Helicopter electric tail rotors

[Oskar]

oskar

Beware that the Gyrotech blades may not be a direct bolt on and go, the weight distribution through out the blade from the metal to composite blades could be different. From my understanding and findings on their composite blades they do not chordwise balance at the normal 25%. so what they do is overbalance the blade at the tip, so the blade thinks it is balancing at 25% chord. with all the weight at the tip the cone angle and undersling may need to be adjusted. I found this out with the Helicycle I had them make up a set for mine they were to be a direct bolt on with no changes to the rotor system Because the weight distribution through the composite blade was different from the metal blades the cone angle and undersilng would need to be changed.They were going to make up another set of blades that would more match the weights of the Helicycle metal blades. That was almost 2 years ago have not heard a word since then.

Doug

Just my uneducated findings

Doug,

I spoke to someone who installed Gyrotech blades on a Mosquito and he was very happy with the way they flew. Maybe they learnt something from your experience.

Will just have to see how the Gyrotech blades behave when I get into the air.

Oskar

 

[Oskar]

Congrats, Oskar. I'm happy to hear of your progress and would love to see a video.

It sounds like the flying qualities improvements are enough justification for the tilted tail. But I want to make sure I'm not crazy...there is a small efficiency penalty involved, correct? In other words, getting some lift by taking it from the tail rotors (small diameter) rather than the main rotor (large diameter) costs something?

Will you be doing the endurance test soon? Cheers!

Thanks Aaron,

Important to note is that the main and tail are independent of each other, they both have their own batteries.

Looking at ballpark numbers:
AUW = 215 kg.

With non-tilted tail:
MR thrust = 215 kg.
TR thrust = 15 kg.

With tilted tail:
MR thrust = 215-4 = 211kg.
If we assume that MR power is proportional to MR thrust then MR power will drop by (211/215), and
TR thrust = 15kg * (211/215) * 1.035 = 15.236 kg.

MR thrust thus drops by 1.9%, whileTR thrust needs to increase by 1.6%.

Because MR power is much larger than TR power there will be an overall gain, but it will be less than 2%.

The endurance test will be done using the new full carbon machine which is coming along very nicely.

Oskar

 

[MikeBoyette]

So Oscar are you affiliated with Mosquito? What blades are they using now that the blades that made them a viable flying machine no longer available? Would love to see pictures of a set.

 

[Barney Bahle]

I don't have any pictures but CFX is now building their own blades in house. I don't know if they are "technically" available for sale yet but they do have a couple sets on machines being tested.

 

[DASBUR]

Doug,

I spoke to someone who installed Gyrotech blades on a Mosquito and he was very happy with the way they flew. Maybe they learnt something from your experience.

Will just have to see how the Gyrotech blades behave when I get into the air.

Oskar

oskar
Good to hear that. At least you know you wont end up with $6000 + dollar paperweights. I spoke with Dwight at Osh 2021 about the blades. it is the airfoil that chuck and Ernie recomended it looks like a NACA2312. they are a 2 piece blade, a spar and a full wraparound skin. oven bonded. He said it was a 6061 extruded spar machine down to size on a milling machine. Mike did Ernie use an extruded spar or a machined spar on the dragon wings.

Doug

 

[MikeBoyette]

oskar
Good to hear that. At least you know you wont end up with $6000 + dollar paperweights. I spoke with Dwight at Osh 2021 about the blades. it is the airfoil that chuck and Ernie recomended it looks like a NACA2312. they are a 2 piece blade, a spar and a full wraparound skin. oven bonded. He said it was a 6061 extruded spar machine down to size on a milling machine. Mike did Ernie use an extruded spar or a machined spar on the dragon wings.

Doug

It was an extruded spar with an upper and lower skin bonded to the spar and to each other at the trailing edge. The tip weights are bolted and bonded to the inside of the spar. I too saw what Dwight had planned for blades. I was just wondering if they actually got them flying yet. I honestly wish they would have just bought the blade business from dad.

 

[Aaron R]

Because MR power is much larger than TR power there will be an overall gain, but it will be less than 2%.

This is interesting. I always assumed optimal efficiency is achieved with the fewest blades of largest diameter. So I did not think it was possible to steal from the little rotors to augment the big one, and actually gain efficiency overall. But your numbers seem to show that it works.

