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Going to a 72" prop

 
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Richard Pike



Joined: 09 Jan 2006
Posts: 1649
Location: Blountville, Tennessee

PostPosted: Tue Dec 29, 2020 3:47 pm    Post subject: Going to a 72" prop Reply with quote

Still thinking about upgrading my Kolb MKIII, planning to go from a 68" Ivo to a 72" Warp Drive prop, will need to raise the engine so the prop will clear the boom tube.
The attached picture shows the typical / normal Lord shock mount method of attachment between the airframe and the motor mount plate.
One easy way to gain more prop clearance is to flip the Lord mounts over, they are 1" taller one way than the other, but I have never seen anybody do that.
Is there a reason why this is not a good idea?


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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.
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Eugene Zimmerman



Joined: 10 Jan 2006
Posts: 392

PostPosted: Thu Dec 31, 2020 5:36 am    Post subject: Re: Going to a 72" prop Reply with quote

Richard,

I turned my mounts with the high side up. I found that it is critical to use large snubbing washers on the bottom side of the mounts to prevent over stressing the rubber part of the mount, especially so on the rear mounts which experience high tensile stress under full thrust.
In my experience, I found that the main advantage of rave valves is improved fuel efficiency at cruise power settings.

The disadvantage is that, some two stroke oils may cause the rave valve to hangup causing higher fuel burn.


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chic



Joined: 12 Apr 2019
Posts: 46
Location: Riverside Calif

PostPosted: Tue Mar 30, 2021 4:41 pm    Post subject: Re: Going to a 72" prop Reply with quote

I have also heard of guys only turning the rear mounts over and leaving fronts in lower position when going with larger prop for clearance. Was told it will give you a little more clearance for prop against boom and lessens the "nose over" effect at full power when getting the thrust line too high. Havent done it myself.

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Richard Pike



Joined: 09 Jan 2006
Posts: 1649
Location: Blountville, Tennessee

PostPosted: Wed Mar 31, 2021 12:41 pm    Post subject: Re: Going to a 72" prop Reply with quote

All done and flying great. Had a few teething issues:

Initially started out with an extra 3/8" motor mount spacer at the rear, giving it a bit of downthrust to counteract any possible pitch over tendencies. Flew it four times that way, evaluating handling while trying to get the Warp Drive prop pitched properly. (Made me really appreciate the Ivo's ultra simple prop adjustment method!)

Short version: the airplane simply felt wrong. Constantly fighting it as it kept trying to nose up at most every throttle setting, plus on final with minimal power, it just did not feel right.
Removed most of the rear spacer, now it handles just like it always did, deviation from stock thrust angle is two extra 1/16" washers on top of the rear Lord mounts.

Spent one afternoon playing with brass shim stock between the prop hub and the gearbox prop flange, finally got all three blades tracking within 1/16" of each other.
Spent several days trying to get the prop pitched for a 6300 rpm climb and a 6500 rpm max in level flight. Finally got within 50 rpm and called it quits.
Plugs look good, EGT gauges were lying to me. The new dual EGT gauge arrived today, no hurry putting it in, wx is rainy today, uber windy tomorrow.

Anyway, everything is now as it ought to be, it runs smoother than it ever has, and the climb rate is typically right at 1,000'/min solo. Looks like normal cruise is going to be about 53-5400 rpm at 65 mph. And boy is it quiet!

Now I need a pretty day so I can take some pictures of that old 2-seater trike, it's 582/w electric start, B box, BRS, and my 68" Ivo, get that thing sold and out of the hangar. $3k if you guys know anybody looking for such.

Thanks for the suggestions & advice along the way.


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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

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Charlie Mike



Joined: 06 May 2021
Posts: 25
Location: West coast

PostPosted: Thu Jun 17, 2021 11:34 am    Post subject: Re: Going to a 72" prop Reply with quote

Richard Pike wrote:
All done and flying great. Had a few teething issues:

Initially started out with an extra 3/8" motor mount spacer at the rear, giving it a bit of downthrust to counteract any possible pitch over tendencies. Flew it four times that way, evaluating handling while trying to get the Warp Drive prop pitched properly. (Made me really appreciate the Ivo's ultra simple prop adjustment method!)

Short version: the airplane simply felt wrong. Constantly fighting it as it kept trying to nose up at most every throttle setting, plus on final with minimal power, it just did not feel right.
Removed most of the rear spacer, now it handles just like it always did, deviation from stock thrust angle is two extra 1/16" washers on top of the rear Lord mounts.

Good info, thanks….
Spent one afternoon playing with brass shim stock between the prop hub and the gearbox prop flange, finally got all three blades tracking within 1/16" of each other.
Spent several days trying to get the prop pitched for a 6300 rpm climb and a 6500 rpm max in level flight. Finally got within 50 rpm and called it quits.
Plugs look good, EGT gauges were lying to me. The new dual EGT gauge arrived today, no hurry putting it in, wx is rainy today, uber windy tomorrow.

Anyway, everything is now as it ought to be, it runs smoother than it ever has, and the climb rate is typically right at 1,000'/min solo. Looks like normal cruise is going to be about 53-5400 rpm at 65 mph. And boy is it quiet!

