Cessna 172 Elevator sticks out above the stabilizer on the edges... why?

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RyukyuPilot

Filing Flight Plan
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Jeremiah
Hey everyone!
I am a new certified flight instructor that instructs in a Cessna 172G model and I noticed something that I haven't really thought about my entire training. I noticed today that the edges of elevator on the plane stick out above the stabilizer when deflected down(and visa versa when deflected up). I asked a couple instructors and they didn't have an answer. I looked at the top of the rudder and low and behold it does the same thing at the top!
I have been researching google titles for the past 30 minutes and I can't seem to find an answer. They all think i'm referencing the trim tab. The POH doesn't mention anything about it either.
Any of you whiz kids know anything about this or can send me a link to a thread that talks about it?

Thanks!
 
flyingron said:
If I understand what you're saying, it's called aerodynamic balancing. The pivot point isn't at the leading edge of the elevator, such that it pops up into the slipstream in the opposite direction it travels. This allows you to keep the control forces reasonable.

Here's an AVWEB article on the subject: https://www.avweb.com/flight-safety/control-surface-design-keeping-them-balanced/
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Aerodynamic balancing as well as mass balancing for flutter prevention, even at 172 speeds, I think. IIRC, the tip of the horn is a solid weight.
 
Salty said:
Here’s a pic of what the weight looks like on a Mooney. The pic is from a recent AD on them.

View attachment 136788
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First someone shares a link and then a picture of exactly what I was talking about… you guys rock.
Been a long time enjoyer of this website but this was my first post and you guys have shown up and showed out! Thanks!
 
Timbeck2 said:
Based on your call sign here, you wouldn’t happen to be an instructor at the aero club at Kadena would ya?
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Whoa! No sir! But I am a Japanese American born and raised on the Island! Currently stateside working. How do you know about the aero club on Kadena?!
 
Interestingly (at least to me), I can’t find any FAA Pilot handbooks that address this, either in terms of aerodynamic balance or mass balance. I would think that at least flutter would be relevant to pilots.
 
MauleSkinner said:
Interestingly (at least to me), I can’t find any FAA Pilot handbooks that address this, either in terms of aerodynamic balance or mass balance. I would think that at least flutter would be relevant to pilots.
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I also looked into the PHAK because they talk about different aileron types and flap types so I was expecting to find something on elevators but they just talk about T tails and stabilators.
 
MauleSkinner said:
I would think that at least flutter would be relevant to pilots.
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Not really as flutter is a control design issue that would never make it out the gate to be experienced by a pilot. However, where it can surface beyond the design stage is when performing alterations to TC'd aircraft that could induce flutter or in the E/AB world where someone is pursuing a non-standard control arrangement.
 
Don’t exceed Vne and you shouldn’t get flutter in a certified aircraft.
 
Salty said:
Don’t exceed Vne and you shouldn’t get flutter in a certified aircraft.
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Key word “shouldn’t.”

We got what turned out to be trim tab buzz that shook the stick well below Vmo in a Hawker, and one of the winglet mods was prone to flutter for a while.

Much like Mach buffet, if you don’t know it exists, it’s pretty hard to identify what it is and/or what to do about it if it occurs.

Edit: Now that you mention it, a quick check of the Amateur Built Aircraft and Ultralight Flight Testing Handbook has a couple of pages about flutter.
 
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Balance horns were part of the primary groundschool when I took it in 1973. The Canadian textbook, From The Ground Up, covered it, and it's still there in newer editions.
 
MauleSkinner said:
Key word “shouldn’t.”

We got what turned out to be trim tab buzz that shook the stick well below Vmo in a Hawker, and one of the winglet mods was prone to flutter for a while.

Much like Mach buffet, if you don’t know it exists, it’s pretty hard to identify what it is and/or what to do about it if it occurs.

Edit: Now that you mention it, a quick check of the Amateur Built Aircraft and Ultralight Flight Testing Handbook has a couple of pages about flutter.
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Yeah, any type of test pilot should be aware for sure.