So maybe the problem with my thinking was, I was not accounting for the real cost of the antitorque demand of a conventional helicopter. But this leads me to other questions, like: Then why don't all helicopters have a tilted tail rotor? What is the optimal tilt angle (flying qualities aside)? What is the optimal helicopter configuration for efficiency... e.g. - is a two rotor tandem better than a single main rotor with antitorque tail rotor?

Aaron

 

[WaspAir]

I wouldn't put the flying qualities aside for this purpose. Depending on how high or low the tail rotor is mounted, and how much tilt it has, you can have effects on translating tendency, whether it wants to hover with one skid low, what it does in low g, behavior in tailwind hovers, when you will run out of pedal, etc.

In most helicopters the rotors are not independent, and power is shared between them. The separate battery sources in the design under discussion here is atypical and may mislead for efficiency for other designs.

 

[Aerofoam]

In most helicopters the rotors are not independent, and power is shared between them. The separate battery sources in the design under discussion here is atypical and may mislead for efficiency for other designs.

This is an important point, the efficiency losses of a shared drive shaft with 2 directional changes are probably upwards of 15% to 20%.
The electric drive with it's own battery probably has less than 10% loss. Maybe less because the response time doesn't involve the inertial losses of accelerating the entire drive line.....
I am very curious about seeing how this plays out.....Its will be easy to monitor the actual power requirement since they are separate....

 

[Aaron R]

I wouldn't put the flying qualities aside for this purpose

No, I wouldn't do that in a design. But for geeking out on the optimization problem, it simplifies things.

 

[Oskar]

So Oscar are you affiliated with Mosquito? What blades are they using now that the blades that made them a viable flying machine no longer available? Would love to see pictures of a set.

Mike,

No affiliation with CFX, have just built a few Mosquito kits and now flying the electric Mosquito. I did have a few chats with Norbert though when they were planning on getting their electric Mosquito going.

CFX are building their own blades now but it will still be a long time before guys like me will be able to get their hands on a set, kits have first priority. Also they are slightly thicker than the old DWs which means I would have to machine my blade grips to use them.

The Gyrotech blades look like Sportcopter blades because they are painted, they look nice but for me the flying characteristics are much more important than looks.


Oskar

 

[Oskar]

Its will be easy to monitor the actual power requirement since they are separate....

Have a look at post #106 for some MR and TR power measurements.

 

[MikeBoyette]

This is interesting. I always assumed optimal efficiency is achieved with the fewest blades of largest diameter. So I did not think it was possible to steal from the little rotors to augment the big one, and actually gain efficiency overall. But your numbers seem to show that it works.

So maybe the problem with my thinking was, I was not accounting for the real cost of the antitorque demand of a conventional helicopter. But this leads me to other questions, like: Then why don't all helicopters have a tilted tail rotor? What is the optimal tilt angle (flying qualities aside)? What is the optimal helicopter configuration for efficiency... e.g. - is a two rotor tandem better than a single main rotor with antitorque tail rotor?

Aaron

Have you looked at a Black Hawk?

 

[Oskar]

Then why don't all helicopters have a tilted tail rotor? What is the optimal tilt angle (flying qualities aside)?

Aaron

The benefits and control cross coupling both increase as the angle increases.

The UH60, CH53 and others typically have a tilt of about 20 degrees which generates lift equal to ~34% of TR thrust, but most (if not all) have automated flight control systems to manage the control cross coupling.

My tilt was 15 degrees which generates lift equal to ~26% of TR thrust. From the flight tests I did the resultant control cross coupling is very noticable but can be comfortably managed by the pilot. My gut feeling says that at 20 degrees, however, pilot workload without an automated flight control system would become unacceptably large.

As shown in post #162 at 15 degrees the overall gain is less than 2%, at 20 degrees the gain might be a bit more than 2%. In the end the helicopter designer has to decide if it's worth the extra effort for a relatively small gain.

 

[Smack]

Oskar, you have more helicopter knowledge than any else on this site, thanks for sharing !

 

[Aaron R]

As shown in post #162 at 15 degrees the overall gain is less than 2%, at 20 degrees the gain might be a bit more than 2%.

I believe it. That said, it did occur to me since the last post, we haven't accounted for the rotor efficiency in post #162. For example, a 1 kg thrust increase will require more power in the small rotor than a 1 kg thrust increase in the big rotor. I imagine your data would show how they compare. But like I said, I'm a believer that there is a real gain. I tried to work out the optimum (theoretical) angle...failed badly. I suppose it comes out to about 20 deg like the military helicopters.