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Made a prop-duplicator machine (pic) but I still have to work out the details of making the blank prop and finding a likely prop to copy.  My present Lightspeed prop is just not pitched enough.   The engine will easily overspeed in cruise but it sure leaps off the ground.

 

Funny thing about props: they all look different!  Duh!  I have a 3-blade Performance Prop on the Cozy.  It has long narrow blades.  Compared to say, a Catto, it doesn't look like it has enough blade area do the job but it performs pretty well.  Initially, this used prop was a disappointment--that's why the seller sold it, I suppose.  In fact, it had written on it "[buyer's name], replacement #2."

 

It was not giving me enough RPM either.  I shortened the blades on it inadventently after a tip-back incident.  That did not make any appreciable change.  Then II got the idea from Paul Lippse to thin the prop tips, and glassed it.  That turned it into a pretty good prop. I got about 125-150 RPM increase and it will turn about 2750 in peak-power cruise.

 

Lippse (now deceased) has some very interesting posts on the RV site.  

http://www.vansairforce.com/community/search.php?searchid=23650218

 

He invented the Elippse Prop and was, as I understand it, the guy who did the electronics design for the Lightspeed ignitions.

http://www.rexresearch.com/lippsprop/lipps.htm

 

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Great looking work Kent!  Quite impressive. 

 

What material did you use for the tabletop work surface?

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Way cool, Kent!

 

Did you buy plans for the prop duplicator or buy a kit?

 

I need to do this asap.

 

I found another site that attached a belt sander to finish the surface better.

At least on the video it looked good. I remember being told to first try the

patterns on good cheap wood. Then make a real prop. I am having a hard time

with the way they put the 3 bladed props together. 3 separate blades glued

together and cover in composites. What do I know. In my mind 3 blades should

be laminated over hub joint with 6 -9 layers. That way each blade has a bond

into the hub not just the 2 bolt hole 1/3 section.

 

Having a 2 blade ready to drop-ship was a good idea I read. Sounds like a great

idea in case one needed it and had the time.

 

Updates request.

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Nice work on the duplicator!  I have seen a few MDF garage built duplicators on the internet that did not look like they would be very accurate or likely to hold up to more than one or two uses.  Look forward to seeing it in use

 

The Elippse Prop link was a good read also.  Is anyone using his ideas since he has passed?

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The Elippse Prop link was a good read also.  Is anyone using his ideas since he has passed?

 

I get the impression that Lipps came to the same conclusions as Jack Norris, i.e., thin low-drag tips.  Don't buy his book to learn how to build props though.  It is just a discussion of the principles of propellers.

http://www.propellersexplained.com

 

A couple of prop builders are using Norris's ideas.  Whirlwind props is building a lot of props for the RV crowd.

http://whirlwindpropellers.com/aircraft/

 

Jan Carlson designs props using the same principles.  I think Whirlwind uses Carlson's prop program

http://www.jcpropellerdesign.com

 

I have never read exactly why Gary Hertzler's props are said to be so good but from the look of them, he also builds them close to what Norris suggests.  

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I get the impression that Lipps came to the same conclusions as Jack Norris...

I have never read exactly why Gary Hertzler's props are said to be so good but from the look of them, he also builds them close to what Norris suggests.  

Lipps and Norris say very different things - Norris accepts classical propeller theory, based on Betz, Goldstein and Theodorsen's NON-elliptical loading calculations. Lipps throws out all of that and claims that an elliptical lift distibution is better on a propeller, against what everyone else thinks - hence his props look very different.

 

There is zero evidence (read the contact articles carefully, and talk to the builder of the propeller on the racing biplane with an Ellipse prop) that Paul's propellers perform any better than a GOOD standard design prop (think Hertzler or Catto, based on classical propeller theory). And in fact, they're more point designs, so do not do as well across a wide range of operating conditions as standard props do.

 

With respect to Norris, his theories are standard, but reading his book gave me an epileptic seizure... He's nigh on incomprehensible, IMO. Jan Carlson uses classical propeller theory, judging by the shape of his props - NOT Lipps' ideas. Lipps was the only guy using Lipps' theories.

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With respect to Norris, his theories are standard, but reading his book gave me an epileptic seizure... He's nigh on incomprehensible, IMO.

 

What!?  You couldn't wrap your mind around the sheer explicit horse sense of Norris.   :)   Yeah, that book needed to be a pamphlet.