Now I need a pretty day so I can take some pictures of that old 2-seater trike, it's 582/w electric start, B box, BRS, and my 68" Ivo, get that thing sold and out of the hangar. $3k if you guys know anybody looking for such.

Thanks for the suggestions & advice along the way.


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Charlie Mike



Joined: 06 May 2021
Posts: 25
Location: West coast

PostPosted: Fri Jun 18, 2021 3:24 pm    Post subject: Re: Going to a 72" prop Reply with quote

Richard Pike wrote:
All done and flying great. Had a few teething issues:

Initially started out with an extra 3/8" motor mount spacer at the rear, giving it a bit of downthrust to counteract any possible pitch over tendencies. Flew it four times that way, evaluating handling while trying to get the Warp Drive prop pitched properly. (Made me really appreciate the Ivo's ultra simple prop adjustment method!)

Short version: the airplane simply felt wrong. Constantly fighting it as it kept trying to nose up at most every throttle setting, plus on final with minimal power, it just did not feel right.
Removed most of the rear spacer, now it handles just like it always did, deviation from stock thrust angle is two extra 1/16" washers on top of the rear Lord mounts.
Spent one afternoon playing with brass shim stock between the prop hub and the gearbox prop flange, finally got all three blades tracking within 1/16" of each other.
Spent several days trying to get the prop pitched for a 6300 rpm climb and a 6500 rpm max in level flight. Finally got within 50 rpm and called it quits.
Plugs look good, EGT gauges were lying to me. The new dual EGT gauge arrived today, no hurry putting it in, wx is rainy today, uber windy tomorrow.

Anyway, everything is now as it ought to be, it runs smoother than it ever has, and the climb rate is typically right at 1,000'/min solo. Looks like normal cruise is going to be about 53-5400 rpm at 65 mph. And boy is it quiet!

Now I need a pretty day so I can take some pictures of that old 2-seater trike, it's 582/w electric start, B box, BRS, and my 68" Ivo, get that thing sold and out of the hangar. $3k if you guys know anybody looking for such.

Thanks for the suggestions & advice along the way.


Richard, is this setting with the lord mounts flipped? Or standard orientation and just spacers at the rear?


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Richard Pike



Joined: 09 Jan 2006
Posts: 1649
Location: Blountville, Tennessee

PostPosted: Sat Jun 19, 2021 7:00 am    Post subject: Re: Going to a 72" prop Reply with quote

I did end up flipping the motor mounts over, plus the original spacers, and also added two extra washers to the rear mounts to get the required 1" of clearance from the tail boom. Once everything was installed, I hung all my body weight onto the prop hub and the prop tip still had about a 1/2" clearance, so that's good.

It is now a lot trickier to take off, you can't just cob the throttle and go like previously, it now wants to yaw hard to the right if you try that. You have to keep the tail planted firmly on the ground and use partial throttle until the airspeed gets to 30 and the rudder becomes fully effective, then raise the tail and go to full throttle. In cruise the ball wants to be 1/2 out to the left, will need a bigger rudder trim tab.
Rate of climb is better by about 300'-400'/min, very pleased at the smoothness and that it is quieter, but getting the 582 to be happy with this gearbox/prop combination was & is perplexing. For whatever reason, it has to be a lot leaner at cruise.

Idle jet is down from a 55 to a 50.
Needle clip position is supposed to be a 3, it is now a 1. This is with new needles.
RPM on climbout is 6350, EGT's at 950-1000.
Cruise is normally 5350-5400, airspeed around 65-70, EGT's 1050-1100.
If you throttle back to less than 5350, the engine falls off the pipe and the rpm will decay down to around 4600 and then stabilize at that rpm, with EGT's around 950.
As soon as you give it the least bit of throttle, then the rpm begins to rise, eventually stabilizing again at 5350, EGT's back to 1050-1100.
Ignition system was completely replaced last year, plugs are new, plug caps are new, EGT gauge and probes are new, jet needles and carb boots are new, choke pistons are new, air filter is clean.
It starts easily, runs smoothly and seems entirely reliable, the only other thing that is different than from before when it had the B box and the 68" Ivo is that I have not yet put the after-muffler back on it. That shouldn't make a difference but it is the only variable that has not been tested. It wasn't like this before, where ever you put the throttle back then, that is where it ran. I can live with it, but I'd like to get it resolved.

Different topic: Last week completely reloaded Windows 10 to fix an ongoing problem, and lost my image resizer. The one that MS offers is a total pain, finally found this one, works like it should. https://en.lo4d.com/windows/image-converter


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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

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Charlie Mike



Joined: 06 May 2021
Posts: 25
Location: West coast

PostPosted: Sat Jun 19, 2021 2:21 pm    Post subject: Re: Going to a 72" prop Reply with quote

Richard thanks for the detailed report!
I just spent 4 hours flipping those dang lord mounts. No easy way to get to them. I put one additional washer between the lord mount and mounting plate at the rear. That will slightly increase the downward thrust angle. I have a 68” 3 blade Kool prop. Like a Luga. Very light weight. Hopefully next week I will be making some static thrust runs……


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