HamzaLippisch heli-design

[lippischh]

hi folks, i wanted to present you some ideas of mine concerning rotorcrafts and it would be here, well i will use a helicopter model to illustrate the features im talking about.

Lets start by the fact that helicopter fuselage cross section affects on its performance cause the rotor is blowing on it, most helicopters have round or even rectangular cross sections which are not very suitable aerodynamically so i propose to use a streamlined cross section.

we could also use the rotor downward flow to counter torque and that is possible by different ways, using aerodynamic surfaces that creates horizontal counter facing force or using the tail as a vertical wing. those ways can be improved by using tip compressed air blowing, air that come from the turbines themselves.

you guys C&C are very welcome and very important so feel free to leave your impressions.

 

[Jemiba]

we could also use the rotor downward flow to counter torque and that is possible by different ways, using aerodynamic surfaces that creates horizontal counter facing force or using the tail as a vertical wing.

IIRC, this idea was formulated by Raoul Hafner, too. His PD.6 (http://www.secretprojects.co.uk/forum/index.php/topic,2820.msg22517.html#msg22517,
http://www.secretprojects.co.uk/forum/index.php/topic,1291.msg141032.html#msg141032 ) should
use this way of counter torque, AFAIK.

 

[Bill Walker]

Quite a few modern helicopters use some of the downwash over the tail boom to counter some of the torque, thus reducing (but not eliminating) the power consumed by the tail rotor. Look at recent AS350 models, and updated Sea Kings of several armed forces, that have aerodynamic strakes added to one side of the tail boom to enhance this.

The effect of downwash on the fuselage is actually quite small, because only a small part of the downwash actually strikes the fuselage, and most of that is the relatively low velocity core of the downwash. This statement is based on theory and on many years spent measuring the effect of external stores on helicopter hover performance, and often being hard pressed to find any change.

The vertical velocity of the downwash is roughly zero near the hub, and increases to a maximum at the maximum rotor diameter. Yes, the cabin of many helicopters is boxy, because it is in the low velocity portion of the downwash. The tail booms of the same helicopter are a much nicer aerodynamic shape, since they are in a higher velocity portion of the downwash.

The anahedral kinks in the rotor blades you show will either go away under centrifugal force once the rotor starts turning, or add significant structural weight to the blades if you need the kink to stay there.

 

[lippischh]

@Jemiba: I didnt know of it thanks for the info
@Bill Walker:

Quite a few modern helicopters use some of the downwash over the tail boom to counter some of the torque, thus reducing (but not eliminating) the power consumed by the tail rotor. Look at recent AS350 models, and updated Sea Kings of several armed forces, that have aerodynamic strakes added to one side of the tail boom to enhance this.

1 - in the presentation you can see that i mentioned the use of compressed air blowing over the tail-wing surface to increase significantly the force generated, a control surface would then replace the tail rotor throttle use to achieve yaw, the compressed air can be also directly ejected from the tail tip.

he effect of downwash on the fuselage is actually quite small, because only a small part of the downwash actually strikes the fuselage, and most of that is the relatively low velocity core of the downwash. This statement is based on theory and on many years spent measuring the effect of external stores on helicopter hover performance, and often being hard pressed to find any change.

I dont doubt on your experience sir, but is the fact that the fuselage have a more streamlined shape doesnt improve anything? i mean not only in hover but also in forward flight and so on.
finally for the anhedral kink it wasnt really my idea saw that on model, but isnt there heli rotors with winglets ?

Thx guys very much for your exquisite replies, i appreciate it.
regards

 

[Stargazer]

But no-one has commented yet on how elegant your design was!

I can only encourage you to carry on with your awesome work. You keep improving as each day passes, and your understanding of aerodynamics and physics is a huge plus that I truly admire. Keep it up!

 

[Bill Walker]

1 - in the presentation you can see that i mentioned the use of compressed air blowing over the tail-wing surface to increase significantly the force generated, a control surface would then replace the tail rotor throttle use to achieve yaw, the compressed air can be also directly ejected from the tail tip.

I think MacDoug already patented this, try Googling MD900.

I dont doubt on your experience sir, but is the fact that the fuselage have a more streamlined shape doesnt improve anything? i mean not only in hover but also in forward flight and so on.

Some streamling helps of course. But we are talking low forward speeds, less than 200 knots, and even lower downwash speeds. Like everything in aircraft design (or any design for that matter) you need to make trade offs. Is 2 or 3 knots more forward speed worth the loss in cabin volume? That is up to your customer and what they intend the helicopter for. If you look at a Robinson, for example, where the goal is to fly at minimal cost and minimal power, the fuselage is very streamlined, both for hover and forward flight, but the cabin is painfully cramped for "normal" sized people like me. That is the trade off Robinson decided on. The Huey and the CH-53 need room for stuff in the cabin, so their designers arrived at a different trade off.

Concerning your interesting presentation, the box section with the high Cd that you show really only occurs near the rotor hub on the Huey, in the lower downwash speed. The cross section of a Huey nose and tailboom, further out from the rotor hub, looks more like your example of a low-drag cross section. Designers have been aware of this issue for some time now.

I agree with Stargazer that we are not trying to slow you, but to help you grow. If you want to build a real helicopter, and make money doing it, the first question you MUST ask is what does the customer need and/or want.

But if you are designing helicopters just for fun, go crazy! ;D

 

[lippischh]

Thanks Stargazer a lot for very encouraging words.

and Bill, well the MD900 uses a slightly different appartus it uses Coanda effect on a cylinder not a wing. I really appreciate and find huge intrest in your detailed replies so i'd say that the streamlined shape idea is weak to find pratical use.

and for you to know im only 17years old not making money yet, so its half fun but full passion and this thread will be updated with other intresting things i think, so i'd be pleased if u keep an eye here