Build thread on the GT-VX2 Explorer.

[Capt'n Gator]

Post No 27 Bobby.

I just ordered mine

 

[Sv.grainne]

Thanks, great price!

 

[Resasi]

Talk about bang for the buck when compared with ‘Aviation’ strobes!!

 

[Resasi]

Denis and I had questions about a starting point for pitch for our particular set-up and Daryl at Warp Drive had responded to our initial enquiry with a figure of 14 degrees.

I am not a techie and have only a basic understand of pitch in the various phases of flight. Propellor aerodynamics is a specialised subject so trying to dig just a little deeper, and felt we could give Daryl a bit more information.

Take-off and landing occur at low speeds and a fine pitch configuration the most preferable to produce the greatest thrust, or, have the greatest possible available thrust in the case of a take off or go-around during the landing.

Climb configuration generally most efficient where the pitch is slightly more coarse than during take-off, but finer than will be in cruise.

‘Cruise' is generally flown at relatively high speeds with a coarse pitch the most efficient configuration to generate the thrust required to overcome the cruise drag.

So propeller pitch is a crucial factor to the performance of the propeller, and resulting aircraft performance. I am also aware that with a fixed pitch/ground adjustable propeller, a compromise between coarse pitch for cruise and a fine pitch for take-off and landing must be made.

The 4 blade Warp Drive I purchased was due to my wish to have a very durable propellor for the Rotax 912ULS 100 hp engine I had purchased, its 62’' 4 blade configuration due to the limitation in diameter imposed by the design of the tall tail, and, ability of the propellor to most efficiently utilise the power available for our chosen power plant.

The variation in engine power of the Rotax 912 UL can be plotted as a function of engine RPM and external conditions of weight, temp, and alt.This particular gyro is intended in principle be operated at sea level, with cruise altitudes generally not above 4,000’. It can be assumed that the majority of flight time will be at 4300 RPM or 75 % of the maximum engine speed of 5800 RPM. Cruise at an engine speed of 4300 RPM representing an initial estimate of the typical cruise condition.

Of the three stages, TO/Landing climb and cruise, my initial concern/priority is with the first two, the cruise performance then whatever results. At a later stage in the phase 1 testing I can then begin deciding if the priorities should remain that way.

Pitch can be calculated given propellor design, WAT conditions, and engine parameters, and, as we didn't have the propellor design parameters I decided to go back to Daryl hoping to give him more information and hoping with his greater knowledge of the prop he might give us input on what we should be aiming for with our initial pitch setting given the above information.

It will be interesting to see what he gives us.

 

[DavePA11]

For me it was a bit of trial and error setting the pitch to achieve the correct take-off rpm for the 912. I don’t recall the setting I used, but had the same engine and prop as you have described above. I pitched mine For 5150rpm on climb for better cruise performance if I remember correctly. I made a tool to measure it and will look for photos.

 

[Resasi]

Got word back from Nick at Warp and it appears with our set-up that the 14 degrees should give us about 5,300 static rpm. This will increase a bit in flight but still be safely below the 5,800 max rpm and a good place to begin fine tuning when we have had a chance to see what this produces in the way of TO, climb and cruise.

Around 5100-5300 rpm I gather is a reasonable cruise rpm from the Rotax Forum.

A kind reminder from Warp.

Warp-Drive-Propellers_001-02-21_Setting-Propeller-Blade-Pitch-Instructions.pdf

 

[wolfy]

Personally I think at that pitch you will be over loading the engine using more fuel than it should and loosing climb performance.
I think you should aim for at least 5500 static, gyros don't fly that fast so at top speed you will only rev the engine about 100-150 rpm higher than static.
On the other end of the scale I used to set mine up for max climb so 5800 static which meant I would hit 5900+ rpm at 70 kn.
I am not suggesting that rpm for a mainly cruising around machine but Rotax have designed there engines to spin and not be lugged.

wolfy

 

[Resasi]

Interesting Wolfy.

Yes rpms will also govern fuel consumption as well as performance in the various phases of flight.

What I am not getting is why you would pitch to be able to over rev in level flight.

If I understand you correctly, you would of course not deliberately over rev in cruise, but simply pitch the prop that way to optimise climb performance?

So you would recommend a slightly lower pitch then, with max climb as the aim?

I guess it does fall between optimum TO and cruise, so a compromise between the two.

What did you figure was an optimum cruise rpm for the 912ULS?

 

[wolfy]

Interesting Wolfy.

Yes rpms will also govern fuel consumption as well as performance in the various phases of flight.

What I am not getting is why you would pitch to be able to over rev in level flight.

If I understand you correctly, you would of course not deliberately over rev in cruise, but simply pitch the prop that way to optimise climb performance?

So you would recommend a slightly lower pitch then, with max climb as the aim?

I guess it does fall between optimum TO and cruise, so a compromise between the two.

What did you figure was an optimum cruise rpm for the 912ULS?

But lower rpm in a petrol engine is not always the most fuel efficient, it is more to do with load on the engine.
Cruising your car in 4th as apposed to 5th (at a reasonable speed) will often use less fuel. But that is for engines with carby's not computer controlled engines.

I wanted to be able to climb out of the hole (so to speak) so optimized for max climb performance. And in an open frame machine flying at WOT straight and level was to fast to be comfortable for any length of time so the engine was not over revved often.

Yes in my opinion for your uses I would aim for 5600 static, which would probably give you about 5700 or so at WOT S and L.
Rotax considers anything under 5500 at WOT to be over loaded.
With that pitch I would think cruising continuously in an open machine would be uncomfortable at much over 5300rpm anyway.
I would think that would give you a nice cruise speed at about 5100 rpm.

