Rotax 583 powered KR2

[Rudix]

Great news Henni!

What size/make prop do you have? Smaller diameter prop with more pitch than normal would be great for the KR2 else you will run out of revs before reaching the speeds KR's like to operate at.

Keep well,
Rudi

[Henni]

Hi Rudi,

'This is my specific engine & prop. It is a Geo Kelly 66x37 off a dual Pioneer Flightstar. I know for a fact that a longer slower turning prop gives more thrust which is excellent for take-offs two up which is my main concern initially. I will try my utmost best to keep prop as is for now, even if I HAVE to mount the engine inverted. The current prop should be good for 90 - 120mph as is which is okay for now. Remember that a prop is designed to keep the tips just under the speed of sound at operating RPM. A slower shorter prop will sacrifice a lot in performance as the gearbox/engine will only turn so fast safely. Short props are used on the VWs as these need to turn at least 3300 RPM to produce enough power. Aircraft engines normally run around 2400 RPM.

As soon as she is flying, I'll change to a coarser prop that will yield slightly more speed. But first I'll see how this prop performs. That curved trailing edge on the Geo Kelly props helps a lot during the climb - I talk from personal experience.

Once I'm flying I will look into a Warp drive or similar.

I'm AMAZED at the slow response over here when I'm asking for scrap aircraft aluminium. I don't want it for free, I'll buy it. Same for engine vibration rubbers. I've accumulated so many pieces of aircraft material over the years of microlight flying - I thought everyone goes through the same experience. Unfortunately I gave it all away as I thought I'll never be involved in building again...

Anyway, have a peaceful night my friend.

Henni

[Rudix]

Hi Rudi,

'This is my specific engine & prop. It is a Geo Kelly 66x37 off a dual Pioneer Flightstar. I know for a fact that a longer slower turning prop gives more thrust which is excellent for take-offs two up which is my main concern initially. I will try my utmost best to keep prop as is for now, even if I HAVE to mount the engine inverted. The current prop should be good for 90 - 120mph as is which is okay for now.

As soon as she is flying, I'll change to a coarser prop that will yield slightly more speed. But first I'll see how this prop performs. That curved trailing edge on the Geo Kelly props helps a lot during the climb - I talk from personal experience.

Once I'm flying I will look into a Warp drive or similar.

I'm AMAZED at the slow response over here when I'm asking for scrap aircraft aluminium. I don't want it for free, I'll buy it. Same for engine vibration rubbers. I've accumulated so many pieces of aircraft material over the years of microlight flying - I thought everyone goes through the same experience. Unfortunately I gave it all away as I thought I'll never be involved in building again...

Anyway, have a peaceful night my friend.

Henni

Great Henni!

I think we need to look at the max speed you can expect with the prop. What is the gear ratio on the motor and cruise/max rpm? I am sure the prop will give plenty thrust for takeoff I am just worried you will end up flying very slowly around the circuit with the motor red-lined due to low pitch, I have been there, not fun....

I hope you can get the materials you need, wish I had something you could use

Have a great evening/night as well, by tomorrow the weekend is in sight
Rudi

[Henni]

Hi Rudi,

She'll most definitely fly slower than she could, I expect that. Luckily she has the RAF48 airfoil which yields best climb at 70 mph. The newer airfoil needs 110 mph for that. So she should be good for initial fun & tests two up. Remember when you mention KR2 and Henni in one sentence your automatically talking two-up. I have to make sure that this is achievable.

Maybe I'll have a 6 cyl Jabi before I even tamper with the prop & then off course my problems are all solved! I don't mind the extra work, as long as I can have some flying fun in the interim!

Keep well my friend,

Henni

[Rudix]

Hi Henni!

I am just worried she would not really fly at all or be dangerous! A quick, ball-park calc shows that if the gearbox is a 2.53 (guessing) and you run the engine at 6500 rpm the max speed you can expect is around 76mph! That would be dangerous.....

But I am sure we can make a plan!

Keep well,
Rudi

[Henni]

Hi Rudi,

If push comes to shove I can always sell this prop (unused) and have a new one made by the same manufacturer. I still have a few months realistically so there's still time for that.

