So I was all set up to take out a rental 172 today up to petaluma for lunch. Preflight is fine (Tiny bit a water in the sump, flushed out just fin) run up is fine (Mag checks are good) go to take off. Throttle to full. Then I go through my three checks on roll (Power, engine, speed) I look at the tach. Its at the bottom of the green are (2200 RPM). I watch it as we roll. Get about halfway down the runway and still now change. I chop the throttle and hit the breaks. Back to the runup area. Throttle full forward. Same thing, bottom of the green arc. I take it back to the FBO and explain the deal to my old flight instructor. He is surprised about it. I talk to the MX guys. they tell me to squawk it. So I do. I tell the owner of the FBO. He goes out and tries it. Same deal. And says (Oh 2200 is fine it will fly no problem. RPM will rise) I have never seen a plane that does that. Including other 172s. If it aint WELL into the green I aint taking it up. Whos right here? Thanks in advance!
Lack of RPM
- Thread starter gator4798
- Start date
JDMcFly
New Member
Who's the one flying the plane?
WalterSobchak
Well-Known Member
:yeahthat:
I belive the other 172 I flew was the same type. I went to take off and at the halfway point when I saw no change in RPM chopped the throttle and hit the breaks. If it aint well in the green I am not going flying. We MX is taking it in for a few other things and their gonna look at the engine at the same time. We all have our fav planes to fly at the FBO. I don't think this will be mine. Simple as that.
Maurus
The Great Gazoo
You should have max power on takeoff, I have yet to fly a C-172 that doesn't hit at least 2500 RPM on takeoff. That is including short-field takeoffs with me checking the power before releasing the brakes. If you start up an engine and go to full power, you should get an almost full power indication. Pipers do the same thing. The Arrows I have flown with the constant speed props show 2600 to 2700 RPM on takeoff.
If you don't get full power on your takeoff roll once you put in full power, abort the takeoff. Simple as that. You did right by aborting the takeoff and taxiing back to the FBO.
If you don't get full power on your takeoff roll once you put in full power, abort the takeoff. Simple as that. You did right by aborting the takeoff and taxiing back to the FBO.
Nihon_Ni
Well-Known Member
The POH and I disagree with you:
Amplified Procedures
Takeoff
Power Check
It is important to check full-throttle engine operation early in the takeoff run. Any sign of rough engine operation or sluggish engine acceleration is a good cause for discontinuing the takeoff. If this occurs, you are justified in making a thorough full-throttle static runup before another takeoff is attempted. The engine should run smoothly and turn approximately 2300 to 2420 RPM with carburetor heat off and mixture leaned to maximum RPM. (p. 4-13)
I too have never seen a plane that wont hit at LEAST 2500 on full throttle. Did not seem right. But all is well. I got to do my first aborted take off. MX is going to take a look and I'm gonna keep an eye on the squawks. But thanks for all the input.
Shorts465
New Member
I had the same thing happen to me about 2 years ago as a CFI. We were going to do a cross country; the engine started and had a good run-up. It was a 172R with a fuel injected engine, so we would bring the engine up to 2000 rpm for the run-up. On takeoff I checked the tach and noticed that it stayed at 2200 rpm, which was a little low, but there was also no increase as our speed increased on the takeoff run. We aborted, tried a static run-up; it would still only produce 2200 rpm. We tried a "high speed taxi run" on the runway and the condition did not improve. We brought it back and latter MX said they did a static run-up on it and it worked fine. I was never been able to figure it out, and took the plane up in the future with no problems. It was a pretty cold morning, and I'm not one of those guys that runs the engine on the ground until the oil temp is in the green, but I don't think that would have a significant effect on a NA low performance piston engine.
caliginousface
Frank N. Beans
Where do you fly out of?
E_Dawg
Moderator
Or, beat the crap out of the gauge until it shows what you're looking for.
If that doesn't work change your vantage point so the needle lines up with what you want to see.
If that doesn't work, well the above probably took long so long it's time to rotate anyway.
Just kidding, don't do any of those.
DE727UPS
Well-Known Member
If it was a cruise prop, I'd not get worried about 2200. I've seen it before. It should turn up fine at cruise airspeeds. However, if you've flown this airplane before and it had a higher static RPM, I'd be concerned. Did you try to lean it out to max RPM? Sometimes you can get an extra 100 rpm static by leaning the mixture.
ILS37R
Well-Known Member
If you're not comfortable with the plane, don't fly it. If, after you taxi back, a look through the POH and a talk with maintenance can convince you that your trepidation is unwarranted, great. If not, oh well. This is especially true for a rental aircraft with which you're not individually familiar.
Was it safe to fly? Probably. Maybe it had a cruise prop. Regardless, as PIC it is your responsibility to ensure the safe conduct of the flight. If you're not fully confident of the plane's (or your) ability to complete the flight, don't leave the ground.
You made the correct decision.
Was it safe to fly? Probably. Maybe it had a cruise prop. Regardless, as PIC it is your responsibility to ensure the safe conduct of the flight. If you're not fully confident of the plane's (or your) ability to complete the flight, don't leave the ground.
You made the correct decision.
trafficinsight
Well-Known Member
Static RPM should be 2270-2370 for a 172M and 2280-2400 for a 172N.
A little error in the tach, a little wind, a little parallax error and, who knows, maybe the engine is a bit tired... Now you have it reading a bit low.
My guess, it was probably okay, perhaps the tach is reading a bit low, but I'll bet the mechanic was impressed that you actually checked static RPM. We had a 182RG that flew around for weeks before anyone mentioned it was only making 2150 on takeoff. Must have made for some interesting departures
. Constant speed props should make redline every time with the prop full forward whether you are moving or not.
That's the problem with renting... if it was your plane and you flew it all the time you'd know when the slightest thing was amiss.
A little error in the tach, a little wind, a little parallax error and, who knows, maybe the engine is a bit tired... Now you have it reading a bit low.
My guess, it was probably okay, perhaps the tach is reading a bit low, but I'll bet the mechanic was impressed that you actually checked static RPM. We had a 182RG that flew around for weeks before anyone mentioned it was only making 2150 on takeoff. Must have made for some interesting departures
. Constant speed props should make redline every time with the prop full forward whether you are moving or not.That's the problem with renting... if it was your plane and you flew it all the time you'd know when the slightest thing was amiss.
Yea I'll read through the POH later (Its currently outside in my truck and its COLD out there) and talk with MX and see what they say. Maybe take my old CFI out to lunch in it just to be sure. It was the first time in that plane. It was also the first time I saw the needle that low while rolling down the rwy. Thanks for all the input!
trafficinsight
Well-Known Member
The 172R is a little different, it's a 180hp engine de-rated to 160hp. Basically the length and pitch of the propeller limit the RPM to those low numbers so the engine can only make 160hp.