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  #41  
Old 07-31-2018, 06:21 AM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
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Default Another Update

"Just got back from an airshow here in QLD. Seem to be getting a handle on this aircraft at last. Cruising at 8500ft amsl, temp 42deg F, 4200rpm for a prop speed of 2320, 2 POB, luggage, full fuel etc, etc, we averaged 166knots. I am beginning to think I will stay with the IVO prop and just upgrade the blades and the turbo. Cooling is perfect…the logging for coolant temp varied 4-5 deg C for all conditions.

In constant climb to 8500amsl at 5 lbs boost,5000rpm, 90 knots, 2000fpm, 2 POB, 80 litres fuel and luggage, sees coolant temp at 84 deg C constant."
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 424.4 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #42  
Old 07-31-2018, 06:56 AM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
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Fuel burn numbers in that cruise config?
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  #43  
Old 08-11-2018, 12:07 AM
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charosenz charosenz is offline
 
Join Date: Aug 2009
Location: Longview, Wash
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Quote:
Originally Posted by rv6ejguy View Post
"Just got back from an airshow here in QLD. Seem to be getting a handle on this aircraft at last. Cruising at 8500ft amsl, temp 42deg F, 4200rpm for a prop speed of 2320, 2 POB, luggage, full fuel etc, etc, we averaged 166knots. I am beginning to think I will stay with the IVO prop and just upgrade the blades and the turbo. Cooling is perfect…the logging for coolant temp varied 4-5 deg C for all conditions.

In constant climb to 8500amsl at 5 lbs boost,5000rpm, 90 knots, 2000fpm, 2 POB, 80 litres fuel and luggage, sees coolant temp at 84 deg C constant."
Ross,

Thanks for posting the numbers, very valuable information.

Charlie
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  #44  
Old 08-13-2018, 01:29 PM
Canadian_JOY Canadian_JOY is offline
 
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Location: Ontario, Canada
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Let's face it... who wouldn't want two cool under-wing rads as neatly packaged as these ones? Can you say "shades of Spitfire"?

Pretty impressive performance numbers.
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  #45  
Old 08-24-2018, 05:28 AM
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Lufthans Lufthans is offline
 
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Location: Hilversum, The Netherlands
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Awesome!

Next to our RV4, I am flying (500+ hours by now) a normally aspirated EJ25 with MT constant speed prop and under-wing radiators on my Jodel. I too have gone through loads of trials and tribulations to get this to run properly. I too now have perfect cooling, excellent performance (for a Jodel) and complete reliability.

My next project (once the current car project is done) will be an F1 Rocket (hopefully with the Evo 2 wings, which seem to be in the making), which I would like to outfit with an EJ257 with Turbo and under-wing radiators. So pretty much like this -8.

I'd be very curious to know the dimensions of the wing radiators! Ross, do you have these?

And I concur on the comments on Ivo, MT and redrive ratios.

I have run mine with 2.12:1, 2.2:1 and now 2.29:1. The higher the reduction ratio, the better the performance. In fact, I feel that the 2.29:1 is still too low for my Jodel. I get better top speeds from 4300 engine rpm than I get from 5000+ engine rpm, despite the fact that the engine then is producing significantly less power there. So all the extra power that I am producing at higher rpms is actually lost in the faster spinning of the prop, and then some. (That's 1875 vs 2185 prop rpm, with the 1875 being faster).

The fact that we are typically using around 2700 rpm for our props comes from necessity of our direct drive engines. It is a compromise between engine power and prop efficiency. Now if one has a redrive, one can choose prop rpm. Those who select a reduction ratio based on 2700 rpm just haven't gotten the point, if you ask me.

As for props - I have seen EJ engines with Warp drive props underperform significantly, losing most of their power in drag, rather than thrust. I have had 74" two-blade Whirlwind constant speed props (with NSI hub) on my first two engine/redrive combos, and now have a 74" three-blade scimitar MT on it. With the MT (and higher reduction drive ratio), for the same speed, I need about 3 fewer inches of MAP. Go figure the effects of a prop.

And thus my ideal setup would be the Rocket, with the same 2.29 redrive that I have now, EJ257 Turbo, under-wing radiators and a properly matched MT prop.

This is going to be fun!

Ross, if you have some contact details in Oz for me, that'd be awesome.

Thanks!

Hans
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Hans Teijgeler
Hilversum, The Netherlands

PH-SUM RV-4; Imported and upgraded.
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-EIL RV4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.
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  #46  
Old 08-24-2018, 05:57 AM
rv7charlie rv7charlie is offline
 
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In the quote from post #32, he said to email him if we had questions, but I didn't see an address.

One reason to shoot for 2700 at the prop is that if you're using a fixed pitch wood prop (all some of us can afford), it's much simpler to get a properly carved prop. You'd probably be surprised at the name of one *very* well known and respected carver that made about a 200 hp mistake, carving one for a rotary & around 2200 rpm. The blades looked like canoe paddles, and he couldn't get above about 4000 rpm static. Builder had never seen a proper prop for his engine, so couldn't do a 'sanity check' looking at his new prop. He spent months building new intake manifolds, etc, thinking he'd made a build error. We had a rotary gathering at his airport; several experienced guys took one look at his prop and said, 'there's your problem. Swapped a prop from a flying rotary a/c, and instantly got proper static rpm.

Another, in many cases, is simple prop clearance (dia limit) vs HP. If all you can afford is a f/p 2 blade prop, it's tough fitting more than ~74" dia on a 2 seat RV and really tough efficiently absorbing a lot of HP with 74" and rpm down in the low 2000s.