 

Yep, I do not really understand props.   My question is: Take my little tip mod.  If the RPM goes up and the HP developed goes up, does that make the prop more efficient or does going faster on the same RPM/HP make it more efficient?  The "horse sense" of it tells me that if the tips are made to produce less drag, a prop is more efficient but maybe my prop is the same efficiency but only turning faster.

 

From Wikipedia "The best helix angle is when the blade is acting as a wing producing much more lift than drag."

 

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http://en.wikipedia.org/wiki/Propeller_(aeronautics)

 

If I interpret the formula correctly.  If axial speed goes up and rotational speed goes up, they cancel out and there's no increase in efficiency.  Correct?

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If the RPM goes up and the HP developed goes up, does that make the prop more efficient or does going faster on the same RPM/HP make it more efficient?

Prop efficiency is the measure of how much of the engine power produced goes into propulsive power. If your engine is producing 100 HP, and 80 HP goes into moving the aircraft forward, then the prop is 80% efficient. If the RPM increases, the power increases, and you go faster, you may have made the prop MORE efficient or LESS efficient, depending. Let's say that you now produce 105 HP at the engine, and 83 HP go into moving the plane forward, with 22 HP going into fighting drag on the prop, rather than the previous 20 HP. You're going faster, yes, but the efficiency of the prop has dropped to 79% (83/105) from 80% (80/100). Conversely, if you were using 85 HP out of the 105 HP to move forward, then the efficiency would have changed to 81% from 80%. So the answer is, it depends.

 

The "horse sense" of it tells me that if the tips are made to produce less drag, a prop is more efficient but maybe my prop is the same efficiency but only turning faster.

Allowing the engine to produce more power (and hence go faster) is not necessarily the same thing as being more efficient.

 

From Wikipedia "The best helix angle is when the blade is acting as a wing producing much more lift than drag."[/size]

That's a meaningless statement. The lifting surface is ALWAYS producing more lift than drag, else the L/D ratio would be less than one and no-one would use such a crappy wing. "Much" just means that a higher L/D ratio is better.

 

If axial speed goes up and rotational speed goes up, they cancel out and there's no increase in efficiency.  Correct?

Only if they increase in the same proportion, while thrust and torque stay constant. That's almost never the case, however - all four components change at the same time, so you have to know by how much each is changing to know whether efficiency is better or worse.

 

Spin the same prop faster and thrust and torque both increase, as does axial speed (and obviously rotational speed). But unless you know by how much, you don't know the efficiency change.

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Thanks, Marc.  That is what I surmised.  So I conclude I am turning my prop faster, making more HP, and likely going somewhat faster but possibly at a higher or lower efficiency.  Wish I had done some careful speed tests.   I have an old post by Paul Lipps along that line:

 

 I modified the tips of my friend's prop on his Lancair to reduce tip drag. The speed increased from 215 mph at 2600 rpm to 219 mph at 2650 rpm. To increase speed that much required (219/215)^3, 5.7% more power.  But 2650 rpm/2600 rpm is only 1.9% more rpm, so only 1.9% more power.  And the speed increase was 1.9%. So, 1.9% more speed, 1.9% more rpm! The speed increase was due to the prop's increased efficiency due to much less tip drag!

 

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Wow, this site had been dead but there is not much traffic anywhere these days.

 

I was talking to a guy about improving airflow into a Cozy NACA.  A few years ago, I put a pitot tube in my NACA opening hooked to an airspeed indicator.  The ASI would fluctuate rapidly between zero and near-freestream velocity.  I think the flow was turbulent enough that far back on the fuselage that a lot of it would just skip over the scoop.  Klaus Savier told me once that adding gear doors to his Vari did not improve his speed but it helped his cooling quite a bit.  I imagine his NG doors smoothed out the flow back to the NACA.

 

Following others, I experimented with large VGs ahead of the scoop which smoothed out most of the ASI fluctuation and helped the CHTs.  (pics).   BTW, don't use an ASI, the fluctuations finally killed it.  :-(

 

The fellow I was talking to has a 220 hp engine.  I suspect the real answer to his cooling problem is a larger scoop.   If we consider that the plans Cozy IV NACA is sized about right for 180 hp which seems to work for most guys, then a 220 hp motor needs about 22% more cooling air!  Compare the prefab NACA that Lightspeed Engineering sells.  It's huge.   http://www.lightspeedengineering.com/Services/NACAduct.htm

 

The question came up about which way to angle the VGs.  I angled them as shown reasoning that they'd create a counter-rotating swirl into the NACA but you can see that the flow along the surface initially takes a vector away from the NACA sides, so maybe the opposite angle is worth a test.  I eventually went to four smaller VGs along the sides of the NACA.  Can't say they were better than the large ones but they help.

