NR Props & AK7 PSRUs in the news this week

[N962GT]

I got an email from Roman at NR Props in Kiev, Ukraine this morning. Happily, he reports it is business as usual, so I am placing an order this week. If anyone has been considering getting one of these light-weight, super-thrust props then now is the time to order. Email [email protected] ASAP to facilitate international money transfer and shipping.

As you may be aware the Russian-built Tango gyros suffered a lot of hollow prop failures, regardless of blade manufacturer. As for Mohawk Aero, we never had any problems, and no one in the Yamaha STOL community reported any prop failures either - regardless of running a YG3 or YG4.

So what is/was the problem with Tango Gyros breaking hollow props? It's a legitimate question that received a few stabs at answering it - none of which panned out or held up to investigative scrutiny.

There is one answer that makes sense - only one, across-the-board, point of difference, between all Tango Gyro power plants and all the rest of the Yamaha aircraft flying to date. (And there are a LOT!) First, let's eliminate all the tractor aircraft and concentrate on just pushers with turbulent airflow to the prop. What's left are all of my airboat & gyro customers, and Air Trikes' trike customers; and all Tango Gyros ever built and flown.

Where we all used the same, basic Airgear350 type B PSRU platform, only Mohawk since 2015, and Air Trikes (after Vasilli finally saw the wisdom of my choice here), ordered 4" prop bolt pattern flanges.

Tango, on the other hand, used exclusively the older, original Type B PSRU 75mm prop flange bolt pattern. Why? well...It cost Mohawk (and Air Trikes) $50 more for the larger prop flanges.

So there ya have it. If you have one of these 75mm Tango or Air Trikes SPG gearboxes then I strongly recommend using a Warp Drive prop. There has never been a failure of a Warp mounted on a 75mm flange, or any other flange, on any gearbox.

If you have a 4" flange, then a hollow NR prop should be fine.

AND HURRAY!!! Our gearboxes arrived from Belarus at long last!

Oh, dear, did someone write all over my new gearboxes with a Sharpie? Hey, it's no big deal. A clean rag and some pure alcohol will wipe that off like a dry marker on a white board, no need ter gitcher panties in a bunch, Butch, LMAO.

 

[Abid]

I used SPG-2 gearboxes from Vassilli on trikes on Suzuki engines (65, 100 and 115 HP versions). All with 75 mm prop bolt patterns and never had a problem with hollow prop blades like Kiev or others. There must be some kind of issue with those prop blades and Yamaha in some frequency interference causing resonance to break apart a blade shaft like that

 

[N962GT]

Thank you Abid, hope your day is going well! That's certainly interesting to note, but please bear in mind there's a huge 15-18% difference in torque at the prop at same PRPM between 115HP and 135-140HP, which is where the YG3 Nytros run, so the pitch is set far less aggressively on the former creating far less stress on the blades.

 

[Abid]

Thank you Abid, hope your day is going well! That's certainly interesting to note, but please bear in mind there's a huge 15-18% difference in torque at the prop at same PRPM between 115HP and 135-140HP, which is where the YG3 Nytros run, so the pitch is set far less aggressively on the former creating far less stress on the blades.

Is it a 3 blade prop they are using on the Yamahas (135 to 140 HP)? They should have used a 4 blade prop with 72 mm pitch. If these props were properly tested, they are supposed to run these props at max recommended pitch at 2 x the max operating RPM for about 30 minutes to show compliance. That is what is required for Prop ASTM standard for light sport. Prop manufacturers do that by hooking up the props to big block Chevy engines etc. running like like banshees and standing away in a safe room watching

 

[Strike]

tuUn tripala da 140 CV è semplicemente troppo borderline!!
I use a 182 diameter full carbon 4 blade on my 170hp

 

[wolfy]

Wow 170hp also, mate loving your gyro more and more.

wolfy

 

[N962GT]

Is it a 3 blade prop they are using on the Yamahas (135 to 140 HP)? They should have used a 4 blade prop with 72 mm pitch. If these props were properly tested, they are supposed to run these props at max recommended pitch at 2 x the max operating RPM for about 30 minutes to show compliance. That is what is required for Prop ASTM standard for light sport. Prop manufacturers do that by hooking up the props to big block Chevy engines etc. running like like banshees and standing away in a safe room watching

The 1750mm four blade props broke as often if not more so than the three-blade on the 75mm PSRU prop flange, and their performance was not nearly as good due to increased turbulence and drag.

 

[N962GT]

tuUn tripala da 140 CV è semplicemente troppo borderline!!
I use a 182 diameter full carbon 4 blade on my 170hp

What engine is this? Sounds interesting. Please post more photos, thanks!

The Yamaha Apex and RX1 STOL aircraft have a history running 3-blade NR props up to 84 inch diameter, up to 200HP with NOS in racing from 2014-2019, and 150 HP NA cruise for thousands upon thousands of miles without any cracking.

In our experience four blade is not necessary for a 140HP engine.

In fact, two-blade hollow props are often used on YG4 150 HP STOL airplanes.

 

[Strike]

Che motore è questo? Sembra interessante. Posta altre foto, grazie!

Gli aerei Yamaha Apex e RX1 STOL hanno una storia con eliche NR a 3 pale fino a 84 pollici di diametro, fino a 200 HP con NOS nelle corse dal 2014-2019 e 150 HP in crociera NA per migliaia e migliaia di miglia senza crepe.

Nella nostra esperienza quattro pale non sono necessarie per un motore da 140 CV.

Sui velivoli YG4 150 HP STOL, infatti, vengono spesso utilizzate eliche cave a due pale.

NONew model powers from 120 to 160hp coming soon with the 240hp turbo version

 

[Abid]

The 1750mm four blade props broke as often if not more so than the three-blade on the 75mm PSRU prop flange, and their performance was not nearly as good due to increased turbulence and drag.

Then it isn't a strength issue. Trust me. It is a resonance issue between the engine, prop and engine mount.
This is the reason why all ASTM and certified design standards require a vibration analysis between the prop and engine and minimum hours between prop, engine and fuselage interface in flight before claiming compliance.
Sensenich Prop will do vibration analysis for around $14k. Technically a PB-4 can be used to get a frequency spectrum as well but reading it to determine resonance and evaluating them requires experience. Mike Goodrich would be able to help.

 

[Sv.grainne]

I've worked on several of these props. Did a destructive investigation into several and what I found was that the failed blades had resin starved glass at the blade joints. I was able to repair several but the underlying issues reappeared over time. These were both on Tangos running the 3 cylinder nytro engine. Been awhile but I think the blades used were in the 4 blade configuration.

 

[meglin]

Dear aviators!
Using a propeller on a new engine is always a risk. The manufacturer does not always have the possibility to carry out full tests of the propeller on a given propulsion system. Therefore, if you want to minimize the risk, order a particularly robust pure carbon fiber blade design. It costs more, but it can save you a lot of money and possibly save your life.
Particularly strong blades can be made much stronger at the customer's request, if he notifies in advance of the power and torque dimensions, I will not even mention now the power ratings of the engines on which they are already installed, so as not to provoke anyone.
If you do not want to take any risks at all, it is your right to order a customized design and manufacture of a wooden propeller.
As for the saber-shaped blades, they were specially designed by our designers for use on the X-32 Bekas aircraft with a pusher engine. These blades are much less sensitive to swirls and flow beveling after the engine and wing. By the way, it is allowed to test the blades not only by double revolutions, but also by burst tests with all additional safety factors.
Let me also add that our blades, unlike Kyivprop blades, are not hollow. Inside the blades there is a powerful spar, which significantly increases the blade stiffness and changes its frequency characteristics.