happy to share information 👍👍next time making blades I would machine the spar as before but would fold a single skin around the spar. Probably use adhesive and minimal rivets. A single wrap around skin would be a better design in my opinion.

Thank you. Next time I would machine the spar as before but in 2024 instead of 6082 but wrap the skin completely around the spar instead of riveted. I used 2024 skin material but I'm not sure if the leading edge could be bent to that degree in 2024 without cracking so might have to use a lower strength sheet aluminium. The ones i made have been ok but only due to the helicopter leading edge tape preventing air from getting underneath the skins. Not ideal but all good learning.

Thanks Cam. Means a lot coming from you!

Yes, I wouldn't build them like this again. Rivets have been used historically but as you say aren't efficient. I need to make some more blades at some point and next time I will wrap the skin completely around the spar. The mosquito blades are made like this and it's only adhesive that holds the skins together, no rivets. Not seen how the Bell 206 blades are manufactured, I'm sure there's some very expensive technology and equipment involved as that's a helicopter way above the kit world.

@@Ben-Dixey The leading edge of the 206 blade is a backward D shaped milled piece of aluminum. The skin following the leading edge is very thin aluminum over a light weight aluminum honeycomb inner core. at the trailing edge theres a thin triangular filler that the skin is attached to (not sure what this is made of). At the blade root there's multiple layers of laminated aluminum bonded together to provide stiffness and strength near the attachment point. At the outer edge there's some brass weights inside the leading edge to provide higher inertia in autorotation. On some blades there's thin stainless steel laminated to the front of the leading edge to prevent abrasion. I'm fairly certain you could substitute a foam core for the aluminum honeycomb. This would allow you to reduce the skin thickness and overall weight. Preventing delamination has been a crucial aspect of design (especally in modern carbon blades ) from what I understand. The tail rotor blade's design is pretty similar to your main-rotor construction BTW. One thing of very worthy note is that there is an overall twist to the main rotor blade from the root to the tip. This twist gives the driving and driven regions of the MR better angles of attack during autorotation.

Thanks for the detailed description, great information. Hadn't thought about blade twist helping autorotation but it obviously would. I found making the blades the hardest part to all this, incorporating a blade twist would certainly add to that. You could be right about the filler material enabling a reduction in skin thickness. What do you think the reason was for using a brass tip weight rather than lead ?

There is no laminar flow on trailing edge, not a bit in any airfoil, and that is not even laminar airfoil in blade design. That look normal symmetrical NACA airfoil, and those separation bubble is somewhere 25-30% of chord, after that point there cannot be laminar flow. Laminar flow airfoil just move separation bubble further back, 40-50 % of chord, and after that point, there is no laminar flow even laminar flow airfoil. Rivets just add little drag on that turbulent air behind separation point. Not a big deal. Great work, your skills is perfect to this complex project!

@4trade2 Thanks very much for this information, I didn't know about the laminar flow details. The airfoil is a naca 0012, good to know about the trailing edge rivets not reducing efficiency too much. I'd rather have them instead of relying on adhesive. 👍

How many rotors are you thinking of? With enough rotors you will have redundancy and may not need collective pitch. Bare in mind you will loose altitude transitioning from powered flight to autorotation with collective and you need high inertia rotors which adds a lot of weight. Up to 50 feet is the danger zone in most commercial helicopters where collective might not save you if hovering with no forward speed. The jetson one has 8 motors and props with triple redundant flight controllers. It can still fly with a motor out and has a ballistic parachute system. Have you seen amazingDiyprojects on KZfaq ?

@@Ben-Dixey true, perhaps autoing a miltirotor is impossible for inertia reasons alone. The safest design is almost certainly 6-8 rotors to handle the loss of one or two, perhaps with a ballistic parachute, which itself has a danger zone. I'm partial to pixhawk flight controllers which can be had with redundant IMUs, not sure if me adding multiple entire flight controllers and switching electronics wouldn't just add another big point of failure. Pixhawks can also support downward lidar, pitot airspeed, autonomous modes, etc. amazingdiyprojects has some very interesting designs, you are both an inspiration.

Thanks for the compliment. When is comes to flight controllers I can't offer any advice I'm afraid, really don't know anything about them. I would very much like a jetson type machine though, looks a lot of fun and I would think simpler to build than a helicopter. I would consider making mine electric if it was feasible which it might be. There seems to be an opinion that says it's more efficient to move a large amount of air slow than a small amount of air fast. That's why larger rotors Create more lift for the same amount of power and turbo fan engines keep getting bigger. My coaxial could be more efficient than the equivalent multi rotor, however I'm not 100% sure of this.