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Yep, I agree. There is not much going on for sure. There are some posts on Facebook and a guy just posted up a Vari Viggen he has and it really looks sharp!. I have always like that design.

   Keep us posted on the naca. I am probably going to go with a P 51 for mine. Been building info on it for a while.

 ~~~tg~~~ 

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Wow, this site had been dead but there is not much traffic anywhere these days.

 

Yep, I agree. There is not much going on for sure. There are some posts on Facebook and a guy just posted up a Vari Viggen he has and it really looks sharp!. I have always like that design.

 

Keep in mind that it's also summer, with more opportunities to do things in the shop, at the hangar, and outside in general.

 

Awaiting Kent's next post...

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   Mornin!  Yep, lots more ways to get into trouble!     LOL    I think I am finally going to get to move. I got an offer on the house this weekend and signed the paperwork.

    So, tentatively I have to be out by the 13th of next month and that means I will be moving to N.C. and start looking for a shop and a place to live. Can't wait to start playing with my toys again and a nice shop with some room in it to work!

~~~tg~~~ 

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   I will be moving to N.C. and start looking for a shop and a place to live.

 

Good luck with your move.   Consider living somewhere convenient to the Rowan County Airport (KRUQ).  It's a good airport for canards and for homebuilders in general.  Concord Regional (KJQF) will not allow you to do ANY work in a hangar and does not welcome homebuilders.  Lake Norman and Gold Hill airports are residential airports.  There is lots of homebuilder activity at Lake Norman and it is long enough for canards but the houses are pricey.

 

Funny thing: I moved to Concord because the city was grading ground for Concord Regional.  It turned out to be a hell-hole for a homebuilder; you wouldn't believe the stupid rules.  They finally booted me off the airport for complaining--I was a "financial burden".   The City of Concord spent $130,000 on attorneys fee to do it though.  I'm rusty now but I was quite the expert on FAA Grant Assurances and airport law: three FAR Part 16 complaints and appeals, two petitions for review in the 4th and D.C. circuits, twice in the N.C. Court of Appeals, convicted of trespassing on the airport and beat that charge on appeal.  I even filed a Petition for Certiorari in the U.S. Supreme Court.  "Cert. den.", of course.

https://www.courtlistener.com/opinion/118554/ashton-v-federal-aviation-administration-et-al/

 

Good times!   :P

-------

I made a profile gauge for my prop-making project.  It turns out that the plastic "6" gauges are really 5.5" usable--too small--and a 12" gauge is too big.  I bought some oak strips from Lowes and steamed them, dried them over a 1/4" bolt to give a slight bend that would hold the profile strips, some square hobby sticks I found at Walmart.  It seems like it will work to take-off a prop profile.  I will smooth the curves with a draftman's curve-drawing aid.  I can trig-out the chord angle from measurements off a flat surface.

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Edited by Kent Ashton

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My electric screwdriver pitch trim motor runs too fast to precisely adjust the trim.  (pics)  I tried a big honking 10ohm resister to slow it down, which works, but it's not the elegant solution, I guess.  Will wire in a cheap adjustable pulse width modulator from ebay and just wanted to point them out.

 

The 3A version is $2.00 plus change + free shipping from Hong Kong.  What a deal!  I have also used them to control LED lighting in the cockpit.  Search for DC PWM.  It is sometimes handy to buy them with the pigtail and extend the wires to the panel with the device mounted elsewhere.

 

As an electronics retard, I wondered how many amps my 3.6V DC screwdriver motor would draw and found this good video showing how to determine just that.  Mine appears to draw about .6A when loaded up.   Fun stuff.

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"Good luck with your move.   Consider living somewhere convenient to the Rowan County Airport (KRUQ).  It's a good airport for canards and for homebuilders in general.  Concord Regional (KJQF) will not allow you to do ANY work in a hangar and does not welcome homebuilders.  Lake Norman and Gold Hill airports are residential airports.  There is lots of homebuilder activity at Lake Norman and it is long enough for canards but the houses are pricey."

