Performance Limitations

[Steve Chenoweth]

As the weather gets hot, about 90 degrees, with little wind and high humidity, I find that my performance becomes limited in the no man's land between ground effect and ETL. For example, my Rotor RPM began decaying as soon as I left ground effect departing a local heliport necessitating a quick stop. Gross weight was about 1,566 lbs. Since this was a heliport, I could not do a running take off, so I had to drain out about 5 gal of fuel.

How does this compare with your performance? I think Todd Sanderson said he could do a max performance take off on a 90 degree day with full fuel and 2 people no problem. I've only got 295 hours on the engine since overhaul. Plugs checked, new air filter, etc. Hovers at 25"-26" manifold pressure with 2 on board. Any ideas on "performance robbers" that I should be checking?

[n2141u]

That's the situation I was in just prior to my accident. I don't think it's unusual. As the outside temp increases, the performance really decreases. I think that's called "density altitude".

[donlew]

I also find this with my ship. Hot weather makes it tuff on any aircraft. You really have to watch it when it is hot & humid.

I would like to ride in Todd's ship just to experience all that power. My ship performs well but is subject to the density altitude.

I find that a level attitude transition through ETL helps with rotor RPM. Also you don't want to pull to much collective. I find that this takes concentration on the tach and listening for the sound of the engine to keep up RPM's.

I got some advise from Cy Russem on this and he explained that if you would lean out the mixture just prior to lift off this would increase power. Although he said as soon as you get through ETL go back to full rich being careful not to overheat the engine. He said your passenger might be the one needed to push the mixture back in. Of course making sure the passenger is schooled on the use of the mixture control.

Lets be careful out there. We don't want anyone hurt. Make sure you only land where there is room for ETL.

donlew

[9121u]

Hi Guys I Have Flown In 6 Different Brantlys. Found Out On Hot And Humid Days They Dont Have The Power . Only One Had A Good Power Range And That Was Serial # 5. The Difference Was The BLADES It Had 101 Blades. Witch Ho Dont Know About Them They Are LIGHTER. Witch In Return You Are Going To Have More Power Reserve. But Autos Are Not Going To Be As Gentel. Every Pilot Probley Has Come Across This Problem. I Have. When I Try To Fly Hot And Heavy. I Closely Watch My Manifold Presher When Iam Hovering. You Can Tell If You Have Enough Power. For Foward Flight. When Flight Training Takes Place These Instructors Need To Put More Time Towards This Potincele Problem. Before They SOLO. Before They Find Out The Hard Way. Thats Why We ALL Have To Keep This INFO SIGHT Going.And To Talk About Problems. Even If It Sounds Stupid. You Might Save Some One From aWreck. Or He Or She Might Save YOU. Lets Think Before Take OFF. Be SAFE ITS ONLY A HOBBY. Happy Flying

[bryancobb]

Hi folks:

I'm glad to hear that no one has gotten hurt in these type siuations. I learned to be VERY cautious evaluating my power available at a hover.

My engine is 250 SMOH and it don't make me feel like I have much excess
power with 2 folks and full fuel.

I had to abort a max performance takeoff the other day with my wife on board (PRIOR TO CLEARING THE OBSTACLES). I had to do a 180 degree right yawing turn to get my RPM back, an did a run-on landing.

I was taught to "RECOVER RPM AT ALL COST, NO MATTER WHAT." (Remember RIGHT pedal will help Low RPM Conditions.)

After that experience, I asked myself some questions. I did try Cy's leaning-out procedure and it gave me enough power to get out of here.

I decided that from now on, I WILL NOT do confined-area ops unless my
MAX POWER AVAILABLE is at least 1" of Manifold Pressure, over and above Hover Power.

What do you guys think of this?

[Del Dammann]

A little trick I learned from an old bell 47 spray pilot is to sand
the ridge of paint on the leading edge of the rotor blades so that
it tapers off so you can't feel it. When the paint is sandblasted off the front edge of the blade it leaves a slight ridge, that ridge can rob you of 10 to 15 HP,. the outer 1/3 of the blade is the most important. On a hot day you need all the horses you can find.
also make sure your battery is charged as a low battery can make
your generator pull another 5 to 10 HP

[Steve Chenoweth]

Bryan,

Could you go into a little more detail about how you determine your max power available for confined area operations.

Thanks

[bryancobb]

Steve:

There's lots of exercises and charts and graphs and stuff like that, but I guess the easiest unscientific way is to:

In a stable 3ft hover with the helicopter loaded as you intend to takeoff,
A) note manifold pressure
B) Smoothly roll on FULL THROTTLE momentarily while maintaining heading. ( IF excess power is present, be careful not to overspeed)
C) Note the manifold pressure at FULL THROTTLE.
D) If you cannot get at least 1" above the manifold pressure from step "A"...don't go.