Configure for 170 floats or 172 floats? I could go either way, but is there more availability or issues with one type over the other?

3. 175 tanks; Seems like the consensus is the stock 172 tanks are a bit short-legged for the 180hp. Are the 175 tanks impossible to find, or should I look to other options?

Any input would be great, and if you're in the area, PM me. I'm looking for all the help I can find... moose season is almost here!

J.R.

[GAHorn]

Hi, J.R.! Welcome! (I thought someone shot you down in Dallas!)
Being as how you've apparently re-located up to God's Country, I imagine it'll be a lot easier for you to modify your airplane as you indicate.
I can't speak about floats, but the 175 fuel tanks would give another 10 gallons. 175 wings might be the better route, tho', as you'll save having to cut up the inner bays of a 170/172 wing. You'll want to think about the fuel indicating system.... The 175 had electric gauges while the 170's had mechanicals.
(If money/trouble were no object, I'd install a new set of 175 tanks that had been modified with mechanicals, as my personal choice. This would get around numerous flap/cable issues that can come up with complete wing-swaps. It'd take a good welder tho', which I'm not.)

[N171Q]

Thanks George,

I've been to Dallas once, and managed to escape unscathed...

I was able to get out this weekend and peek under the skirts of some other local Avcon 170s and they all had the rubber mounts on the firewall.

Good advice on the 175 tanks v. wings. I'm still hunting for those.

[jlwild]

J.R.

Look in the library section of the forum. If you are a member, you can contact Velvet at headquarters and obtain a copy of 337's/STC's on: a) Fuel Tank C-175 26.5 gal (170B) or b) Fuel Tank Dual System Left wing.

I don't know anything about the two systems, or whether they are STC's or 337's. Perhaps others have had some experience on these systems for float planes.

[sphillips]

I'd contact Avcon as to the engine mount- to- firewall install to make everything legit.

[n2582d]

In looking at the TCDS for the C-175 it looks like one has to carry around a lot of unusable fuel -- anywhere from 54 to 63 lbs depending on the model. This seems like a high penalty for the additional 5 or 6 gals. of fuel one would have if one were to use these tanks in a C-170 . This weight would be in addition to the heavier C-175 tanks. For comparison, in the 170B we carry around 30 lbs. of unusable fuel. If one is going to go to all the trouble of getting a field approval for longer range tanks would tanks from a 172R or S (56 gal. / 53 gal. useable / 18 lbs. unusable) be a better option? Or maybe the 172 RG/R172K/172P which shows 66 gal. total/ 62 gal. useable/ 24 lbs. unusable. If I'm not mistaken Del-Air's modified tanks retain the same 30 lb. (6 gal.) unusable fuel weight penalty of the original 170 A & B tanks.

[GAHorn]

I believe it's a matter of plumbing, as well as the definition of "unuseable fuel".
Unuseable fuel is that fuel which is not capable of being used in all flight attitudes. The C-175 carries 52 gallons of which 10* are "unuseable" due to the shape of the tank vs. the location of the plumbing. (At high angles of attack, such as during a short-field takeoff, that last 10 gallons may not be reliably fed to the engine. This is due to the "L" shaped tanks, which allow a larger portion of the fuel to flow into the rear of the tank...away from the forward fuel-feed line (in a C-175).
*(-In fact, the exact amount/weight of unuseable fuel varies from 9, 10, or 10.5 gallons or so depending upon which exact year/model 175 is concerned, due to minor plumbing changes.)
The 170 is a different matter for several reasons. It's fuel feed lines are located at mid-chord. Therefore about 5 gallons is not reliably fed to the engine in extreme nose high/low attitudes and uncoordinated turns deprive the low-side tank from feeding. In straight and level flight almost all the fuel will feed...same as in a 175. (Although notice that such "red lined" area of the 170 fuel gauges is not a required placard...but only advisory.)
In both airplanes, a minimum of about 1/4 tank of fuel (in each tank) should be onboard before a takeoff is attempted, and BOTH tanks should be utilized for takeoff and landing.
(I have personal knowlege of a 170B that was flown until 41.5 gallons were consumed, and when the tanks were refilled they accepted 41.5 gals. The same guy also once flew a 175 until 51 gallons were re-filled into the tanks. I know this guy personally... ....name being witheld until the statute of limitations has run out... he claims to have performed this feat in an "experiment" directly over an airport and landed in a very flat attitude with sufficient speed to coast to the fuel pumps.... although I have it on good authority that the 170B "experiment" was due to miscalculataion and inadvertently overflying an intended fuel stop with a tailwind.)

When I finally get to the point that my engine requires overhaul, I'm dreaming of my TCM O-360 conversion, and the installation of the 175 fuel tanks I'm jealously guarding in my hangar. (At the same time, I expect to relocate my fuel vent line and dispense with the gooseneck. Alas, my plane's originality will be thoroughly gone, but I'll have a big performance-cushion for my enlarged ego's miscalculations.)

[N171Q]

George, I can't believe what I'm reading!

In all my searching on this site I've read scores of posts from you encouraging others in the virtues of originality and staying true to the classic lines and lineage of the beloved 170! This is no time for compromise! Don't let your heart be turned by some trumped up stories of higher performance!