I'll contact the prop manufacturer in the meantime and ask him about this. I'll get back to you with his answer. What do you think I should aim for - 140 mph?

In an ad that appeared on page 81 of the February 1976 issue of Sport Aviation, Ken Rand advertised this about the KR-2:

EMPTY WEIGHT = 420 lbs.
GROSS WEIGHT = 800 lbs
ENGINE = VW 1600
TOP SPEED = 150 mph
CRUISE SPEED = 140 mph
SEATS = 2, side by side

I'm sure that Rotax produce AT LEAST the same output as a standard VW1600! I've read on the Bob Hoover forum that those VWs produce only 45 HP or so at the RPM they are running at.

Man, to think of the times with the Mizer where 76 mph would have been a record... The KR2 is really in a class of it's own!

Henni

[Rudix]

Hi Rudi,

If push comes to shove I can always sell this prop (unused) and have a new one made by the same manufacturer. I still have a few months realistically so there's still time for that.

I'll contact the prop manufacturer in the meantime and ask him about this. I'll get back to you with his answer. What do you think I should aim for - 140 mph?

Man, to think of the times with the Mizer where 76 mph would have been a record... The KR2 is really in a class of it's own!

Henni

Hi Henni.

Yes, the KR2 is in a different class!

To get the KR above 100mph you need to look at around 55 inch pitch, even higher, 55" will give you an absolute max of 125mph, taking slippage and inefficiency into account you can expect around 110mph and that is at 6500 rpm! If I am guessing the gearbox ratio correct at 2.53 something around 60x58 might work. At 6500 rpm that gearbox will give you just below 2400 rpm on the prop.

Just check the gearbox ratio, maybe I have it totally wrong!

Trading in the prop will be your best option. I have 2 props around those sizes we can test but the bolt pattern will be totally wrong

As a comparison VYZ runs a 56x59" prop at the moment at up to 3600rpm in cruise for a max speed of 200mph, she also needs more pitch but the motor will go up to 4100 rpm but I don't like running her there....

Rudi

[Henni]

Hi Rudi,

I'll make immediate work of it. Thank you so much for your calcs. Found this on the gearbox.

...in real life I have found that a 3 blade IVO, 3 Blade GSC, 3 Blade Powerfin, 4 blade Ultra prop up to 66 inch can be loaded into the "1/2 ton" A or B box - with the Warp Drive 3 blades being too heavy.

Two blade props by the above manufacturers can be used up to 68 inches, if in doubt contact your manufacturer!!!!

Henni

[Rudix]

Hi Rudi,

I'll make immediate work of it. Thank you so much for your calcs. Found this on the gearbox.

Henni

Hi Henni,

Pleasure! Great thanks, lets hope your ratio is at the lower of the 3 versions, will help

Rudi

[AndreJ]

Hi Henri

Die aluminium profile wat jy soek (50mm x 50mm) kan bekom word by NFM Pretoria. Die problem daarmee is dat die spec daarvan 6063 T6 is en nie 6061 T6 nie. Dit behooort moontlik te werk!! Vra die slim manne of dit dalk kan werk!!

Groete

Andre'

[Henni]

Hi Andre,

Baie, baie dankie. Ek is seker dit sal werk. Ek het net 'n paar kort stukkies nodig om die totale las na die firewall hoeke oor te dra - wat ek het is nie genoeg daarvoor nie.

Ek sal die firma more oggend opspoor en nevraag doen.

Groete,

Henni

[AndreJ]

264 Zeiler Street
Pretoria West
Pretoria
Tel: +27 (12) 327 0016

[Henni]

Hi Andre,

Dis sommer naby waar ek werk. Sal more oggend by hulle 'n draai gaan maak. Weereens baie dankie vir hierdie waardevolle inligting!

Groete,

Henni

[Henni]

Hi all,

Just a few interesting installation pics I've found.

All the best,

Henni

[slysi]

Its great reading this thread, well done Henni!

Good luck with the build and remember be safe

Simon