FX 40 and FX46 speed props
 

I have been using an 10-5 or 10-6 on the FX40 and an 11-5 or 11-6 on the FX46 engines. I am getting planes that want more speed and I am wondering if the FX46 can handle an 11-7 without overloading or do I need to go down to a 10" prop?
What can the FX40 handle? Thankx for interested replies on this!

FX 40 and FX46 speed props
 

Knowing what type of planes you will put these engines on might help with prop selection to fullfill your need for speed.

Prop for plane
 

Ok, more facts: the 40FX is on a 40 sized Shoestring Racer with a 55" wingspan which I recently inherited but haven't flown yet. The 46FX is on a World Models T34 Mentor also not flown yet.:D

FX 40 and FX46 speed props
 

I have a quickie 500 with a Webra Speed 40 and a Mac's tuned pipe. The latest prop I have on it is a APC 9x7 prop. It was really fast with this prop... pulling something close to 17K rpm... but I think I could go with a 8.5 x 8.75 prop and really get a screamer... I have a fluttler problem I need to resolve first...

My quickie:
http://members.telocity.com/paulswany/quickie11.jpg

prop chart
 

Fastsky,

Since you already established the load your engine likes, take a look at the attached chart, find the load of your current prop, next look for a prop with a lower diameter and a higher pitch that has a similar load. Remember by gaining speed you will loose torque.

Pauls Plane
 

Thankx for the info and plane pic. It looks fast just sitting there! :D

real world experience
 

I already have a thrust program on my computer. I fing the chart from MM kind of confusing. I was hoping to hear back from real world experiences,specifically from someone who has tried a 10-7 prop on an FX40 and an 11-7 prop on an FX46. I guess I can just put the prop on and see what happens but different props definetly work better on different airframes and it would be nice to have a starting point. :eek:

chart
 

Fastsky,

The chart works, I can tell you that from real world experience. Keep in mind that you must fly a prop to really know what performance you will get. I use the chart to determine which props to buy. I will then go to the field and start testing. I've found the same prop on the same engine will behave differently in different planes. Email me if you need help understanding the chart.

Question for MMallory
 

I downloaded your chart. Had to do a bit of cleanup work, as tabbed text doesn't always come out as clear as you'd like! :D

The information presented there does seem to be pretty accurate - my .46VFs turn 10X7 props @ 15,000 plus & 9X9 props @ 15,300 plus. According to your numbers, the 9x9 props actually present a lighter load, hence the extra RPM.

Anyway, I'd like to know what formula was used to generate these numbers. I'd like to add some of the fractional-sized props to the data! (like the APC 12.25x3.75)

Chart
 

Visioneer,

I will email you the Excel file. The formula is Diameter(to the 3rd) x Pitch. For a 10 x 7 prop you will get: 10x10x10x7 = 7000

Excellent!
 

Looking forward to receiving the spreadsheet.

Thanks for the quick reply. I have a .40-sized Sukhoi with a cranky YS .53 that hasn't liked any prop I've put on it. Tried 12x6, 12x7, 11x7, 11x8 with no sucess. The 12" props were too much of a load, and detonation was a problem. The 11" diameter props ran well, but didn't generate enough thrust to move that barrel-nosed beast with authority.

I flew it this weekend with a Zinger 12x5 woodie I "discovered" in my flight box. Holy crap! The engine loved it, and the thrust was way up. Checking the numbers, the 12x5 falls right in between the 11x7 and 11x8. 12x6 & 12x7 load figures are way higher. More proof in action, I guess.

FX 40 and FX46 speed props
 

Fastsky: For pure speed my vote is for either an APC or MAS 10X5 for the 40FX and 10X6 for the 46FX. You can go faster if they were piped but putting on larger props like an 11X7 on the 46FX will not overload it on the planes you have mentioned however it will take longer to get up to terminal speed. You want higher RPMs in your case not more torque load on the engine although there is a trade off point to all this. Keep in mind that 40 size Q500 engines often use smaller than 9" props as they want max RPMs which gives them both acceleration and good top end.

46 Speed props..
 

I use 9X8 on my 46VF's...I don't think 5 or 6 inches of pitch would be what I would call a speed prop. Just my opinion.

FX 40 and FX46 speed props
 

Jeff: You are right but aren't the VF's required to use a pipe? A 10X6 on a 46FX on 15% should turn around 14000 give or take a few RPMs. If you piped the engine and ran a 9X8 you would likely see a nice increase in RPM. Do you think running a 9X8 on a stock 46FX would be suitably worthwhile? As a means of comparison there are a few guys I fly with - we all have either Hobbico Vipers or Scats or similar older style Q500 that we race around the field with. I run a 32SX with a 9X6, others run 32F's with a 9X6, 40FX with a 10X5 and 46 FX with a 10X6. The 32 size planes move around quickly but the 40 size are a bit faster - all are stock muffled. However we are all old fart types (50+) so these speeds are fine for us. I guess if Fastsky wants more poop then a Perfomance Specialties muffler or the equivalent Jett version will add another 1500 RPM to his FX engines.

props
 

One example are the props I've used on my Twinstar. It has 2 Irvine 40's ABC BB. The prop that these engines love is a 10 x 6 APC. With the 10 x 6, I can take off and go vertical until I want to stop, but I figure the speed to be average to any sport plane (about 70-80 mph flat and level). Torque is awsome though. I changed to 9 x 9 APC's to see how much speed I could get. I figure speed jumped up to about 100 mph but I lost the unlimited vertical and I lose a lot of speed in the turns. This plane was much more fun with the 10 x 6's.

The design of the plane will have a lot to do with prop and engine selection. Your ultimate selection will determine your speed.

Good luck and happy test flying!

FX 40 and FX46 speed props
 

MMallory- Would you happen to know what the load to hp ratio is?
For instance, a 1hp engine could turn what load for the best performance in a sport plane?

Load to HP
 

Gubbs3,

That I am not sure of. You might want to ask that question on one of the Jet or electric boards. The electric guys really pay attention to load & HP.