(I’m trying to keep issues in their own topics, hope that’s OK)
If I pick up into a low altitude IGE hover, basically 1-2 meters (3-6ft), my understanding is that I should be able to take off by easing forward until I pick up enough speed for ETL and then I should be able to climb out. “If you have enough power to hover, you have enough power to fly” is what I was taught.
I should also be able to hover-taxi around at this altitude with no problems so long as I take it slow and don’t outrun my ground effect.
What I’m experiencing, however, is that no matter how gently I ease forward I outrun my ground effect and descend towards the ground. I continue descending as I accelerate until I either hit the ground and stop or achieve ETL and climb out (And from those low altitude hovers I always hit the ground first)
So not only can I not take off this way (I either need to start from a higher hover or add collective as I go), but I cannot hover-taxi around the airfield without sinking down to the ground constantly.
Is my understanding of this issue correct? Is this something that can be addressed?
This is probably hard with the governor.
What you can do, is to ‘top of the rpms’. Get the RPMS in the high end of the green, pull it op a little bit, milk the RPM’s back and then gently nudge forward.
You’ll still lose a foot or two, but as you drop down, you’ll gain a bit more ground effect.
Terminus thank you for the feedback. I’ll talk this over with our flight model expert. My assumption is that there’s a zone between a hover and ETL, where some of your lift is lost to acceleration, but I could be wrong on it, or that zone could be too large. I’ll find out for certain.
If you need me to clarify or to record a video demonstrating anything let me know, I can definitely do that.
My assumption is that there’s a zone between a hover and ETL, where some of your lift is lost to acceleration
Yes that’s true, but ground effect (especially so close to the ground) should negate most or all of that as long as you don’t outrun it.
What concerns me is that I can’t move at all without sinking. I should, for example, be able to hover my way over to the parking spot beside me without constantly descending when I move.
I could also be trying to hover too low, but I’m lead to believe that helicopters like this one typically don’t hover very high. So it would be interesting to know:
- What is the optimum hover height for the 47?
- What is the minimum hover height to be able to take off with cyclic inputs alone?
Ground effect should be half of the rotor disk diameter. I’m experiencing the same loss of lift in ground effect but since I’ve never flown a Bell 47 I can’t pinpoint whether it’s type related or flight model inaccuracy.
The B47 rotor diameter is 37’ minus the height of 9’ is 28’. So you can expect to be ground effect up to 14’
The effect gradually reduces the further from the ground and is also dependent on surface variation. So 10’ would be a good safety factor to remain within.
In a R44 I was taught to maintain a 3-5’ hover for ground maneuvers. I would expect similar on the B47. At that height you would be in ETL before you outran the ground effect.
During a takeoff run in a 44 starting from a 5’ hover you may sink to 3-4’ before ETL takes effect and you have to push the cyclic forward to avoid climbing prior to accelerating to 45 kts for climb out.
I just confirmed with our Rick - it’s normal that you’d have to feed in power as you transitioned. As you pitch forward you’re going to lose lift (after all, part of your lift is now tilted backwards), and it will take a few seconds to reach proper ETL speeds.
It’s definitely possible to do it without, but it does require good RPM management.
It would be great if Rick could do a familiarization training video for pilots new to a B47.
Take us around the pattern. Run through maneuvers, speeds and power settings. What speed for rate of climb, decent, auto entry. Anything useful he can think of.
So far, I feel like it behaves like a real helicopter, but feels mushy and sluggish for a ship this size. As compared to my experience in Robinsons. Kind of like flying the Raven II with the hydraulics shut off. Right on the mark for what I would expect from a design of this era.
I got a bunch of autos from my training here:
Best speed: 45mph (Also minimum speed for the flare)
Extended range up to 60mph
I also found a transition/take off:
21"-21.5" on take off. It’s not a lot of extra power.
Another good video showing IGE to ETL 21"- 21.5"