Prop for BMW or Rotax 503

[RickH]

Hi to All

 

I am in the finishing stages of building a mid wing version of a Texas Parasol (I gues you'd call it a Texas Midwing) .

 

I have both a BMW R90S Engine (67hp) fitted with a Rotax B type Gearbox and a Rotax 503 (50hp) also B gearbox, due to Finances I am going to mount the 503 initially and will fit the BMW when I have finished its overhall.

 

I don't really want to be buying a new prop when I finally fit the BMW.

 

My thinking is to try to source a prop which can be used on both with a change in pitch.

 

I figure 58" or 60" diameter.

 

Does anybody out there who has experience with either engine have some views on this proposal.

 

I would like to hear.

 

Regards RickH

 

 

[facthunter]

I think the engines are too different. You have a HP difference 50/67, but that is not all . There would be a need for different ratios in the gearboxes, because of the rpm's and torques. You may have already allowed for this, but the increase is 34% horsepower-wise, probably too much for the compromise prop to do the job for both. It's hard enough to get the exact right prop for one motor, let alone have it work well on two. Nev

 

 

[RickH]

hey Facthunyer

 

Certainly there is the hp difference but RPM are similar BMW 7000max Rotax 6800max max torque on both at 5500 given that prop dia is relative to prop speed Ibelieve I can compensate, @ 2.54 reduction, propspeed for BM is 2755max for 503 2577max not that much diff. If I choose a diamater to suit the BM ie shorter of two then surely a re pitching of the prop would be all that is required. why I tend to think of this is the varying Dia of props I see reported as being used on both of these engines ie from 56 thru to 60 on both of them or am I missing something.

 

RickH

 

 

[fly_tornado]

my tornado both have 60"x3 ivoprops and 503s. I don't know how to tell how much pitch they have

 

 

[RickH]

Not familiar with Ivoprop but if they use pitch blocks then the blocks would be marked somewhere.

 

I assume that by 60x3 you mean three bladed.

 

 

[fly_tornado]

have a look @ the ivoprop website for how the props work.

 

 

[RickH]

Hey Fly Tornado

 

Thanks for the tip. Had a look at the website Ivoprop could well be the way to go.What are your thoughts with regard to their quality. Had a chat with a LAME (Engines) mate of mine and he reckoned that the idea of one prop to suit both engines should be "quite do able". I like the way Ivoprops are adjusted.

 

Regards rick

 

 

[fly_tornado]

I think rotating props in the hub are the way to go. The ivoprop is twisted which changes the shape of the blade.

 

 

[skyfox1]

Hi first you need to know the ratio of the boxes B type normaly has 2.58 to 1 if they are the same then either a ivo or a brolga prop should be interchangeable both have pitch adjustable l have done simailar to you having a 503

 

then changing to a 582 using the same prop l settled with the brolga it has pitch blocks maximan pitch 18 degrees down 12 degrees.

 

cheers Geoff.

 

 

[RickH]

Much appreciated Geoff I will certainly look at the brolga.I do like the Idea of pitch blocks, positive lock.

 

Yeah you're right regards ratio, in one of my previous posts I said 2.54 :1, as you say it is 2.58.

 

Cheers Rick

 

 

[eastmeg2]

Hi Rick,

 

I had a 60x3 IvoProp on a R503 + 2.58 B-Type box, which I replaced with a 62 inch Bolly BOS-3.

 

Both were pitched for max static revs of 6,400 rpm.

 

Take off roll and ROC were noticeably improved with the new 62 inch prop.

 

Revs at 50kt cruise was also down from 5,600rpm to 5,400rpm.

 

This is on a Pursuit-10 single seat trike.

 

Cheers,

 

Glen

 

 

[RickH]

high Glen

 

Thanks for the input. How does the Bolly compare price wise.

 

Regards Rick

 

 

[eastmeg2]

Hi Rick,

 

I'm not too sure about IvoProp pricing but I do think Bolly pricing is higher even with the new composite hub which I'm using on the 62 inch prop. Pricing is on their website.

 

 

[RickH]

Cheers Glen

 

I'll try to upload a photo of my bird