Hey Guy's... So I'm getting ready to weigh my Cessna after all the mods are complete. But I have a question about useful load and flap settings. My setup is a 172D with the 220HP Franklin conversion. The gross weight in the STC is listed at 2,499 and there is no limitation on the flap setting. I can go all the way to 40 degrees at 2,499lbs.

So here is the question: Why do the other engine conversions limit the flap setting to 30 degrees to get to 2,500lbs? Otherwise at 40 degrees the useful load is 2,300'ish.

Thanks for any insight!

Jim

I am unfamiliar with the legal restrictions. From a how do they fly point of view, weight, high density altitude, and lack of horsepower or gravity energy all make the airplane work harder. Think slow flight with sloppy controls and poor zoom reserve. Pulling the extra air (parasite drag) of the last notch of flaps will work fine going down (gravity energy) but make level or climb more difficult.

I have gotten around the patch with pretty heavy 150 hp 172s and 40 degrees of flaps. I would think 220 hp more than enough. Breakers are better than fuses because you can find them and hold them in. Just don't try to go up. Use critical vertical space available.

contactflying wrote:I am unfamiliar with the legal restrictions. From a how do they fly point of view, weight, high density altitude, and lack of horsepower or gravity energy all make the airplane work harder. Think slow flight with sloppy controls and poor zoom reserve. Pulling the extra air (parasite drag) of the last notch of flaps will work fine going down (gravity energy) but make level or climb more difficult.

I have gotten around the patch with pretty heavy 150 hp 172s and 40 degrees of flaps. I would think 220 hp more than enough. Breakers are better than fuses because you can find them and hold them in. Just don't try to go up. Use critical vertical space available.

Dude, you lost me? I get the whole its harder to get out of trouble with 40 degrees and it takes horses to do it... I'm just asking why the limitation on other conversions...

There are lots of things that MAY place a restriction on an airplane. And one of those things is which office of the FAA approved the airplane or modification.

Lots of examples out there. Also, bear in mind that certification sort of assumes that a pilot with “average” skills is going to be flying this thing. Subject to a little interpretation?

So, the mod on your plane may have been certificates in a different office than the others, or it’s possible that the extra horsepower and a more common sense engineer considered use of full flaps to be safe on your conversion.

Every set of floats I’ve seen that have compartments are required to have weight limit placards.....except one model of floats. I asked the manufacturer off line what that meant.....response was there’s no limit, but don’t make noise about this, or they’ll go back and issue a new requirement. In this case, the FAA engineer who inspected them for certification missed that......

And, in any case, lawsuits are the single biggest driver of such limitations. Maybe your mod just hasn’t been really unlucky yet.

Lots of possibilities.

MTV

mtv wrote:There are lots of things that MAY place a restriction on an airplane. And one of those things is which office of the FAA approved the airplane or modification.

Lots of examples out there. Also, bear in mind that certification sort of assumes that a pilot with “average” skills is going to be flying this thing. Subject to a little interpretation?

So, the mod on your plane may have been certificates in a different office than the others, or it’s possible that the extra horsepower and a more common sense engineer considered use of full flaps to be safe on your conversion.

Every set of floats I’ve seen that have compartments are required to have weight limit placards.....except one model of floats. I asked the manufacturer off line what that meant.....response was there’s no limit, but don’t make noise about this, or they’ll go back and issue a new requirement. In this case, the FAA engineer who inspected them for certification missed that......

And, in any case, lawsuits are the single biggest driver of such limitations. Maybe your mod just hasn’t been really unlucky yet.

Lots of possibilities.

MTV

I would have thought that more HP would be safer with more flaps then less HP with more flap. Counterintuitive...

FWIW the 150hp conversion STC for my old C150TD called for an "intentional spins prohibited" placard.
Reason being is because the STC holder didnt want to spend the money to test spin recoveries.
30 drgree flap limitation might be for a similar reason.

Just consider it a small gift from the STC gods, smile, and go fly that thing at whatever flap setting makes you happy.

jaudette wrote:I would have thought that more HP would be safer with more flaps then less HP with more flap. Counterintuitive...

Have you performed a trim stall? Will make it very intuitive.

-asa

asa wrote:

jaudette wrote:I would have thought that more HP would be safer with more flaps then less HP with more flap. Counterintuitive...

