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  #31  
Old 11-11-2005, 12:18 PM
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Very odd results. I have a 76 inch diameter and get about 4400 rpm at 38 inches MP which is about 170 hp at neutral pitch. I run 3 amps fine of neutral for takeoff and get about 4600 rpm. 2.2 to 1 redrive ratio. Acceleration is noticeably faster at the slightly finer setting than at neutral. Something weird here as I'd expect that your engine is making more power than this, has similar redrive ratios and you have less diameter. I am at 4000 feet MSL but the extra 6 inches of blade should negate that.

Hungry for more info.
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  #32  
Old 11-11-2005, 08:20 PM
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Ok, let us discuss constant-speed theory here.... Full fine pitch will NOT get you amazing acceleration. The prop is more efficient at the higher RPMs to get you rolling, but it quickly falls out of efficency as you start rolling faster.

Why does a constant speed accelerate so much better than fixed then? Because it varies its pitch as it accelerates. You are not controlling pitch on a constant speed prop, you are controlling RPM. As you accelerate with a constant speed, if it held its pitch it would want to overspeed, so it starts adding more pitch as you roll faster and faster to keep the RPMs the same. THAT is what gets you the amazing acceleration gains.

Now, how does this translate to an IVO without a constant speed box? You need to keep adding pitch on roll or you need to find a nice inbetween setting to take off with.

Edit: I forgot to add, the latter method is safer than the former, because if your prop happens to not change pitch as you accelerate by the time you find out you might be at the point where you will not be able to stop nor able to rotate.... running off a runway is not fun.

*preaching mode off*
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Last edited by JonC : 11-11-2005 at 08:37 PM.
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  #33  
Old 11-11-2005, 08:23 PM
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Quote:
Originally Posted by JonC
*preaching mode off*
did not notice a preach - just good info that us mere mortals sometimes forget
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  #34  
Old 11-11-2005, 11:20 PM
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Quote:
You need to keep adding pitch on roll or you need to find a nice inbetween setting to take off with.
I think I prefer the latter for the reasons you mentioned. Acceleration seemed pretty good at the "midway to fine" setting. More than enough to get airborne by the midpoint on the runway (1500'). Once safely airborne, I should probably coursen it up a little. As you say, rpm will be a good indication of my pitch setting. It's going to take a little experimentation to find the optimum but I think there will be a fairly wide range in the safe catagory.
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  #35  
Old 11-12-2005, 12:53 AM
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Quote:
Originally Posted by John Slade
For those who are waiting for news on the IVO....

After getting some backlogged work out of the way I ran it again today. This time I was on full fine pitch. I got a static of 4500, (up from 4000) but acceleration was well down from what I'm used to with the fixed pitch prop. Basically it was spinning the prop, but not doing much of anything else. I was barely at rotation speed by the time I had to brake. Hmmm. I coursened it up by about 4 seconds (i.e about half way toward the neutral position) and tried again. 4250 rpm static and this time she accelerated much better and would have rotated a little earlier than the fixed pitch. I aborted the take-off anyway because I was about 5 psi down on the fuel pressure on one side.
snipped ...
John, you know I know very little about rotaries, but, last time I checked, RX-7 max power was at 6500 RPM and max torque at 5000, RX-8 max power at 8500 RPM and max torque at 5500. It seems to me you are not even getting full torque, let alone full power out of your engine. What gives?
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  #36  
Old 11-12-2005, 08:37 AM
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Quote:
It seems to me you are not even getting full torque, let alone full power out of your engine.
Yes. I have the same feeling. It's as though there's an rpm limiter on it. There's enough power to fly, for sure, but not as much as I ought to be getting. I'm beginning to wonder if the intake is too restrictive, and it's not getting enough air until the outside airflow boosts the intake pressure. At some point I plan to fly it up to Tracy and/or Bruce and get their take on it.
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  #37  
Old 11-12-2005, 09:21 AM
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Fuel and/or air starvation problems could be due to Ivan, Katrina and Co. Also stripping your old paint coat off, spraying several coats on, then the decorative striping. Airborn debris, high humidity, who knows what your filters may have picked up. I'd think it's worth taking a look.
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Last edited by Kumaros : 11-12-2005 at 10:59 AM.
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  #38  
Old 11-12-2005, 11:50 AM
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Quote:
Originally Posted by JonC
Ok, let us discuss constant-speed theory here.... Full fine pitch will NOT get you amazing acceleration. The prop is more efficient at the higher RPMs to get you rolling, but it quickly falls out of efficency as you start rolling faster.

Why does a constant speed accelerate so much better than fixed then? Because it varies its pitch as it accelerates. You are not controlling pitch on a constant speed prop, you are controlling RPM. As you accelerate with a constant speed, if it held its pitch it would want to overspeed, so it starts adding more pitch as you roll faster and faster to keep the RPMs the same. THAT is what gets you the amazing acceleration gains.

Now, how does this translate to an IVO without a constant speed box? You need to keep adding pitch on roll or you need to find a nice inbetween setting to take off with.

Edit: I forgot to add, the latter method is safer than the former, because if your prop happens to not change pitch as you accelerate by the time you find out you might be at the point where you will not be able to stop nor able to rotate.... running off a runway is not fun.

*preaching mode off*

We don't find a need to change pitch during the takeoff roll. What is quite surprising is that we get about the same rpm in a static runup at WOT and 38 inches as we get in climb at 85 knots and 35 inches. I don't need to adjust pitch for flying circuits. The acceleration from 20 knots and up is pretty impressive as a new passenger/ pilot I took up yesterday who owns a similar aircraft attested to. If I lower the nose to see better say to 95-100 knots, I need to coarsen the pitch a bit to stay at 4600 rpm and as altitude increases, I need to coarsen slightly evry couple thousand feet as well to keep the rpm constant.

