Cessna 172R Flight Characteristics vs. Previous Models

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silentsage
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by silentsage »

Replies to some questions and tips:

Elevator trim is assigned to joystick buttons using the C172 input configurator.

I ran Accusim after deleting the folder containing client.wyc, no effect.

Same behavior when running AS16 or not.

No issues in the maintenance hanger.

silentsage
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by silentsage »

I think I may have the answer.

I have a copy of the official Cessna 172 1977 thru 1986 service manual. According to the manual, prior to 1981, the elevator trim tab travel was 28 degrees nose up, and 13 degrees nose down. In 1981 it was changed to 22 degrees up and 19 degrees down. The 172P was introduced in 1981 along with a new engine. In the 172P maximum flap travel was reduced from 40 degrees down to 30 degrees down.

The 172R was based on the 172P, and had the same elevator trim tab travel and flap limits. So there is a significant difference between the R model and models prior to the P.

According to the service manual the 172P and 172R used 160 HP engines. I believe the A2A model uses a 180 HP engine. If so, the A2A sim represents a 172R up-engined to 180 HP, which would make it comparable to some of the earlier models (which is a common change when the engine reaches its TBO limit).

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Nick - A2A
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by Nick - A2A »

Interesting points regarding the different version of the Skyhawk silentsage, though it doesn't explain why we're seeing different behaviour with our installations in the sim. :?

Afraid I can't be 100% sure which version of the prop was fitted for my test (away from home right now) but I'm pretty sure it was the standard 75" 70° prop which gives 160 rated BHP. The optional 76" 60° 'S equivalent' prop which can be selected in the maintenance hangar (shift 7) gives 180 BHP as you say, so maybe check which one you've got fitted.

Nick

P.S. ASN-SE wasn't running for the quick test I did. No weather in fact.

EnDSchultz
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by EnDSchultz »

Just tried with the W&B specified (Full fuel, 170lb pilot) with no weather, at sea level, with trim set for takeoff. Looks like there's a substantial difference in takeoff performance between the R and the S prop. The S prop produces substantially more nose up moment than the R. The plane does leave the ground around 65kts and will pitch up until the stall horn comes on around 45kts if you leave the elevator neutral. The coarser R prop rotates closer to 75kts, pitches up to a minimum airspeed of 60-65, and eventually stabilizes around 70.

So based on this, I'd guess the observed difference in behavior is a result of using different props. What a difference it makes!

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Nick - A2A
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by Nick - A2A »

EnDSchultz wrote:So based on this, I'd guess the observed difference in behavior is a result of using different props. What a difference it makes!
Yeah, sounds like it is indeed the difference in props which is the factor here - thanks for doing the test with both. I confess I'd actually forgotten that the prop could be changed until the OP mentioned the 160 BHP vs. 180 BHP thing.

That difference in pitch behaviour during the take-off roll is a bit of a surprise to me. I'll have to take another look at the 'S' prop version when I get home - I guess I've really just flown the standard 'R' prop, except perhaps when I first installed the A2A 172.

Thanks,
Nick

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taildraggin68
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by taildraggin68 »

Just to add to the prop differences observations, the differences between the "R" and the "S" are quite dramatic in many phases of flight. Most notable are the take off pitch and the changes in pitch on power changes. The "R" prop being almost benign and comfortable and predictive, while the "S" is more aggressive and dynamic. I must admit to having been using the "S" prop since purchase and always revert to it after a reinstall. A couple of flights today switching between the two really made obvious the differences using P3Dv3.3.5. Other than this, the 172 seems to function and fly very close to the same in P3D and FSX-SE with no notable differences.

Nick, another way to tell if the update took affect would be to look up and check for the mesh on the overhead speaker.....no mesh=earlier revision (Somewhere around the 182 release/1st update they added the mesh I believe)

Would be curious to know whether the performance differences were intended to be that dramatic or if evolution of the accusim package compounded it?

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Nick - A2A
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by Nick - A2A »

taildraggin68 wrote:The "R" prop being almost benign and comfortable and predictive, while the "S" is more aggressive and dynamic.
Yeah, I'm the other way round Scott! Confess I haven't spent much time in the 172 since the release of the Accu-Sim Pipers and the Skyhawk's bigger sibling, so I'll have to get reacquainted. :)

Useful point with respect to checking if the update took successfully. It would be really handy if A2A could introduce a version number stamp somewhere within the installation (for instance, visible on the shift 2 menu). Quite a few users seem to get caught out when the update doesn't work as expected because they've reinstalled as part of their troubleshooting process. Unless the version number is shown somewhere, and I've missed it...

Cheers,
Nick

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Scott - A2A
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by Scott - A2A »

silentsage,

Just a few notes, first thanks for posting. We love questions like this.

First, the R model is very different in terms of it's weight and balance. We flew both old and new 172's during development and it's actually a bit shocking how different the R feels. It's not nearly as nimble, simply because of it's weight. But it has the larger 360 engine, and even though it's still 160 hp, these same power numbers are deceiving. The 360 feels a bit like driving a big block vs a small block Chevy. Not quite that dramatic, but close.

As for the trim, out of every 172 we flew, every one had it's trim rigged differently. It was a bit shocking to me how many mechanics don't even pay attention to this during annual. However the three R's we tested, while all different, required a distinct trim down after rotation even after we verified the trim was properly set. So we tuned our 172 to these three airplanes.

The 182, otoh, is entirely different in that it won't lift off without you actively pulling it off the ground.

Scott.
A2A Simulations Inc.

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ilya1502
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by ilya1502 »

I dream one day you decide to make an older C172. M, N or P :roll:

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bobsk8
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by bobsk8 »

Nick M wrote:
taildraggin68 wrote:The "R" prop being almost benign and comfortable and predictive, while the "S" is more aggressive and dynamic.
Yeah, I'm the other way round Scott! Confess I haven't spent much time in the 172 since the release of the Accu-Sim Pipers and the Skyhawk's bigger sibling, so I'll have to get reacquainted. :)

Useful point with respect to checking if the update took successfully. It would be really handy if A2A could introduce a version number stamp somewhere within the installation (for instance, visible on the shift 2 menu). Quite a few users seem to get caught out when the update doesn't work as expected because they've reinstalled as part of their troubleshooting process. Unless the version number is shown somewhere, and I've missed it...

Cheers,
Nick
I think that is a great suggestion. I bet there are many users of the 172 that are flying it without being updated.
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silentsage
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Re: Cessna 172R Flight Characteristics vs. Previous Models

Post by silentsage »

Scott - A2A -

Thanks for the info. It's great that we have aircraft that are modeled so carefully that we can have these discussions.

Regarding aircraft-to-aircraft variation, I can confirm that for the older versions of the 172's. I always attributed it to the pounding that rental aircraft receive over the years from use as trainers. The older versions that had Continental engines perform differently from the Lycoming engine versions too.

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