Prop and performance

[tenniecoleman]

Hello
I am wondering if someone can help me with Propeller selection.
I have owned a bc12d 85 modified with an 0-200 crank. supposedly bringing the upgrade to roughly 94 hp. I fly both on wheels and skis. I have a mccauley 7146 prop. I have roughly 120 hours in the plane and I am very happy with the short field performance however I only cruise at 90 mph on a good day. Everything I read about t-crafts states that the cruise should be 95 to 100 mph on a 65 hp. I would think that I should be able to at least make that with the engine I have. I do have a little bigger wheel and no wheel boots, so maybe a little more drag. I figure maybe the cruise speed could be increased a little with a different prop. I am thinking i'll probably keep the prop I have for ski flying and summertime when I travel further put on a different prop. However I'm not sure what to get. Some makes list cruise props and some don't. Wood is cheaper... but I have no experience with them. Is a 50 pitch prop too much?
Any information would be appreciated. Thanks

[Bird]

Re: Prop and performance

Best that you check out the next post in this forum and from there do a advance search on props and engines. I don't know diddly but the rest of the clan will be showing up shortly.

[cvavon]

Re: Prop and performance

Ok first i have a pre-war it weighs 777 lbs the engine is a C85-12 f with 26 hr on it jest removed a Mc74/43 prop with it would cruse at 109 knots that was ground speed on GPS now it has Sensenich 72/40 prop and have seen 106 MPH on GPS and that was at 2550RPM. First i would check the Instruments in your plane then see what the engine is turning for RPM as the prop you have has a lot of pitch, so if you aren't turning more then 2550 flatten the prop to a pitch that will let it turn up to red line +

[tenniecoleman]

Re: Prop and performance

my engine is a -12 engine with a lot of electronics, so I am heavier. I don't think that should make too much difference in cruise though. the engine is also in very good shape with low hours, about 400 since rebuild, I can check the actual rpm against the tach but I think it is close, I use 2350 for cruise and that's about 90 mph, I can redline in straight and level flight with full throttle. My understanding is that If I flatten the pitch to turn up higher that I would gain take off performance but lose in cruise?

[Ragwing nut]

Re: Prop and performance

my engine is a -12 engine with a lot of electronics, so I am heavier. I don't think that should make too much difference in cruise though. the engine is also in very good shape with low hours, about 400 since rebuild, I can check the actual rpm against the tach but I think it is close, I use 2350 for cruise and that's about 90 mph, I can redline in straight and level flight with full throttle. My understanding is that If I flatten the pitch to turn up higher that I would gain take off performance but lose in cruise?

If you redline when you hit full throttle and not before, you can't get anymore speed out of it. You are correct if you flatten prop, you will gain climb and lose top end. To gain more speed you will need to clean up the aero on it. Double check the wash in the wings to make sure you dont have too much for starters.

[cvavon]

Re: Prop and performance

And also when was the prop in the prop shop and who worked on it last as they can be bent and not be what they say they are on the hub

[tenniecoleman]

Re: Prop and performance

And also when was the prop in the prop shop and who worked on it last as they can be bent and not be what they say they are on the hub

the prop has been worked on from a previous accident, in the log book it says 7146 however it is shorter than that. It measures about 70". I don't want to sacrifice performance too much, but with the 0-200 conversion it performs quite well. I am really just looking to get the plane up to 100mph. I can check out the wings and airframe and see what I can do there

[cvavon]

Re: Prop and performance

Check the air frame out to see if it's ok then i think if it were me i would take the prop to the prop shop and have it looked at to see were it's at as far as pitch. then you know what you have and can adjust from there, rule of thumb 1in of pitch will change rpm by about 50RPM and speed will change too also it don't hurt to turn a small continental more rpm 0200 red line is 2750 c85 is 2550.The recommended cruse RPM for a 0200 is 2500 RPM and that is what the STC turned your engine in to and that said will increase your speed.

[Robert Lees]

Re: Prop and performance

Hello tenniecoleman (and welcome to the Forum!).

I have the 0-200 crank mod in my C85 (non-electric) 1946 BC12D , and I see 105mph indicated at 2300 rpm. Flat out, she'll cruise at ~120mph IAS.

My prop is a McCauley IB90 71*45, and I get about 2250 static rpm. What is your static rpm?

At ISA (approximately) I get about 950 fpm climb at my gross weight of 1280lb at 65-70 mph and 2300 rpm in the climb.

How much bigger are your wheels (I think you will lose a bit more than you think).

Regards,
Rob

[cvavon]

Re: Prop and performance

Robert i get numbers very much like you only i have 26/12.50/6 bush wheels. when i put the bigger tires on i to though i would loose a lot of speed but it's not as bad as i though it would be maybe 2 or 3 mph. With a sensenich 76ak-4 72/40 2375 static 60 mph climb 2500 rpm at 1100 fpm 2600 cruse rpm 106 mph. My sensenich pulls better then both McCauley props i have had on the engine.

[tenniecoleman]

Re: Prop and performance

Robert
I will check on the size of my tires when I get back, at this point i'm not sure. What is your fuel burn at cruise? I burn 6.0 GPH at 2350 that's figured on tack time.

[Robert Lees]

Re: Prop and performance

Hmmm..my "other" Taylorcraft (the cream-and-black one, it's not mine any more, and a pre-war model) has a metal Sensenich, and it for the same pitch/dia numbers as the Mac, was finer than the Mac. It climbed like a homesick angel when lightly loaded (see picture below).

My "feel" was that the Sensenich was a finer prop than the Mac for the same pitch/dia (their airfoils and tip design are different, I assume).

This was for A65 engines, mind you.



(incidentally, the above photo is taking off diagonally across the tarmac runway 15 but in to wind).

[Robert Lees]

Re: Prop and performance

Robert
I will check on the size of my tires when I get back, at this point i'm not sure. What is your fuel burn at cruise? I burn 6.0 GPH at 2350 that's figured on tack time.

Tennie,

My fuel burn in the cruise is the same as when I had an A-65 in it...about 4.4 USG per hour (tach time).

For the record, my aeroplane used to have an A-65, the average fuel burn over three thousand hours was 4.32 USG per hour.

300 hours ago, we fitted the 85 stroker, and average fuel consumption over that time is 4.39 USG per hour.

In the cruise, I use the same rpm (2250-2300) for the same IAS (95-105mph) as when I had the A-65. As I'm sure you know, fuel in the cruise is used to overcome drag, so for the same airframe, the drag (and hence fuel burn) will be similar, whatever engine is fitted (within reason).

[You may note I am being very specific about US Gallons...you may have also noted I'm in the UK where we have Imperial gallons. I do all my fuel calculations in litres anyway, but I am careful to differentiate between the the US and Imperial gallon]

[swoeric]

Re: Prop and performance

check your weight and balance...with a very aft loaded plane and at gross i get 105mph-108mph at 2200 rpm maybe 110-112 at 2500 on 8.50 tires empty the plane flew 94-96 ish maybe a bit better @ 2350 rpm

now on 30 in tires and way forward cg empty i pray for 95 at 2350 empty with some good weight in the back i get 100mph

speed is only a function of drag..prop and rpm

larger motor etc just gets static rpm up for given prop size...the 65 hp will cruise just the same as the larger motors for the most part in these planes due to the significant effects and constraints of aerodynamics....


the answer to this post is to call catto and be done with old technology