OGE Power in Helicopters

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OGE is commonly associated with a height of 1 rotor diameter above the ground. That is, if your rotor system is 30’ wide, at about 30’ above the ground the helicopter leaves ground effect and operates OGE. Simply put, this height and anything above it requires more power because the rotor vortices can build much more drastically than if the ground affects them. It’s important to know if you have enough power for this condition prior to getting into to a point where you may need it. Failure to do so frequently results in aircraft accidents / incidents.

Let’s say you want to fly your helicopter from sea level to a helipad in a mountain city at an elevation of 5,000’. You want to pick up 500 lbs. of cargo and bring it back. Prior to departing, every good pilot should do some performance planning to find out power required and power available. Doing this you’ll use weather information to gather temperature and pressure altitude to determine engine power or Max Torque Available (MTA). Then, you’ll compare aircraft weight to determine how much power is required to hover. All of this information will be unique to your aircraft, the mission weight, and the environmental conditions. All of this information is calculated sing your aircraft’s performance charts in the operator’s manual.

For this example I’m making up figures for the sake of easy math and teaching. Let’s say I calculate at sea level with +20 degrees Celsius my aircraft can weigh as much as 7500 lbs. and have OGE power. My aircraft takeoff weight is planned to be 5,000 lbs. MTA for the environmental conditions is 100%. OGE calculates to be 75% and IGE is 65%. Now lets run the numbers for our destination. Max weight for OGE power comes to say 6000 lbs. We plan on weighing 5500 lbs. after refuel and picking up 500 lbs. of cargo. MTA is now 90%, OGE is 85%, and IGE is 75%. The margin between power available and power required shrinks (from 25% difference to 5% difference) as weight and altitude goes up. The power available comes down because there is less oxygen as you climb and engines hit their limiters sooner.

So now I check the numbers. There are 3 easy ways to validate that you have OGE power. 1st: OGE power required should be less than MTA. 2nd: Actual weight is less than max allowed OGE weight. 3rd: IGE is less than the OGE go/nogo weight. By this I mean there’s a 5% margin between OGE and MTA. So if I add that 5% margin to my IGE number I come up with 80%. Thats my go/nogo number for OGE power. If IGE is less than 80%, I have OGE power. If its greater than 80% I won’t.

One last reason this is useful is that you can adjust based on contingencies. Let’s say at arrival they ask if you can carry 800 lbs. of cargo instead of 500 lbs. Looking at the numbers I can bring up to 1000 lbs. of cargo (Max OGE weight minus non-cargo takeoff weight) and still have OGE power. But if they want me to pick up 1300 lbs. I would have to say no or come up with a takeoff than didn’t require OGE power.

So that’s how you pre-plan power. What if you’re flying right at the edge of OGE power and need a little more lift to just get up and going? That is, OGE power is right at MTA. Here are a few tips:
2. Hunt for the winds. Relax on the pedals and let the aircraft weathervane into the wind. Once you find it, translational lift slowly takes effect and the helicopter climbs more efficiently.
3. Springboard takeoff. Starting from a hover, slightly reduced collective then rapidly pull up collective to MTA/OGE power. The aircraft will momentarily descend and create a high pressure cushion underneath which acts like a springboard to push the helicopter up. The springboard is gives the aircraft extra inertia and is most effective in confined areas where the air cannot escape as easily under the rotor system.

By using one or more of these techniques you can squeak out just a little bit ore lift on your OGE takeoffs. As always, I’m Jacob. Safe flying.

[djameshayes]

I am an old guy who flew Hueys in Vietnam. I love all your videos! Makes me wish I could 'strap' a Huey on again and do some flying.

[rgardner]

Glad you explained the techniques on creating slightly more performance for OGE takeoffs.

[georgedemeris]

Watched your videos on the way in to work and home again for a few weeks leading up to taking the SIFT. Ended up with a 65! These were a huge help, thank you!

[OculusQuestFun]

I've talked about how I'm most interested in the Mosquito Helicopter (XEL), so not every video is pertinent to me, but know that I watch then all.

[Shopweasel]

Now let's cut through the fable scenarios.
Tell us the same parameters on the famous bell 429.
If you would cater to such a request.
These model parameter specifics are non existent on this beautiful fabulous bird.
Would you give a few moments on this?
If so...much appreciated.bezt regards.

[OculusQuestFun]

Those intros man...nice. and thanks for the Out Of Ground Effect video. Super helpful.

[lennertpraet]

Is it posssible to calculate the HOGE ande the HIGE without the charts, if you know the parameters?

[jaafarmahmood]

Is the angle of attack in OGE same in IGE? Can you explain that Jacob … much appreciate

[rszkodzi]

Jacob, the springboard and spiral tips to gain a bit more OGE during takeoff are really interesting. However, doesn't that end at the momemt you reach OGE, so in effect you can get to OGE, but once there, you are still underpowered. I assume the followup technique is to transition to ETL to gain more lift and then begin working your way down the mountainside to thicker air where you no longer have a small variable. Can you explain?

[harishkrishnachaitanya]

Hi, Extremely helpful videos
Can you please make a video on Power Availability and requirements with special emphasis on Range and Endurance.
Density altitude and problems at high altitude...

[biblewaytolive]

To fast and complicated needs to make three out of one video

[cillersbadass]

hey I´ve seen you make really good explanations of helicopters, could you tell me what the advantages of having a rotor design like the Ka50&52 Heli vs the the Mi28 (no back tail rotor vs having one)
I am looking forward to hearing from you!!!

[daycrumpler]

I'm surprised you left out the other option to do a rolling take off if you have a flat area or an aircraft on wheels? Where you have ground run and once you pick up enough speed and the blades experience ETL you now have sufficient lift to climb. Great video nonetheless!

[australianchad]

Nice job mate
Need a new sharpie haha

[truckerray]

Is your onboard fuel weight a cosideration of somekind in these type of factors as well??? Can ya perform a good "springboard" lift off in an wide open accessed area as well???

[dakotarager]

Hey Jacob, I'm very interested to learn more about the springboard takeoff and how the aerodynamics of it work. I can't seem to find anything by looking it up online. Do you have any materials or sites that explain it or another name it is known by? Thanks a lot and thanks for the videos.

[PLISNO]

I like your videos a lot, but I have a question: when someone makes an "spiral takeoff" aren´t they actually decreasing the "Rotor RPM" in relationship to the airflow? Example when you make a 2RPM spiral T.O. isn´t that RPM going to be subtracted from the main rotor (not in the gage, off course), so you end up with 2RPM less, thus decreasing the actual rotor RMP and increasing the conning angle?

I fly Sikorsky S-76 in the offshore industry, sometimes when we are near or at max gross weight with little or no headwind, I feel it´s easier to T.O. by pulling the collective gradually, but with no hesitation, from full down to max takeoff power, being preppare to abort if it fails to leave the ground at 90%Q or have any tendency to a dinamic rollover. This way we are able to takeoff vertically until the 20ft decision point and can fly away, that would be very difficult otherwise.


Best regards from Brazil and keep up the good work!

[OculusQuestFun]

Is there anything I can do to support your channel? Merch, patreon, channel membership? Anything like that? Thanks.