I’m looking at replacing the engine in my 172 within the next 18 months with a 180hp O-360. By doing that I can get an STC to raise my gross weight from 2300 to 2550 by limiting my flaps to 30 degrees.

My “normal” load is around 2100 - 2200 gross when loaded with all of the camping gear and looking for a grass strip to land on. I plan to spend as much of my vacation time looking for new strips in the mountains to camp on after landing. I have large tires and the Cleveland double puck brakes along with the Sportsman STOL kit and PowerFlow exhaust system.

I have no intentions of selling the plane.

I see myself with three options:

1. Modify the flaps and go for the gross increase;

2. Get the STC, stick it in the aircraft files, and do nothing unless I sell the plane. If I decide to sell the plane, offer to have my mechanic perform the STC mod to the flaps if it helps with the sale;

3. Do nothing, save the $100 or so that the STC will cost me.

What advice to you have for me – and why?

Don

Don,

First, what fuel tanks do you have currently installed? You'll find that the O-360 is actually quite a bit thirstier than the 320. So, take that into account in planning.

If twer me, I'd get the stc installed, and limit flap travel, and just not worry about it. In my opinion, you can do most of the things with 30 flaps that you can do with 40. The difference really doesn't change the stall speed much, but it does in crease drag a bit. So--if you really need to lose altitude, practice up on slips to a landing.

I think you may find that the higher GW could come in handy sometime, and I doubt you'll miss that 40 degree flap setting all that much.

I think any of your proposed avenues would work. If you have the small fuel tanks (38 gallons?) then you'll be looking for gas all the time, and you'll want to go to bigger tanks or tip tanks. That equals more weight, both in tanks and fuel.

MTV

How did I put this in Flying Humor?

MTV - I've got the 38 gal tanks, but my bladder range is usually in the three hour range so I don't see that as a problem. I'm just doing it for the bigger horses.

Jr - I even considered (for about 5 seconds) to just consider it a 2550 gross and self limit myself to 30 degrees when above 2300 pounds, but we all know that would be highly illegal.

I don't think I'll ever get it above 2300 since I took the back seat out since I never have more than one friend to take up

Thanks Zane

Don,

With the 38 gallon tanks, you are going to be looking for fuel at less than 3 hours airborne, if you are conservative like me. They just don't give you much range with the bigger engine. My bladder is a limiting factor as well, but I really think you'll find the small tanks kind of scary at times. Also, nowadays, having the ability to SELECT where you fuel up is huge as well. If I top off to 60 gallons, I have LOTS of options on where to buy fuel. If all I have is 37 gallons, I MUST fuel more frequently, and have less options on what price I pay. And, airports as little as forty or fifty miles apart have HUGE differences in fuel costs.

Finally, dodge thunderstorms just a few times, and land at an airport that is supposed to have fuel, but they ran out last week , and you'll suddenly be a believer in bigger tanks, believe me.

I have been there, and done that.

In any case, I think for the price, I'd have the STC done. If I could do it to my 170, I'd do it in a heartbeat, and I'm like you--generally flying by myself with gear and gas.

I think it's a pretty easy decision. And, if you ever do decide to sell, it'll increase the value of the plane.

The loss of the 40 degree setting on the flaps is not a huge deal, in my book.

MTV

Considering he cost of puting an O-360 in a 172, why not just sell the 172 and buy a 182. You can fly the 182 at 65% power and burn about the same fuel per mile as that 172. I sure like 40 deg flaps in the 182B.

Think this has been hashed out before on this forum and probably every other forum.

A good friend has done the 172 engine upgrade and just loves it. He has also put up the money for extra wing tanks. Now he really loves it.

Tim

Does the gross weight upgrade stc require that the flaps be physically limited to 30 degrees? Or can you just placard against use of 40 degrees while loaded above 2300? That'd be the ideal solution.

Eric

Eric, Eric, Eric.....that kind of an approval would suggest that the FAA trusted pilots....

That ain't gonna happen

MTV

Well ! my feelings about the FAA are mutual.

mtv wrote:Eric, Eric, Eric.....that kind of an approval would suggest that the FAA trusted pilots....

That ain't gonna happen

MTV

Well, it's no different than having a different (lower) weight limit for utility category than for normal category. And they do that with factory operating limitations. My 150/150 stc sets a weight limit of 1600 pounds for utility and 1760 for normal. It's a honor system deal for the pilot not to do any utility-only op's at more than 1600 pounds.
But what matters is the wording (or interpretation thereof) of the STC. If it sez "flap travle shall be limited to 30 degrees" I can see a placard, if it sez "adjust flap mechanism to limit the travel to 30 degrees" that's another story.