I would not want to fiddle with pitch on the T/O roll. Kinda busy keeping it straight. We were off the ground in 450-500 feet gently pushing the throttle forward. 4000 feet MSL, +5C, 3/4 fuel and 2 people in the RV. My passenger remarked on how impressive the climb rate and angle was.

I'm not sure what type of intake John is using but I'd be concerned if it's one of the long runner/ small tube designs seen on many atmo Wankels. I believe the frictional losses of the small runners on a turbo engine with higher mass flow would be highly restrictive and possible choking off the engine at high rpm and manifold pressures. We have seen this many times before in the course of building intakes for various engines.

The basic data so far would seem to indicate that John is down on power for some reason.
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  #39  
Old 11-12-2005, 04:07 PM
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when i was at Atkins rotary,he sells a intake that is about 2" long and he has the Dino to show how well it works.
John, why dont you give a call and see what he says about your current configuration? maybe he can get you 50 hp weal fast? or not
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  #40  
Old 11-14-2005, 11:48 PM
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Quote:
The basic data so far would seem to indicate that John is down on power for some reason.
I just had a Eureka moment in the shower. It needs more fuel! The tables of injector pulse width against manifold pressure in both EC2 computers are programmed for the big blade fixed pitch prop. With the IVO I can draw more power at any specific MAP. More power = more fuel. I need to reprogram the EC2. Duh! (Smacking forehead).

Quote:
[Atkins] sells a intake that is about 2" long
Thanks, but that won't work. I have a turbo there. Also, from what I've heard and read I dont think short manifolds are the best solution, even for an na engine. The guys on flyrotary have talked about this stuff a lot. Atkins intake system is based on 2 injectors. That seems like a very bad idea to me. You loose all the redundancy. I like redundancy.
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  #41  
Old 11-15-2005, 08:08 AM
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Quote:
Originally Posted by John Slade
I just had a Eureka moment in the shower.
snipped ...
The Greeks to the rescue again
I hope you didn't run out naked, proclaiming EUREKA, EUREKA! as the original Archimedes
From your site, I see you are a member of a nudist club. I used to be a nudist too; our beaches, especially beautiful secluded beaches in the islands, are ideal for it.
Hurry up and get the 4 hours behind you, then do fly commercial, 99 dollars is indeed but a pittance.
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  #42  
Old 11-15-2005, 10:49 AM
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Quote:
Originally Posted by John Slade
I just had a Eureka moment in the shower. .
John,

you gotta stop taking the Vacuum cleaner into the shower in an attempt to suck ieas out of your brain.

What you come up with may be schocking
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  #43  
Old 11-29-2005, 11:11 PM
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Quote:
Originally Posted by crx
What's the cost delta between an IVO variable pitch prop, and a constant speed unit?
A $300 box of electronics with four lights and a knob..
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  #44  
Old 11-29-2005, 11:14 PM
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Quote:
What's the cost delta between an IVO variable pitch prop, and a constant speed unit?
"Cost delta" = "price difference" - right?

You can add a constant speed unit to the IVO for about $300. Its fairly new and the reports I've heard havent been that good, but I'm sure they'll get it right eventually. If, byconstant speed, you mean an MT or similar, then I think you're talking about $10k. That's $10k difference
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  #45  
Old 01-16-2006, 11:20 PM
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This thread got left hanging, and a lot of people are asking (even ordering), so maybe a brief update on the IVO is called for.

After sorting out a high rpm fuel flow problem I'm now getting 4950 static (just under 2300 prop rpm) on the IVO on full fine pitch. There may be a bit more to be had with a bit of mixture tweaking. When setting up the IVO you install washers to set the course and fine pitch limits. I installed 2 washers at each end, so that and boost setting currently define my static rpm. Interestingly, my hangar mate with a Franklin 6 on his Velocity claims 2500 static on the exact same model prop. Maybe he has less washers on his fine limit setting

Take-off acceleration is excellent. I haven't been able to measure it but observers and my own feel tell me that I'm airborne at least 500 feet earlier than I was with the fixed pitch prop. One observer said I was airborne in less than 1000'. Gross weight on that flight was about 1800 lbs. (75 F day) After take-off I coursen the pitch a little and climb is much improved over what I've been used to. Measurements will come as soon as I get chance to write them down. Some of the improvement is certainly due to correcting the fuel flow issue. I now have my 3 blade Performance prop back from tweaking and finishing, so at some point (once I get it back from Buly) I'll be able to swap them and get some really definitive data.

According to the notes on the IVO blades, they were balanced at the fatory to with 0.1 grammes. It certainly feels as though this is true. The prop is very smooth and quiet. Noticably smoother than the Performance Prop it replaced. I did just barely "touch" the tips on one landing. I repaired the slight damage with flox and added a 1/8 curve at the end of each blade while I was at it - the blades come cut off square and the curve (now painted gold) looks better.

I measured the IVO pitch change at 14 seconds end to end. So far I've used maybe 9 or 10 seconds of that with very good results. Typically I'm keeping the rpm below 5500 and the boost below about 36 to baby my temporary stock turbo. At these numbers I saw around 170 kts GS at 3000'. High power climb and high speed high altitude cruise numbers will have to wait until my turbo upgrade gets done.

After about 3 hours on the prop I found that the bolts no longer needed retorquing afer each flight. They didn't move for four flights in a row (checked with two calibrated torque wrenches), so I fitted the spinner. Removing and replacing the spinner only takes a few minutes with the small alignment holes I've drilled, so I plan to recheck the torque regularly.

So far, my vote on the 68" IVO magnum 45-105 3 blade prop is

I'll add more data to this thread when I have it.
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