Have you performed a trim stall? Will make it very intuitive.

-asa

I have... Useful practice!

jaudette wrote:

asa wrote:

jaudette wrote:I would have thought that more HP would be safer with more flaps then less HP with more flap. Counterintuitive...

Have you performed a trim stall? Will make it very intuitive.

-asa

I have... Useful practice!

Yeah they can be eye opening. No idea if that's why flap use is restricted with more HP, but it just popped into my head. Sounds like you got a good STC!

I think all pilots should be required to do five hours of spin training. In the last month I went up with an acro instructor and did a few hours of spins in my RV-7. It had been years since I had done them. With as anal as the FAA is, can't believe they haven't made it a requirement.

Jim

jaudette wrote:I think all pilots should be required to do five hours of spin training. In the last month I went up with an acro instructor and did a few hours of spins in my RV-7. It had been years since I had done them. With as anal as the FAA is, can't believe they haven't made it a requirement.

Jim

It used to be. Then CFI's did them stupidly and killed students, and I think the FAA determined there were more people dying from incompetent practice than there were from actually encountering one in normal flying. For a while I think it was mentioned as optional in the syllabus, and now it just isn't there at all.

I guess they're hoping that if they train students to stay in the envelope well enough, they won't leave it until they've had more advanced training. Of course, every year at least a handful of pilots prove that idea wrong, but it sounds nice anyway.

Because full flaps have been my default setting, I have found leaving the trim at cruise setting works fine for 100 series Cessnas. The 172 with the O-360 and 180 or 182 , is a little heavier. I assumed the ones with original engines were designed assuming full flaps to be the default.

colopilot wrote:

jaudette wrote:I think all pilots should be required to do five hours of spin training. In the last month I went up with an acro instructor and did a few hours of spins in my RV-7. It had been years since I had done them. With as anal as the FAA is, can't believe they haven't made it a requirement.

Jim

It used to be. Then CFI's did them stupidly and killed students, and I think the FAA determined there were more people dying from incompetent practice than there were from actually encountering one in normal flying. For a while I think it was mentioned as optional in the syllabus, and now it just isn't there at all.

I guess they're hoping that if they train students to stay in the envelope well enough, they won't leave it until they've had more advanced training. Of course, every year at least a handful of pilots prove that idea wrong, but it sounds nice anyway.

Makes sense. I don't recall if it was a requirement when I got my ticket. Of course that's been 28 years ago! I can remember being 15 or 16 and my grandfather throwing the cub into spins and making me recover. A little different back then. I thought it was a perfectly normal thing to do.

contactflying wrote:Because full flaps have been my default setting, I have found leaving the trim at cruise setting works fine for 100 series Cessnas. The 172 with the O-360 and 180 or 182 , is a little heavier. I assumed the ones with original engines were designed assuming full flaps to be the default.

Funny thing... The trim for full flaps and cruise is the same in my RV-7. One bar more for takeoff. They are sweet planes!

On a 172 or a 150, it seemed to take a bit longer to recover with flaps. Tail blanketed more perhaps? Perhaps at rear CG and gross, there might be an issue with cert standards?

Anyways, there's this, for what it's worth:

http://naca.central.cranfield.ac.uk/rep ... n-1643.pdf

asa wrote:.... No idea if that's why flap use is restricted with more HP, but it just popped into my head. ....

Pretty sure the flaps 30 restriction form some conversions is due to the higher gross weight, not the additional horsepower.

hotrod180 wrote:

asa wrote:.... No idea if that's why flap use is restricted with more HP, but it just popped into my head. ....

Pretty sure the flaps 30 restriction form some conversions is due to the higher gross weight, not the additional horsepower.

That’s how the airplanes 360 conversion for the 172 is. Limit the flaps to 30 and get 200 more GW

So that's my question... My GW is already 2,500, not 2,300 and there is no restriction on the flap setting?

Jim, you've seen my airplane. Here's the weird thing about the Avcon conversion--the 2500 lb. GW of the standard P172D (which was 200 lbs. higher than your 172D's 2300 lbs. before your Franklin conversion) was reduced to 2350 lbs. by the Avcon STC--why 2350, I have no idea. No effect on the flaps, however, so I have the full 40 and use it routinely.

I think Mike nailed it--it has a lot to do with the office that approved the STC and not much to do with real aerodynamics.

Cary