Charlie
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  #47  
Old 08-24-2018, 06:57 AM
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Lufthans Lufthans is offline
 
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Yes, very valid points.

It seems that many people don't understand that besides diameter and pitch, the washout in a prop is of utmost importance. Also with a constant speed prop. ANY prop maker should take the engine and aircraft characteristics into account when specifying a prop for your application. If they are unable to produce a proper prop based on that, then it seems their engineering is more eyeball and less science than would be ideal.

Some background:

A prop is not there to absorb horsepower, it is there to create thrust. Rotating it will create drag for which you need power to overcome it, and you would like the maximum amount of thrust for the minimum amount of drag.

So we aim to achieve that:

A prop is a rotating wing. This is common knowledge. An aircraft has forward motion, and that forward motion is the same for each point on the prop. The prop rotates, giving it a sideward motion. This is different for different point on the prop. The further form the hub, the more sideward motion.

Now vector these. Forward motion versus sideward motion. The resulting vector is where the apparent wind is coming from. Now angle your airfoil (prop blade) for its optimum angle of attack (around 4 degrees for most airfoils).

You'll see that the further from the hub, the flatter your blade must be (since the rotating motion is getting more and more dominant with respect to the forward motion). Closer to the hub, you'll need the blades more into the airstream.

Now this washout is specific to a combination of aircraft speed and prop rotational speed. Faster aircraft need more washout than slower ones.

And thus simply bolting on a constant speed prop and thinking that it will self-adapt to your aircraft simply because its blades rotate will - unless you are lucky - only get you optimum airflow over your blades at one particular point along the span of the blades. And so most of your prop airfoil is operating at other than its optimum angle of attack, resulting in reduced thrust and increased drag.

How do you notice? You need more hp to achieve the same speed, whereas the aircraft with the optimized prop will be faster on the same hp.

I've discussed with MT when ordering my prop. They wanted my engine speed, reduction ratio, engine power and torque curves, my cruise speed, my climb speed, etc. Based on that, they advised a blade. In my case the MTV-12 188/53 (top of my head), where the 53 specifies the washout. A fair amount of data required, for what turn out to be VERY good results.

And indeed, slow rpms tend to need more prop area. Three blades are the way to go there, and as long as you can make them. Look at how a Robinson helicopter has enough thrust to go up vertically on an O-320 and we do not. The only difference - their "prop" is big and turns slowly. Hmmmm...

Hans
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Hans Teijgeler
Hilversum, The Netherlands

PH-SUM RV-4; Imported and upgraded.
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-EIL RV4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.

Last edited by Lufthans : 08-24-2018 at 07:04 AM.
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  #48  
Old 08-24-2018, 07:28 AM
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rv6ejguy rv6ejguy is offline
 
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Location: Calgary, Canada
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Hans, I'll PM Geoff's email to you.

Turbo auto engines really need a VP or CS prop if you want to reap the benefits of the turbocharger. FP props are a massive compromise here.

When MT built my RV10 prop for my twin turbo EG33, they asked all the same questions and said most efficient range would be 2300-2550 rpm.

We had MT CS props on both the other turbo EJ257 RV7s and these worked really well- over 200 KTAS was easy stuff at low MAP and medium altitudes.

I agree with the comments on the prop rpm. No need to think in the same terms as direct drive engines when you are geared. I turn mine at around 2050 max and keep the engine rpm down to about 4500 max. This gets me close to torque peak and highest VE while reducing frictional losses.

Looking forward to seeing your project progress Hans. Cool stuff! They have some great parts available for the 257 these days.
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 424.4 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #49  
Old 08-24-2018, 09:44 AM
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Lufthans Lufthans is offline
 
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Thanks Ross.

I'll contact Geoff shortly.

Unfortunately, it will be some time (could easily be 2 years or so) before I will be ready to start this project. First, I will have to finish this one: https://www.instagram.com/minottocars/ and hopefully sell a few of them.

There's no rush. I'm collecting information so that I can build my ultimate dream aircraft when the time comes.

How's your RV10 project doing by the way? It seems to have disappeared from your web site?

Cheers,

Hans



Quote:
Originally Posted by rv6ejguy View Post
Hans, I'll PM Geoff's email to you.

Turbo auto engines really need a VP or CS prop if you want to reap the benefits of the turbocharger. FP props are a massive compromise here.

When MT built my RV10 prop for my twin turbo EG33, they asked all the same questions and said most efficient range would be 2300-2550 rpm.

We had MT CS props on both the other turbo EJ257 RV7s and these worked really well- over 200 KTAS was easy stuff at low MAP and medium altitudes.

I agree with the comments on the prop rpm. No need to think in the same terms as direct drive engines when you are geared. I turn mine at around 2050 max and keep the engine rpm down to about 4500 max. This gets me close to torque peak and highest VE while reducing frictional losses.

Looking forward to seeing your project progress Hans. Cool stuff! They have some great parts available for the 257 these days.
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Hans Teijgeler
Hilversum, The Netherlands

PH-SUM RV-4; Imported and upgraded.
PH-BRR Bowers Fly Baby; Imported and upgraded
PH-MGA Jodel DR1050; Built, with Subaru EJ25
PH-EIL RV4; Imported and upgraded for friend. Sadly crashed
PH-ERD Robin DR300; Built with Subaru EZ30 for friend.
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  #50  
Old 08-24-2018, 10:18 AM
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rv6ejguy rv6ejguy is offline
 
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Location: Calgary, Canada
Posts: 4,750
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I sold the RV10 a couple of years ago now. Life situation changed.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 424.4 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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