 

      Thanks for the info and heads up. Funny that my project is sitting in China Grove, about 30 mins from there. I hope to find a place in Kannapolis or close by as thats where I used to live. 

   I had been looking there in Landis but I have a friend that has a shop there and the city of Landis re sells the electric and he told me that if he does nothing all month long, his electric bill will be a minimum of $400.00!!!!

     So, when I get there, I will have to hit the ground running so to speak till I can find a good place big enough to have some room to work and a place to park a motorhome also later on.

    I'll keep posting as I go along!

~~~tg~~~. 

 

 

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After waiting more than a year for the "driver's license medical" rule to pass, I finally gave up and renewed my special issuance.  Paperwork received by the FAA on October 10th; it was not scanned into the FAA's records until October 23rd; finally got the ticket on December 22nd.  It is only valid through October next year so two months of use are already gone.  Thank you, Mr. Huerta.

 

The Cozy has been sitting on a dehydrator for the past year.  Gave it a wash and a condition inspection.  Flew it for a hour.  I was pleased with the new pitch trim (see post #73) which was easy to adjust.  It turns out that my airfield changed Unicom freqs several months ago.  After a half hour, another pilot was kind enough to tell me I was making position reports on the wrong freq.  Duh! 

 

Anxious to try the Long-ez since I completed the winglet surgery documented above and also see if my cowl mod (pic) will improve the cooling.  I am hoping for a very short, direct path for the downdraft air out of the cowl.  I don't think I had adequate square inches of exhaust area before.  We'll see.

 

Here (pic) is what happens when you use Matco plastic brake reservoirs with DOT-3/4 brake fluid.  I replaced them with some Ford Ranger reservoirs.

 

And finally, an idea for a device to copy a prop profile made from some small stir-sticks from Walmart hobby section.   I looked to buy one but the smaller ones are too short.

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Anxious to try the Long-ez since I completed the winglet surgery documented above and also see if my cowl mod (pic) will improve the cooling. 

 

And finally, an idea for a device to copy a prop profile made from some small stir-sticks from Walmart hobby section.   I looked to buy one but the smaller ones are too short.

Hello Kent,

How do you like your LSE prop on the Long-EZ?  What is the diameter and pitch?  Do you have any performance numbers for that prop that you can share?

 

I have 68" dia. x 80.71" pitch LSE prop for my Cozy MKIV, which will be powered by an O-360 with FI and E.I.  I am curious what kind of static rpm my LSE prop will allow.  I got a great deal on it, so it will be worth a try.

 

Glad you are in the air again,

Andrew

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Hello Kent,

How do you like your LSE prop on the Long-EZ?  What is the diameter and pitch?  Do you have any performance numbers for that prop that you can share?

 

I have 68" dia. x 80.71" pitch LSE prop for my Cozy MKIV, which will be powered by an O-360 with FI and E.I.  I am curious what kind of static rpm my LSE prop will allow.  I got a great deal on it, so it will be worth a try.

 

Glad you are in the air again,

Andrew

 

 

Hi Andrew, this Lightspeed prop was a used prop with no markings that I took a chance on but it is clearly not enough prop for 160 hp.  Diameter is 64.5".  Must have been from an O-235 airplane or something.  The LEZ will leap off the ground but it overspeeds at about 150 KIAS.  No complaints with the prop except it is just not enough diameter and pitch.

 

On the Cozy (180 hp) I am using a 3 blade Performance Prop 61.24 x 76" pitch with modified tips that works pretty well.  That prop only gave me about 2450 RPM until I trimmed down the tips.    Writeup here:  http://forum.canardaviation.com/showthread.php?t=5170

 

Here are some notes I have collected:

- Hertzler is recommending something like a 66x78 2-blade for 180 hp

- Tim Andres reported using Hertzler 66x78 with IO-360

- Del Shier reported using 66 x 75 Hertzler with IO-360 but said it overspeeds

- Someone using 63 x 74 (mfg?) with 180 hp says it overspeeds

- Chuck Wolcott Catto 3-blade 64 x 81 (hp?) underspeeds @ 2450, Catto 64 x 80 3 blade slightly underspeeds at 2600.  He suggests 64x79 Catto

 

I don't think you can't tell much from static RPM.  I shoot for 2700 RPM at my average cruise altitude (say 14000' MSL) leaned to peak power.  However, in practice, I am usually much leaner than that so the RPM is lower.  Not sure how others do it.

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Here are some notes I have collected:

- Hertzler is recommending something like a 66x78 2-blade for 180 hp

- Tim Andres reported using Hertzler 66x78 with IO-360

