What's your minimum RPM to maintain level flight

[Jim]

I believe Roger mentioned in the carb bowl thread that he needed 4000+ RPM with 2 people. I know that's a lot higher than I use as I generally fly the pattern at 3500 RPM passenger or not. I went out yesterday and sure enough, I could maintain level flight down to about 3300 RPM. That's with 30 gallons of fuel, a 190lb pilot and no pax. Density altitude was about 1200 feet at the time.

 

What's your numbers?

[FlyingMonkey]

Don't you also need to know the prop pitch for a comparison to matter?

[Jim]

Prop pitch will be the most significant factor, but it's not something most CT owners know the absolute value of. I'm still interested in the RPM number.

[Ed Cesnalis]

Don't you also need to know the prop pitch for a comparison to matter?

 

and flap setting and field elevation. At 7,100' I use 4,500 but I am usually slowing as well.

 

when you say maintain at 3,300 that must be at a pretty slow speed?

[coppercity]

I use 3800rpm for slow flight and stall setup as well as downwind power setting. At 3800 -6 flaps you will be around 80kts, flaps 0 around 75, flaps 15, 60 kts, and 30-35 flaps, 50-55 kts all while maintaining altitude. 3300 rpm will be marginal at -6 and 0 flaps but tolerable at 15flaps at around 50kts. An SW will achieve the same at a slightly lower RPM.

[rookie]

A couple of weeks ago I had an opportunity to find out what rpm I could maintain altitude. Had small debris in both carbs but was able to maintain level flight at 3300 rpm. I’m something of a light weight and had approx. 30gals fuel and no significant baggage.

 

I might have been able to maintain altitude at lower RPM but under the circumstances I had other things on my mind

[Gmoore7]

3300RPM will get me 70kts on an average day on downwind and base dropping to 2600 RPM on final.I do have to watch out for wind as we have plenty of it most of the time.

I usually land w/o flaps as I find I have more control especially if gusts or crosswinds are around.

I fly it all the way down most of the time.

Works for me.

[WmInce]

WRT, minimum RPM to maintain level flight . . .

 

. . . "Depends on . . . wind?"

 

How so?

[Jim]

Depends on density altitude, wind, weight, and prop pitch. So many variables involved there is no way to say what a minimum RPM is to maintain level flight. But in general the top RPM at cruise is 5300-5500 dependent on engine type, 912ULS vs 912i. 10% power is around 3500 RPM. speed of descent dependent on glide angle and degree of flap.

 

Getting the CT near stall speed crossing the runway threshold is not only tricky but will result in a hiccup if a crosswind develops at that moment. In fact, stall speed and stalling in general are ill advised unless at altitutde, over 1000 feet AGL at least. The best way to chunk the plane is to stall near the ground too high to land. Or stall at 10 feet or so and land hard or worse, bounce.

 

None of this is about getting the CT near stall speed crossing the runway threshold. The gist of the question was to come up with a data point for continuing on to an airport or not if your engine is not making full power. I have no numbers to back it up, but I'd bet that whatever the rpm, level flight at minimum power would put your airspeed at around 60 knots, which is at least 20 knots above stall. If you make it to the pattern at pattern altitude, landing safely should be a non-issue.

[FlyingMonkey]

. . . "Depends on . . . wind?"

 

 

How so?

 

Good point, a head/tail wind only affects ground speed, not indicated airspeed.

[Jim Meade]

 

I'd bet that whatever the rpm, level flight at minimum power would put your airspeed at around 60 knots, which is at least 20 knots above stall.

My guess is it would be about L/D max, which is essentially best glide speed.

[Bobby CAU]

dear all,

i do cruising with -12 with 4800rpm and got 105 - 110kts, is that ok?

[Roger Lee]

Hi Bobby,

 

That would be fairly normal, but you should keep the cruise rpm over 5000.

[Jim Meade]

dear all,

i do cruising with -12 with 4800rpm and got 105 - 110kts, is that ok?

What is your WOT RPM and cruise speed?

[Ed Cesnalis]

Wind is resistance. We are not talking about speed, we are talking about engine RPM and what it takes to maintain level flight...

 

Not surprised some are confused. Still, like most other subjects on this board, the opinions expressed are a laugh.

 

So many experts, so little expertise.

 

Except for sheer ( gusts ) our planes fly in the relative wind. Your 'resistance' does not come into play when maintaining level flight. You could have 100kts on your nose or a calm condition and the RPM needed to maintain level flight would be the same. The time to get to your destination is increased or decreased by the wind.

 

You are perhaps the boards leader of providing mis-information, you should be learning not criticizing the expertise here. Some examples are:

• insisting that wind affects RPM required to maintain level flight
  
• insisting that the luggage area is within the CG envelope
  
• stating that your ctlsi will go 20% faster [ 147kts ]
  
• insisting that the 912iS has more power
  
• stating that checkrides are done without >15 degree flaps
  

There are quite a few more.. What is the source of your information?

[Doug G.]

I took the recommendation and put him on "ignore" - works great.

[FastEddieB]

Tried it today in the Sky Arrow. 70°, 4,000', 185 lb me and about 1/2 fuel (9 gallons).

 

4,000 rpm was easy, 3,900 was just doable and 3,800 might work for a short while as long as you don't get below Vy (65k in my case).

 

Slower than that you're typically on the "back side of the power curve" and would be best served by holding that speed even if it meant a gradual descent.

[Roger Lee]

I couldn't hold altitude with 2 people at 4000. One at 250 and the other at 210 and 30 gals. fuel. I had an extended glide, but would have been in trouble with no landing sites if it had been real. When the winds calm some here I'll try just my weight and 30 gals. fuel. 4000 may be doable by myself and a flap adjustment.

[207WF]

The min rpm for level flight depends a great deal on density altitude and weight. If you are high (like Charlie Tango is) or hot and heavy (like Roger Lee is) you need more rpm. I have seen it vary between 3200 and 4500 rpm in my bird with flaps 15. WF

[FastEddieB]

Can flaps ever help in this situation?

 

I'd think not.

[coppercity]

Can flaps ever help in this situation?

 

I'd think not.

 

Eddie,

 

We get a lot of extra lift with 15 flaps on the CT without a lot of extra drag so they seem to help some for a given power setting. Assuming your just trying to stay aloft and not in a hurry to get somewhere. Our ailerons are coupled into the flaps as well so we get a full span camber increase on the airfoil, not to the same degree as the flap section but some increase outside the flap section, plus a really clean airframe.

[FastEddieB]

I'm open to the possibility.

 

A controlled test comparing no flaps, 15°, and maybe negative flaps should be easy to pull off.

[coppercity]

I'm open to the possibility.

 

A controlled test comparing no flaps, 15°, and maybe negative flaps should be easy to pull off.

 

And I guess you will want Go Pro video too!

[FastEddieB]

 

 

And I guess you will want Go Pro video too!

 

Was there ever any question?

 

Somebody fly a CT into Copperhill and I'll volunteer as cinematographer!

 

Back on point, this, from Aerodynamics For Naval Aviators:

 

When the flaps are lowered for landing essentially the same items must be considered. Extending the flaps will cause these changes to take place:

(1) Lowering the flaps requires retrimming to balance the nose down moment change.

(2) The increase in drag requires a higher power setting to maintain airspeed and altitude. (bolded mine)

(3) The angle of attack required to produce the same lift coefficient is less, e.g., flap extension tends to cause the airplane to “balloon.”

 

The CT may be a different animal, but I believe that, in general, flaps will generally lead to more power needed to maintain altitude.

[Ed Cesnalis]

i think best l/d is with 15, If i ever hit 15 inadvertently I always balloon.