Eric

hotrod150 wrote:Does the gross weight upgrade stc require that the flaps be physically limited to 30 degrees? Or can you just placard against use of 40 degrees while loaded above 2300? That'd be the ideal solution.

Eric

Come on, you can't apply common sense to the governmental decision making proscess. Actually, I bet the STC holder might have gotten that if they had asked. For example My 210 with flint tanks has a gross weight increase if there is 7gl. in each tip and 2/3 in the mains.

a64pilot wrote:I bet the STC holder might have gotten that if they had asked.

Is the new engine/prop combination heavier than the stock set-up? If the answer is yes, then perhaps flap travel had to be limited in order to avoid running out of elevator at max forward cg. during the flare. Or maybe that's just a possibility and the STC holder didn't want to pay for the testing to determine whether there actually is a problem. So limiting flap travel was the quick fix. I don't know the answer, but if the new engine/prop is heavier, I wouldn't discount there being a real reason.



FWIW.

CAVU

Good point about a heavier engine, but unless the STC changes the allowable CG range, it doesn't matter. I doubt the CG range is different, that does require spending quite a lot of money on your favorite DER.

I'm not sure I understand the terminology well enough to discuss this intelligently, but I won't let that stop me from trying. Anyway, if the engine and prop are heavier, it seems like the cg of the empty airplane would shift forward, and it would become easier to load the airplane out of forward cg limits. So allowable the envelope would not change, but the actual center of the empty airplane would shift. I'm no DER and couldn't play one on TV. I can understand why someone might not want to do all of the engineering, though.

CAVU

CAVU, your correct in everything you say. To certify an airplane to a certain CG envelope, the aircraft must be flown at min. weight and max gross weights at those limits. So there is no difference in a heavier engine and prop, except less ballast would be necessary to achieve the most forward CG limit for testing.
Now real world it may be a lot easier to load an aircraft out of CG, or the aircraft may be operated a lot closer to one of the limits than previously, but that is irrelevant for certification because the aircraft is acceptable anywhere within the CG envelope. You may fly it and think, gee it sure is nose heavy, or I run out of elevator on short final, because it's CG is farther forward, but it's within limits.
Now higher than previously certified gross weights may cause a smaller CG range or some other restriction such as flap travel limits to pass the test flights, hence the possibility of a placarded restriction
I haven't flown the airplane of course, but I'd bet money that at the higher gross weight, at the most forward CG, it run's out of elevator. It doesn't matter that it may not be possible to load the aircraft to max gross and most forward CG. Often as weight goes up, you will see the forward CG limit taper aft for this reason, which would be another way to accomplish the same thing.

I'm just guessing here, but I would venture a guess that the 30 degree flap restriction is tied to the later model higher gross weight 172's being certified by Cessna with max flaps of 30 (I believe to meet balked landing certification requirements with the 160 hp engine). When the STC holders went to the FAA for approval of the gross weight increase they used the later model 172's (including the fixed gear Cutlass which has the 180 hp engiine) as examples. This use of acceptable date (as opposed to approved data) would be less costly than certifying the airplane at 2 different gross weights or the required test flying at the new max gross weight . Just my opinion of how it happened.

Tim

Was just at the annual MN Seaplane jamboree on Gull last weekend.

http://www.backcountrypilot.org/gallery/thumbnails.php?album=725

So speaking of larger fuel tanks for a 172, here's an interesting mod:

THat's a baggage compartment tank. I never liked them, though they are stc'd for the 172 and 170 alike. They add a lot of weight aft, take up baggage space and put a LOT of gas inside the passenger compartment.

As to the limitation of flap deflection, it may be related to load limits at the higher gross weight. Flaps up load limits are quite a lot different than flaps down load limit, and when those flaps go down to 40 degrees, it puts quite a twisting load on the aft spar. That and the climb capability with full flaps might be the reason.

MTV

Okie Bush Man wrote:How did I put this in Flying Humor?

MTV - I've got the 38 gal tanks, but my bladder range is usually in the three hour range so I don't see that as a problem. I'm just doing it for the bigger horses.

Jr - I even considered (for about 5 seconds) to just consider it a 2550 gross and self limit myself to 30 degrees when above 2300 pounds, but we all know that would be highly illegal.

i may be wrong, but the only stipulation for the gross weight increase is the flap limit. Also depending on your type of electric flap control, the ones i have seen is a simple piece of metal screwed to the pannel to limit the flap handle to go past thirty.

What i would do is get the stc, and leave the flaps alone, that way you have it if you ever need it.

P.S. the 180 really woke our skyhawk up... The VG's also helped too

Tom