- Del Shier reported using 66 x 75 Hertzler with IO-360 but said it overspeeds

- Someone using 63 x 74 (mfg?) with 180 hp says it overspeeds

- Chuck Wolcott Catto 3-blade 64 x 81 (hp?) underspeeds @ 2450, Catto 64 x 80 3 blade slightly underspeeds at 2600.  He suggests 64x79 Catto

 

I don't think you can't tell much from static RPM.  I shoot for 2700 RPM at my average cruise altitude (say 14000' MSL) leaned to peak power.  However, in practice, I am usually much leaner than that so the RPM is lower.  Not sure how others do it.

Kent,

Thanks for the information.  Since we don't know how the pitch number of a Lightspeed prop compares to the pitch number of a Hertzler, Catto, or any other prop manufacturer, I'll just have to give it whirl when the time comes.  If the static is unacceptably low, I'll need to find a different prop.  Taxi testing should tell me quite a bit (still a long way off).

 

Its too bad that Savier didn't fill in the blank space on his LSE Prop sticker which would have told you what his pitch number is for that prop.  My stickers are blank too.... although the original owner had the numbers in his records.

 

Thanks Again,

Andrew

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The Cozy has been sitting on a dehydrator for the past year.

Congratulations on your flight! What's the dehydrator you used? I suspect I may need one in anticipation of the longer than desired period from when I get my engine and when I am flying.

 

Nice curve gauge as well!

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What's the dehydrator you used?

It is a homemade one: Ammo can, fish tank pump, 500 gram silica gel packs from ebay.  I put the fish tank pump in a cloth bag to keep the silica gel out of the pump and bury it in the bottom of the ammo can.  Run it about 3 hours a day.  The dry air circulates between the oil filler tube and the crankcase vent tube,  I put stoppers on the exhaust pipes.  I don't think the dehydrator does much in the cylinders but it probably keeps the camshaft and lifters dry.

 

After having rust problems before, I also blow the moisture out of the engine for a minute or two after landing and before hooking up the dehydrator.  I use a little air mattress pump for that.  I can't really say how effective all that is but a new cam is $3-4K and I have had to replace one in less than 500 hours.

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I was just telling a friend about the BD-5 Truck-a-plane.  The  BD-5 was so tricky to land and takeoff that Bede invented this truck-mounted airplane with limited up/down/left/right movement to let people experience takeoff and landing

 

I fell under the BD-5 spell in 1970 when I was a Lieutenant  "$1800 for a complete BD-5 kit, engine included!"  This one (pic) has languished for many years but I recently pulled it out of the hangar and replaced the nose cone, which was mounted crooked.  Need to track down that truck-a-plane.  :-)

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Went out intending to test my winglet and cooling mods but the starter was weak and would not get over the compression stroke.  It is either a weak battery or high resistance somewhere; this A/C has always hesitated on the compression stroke.  I used copper-clad aluminum battery cables for the run to try to save weight.  Thinking to get a good bond with the end connectors, I tried to solder the connectors to the cable--something that works well with copper cables--but I could not get a good solder joint there.  The aluminum cable is thick and the aluminum seems to wick off heat too fast to get solder fully into the joint.  A lot of heat melts the cable cover.  Overall it made a nasty-looking joint.  Live and learn.

 

I ended up cutting some connectors off and adding a piece of cable so I would not be surprised to find high resistance.  Skytec has a good chart for testing a weak starter system.  http://www.skytecair.com/images/PDF/Troubleshooting%20Diagram_5.0.pdf  I will first piggy-back a good car battery on the system and see how it cranks over.

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After putzing with ways to measure a prop profile, I came across this good idea that uses thin plywood and bondo: See "Using Templates" here http://www.mh-aerotools.de/airfoils/propgeo5.htm

 

Another thing I have puzzled over is where prop pitch is measured.  Most prop-builders, it seems, just use the flat side but that doesn't work on a rounded airfoil.  I have tried to measure actual chord pitch by bolting the prop to a milling table, measuring the LE and TE height and horizontal component and trigging-out the angle but the device below looks easy to make and should work better.  Found it here http://twistedcomposites.com/journey.html

 

Interestingly, he (Steve Hill) says "one inch of pitch change is only about three tenths of a degree!"  No wonder wood props are so easy to repitch.

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