And I hear what you’re saying, but if a pilot gets that type of feedback from the plane, I would think get on the ground and don’t go back up would be sufficient. Would I want to know about it? heck yeah, I knew about it long before I took my first training flight. Does it need to be on the test? I dunno.
 
Salty said:
Don’t exceed Vne and you shouldn’t get flutter in a certified aircraft.
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You mean”Don’t exceed TAS Vne and you should get flutter”

I wonder how many pilots can say VNE is TAS by rote, but haven’t really got to the point that they would apply it when flying 15 mph under VNE IAS at altitude. My glider now has a sticker showing the differnt IAS VNE’s at various altitudes.

Brian
CFIIG/ASEL
 
Salty said:
Way And I hear what you’re saying, but if a pilot gets that type of feedback from the plane, I would think get on the ground and don’t go back up would be sufficient. Would I want to know about it? heck yeah, I knew about it long before I took my first training flight. Does it need to be on the test? I dunno.
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I feel strongly both ways. ;)

In our case of trim tab buzz, it was mis-diagnosed. it only happened for 1-2 seconds at a time, normally fairly early in the flight, and we flew with it for the better part of a year before I finally stumbled on the right combination of airspeed and trim that allowed it for a long enough time to realize what it was.

Same with low speed Mach buffet when a couple of our guys stumbled across it…it felt like a stall buffet, but way too low an AOA for that. It was “demonstrated” across a few pilots before we actually buckled down and figured out what it was.

Sometimes this stuff isn’t scary enough to find it necessary to “get on the ground and don’t go back up.”
 
brcase said:
You mean”Don’t exceed TAS Vne and you should get flutter”

I wonder how many pilots can say VNE is TAS by rote, but haven’t really got to the point that they would apply it when flying 15 mph under VNE IAS at altitude. My glider now has a sticker showing the differnt IAS VNE’s at various altitudes.

Brian
CFIIG/ASEL
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Does your glider’s manual provide that info? I’ve only ever seen it in one POH.
 
MauleSkinner said:
Does your glider’s manual provide that info? I’ve only ever seen it in one POH.
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My current glider (LS6b) has various Vne’s marked on the Airspeed indicator. My previous glider (HP16T) was amateur built so only had one. Vne Published, I assumed worst case that it was a Sea level Vne and created Vne Packard based on that.

1736009979827.jpeg
 
MauleSkinner said:
Interestingly (at least to me), I can’t find any FAA Pilot handbooks that address this, either in terms of aerodynamic balance or mass balance. I would think that at least flutter would be relevant to pilots.
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I was going to make a (snarky) comment about "how to get your CFI without knowing about aerodynamic control balance", but if it is not in the current books issued by the govment, then I can see how that would happen.

Maybe the OP should look up "Friese Aileron" as he is flying a C-172.

I remember when the AD came out to add elevator control balance weights to the Single Engine Comanche elevator. I'm sure everyone is familiar with the balance weights on the Piper Arrow III (and others) ailerons.
 
BillTIZ said:
I was going to make a (snarky) comment about "how to get your CFI without knowing about aerodynamic control balance", but if it is not in the current books issued by the govment, then I can see how that would happen.

Maybe the OP should look up "Friese Aileron" as he is flying a C-172.

I remember when the AD came out to add elevator control balance weights to the Single Engine Comanche elevator. I'm sure everyone is familiar with the balance weights on the Piper Arrow III (and others) ailerons.
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Hey man!
Yea pretty weird it’s not really talked about even in the POH. They may talk about it in some newer models if anyone knows.

I knew about frise ailerons from the handbooks (although depending on who you talk to the C172 doesn’t have true frise-type ailerons).
 
Dan Thomas said:
Balance horns were part of the primary groundschool when I took it in 1973. The Canadian textbook, From The Ground Up, covered it, and it's still there in newer editions.
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Sweet! I’ll take a look thanks for the suggestion!
 
brcase said:
I wonder how many pilots can say VNE is TAS by rote, but haven’t really got to the point that they would apply it when flying 15 mph under VNE IAS at altitude.
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I never knew that, I always figured it was IAS just like every other marking on my ASI. I guess I’ll have to do some reading. Thanks.
 
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