Prop Woes

Some time back, prior to really needing to order a prop.. I had done a bunch of research on the options.. There’s the stock Hartzell 2 blade metal prop, and various other 2 and 3 bladed props from the likes of Hartzell, MT, and Whirlwind. I put together the following table based on the options I found.

BrandModelCostNumber bladesBlade lengthSpinner sizeWeight with spinnerMakeupTBO
MTPROP MTV12B/193-531385037643Composite6 yrs/1800hrs
MTMTV915900376or7854.9Composite6 yrs/2400hrs
HartzellPROP C2YR-1BFP/F8068D902528055.6metal6 yr/2400 hr
HartzellPROP C3Y1R-1N/N7605C SPINNER C-4582-P2035537867.5composite
Whirl Wind77HRT1210027743Composite6 yr/800 hr
Whirl Wind375HRT1435537555Composite6 yr/800 hr
Whirl Wind300-771250037742Composite6yr/800hr
RV-10 Prop options

While the stock 2 blade is widely regarded as the fastest prop, I felt the 3 blade was a better look for the Showplanes cowling I had already chosen. It also is much smoother and has a shorter blade length giving more clearance there.. Of course that doesn’t go without consequences largely in removing the lower cowling. The plan there is to split the lower cowl into two halves like several others have done. Just more fiberglass work.. 🙂

I saw several of the recent builders go with the Whirlwind 375HRT prop. I had spoken with them and was also planning on going in that direction. The main downside is the lower TBO times, but at about 100 hours per year.. I’d likely hit the same time limit prior to the hours limit, which is the same as the MT and Hartzell.

Fast forward to prop order time, which I had delayed a bit due to the 4-6 week lead times I was consistently given by Whirlwind. Guess what.. They no longer are selling that prop (support only) in favor of their newest 300-77 prop. Which is all fine and everything, but the weight reduction (of all things) was concerning.

Why concerning, you ask? Well weight and balance concerning.. The RV-10’s CG moves aft as you burn gas.. Ideally, you’d like to have your empty weight as close to the forward CG limit as possible so as to allow for max carrying capability and gas burn as you go longer distances, even if that means throwing in some ballast when solo. Having a prop that is over 10 lbs lighter out front combined with my Air Conditioning (mostly CG neutral, but ever so slightly aft), an O2 bottle, and a standard technology battery (read heavy) behind the baggage bulkhead, I was concerned.

It’s difficult to know exactly what my empty weight will be, but I grabbed 2-3 samples of what I could find and was provided by other builders. I did a bunch of playing with W&B by estimating the arm of the prop (approx at the hub) at 32.7″ from this picture:

I did that by measuring the scale with a ruler between 25″ and 50″ and then calculating the number of inches per 1/32″ and figuring out the distance to add to 25″ to get to a line drawn through the prop location.. I felt that was good enough for my comparison purposes..

I then found an example W&B spreadsheet online that had lots of weight scenarios listed for that given plane. I modified the spreadsheet to subtract out the weight of the prop that plane had on it and added back in the WhirlWind Prop weight. Here is the stock aircraft examples of empty and gross weight.

   AIRCRAFT EMPTY  
       
Location  ARMWEIGHT (LB)WEIGHT (KG)MOMENT
Left Main Wheel  124.31621282.2777197
Right Main Wheel  124.44608276.3675660
Nose Wheel  50.44328149.0916544
Main Fuel Tanks0gallons108.9  0
Pilot  114.58  0
Copilot  114.58  0
Passenger  151.26  0
Passenger  151.26  0
Baggage  173.5  0
Survival Gear  173.5  0
Remove stock prop  32.70 0
Add WW Prop  32.70 0
       
  Totals 1557708169400
       
  C of G Location 108.799  
  Forward Limit 107.80  
  Aft Limit 116.24  
       
   AIRCRAFT AT GROSS  
       
Location  ARMWEIGHT (LB)WEIGHT (KG)MOMENT
Left Main Wheel  124.31621282.2777197
Right Main Wheel  124.44608276.3675660
Nose Wheel  50.44328149.0916544
Main Fuel Tanks60gallons108.9360 39204
Pilot  114.5818680.0021312
Copilot  114.5817680.0020166
Passenger  151.2617680.0026622
Passenger  151.2617680.0026622
Baggage  173.559 10237
Survival Gear  173.510 1735
Remove stock prop  32.70 0
Add WW Prop  32.70 0
       
  Totals 27001028315297
       
  C of G Location 116.777  
  Forward Limit 107.80  
  Aft Limit 116.24  

So about 1″ aft of forward limit empty and slightly out of CG aft loaded up with full fuel and passenger weight somewhat equally spread around.

