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-   -   Prop extensions? (https://vansairforce.net/community/showthread.php?t=200911)

claycookiemonster 11-09-2021 04:19 PM

Prop extensions?
 
Both the Showplanes and James cowls require a prop extension. I've been going back and forth between Aerosport Power and Whirlwind to make sure everyone is ok with this. Now, Whirlwind is balking a bit at mounting their new 3-blade prop on an extension. I contacted the manufacturer of the extension, Sabre Manufacturing, and they said they make a 3" extension used in Red Bull races with 60lb props pulling 10 G's. They don't think this is any problem for me.

I understand manufacturers being hesitant to endorse ANYTHING GOES, but is this a real road block, or just the reality of Experimental airplanes and new combinations? I'm not EVER going to do anything close to the Red Bull guys, so I can talk myself into this. On the other hand, I have no desire to really approach the edge of safety and wisdom.

Anyone with prop extension experience have any perspective on this?

00Dan 11-09-2021 04:23 PM

Donít the current Vanís cowls also require an extension? I know my old fixed pitched Vanís cowl on my -4 requires a 4Ē extension, and I think the CS cowl required a 2.25Ē extension.

BillL 11-09-2021 04:40 PM

You should define what specifications are wanted for an extension. The cranks are the real issue. Are you building a 9?

claycookiemonster 11-09-2021 07:13 PM

Building a taildragger 8. Trying to make sure everyone is on board with the engine room before I make serious plans. Either the James or Showplane cowls require a prop extension, though they don't specify how long of an extension. I believe they need 2.5"

Yes, I understand the stresses in this. I do not want to underestimate them.

Just trying to understand the cautious reply from Whirlwind, which was not actually a, "It's forbidden!" Aerosport power is fine with this. So, their bearings must be up to it.

KatanaPilot 11-09-2021 07:21 PM

Have you considered the extended hub Hartzell props? I believe Team AeroDynamix has used them in the past. You could reach out to them for their opinions.

rmarshall234 11-10-2021 07:18 AM

The prop extension we used on Miss B Haven - the Formula One Racer at Reno - was comically long. Like 12 inches. A different application for sure, and a light weight CF prop at the end, but the biggest challenge was balancing the prop well enough since it was so far out there in space. I tried to post a photo but the size is too large and don't want to spend the time figuring out how to shrink it. PM me an email address if you want to see something that should put your concerns to rest.

BillL 11-10-2021 10:15 AM

Quote:

Originally Posted by claycookiemonster (Post 1567510)
Building a taildragger 8. Trying to make sure everyone is on board with the engine room before I make serious plans. Either the James or Showplane cowls require a prop extension, though they don't specify how long of an extension. I believe they need 2.5"

Yes, I understand the stresses in this. I do not want to underestimate them.

Just trying to understand the cautious reply from Whirlwind, which was not actually a, "It's forbidden!" Aerosport power is fine with this. So, their bearings must be up to it.

Check your sources - - James recommended 2.25"

If you understand the stresses, what do bearings have to do with it?

Aerobatic cranks have the same bearings, just a thicker flange.

You had better assume that your aerobatic limit is 4 G's, maybe 5. Quantify the stresses.

Krea, I asked Hartzell long ago about that hub for aero and they said 4 G. i.e. it was the same as standard with a saber 2.5"extension. That was 6-7 yrs ago and may have changed.

Through private conversations, Hartzell and calculations, I was convinced my M1B, Hartzell composite and 2.5" Saber was good for the a "mild aerobatic" range. Any rapid axis change at high RPM is forbidden. Today I would use the extended hub. This is not an endorsement . . YMMV

Just keep in mind that Earl Findlay endorsed an RV9A for for 230 MPH airspeed (30 mph higher than Vans limit -lesson: be careful trusting your life to critical information provided without corroboration)

PilotjohnS 11-10-2021 12:18 PM

Quote:

Originally Posted by BillL (Post 1567648)

Just keep in mind that Earl Findlay endorsed an RV9A for for 230 MPH airspeed.

For those who dont follow these forums,, this is a joke. RV9a is not approved for this high of speed.

claycookiemonster 11-10-2021 02:28 PM

I'm slowly circling the wagons on this. It appears that the extension made by Sabre Manufacturing is equivalent (but thinner by .5") to the ones they supply to Red Bull and I'm not going anywhere close to those loads. Also their props are twice as heavy as I'm planning. Reading the fine print from Whirlwind, what they actually said was, "Ideally, you wouldn't want to use an extension..." which isn't a line in the sand. Given what Sabre said, I'm happy to keep planning.

Capflyer 11-11-2021 05:23 AM

Just get the Hartzel extended hub prop. No worries about an extension. Hartzel has an extended hub specified for the James cowl. If Whirlwind is having heartburn then just don't get their prop. If anything happens such as spitting grease they will probably point to the extension and deny any warranty work. If you are only worried about the safety, don't. Plenty of planes using them and, personally, I've never heard of anyone having an issue.


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