Home made rotor blades

[Monte55]

I don't believe it's that important that my short rotors need to balance at 1/4 cord which they don't. They are very rigid for their length.
A R/C heli has full length rotors for its length I can understand it's more of an issue. I doubt small R/C coaxial rotors actually balance at 1/4 cord. To me, my rotors are rotor shaped propeller blades. I sure if one would grip the outer end of a full size heli or gyro blade it could be twisted some by hand. Do props balance at that point? Blower fans don't. As a kid I used to carve crude props and put them on electric motors and they never fluttered. With a heli rotor head that changes pitch, I can see it could be a big issure. A long flexible blade changing pitch etc would I'm sure need to be balanced. Even when they are balanced, that doesn't mean they track correctly. Thats why some have trim tabs etc. I know I don't have the knowledge of most on this forum, but some seem to remember some rules and think it applies to everything that rotates.. Also, how many on the forum have made their own blades, tested them, and can give first hand experience of problems that can occur? Just repeating everything you hear is not scientific. If the Wright Brothers had internet back then and asked questions expecting help..they would have never flown with the exception of a select few on these forums.
I thank them.
Nick
PS I'm not saying if one says something I didn't want to hear, that they are not contributing to the issue.

 

[brett s]

It may work ok as-is, but you don't really know for sure until you try - and you may get zero warning before something nasty happens.

It'll depend on exactly how far back the chordwise balance ends up being, you at least ought to measure them & know for sure.

 

[Monte55]

I agree...........I'll take all measurements etc before and during. It may help someone else later. After all, isn't that what the forum is about?
Nick
PS.....there will also be video

 

[Friendly]

Why is that important?
I know it have been stated somewhere here before, but I dont remember.

With Nics very short blades and only 100lb on each blade, would it still be needed?

Read the thread about the 8in cord crash and it will give you more information about the cord balance, flutter and negative pitch, reflex etc. the shape of the blade is not much use with out the proper balancing.

 

[don hillberg]

the Right bros used data of the time and used a wind tunnel (small but efective) and added to there tools of knowlage,Chord weight is very much needed and you need to study more,or you are wasting your time. A rotor is NOT a prop.

 

[Jens]

Why balancing..

Why balancing..

Okay I have studied it a bit. As I understand it now:

In most rotors we have change of pitch (mainly cyclic) which moves / accelerate the blades up and down somewhat.

If blade COG and lift vector is not in line, the cyclic lift force will try to twist the blade.
If blade gets twisted, AOA changes - and things can get out of control.

 

[brett s]

It doesn't matter whether you have pilot cyclic and/or collective pitch control or not.

When a tail heavy blade twists under load it'll increase AoA, exacerbating the problem.

 

[Jens]

Sorry, my explanation where a bit wrong:

The cyclic and/or collective pitch is NOT why cord wise balancing might be needed.
On the contrary, cyclic pitch helps to minimise the problem.

The cyclic change of blade speed, due to forward speed, is the cause of cyclic lift forces on the blade which might twist the blade. This is the main reason why we might need some cord wise balancing of the blade - I think.

 

[brett s]

The blade can twist without any forward speed. Cyclic pitch won't minimize anything either...

Depending on exactly how far out of balance & how stiff in torsion it is, it can flutter & even self destruct once it starts diverging.

 

[Jens]

much less critical..

much less critical..

A rotor for a hovercopter gets no forward speed.
It has fixed pitch.
No (teather) hinges.
1/2 load due to co-ax.
Much shorter and stiffer blades compared to a UL heli.

For sure, cord balancing for this type of rotor, is much less critical - maybe even neglect able?

I don't believe Nick can get away with such a little rotor diameter, but even if or when he makes it bigger, it will still be a very different rotor compared to a 2 bladed UL heli rotor.

 

[Jens]

fully rigid rotor..

fully rigid rotor..