Now comes the effect of doing the prop swap:

   AIRCRAFT EMPTY  
       
Location  ARMWEIGHT (LB)WEIGHT (KG)MOMENT
Left Main Wheel  124.31621282.2777197
Right Main Wheel  124.44608276.3675660
Nose Wheel  50.44328149.0916544
Main Fuel Tanks0gallons108.9  0
Pilot  114.58  0
Copilot  114.58  0
Passenger  151.26  0
Passenger  151.26  0
Baggage  173.5  0
Survival Gear  173.5  0
Remove stock prop  32.7-55.6 -1818
Add WW Prop  32.742 1373
       
  Totals 1543708168956
       
  C of G Location 109.470  
  Forward Limit 107.80  
  Aft Limit 116.24  
       
   AIRCRAFT AT GROSS  
       
Location  ARMWEIGHT (LB)WEIGHT (KG)MOMENT
Left Main Wheel  124.31621282.2777197
Right Main Wheel  124.44608276.3675660
Nose Wheel  50.44328149.0916544
Main Fuel Tanks60gallons108.9360 39204
Pilot  114.5818680.0021312
Copilot  114.5817680.0020166
Passenger  151.2617680.0026622
Passenger  151.2617680.0026622
Baggage  173.559 10237
Survival Gear  173.510 1735
Remove stock prop  32.7-55.6 -1818
Add WW Prop  32.742 1373
       
  Totals 26861028314853
       
  C of G Location 117.202  
  Forward Limit 107.80  
  Aft Limit 116.24  

Note that empty, it moved the CG aft by 0.671″ and by 0.426″ in the gross case.

I, of course, ran a bunch of other configs including our Family profile (Assuming Declan fully grown) and it would all be okay.. but low on fuel you can actually get slightly aft of the limit with lighter prop. All would be fine with the weight of the standard prop. I won’t bore you with several tabs of spreadsheet data I played with here.. 🙂

All of this further reinforced the need to find a prop that was close to the stock 2 bladed prop for piece of mind. That left me with 2 choices.. Hartzell 3 blade (super expensive) or the MT MTV-9 prop..

There were a couple of other builders that have used this prop. Van’s typically recommends the MTV-12. One of the main reasons they used it was the max HP rating of the MTV-12 is around 300HP, and they had similar engines to me.. meaning cylinders ported and polished, cold air induction, and higher compression ratios.. MT suggests the MTV-9 for these applications as it can handle significantly more HP (thus the extra weight). In addition MT says that there is no issue using electronic ignition with this prop at my approx HP. (they didn’t support doing that with the MTV-12, even though I know others have done it). So all of that plus the weight that is very close to the Stock 2-blade and I decided to go with it. I placed an order for the MTV-9-B/198/52 with nickel leading edges in a matte black with white tips configuration. They also suggested this spinner, which I passed by Bryan at Showplanes, and he thought it would work fine.

P-810-5 Spinner.

The issue came with the 148mm prop flange to aft spinner dimension, which I was asked about and didn’t think it would be an issue. Especially seeing Bryan said it would be okay and I know other RV-10 builders that have used this prop.

Until it was an issue..

I bought the cowl installation tool from Flyboy accessories to place the cowl ahead of getting the prop. It is well designed and provides an adjustable 15″ wheel that serves to set the cowl back from the spinner assembly.

I set the spacing to 148mm minus about a 1/4″ gap. Placed the upper cowl in position.

And DoH! the cowling is so far forward it doesn’t even reach the firewall.

I contacted my MT guy and described the issue and to see if they might have any other spinner/hub setups that might work better for me. In the meantime I mulled over what to do.. I had heard of another builder using the Hartzell 3 bladed prop with an I-hub config which pushes the spacing out enough to fit the AC compressor without having to cut and bump out the cowling. I got some info on that as an option.. I also contemplated what would happen if I cancelled my MT order.. Either lose some/all deposit money or continue with the purchase and try to sell it..

MT got back to me with a spinner specification sheet. I used the info I got about the Hartzell I hub spacing and did some mock ups and measuring.. I ended up getting a range of prop flange to aft spinner measurements that matched the Hartzell I hub design at the minimum side and a measurement as far forward as possible with almost no cowling overlap onto the firewall at the max side. I filled out their form and asked if there was anything off the shelf that would work.. I came up with somewhere between 69.3mm and 82mm would work for me.

A couple of days later engineering came back with this .. A P-810-3 spinner with 75mm spacing. It’ll work!!! What a relief..

P-810-3 Spinner

I mocked this distance up and checked the spacing of the AC compressor up front with the lower cowl roughly in place.. There is plenty of room to not have to do any lower cowl modifications for the compressor. Win win!

I told MT that it would work. A change order was put in with no anticipated delays seeing I’m still far enough out in production. I’ve been able to continue forward with the cowling install now that the spacing is known.

I will say that I’ve encountered a bunch of negativity about MT and using their props along my research. While I agree that might become true with months of delays in the case of something catastrophic that needs to go back to Germany to get fixed. For most run of the mill things it shouldn’t ever be an issue (at least I hope not). The local guys are easy to work with and bend over backwards to make things right. I also have a certified MT service shop relatively nearby in CT that I could drive to if need be. Thus far, I’m impressed with MT.

Sorry for the long post… it’s been a few months in the making.

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