Help me save you from yourself and sell me those 175 tanks real cheap!

[n2582d]

George,
Tanks for the response! I really like idea of extending the range with the C-175 tanks rather than using the Flint tanks or the aux. baggage tank. The Flint tanks are expensive ($4300) and, I imagine, reduce the roll rate/aileron effectiveness. The aux. baggage tank are hard to find and put fuel in the cabin--a safety concern to me. The Flint website says aux. baggage tanks "change the CG more, take up cargo space, don't carry as much fuel, can have problems with fumes and in a real hard landing can be very dangerous."

You mentioned that at high angles of attack the fuel flows away from the forward fuel-feed line (in a C-175) but in looking at the IPC for the C-175 s/n 55001-17557119 it appears that the fuel outlet is in about the same spot as our C-170 tanks--at intersection of the two angles on the bottom of the tank. Are your tanks from outside this s/n range? I couldn't find any other styles of C-175 tanks in the IPC.

As an aside, I noticed that the the long range fuel tank in in the C-172 & F172 IPC (fig. 11, pg. 30) look identical to the C-175 tank except that the fuel filler neck design seems to be improved.

I'm still a bit confused over what the FAA will allow as usable/unusable fuel on a field approval of C-175 tanks. Their definition is different than yours.

Unuseable fuel is that fuel which is not capable of being used in all flight attitudes.

According to the FAA's Weight and Balance Handbook, one determines unusable fuel by draining "the fuel until the fuel quantity gauges read empty when the aircraft is in level flight attitude. Any fuel remaining in the system is called residual, or unusable fuel and is part of the aircraft empty weight." So, using this definition, your story about the C-175 that was able to burn 51 of the 52 gallons on board would give one gallon of unusable fuel.

But then to confuse the issue the FAA goes on to say, "the amount of residual fuel and its arm are normally found in NOTE 1 in the section of the TCDS, “Data Pertaining to All Models." For the C-175 note 1 reads, "175, 175A, 175B, 175C, P172D, R172E through R172J … The certificated empty weight and corresponding center of gravity location must include unusable fuel of 54 lbs. at (+46) for Model 175, 60 lb. at (+46) for Models 175A and 175B, 63 lbs. at (+46) for Models 175C and P172D, 36 lbs. at (+46) for R17E through R172J" On a field approval for using C-175 tanks in a C-170 does the FAA require one to use these figures for unusable fuel or does one determine that based on how much fuel can be drained in level flight attitude? Legally it makes quite a difference for figuring empty weight and for flight planning.

[GAHorn]

Gary, the Flint tanks also increase the wing span of the airplane...a serious consideration for some T-hangars, etc.
The unuseable fuel definition varies depending upon the purpose. For weight and balance purposes "undrainable, unuseable" fuel is calculated for empty wt/useful load purposes. But for performance/flight planning purposes, unuseable fuel is any fuel that cannot be used in all reasonable flight attitudes.
My previous wording may have been unfortunate, but I did not mean to imply that the actual location of the 175's fuel plumbing was of a particular routing/location especially. The issue with the "L" shaped tanks is that, even with the plumbing located at the same relative point,...more of the fuel is capable of being away from that fuel line in a nose-up attitude because the rear of the tank is larger than the standard 170 tank. Therefore more of the total fuel is capable of being unavailable in a nose up attitude.
I don't have an answer for your question as to what the FAA may require for flight planning purposes, but I'd imagine they'll require the same as for the 175. (It's just that we all know what the real, practical answer really is.... The 175 tanks give us about 10 more gallons of fuel.)

[cessna170bdriver]

Gary, the Flint tanks also increase the wing span of the airplane...a serious consideration for some T-hangars, etc.

Not so for the Cessna 150,152/170,172,175/180,182/210,210A,210-5,210-5A,205 tanks. For these aircraft, the Flint tanks are internal to the existing span. See http://www.flintaero.com/what_we_have/internal.html

Miles

[GAHorn]

Well, DOH!
I had shopped the Flint tanks for my 206 (they add 36 inches) and forgot they were internal on the 170. Thanks, Miles.

[cessna170bdriver]

At one point in my life I was doing a lot of solo flying and shopped around for a way to take advantage of my long range bladder. The Flint tanks were high on the list, as I like the idea of tip tanks better than having fuel in the cabin. The Flints also offer more range (about 3 hours) than changing to 175 tanks. The $$$ was the reason I didn't take the plunge.

Miles

[lowNslow]

My stock fuel tank capacities already exceed my bladder capacity.

[N171Q]

OK. Engine's on now. I'm still working out the 175 tanks... She's looking better already!

It looks like the float kit that was installed (but not signed off) by the previous owner was done according to the parts manual pg.326, but that does not apply to my serial number (28197). The local float shop said I need to comply with cessna drawings 0501080 and 0500070 for it to be legal. Cessna wants $340 ea. and I just can't bring myself to shell out that kind of cash if in fact the work has already been done correctly. Any one out there happen to have these drawings that they'd be willing to share?