Hi thanks, the wood inserts are just end caps to prevent energy losses due to centrifugal air pumping. The rest of the blade is hollow, the 2024t3 skin is quite resistant to bending and holds it's form well so I didn't feel the need to fill the cavity. Rotorway blades are also hollow I believe. Blade length is 2m chord is 120mm, rotor diameter is 4.3m.

@@Ben-Dixey what about weight each blade?

each blade weighs 2.6kg

Welding aluminium destroys the strength in the heat affected zone, causes heat distortion and increases the likelihood of fatigue cracks. It would be a complete disaster attempting to weld any part of a rotor blade made from aluminium. The skin is 2024 t3 a very high strength aluminium and cannot be welded anyway. For less critical and low strength aluminium welding can be used but you won't find it used very often on commercially made aircraft.

Hi Jeff. The sheet is 0.8mm thick and the ball nose cutter is 3/16" but I wouldn't build them like this again. I would build them like this. kzfaq.info/get/bejne/bJ2YesSLs8nHd6M.html Wrap the skin completely around the spar.

@@Ben-Dixey thank you, I watched this upload, beautiful, I have decided to build like that too. Always wondered if just one spar was enough to lift all that weight, the upload cleared my fears, so am using 7075T6 plate of 1"*3" to get a foil of 20mm max thickness. Is the slot necessary for just weight reduction or does the C shape increase strength or something? Not so good with material science. Then I see you have wood inside and compositefx is just hollow. What made you put wood inside? N which wood is it? Birch?. Thanks mate, for accomodating my nags so far.

Happy to try and help, the spars purpose is to take the centrifugal loads. There are several tons of force pulling horizontally, it is this force that allows the spar to be relatively weak to bending. You will have seen how long helicopter blades droop down until they start spinning. It was quite amazing to me when I found out that some rotor heads allowed the blades to hinge upward, called a flapping hinge. This meant that the centrifugal force was the only thing holding the helicopter in the air. The spar is c shaped in order to keep the weight in the blade as far forward as possible. 0012 blades need to balance at 25% because otherwise the collective stick forces will be too high. Having too much weight at the back of the blade could also cause blade flutter which must be avoided. My blades are hollow too, the wood in the end is just to seal off the cavity. An open cavity will mean the blades are less efficient and will cause drag. If you manage to copy the mosquito blades then you won't have any problems. Ben

Now this clears everything, it's a go now, Found aircraft grade aluminium plates, though skin will use 7075T6 1mm thick. no 2024mm available in this thickness from my contact. Though I don't get how the mosquito blade achieves lift distribution that comes with blade twisting design or reduced profile from root to tip...I kind checked like that build and yours all have uniform blade tip to root...or the spars are strong enough for that extra conical shape in flight. Cheers. 🤝

Ok 👍. You just need to make sure that 7075 will bend ok around the leading edge without cracking. I think the sheet on the mosquito blades is 6061. If you can buy a small bit of sheet to do a trial bend that would be sensible. The blades are straight and parallel on the mosquito because of ease of manufacture. As you say there won't be even lift distribution like on a tapered and twisted blade. It means the blades are less efficient being straight but it's more difficult building tapered and twisted blades.

The blades can be longer and would produce more lift up to a point. The only drawback is longer blades have to run at a lower rpm which means a larger gear reduction. I wanted a single stage reduction but with longer blades I might have to go to a double stage which increases weight and reduces efficiency. Shorter blades are easier to control vibration and fit in a smaller workshop space, blades being lighter means a lighter rotor hub assembly. It's all a trade off but longer blades produce more lift because It's more efficient to move a large amount of air slower than a small amount of air fast.

Hi, thanks for the nice comments. The wood in the end of the blades are just caps about 20mm long and do not go all the way through. Their purpose is to stop energy losses due to centrifugal air pumping which can rob a few hp if left open.

@@Ben-Dixey thank you for your explanation

Robert Hutchings There are a couple things I would change if making again. One is to make sure the blade mounting holes are at 25% chord, this is where a 0012 blade should balance in the chord plane, the other is to etch prime the surface before bonding which makes a big difference to the bond strength and maybe some more leading edge rivets.

@@Ben-Dixey sir how much long can mill on milling machine...if it's possible to mill short length.... How can I mill around 12 ft approx a single piece

Mohamed shafeel Mohamed bilal I was milling about 12" at a time, you can mill as much as your milling machines travel but it needs to be supported well enough. The Bridgeport knee mill has 30" of travel in x, so you will still be machining in stages on a main rotor blade. I made some milling vice jaws with a step so that when you move the piece and clamp it back up it returns to an accurate position. There were still some slight marks where each pass had stopped and started again and for that I sanded the marks out with a block and sandpaper.