I look forward to hear about your rotor tests, Nick :rapture:

I agree – no ‘rocket science’ should be involved in this.
Hovercopter rotors where also made 100 years ago:
https://aviastar.org/helicopters_eng/ellehammer.php


If one wants to build his own rotor – instead of buying some modern carbon fibber props – a fully rigid rotor would be the simplest and safest way to go, I think.
Do 4ft profiled blades in light wood, composite, alu or what ever you like and attach them rigidly to a rigid hub bar.
The rigid hub bar could be made from prefabricated composite plates and be very stiff as well as light.

This solution doesn’t give the most efficient rotor, but is the easiest way for hobby home builders.

 

[Monte55]

rotor blades

rotor blades

Hey Jens...........that's they way I feel about it. By the way,you'll need to reverse one of the rotors in your drawing Thanks for the pics...
Keep them coming.
Nick.................

I
agree – no ‘rocket science’ should be involved in this.
Hovercopter rotors where also made 100 years ago:
https://aviastar.org/helicopters_eng/ellehammer.php


If one wants to build his own rotor – instead of buying some modern carbon fibber props – a fully rigid rotor would be the simplest and safest way to go, I think.
Do 4ft profiled blades in light wood, composite, alu or what ever you like and attach them rigidly to a rigid hub bar.
The rigid hub bar could be made from prefabricated composite plates and be very stiff as well as light.

This solution doesn’t give the most efficient rotor, but is the easiest way for hobby home builders.[/QUOTE]

 

[Jens]

Nick,
I know you have assambled your rotors a few days ago :tape:
Looking very much forward to learn from your experience.
Hope you also will post in a thread here.

 

[joe nelson]

Hey Monte,

How about an update!

 

[Rotor Rooter]

IMHO, the blade is the greatest limitation to the development of rotorcraft that deviate from the existing.

If the interest in ultralight or backpack or ground-hugging helicopters was to develop AND the safety concerns be overcome, then one or more parties would probably start to produce and market efficient and reasonably priced blades.

Could a light, safe and economical helicopter, which is easy to pilot, replace the gyrocopter as the recreational rotorcraft of choice???

 

[Jens]

Wrong or not...

Wrong or not...

Hi Nick,
Instead of just waiting, I will risk to guess or try to predict what has or will happen:
(And I hope you don’t see this as just a bunch of negative thoughts)

1. You have added an extra wide landing gear – to avoid any early tumble – I hope!
2. Very scaring to give more than half power with the blades turning.
3. You don't get near the needed lift.
4. Awareness of the delicate job of ever being able to control that ship.
5. And learned a lot on other mechanical issues.

 

[tyc]

If the interest in ultralight backpack or ground-hugging helicopters was to develop AND the safety concerns be overcome, then one or more parties would probably start to produce and market efficient and reasonably priced blades.
Could a light, safe and economical helicopter, ... easy to pilot, replace the gyrocopter as the recreational rotorcraft of choice???

A light, inexpensive, easy to build, easy to operate and easy to fly helicopter? Could such a thing come to be? Without question Schoeffmann from Austria is on the right track at present but there have been others, designers as well as builders of small, compact and nothing less than brilliant designs which have also flown but never caught the attention of the public; which still illudes me as to why.

Could such an "economical helicopter" catch on and replace the autogyro as "the recreational rotorcraft of choice"? It could happen but so far history suggests it will not. Consider for a moment just how old the basic autogyro design is. Consider for a moment, of those interested in aviation, how many of these are interested in rotorwing machines: autogyro or helicopter? The answer is, not very many. I for one suggest that if ever, it will be a while before such a machine comes along and replaces the "gyrocopter as the recreational rotorcraft of choice.".

tyc

 

[Rotor Rooter]

tyc,

Schoeffmann helicopter and an Ultralight gyrocopter are probably the same price, with the helicopter having the additional advantage of VTOL capability.

The challenge is therefore to provide his ultralight concept with an extremely high level of safety.
The primary questions are therefore, what are shortcomings of Schoeffmann's craft and what can be effectively done to eliminate them.

