Mysterious tach markings

[sbav8r]

I'm not following you on the power setting for load factor thing. I could see a power setting for various maneuvers, but for G's. The amount of available load factor will be a factor of airspeed. Granted power settings will control airspeed, but having fixed power settings for G's just doesn't make sense to me. During aerobatics the exchange of potential and kinetic energy (altitude and airspeed) will be varying widely. One power setting would certainly not protect the aircraft from over stress in a straight dive compared to the same aircraft at straight and level. It just seems to me that using the markings for G's would only work in one pitch attitude. Everything above or below that pitch attitude would change the airspeed and therefore the amount of available G's.

Example: 2200 RPM at straight and level produces about 120 kts. At 120 kts I coulld briefly pull 6 G's, anything above that would increase the angle of attack beyond the critical angle of attack and the wing would stall. If I took the same aircraft in the same power setting, except this time, I put it in a dive. That same power setting would now produce much more airspeed and therefore have more available G's. It could overstress the airframe if the aircraft can't handle a structural load limit of more then 6 G's. Same power settings on both, but due to the changes in potentail energy for kinetic energy, the aircraft can now very easily exceed 6 G's.

 

[erj-145mech]

That was the justification behind my opinion.

SBAV8R, do you have an opinion? Or are you just criticizing?

 

[sbav8r]

no and no.

I wasn't criticizing, just trying to use a little deductive reasoning to answer the original question. If it came across that I was being rude in my post, that was not my intention. I'm as curious as everyone else as to what the answer is. If your answer is right, then great. I'm just trying to test the various theories to see what works.

No harmful intent.

 

[A Squared]

If you were at 8 g's, where would you have the power set at?

well, just off the top of my head, I'd think I would have a fairly high power setting, because in an 8g turn, I'd be bleeding energy pretty rapidly. But then I've never flown an unlimited aerobatics plane.

I have never heard of power setting being a limiting factor for acceleration loads. Why would it be. If you're pulling 8 g in a turn, you're pulling 8g that's what the wings feel, they don't feel the power setting.

Additionally, RPM in generally used very little in power settings compared to throttle setting. Remeber this is an engine with a constand speed prop. Manifold Pressure usually plays a much more sgnificant role in settng power. So why aren't there little "g" stickers on the maniold pressure gauge?


So, let's accept for a moment that you are correct. look at the stickers, they are evenly spaced, so the nmissing "2g" sticker, would be at about 92 percent. meaning that if you pull 2 gs, you gotta pull the power back in a 2g turn, or you risk damaging the airplane, according to your theory. Now, I dunno about you, but every plane I've flown is capable of 2 gs, 60 degree bank is 2g in a level turn. It's within the normal operating envelope for every certificated airplane. And I've never heard the you have to reduce power in a 2g turn to avoid airframe damage. So, you're saying that a power setting that any normal or utilitary category aircraft will withstand with no difficulty, will endanger the structire of an SU-31, one of the toughest unlimited aerobatics planes made?

 

[Lilah]

I agree, I don't think we've hit the nail on the head yet.

My guess, and it's a BIG reach, is that it could be a limitation related to rpm vs. altitude in meters, or perhaps some other cooling issue. Could it be settings for the "gill shutters" in front of the cylinders?

I'm doing some searching, but don't have any other ideas...yet.

Lilah

 

[ISaidRightTurns]

Could it be settings for the "gill shutters" in front of the cylinders?

I like that idea, but it seems that would be overly complex for engine cooling. Having 10 different settings of cooling gills.

SOMEONE MUST KNOW!!!

 

[VNugget]

Well, if it should be any valuable clue, there's pictures of other cockpits without those markings, so they're not essential.

 

[Lilah]

I asked a friend who has a CJ-6; and he didn't know, so I've tried going to the source. We'll see if Luiz knows english (my portugese isn't that good), and replies to my email....

Lilah

 

[FN FAL]

I asked a friend who has a CJ-6; and he didn't know, so I've tried going to the source. We'll see if Luiz knows english (my portugese isn't that good), and replies to my email....

Lilah

I spent about 45 minutes last night reviewing a lot of what I could search on www.google.com about su's and tachometers.

The Re-occuring theme seemed to be tach generators and tach's running backwards although I couldn't find a direct source saying this or that.

Maybe Luiz put a different tach generator in and now the tach indicates reverse...his home brew markings could be in percentages of 100% RPM.

 

[A Squared]

I spent about 45 minutes last night reviewing a lot of what I could search on www.google.com about su's and tachometers.

The Re-occuring theme seemed to be tach generators and tach's running backwards although I couldn't find a direct source saying this or that.

Maybe Luiz put a different tach generator in and now the tach indicates reverse...his home brew markings could be in percentages of 100% RPM.

THat's the first theory that makes any sense to me