Yes but the formulae is massive, I've just copied the Nolan coaxial on blade length and speed. Longer blades would give more lift to a point but there will be a trade off at some point.

Thank you. Yes there's one main bolt holding the majority of the force which will take 15tons yield strength (double shear), the blade centrifugal force calculated was 2.7tons at 900 rpm, I'm running at around 750rpm now due to the reduction gear change. The blade spar will take 7.7tons by itself (6082t6) but surprisingly the skin being 2024t3 does add another 5.7tons of strength to the blade giving it a total yield of 13.4tons. If you work out at fatigue strength the blade is rated at 5.2tons still double what it needs to be. I've also read that when a bolt is clamping material together the friction between the joint can exceed the shear strength of the bolt, which is interesting.

@@Ben-Dixey yep.. I work with pressure vessels for my job. One project , after doing the math for 3.5:1 safety margin , I found myself holding a 2024 tube in disbelief , I was nervous filling it to 3000psi because it defied logic by weight and machinability.. needless to say it performed by the numbers. And yes , clamping friction must be massive although ive never seen it clealry tested.

I've done a video on the rotor blade balancing. I haven't actually done any blade tracking at all, mainly because the rotors run so smoothly. I should check it out of interest. I'm told blades out of track cause a vertical vibration but no vertical vibration has been detected. Gyro stabilising I hope isn't necessary but with todays technology anything is possible.

Hi, if the outside skin retains the shape well enough there's no need for a filler material. As the chord is only 4.75" it's quite stiff in that respect even being hollow. It's important to plug the ends as efficiency will be reduced due to centrifugal air pumping but what's most important is the weight distribution of the blade chord wise. It should balance at 25% chord measured from the leading edge for a symmetrical airfoil.

Hi, I don't have any plans only a few drawings. Tubes can be used for blade spars but you will need weights on the leading edge of the blade for chordwise balance.

I had the special end mill made by a tooling company in the uk. You can get the aerofoil coordinates online from a website called airfoil tools. I used the coordinates to provide the tooling company with X and Z coordinates needed as if you were turning the profile on a lathe. Can't remember the name of the company but most engineering tooling providers have the ability to make special end mills.

Hi, trying to understand if the blades go through more pitch cycles what is the result or problem that causes? Thanks

@@Ben-Dixey Wear on the swash plate and mechanism and fatigue of the blades. Not affected in hover, however when cyclic is applied, one side has more pitch than the other. When you apply input into the pitch it exerts torsional forces into the blade. The faster it spins the higher the frequency of force and the more pitch, the higher the force. No different to a crankshaft where it does not spin at a constant speed. The piston furthest from the flywheel causes that crank to twist a little, the higher the rpm and load on crack the faster and more it twists. The same for the centreline of the the rotor blade. Probably not a factor for you unless you plan on doing A lot of flying.

First Last thanks for that, makes perfect sense on a conventional helicopter with blade feathering for control. Can't get my head around if there is cyclic twisting of the blade on my design, I suppose the angle of attack will change per rotation in forward flight. My blades are very light/ft in comparison to conventional helicopters. Interesting comments, cheers.

Unfortunately welding cannot be used on rotor blades as fatigue cracking of the welds will cause a failure. Also the high strength aluminium will be compromised by the heat and will no longer have the tensile strength required. You also have to bare in mind the chord-wise mass of the blade, it needs to balance at 25% from the leading edge. If doing the job again I would wrap the skin right around the spar like the mosquito blades and epoxy into place. Epoxy can be much stronger than rivets but are usually used together for safety.

Hi, I wouldn't want people copying how I have made these blades because I wouldn't make them like this again. I would wrap the blade skin completely around the spar and not have any rivets. The mosquito helicopter blades are made like this. The blade shape I got from a website where you can specify the blade chord and airfoil and it will plot coordinates giving you the complete airfoil section. If you type in Google, (NACA 4 digit airfoil generator) you will find the website. The blade skin I used is 2024t3 0.8mm think and the blade spar is 6082t6

They are aluminium. 6082t6 spar and 2024t3 skins.

6082 t6

i was thinking 2024they make truck wheels with it''@@Ben-Dixey

2024 is a great material choice, if you can get it. I couldn't find it in the size I wanted. The sheet is 2024 though, cost a fortune but I could get it. The material choice comes down to a few factors. 7075 is another very high strength aluminium, I might have chosen that if it was available.

You have commented this many times, Please explain why you think it's needed?

The sheet is 0.8mm thick, 2024 t3, the blades are 2m long and the chord is 120mm.

Don't think that would be possible. What do you want it for ?