Dave

 

[Sita]

tyc,

...........................................................................................................The primary questions are therefore, what are shortcomings of Schoeffmann's craft and what can be effectively done to eliminate them.

Dave

Hello Dave,

I guess it all depends on who's claiming the "schortcomings". For Schoeffman's need and in his view and with what he expect from the craft,there are no schortcomings.
Any commercial helicopter pilot will see hundreds of schortcommings and the brave experimenter perhaps can see only a few schortcommings for the same machine.
A few of the Schoeffman clone's who are about to test fly will have very little schortcomings regarding the owners if they succesfuly take into the air.

Mountain climbing involves so many risks that only a handful consider the schortcomings neglectable and are prepared to take the risk to have the thrill of their life.

Cita

 

[tyc]

... Schoeffmann helicopter and an Ultralight gyrocopter are probably the same price, with the helicopter having the additional advantage of VTOL capability.

The challenge is ... to provide his ultralight concept with an extremely high level of safety. The primary questions are therefore, what are shortcomings of Schoeffmann's craft and what can be effectively done to eliminate them.

That they can be had for "probably the same price" or close to it, at this point and from what I know of the current market/supplies/parts costs, I suspect Schoeffman's machine could be produced and offered at a lower cost than today's gyrocopters.

As for the "shortcomings" of the Schoeffman vehicle, as I see it there are a few, namely:

. ALTITUDE: Most I believe would suggest that altitude or better a lack of it is one but stop and consider for a moment the advantage of such a machine. In just it's present state of development, being able to skim along at 25 to 50 MPH while just 10 to perhaps as much as 60 feet off the deck is a nice little "trick" if one can manage it. One can cover a lot of ground (lakes, ponds, swamps, etc) rather quickly and as one who lives in such an area, as far as I'm concerned, that's not bad - not bad at all.

. NOISE: At present that Schoeffmann helicopter must be quite noisy, especially for the pilot but that can be taken care of quite readily with present technology.

. RANGE: Suspicision has it, at most, flight time for the Schoeffmann helicopter might be as much as fifteen minutes, which as far as I'm concerned is not sufficient, save for using it as a toy. Now if it had a half hour or an hour or so of flight time - then he's really got something there. Can it be done? Schoeffman's gotten this far, so I'm sure that will happen and probably not in the too distant future at that.

. SAFETY: As reliable as they are these days, small, single engines such as Schoeffmann is using with his little helicopter, do fail; it's not a case of will it fail but when. At present the only way around this as I presently see it would be:
(a) TWIN ENGINES, with all that entails; Fuel Consumption, Weight, Complexity and etc.
(b) EMERGENCY SYSTEMS: Use of more advanced BRS technology. As I understand it, at present BRS systems are to be employed at or above 500 feet to assure full deployment of the parachute. They have and again as I understand it, already been successfully employed at an altitude of 300 feet. A BRS system which will be reliable enough to fully deploy at 30 to 60 feet would very nice indeed.
(c) LANDING GEAR: That tripod, those pointed "sticks" Schoeffmann is using at present for landing gear leave much to be desired. Relying on the pilots legs or such "sticks" is as I see it an invitation to disaster. The employment of mini-skis or even small wheels should offer relief here. I say this as, even with a normal landing, relying on human legs as "the landing gear" is simply a risk not worth the taking; consider the still spinning rotors, the hot engine, ruptured fuel tank, etc. With small wheels or suitable ski or a skid like configuration for landing gear, the spinning rotors and hot engine are essentially secondary problems for one to consideration when putting the machine down in a normal, let alone in an emergency condition.
(d) DEAD MAN'S CURVE: All helicopters that I'm aware of have one; i.e., going too fast and being too low, if the engine(s) quits, you've got a real and immediate problem. The reverse holds as well As was noted just above, an advanced BRS safety device may be the answer here.

Just my two cents.

tyc