I think from memory I used to cruise at about 5200 (climb prop) which was about 40-45kn more than fast enough for an open machine when you do it all day. That gave me an all day average (of every sort of flying) of 15 L per hour.
9 series rotax's become the smoothest at around 5500 that's where rotax designed them to run, I don't cruise at that rpm for the reason above plus it just sounds like it's revving if you sit there like that all day.

Naturally once you do some experimenting you will find the right compromise for your needs, but I would knock a couple of degrees off what warp has said to start at.

wolfy

 

[wolfy]

I should point out that I no longer prop that fine now just flying them for fun. The new one is 5700 in the climb.

wolfy

 

[Resasi]

Thanks Wolfy, all of that makes sense, and with no experience on the 912, very happy to call on your extensive experience.

I will point out that unlike mustering where climb performance would be a priority together with a lot of loitering around the herd, I will be looking at point to point, perhaps slightly faster, along with fuel economy/range.

Looking forward to the phase 1, with its attendant exploration of the machines envelope...if I every get back and get it finished. Right now feeling that my management of reasonable expectation is faulty, and that I may die of old age before I get this creation into the air.

 

[anthom]

Thanks Wolfy, all of that makes sense, and with no experience on the 912, very happy to call on your extensive experience.

I will point out that unlike mustering where climb performance would be a priority together with a lot of loitering around the herd, I will be looking at point to point, perhaps slightly faster, along with fuel economy/range.

Looking forward to the phase 1, with its attendant exploration of the machines envelope...if I every get back and get it finished. Right now feeling that my management of reasonable expectation is faulty, and that I may die of old age before I get this creation into the air.

I feel you are almost done, by the looks of it. When I swapped the yamaha on Kermit for the Rotax 912, I too thought that I would not get it flying. But it happened, and now it's the small stuff that needs working out. Things like prop pitch, climb rate, etc can all be adjusted as one progresses with the testing.
Believe you me, if I could replace the 912 on my AR1 with the 915is, you are way ahead in your build. Denis has a fine eye for detail from what I can see. A lot of the stuff gets ironed out in the testing phase. I'm also working on the Chinese P740 engine on an ultralight. I enjoy watching the progress on your build.
I like Wolfy's reasoning and methodology. Seems like a very practical approach to the mission of the flight.
I learn a lot watching you guys.

 

[wolfy]

I feel you are almost done, by the looks of it. When I swapped the yamaha on Kermit for the Rotax 912, I too thought that I would not get it flying. But it happened, and now it's the small stuff that needs working out. Things like prop pitch, climb rate, etc can all be adjusted as one progresses with the testing.
Believe you me, if I could replace the 912 on my AR1 with the 915is, you are way ahead in your build. Denis has a fine eye for detail from what I can see. A lot of the stuff gets ironed out in the testing phase. I'm also working on the Chinese P740 engine on an ultralight. I enjoy watching the progress on your build.
I like Wolfy's reasoning and methodology. Seems like a very practical approach to the mission of the flight.
I learn a lot watching you guys.

I would value your thoughts on the Yamaha vs 912 if you had the time.

wolfy

 

[anthom]

I would value your thoughts on the Yamaha vs 912 if you had the time.

wolfy

I swapped the Yamaha for the 912 before I had Kermit flying again. So I do not have a comparison. I sold the engine with the re-drive to Bobby (AirCommand Pilot) and he is doing great with it.

 

[Resasi]

Would say the 912 ULS would make an ideal engine for Kermit.

Loved the concept of the quick change enclosed cockpit.

 

[Resasi]

Seems Blue has gone walkabout with Denis.

Right now down at Bensen Days in Florida, seeing the countryside and hopefully her new home.

 

[Sv.grainne]

Shame you can't be there flying!

 

[Resasi]

Can’t grumble too much, I’ve had my second vaccination, they eased the lockdown over here and got to see my son and family here in the UK for Easter.

With any luck Jo will ease the restriction on getting to the US, I’ll be able to see my other son and Granddaughters in Tampa... then maybe see how the beauty flies. Who knows.

 

[Resasi]

A slightly grim detour from the GT-VX2 build log.

It is a global problem. Viruses constantly change through mutation, new variants of a virus expected to occur over time, with new variants emerging and disappearing.

Some variants emerge and persist. Multiple variants have been documented in the United States and globally during the present pandemic. Multiple variants of the virus are presently circulating globally and in the US.

In collaboration with a SARS-CoV-2 Interagency Group (SIG), The US Centre for Disease Control and Prevention (CDC) established 3 classifications for the SARS-CoV-2 variants being monitored:

1. Variant of Interest (VOI).
2. Variant of Concern (VOC)
3. Variant of High Consequence (VOHC).

There are currently five VOCs in the United States:

1. B.1.1.7: First identified in the US in December 2020. Initially detected in the UK.
2. B.1.351: First identified in the US end of January 2021. Initially detected in South Africa in December 2020.
3. P.1: First detected in the US in January 2021. Initially identified in travellers from Brazil tested during routine screening at an airport in Japan, early January.
4. B.1.427 and
5. B.1.429: First identified in California in February 2021. Classified as VOC March 2021.

Full information here:

Cases, Data, and Surveillance

Cases, data, and surveillance to track and analyze COVID-19.

www.cdc.gov

The geographical spread in the US here:

COVID-19 and Your Health

Symptoms, testing, what to do if sick, daily activities, and more.

www.cdc.gov

 

[Smack]

Major thread drift..... post in Off Topic.