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Scotsman

Joined: 27 Aug 2007
Posts: 89
Location: Johannesburg, South Africa

Posted: Sun Oct 17, 2010 9:35 pm Post subject: HDS Speed Problem (lack of)

Quick question to the list and especially for anyone with an HDS operating on 100 hp.



A friend of mine in South Africa is having difficulties getting anywhere near the advertised speeds for the HDS on the Zodiac website (135 mph cruise).  Has anyone else had similar difficulties and if not:



- What prop are you running

- What hp is your engine

- What pitch is it set at

- What is your empty weight

- What speed to you achieve at sea level with full throttle - straight and level



And to anyone else on the list if you have any recommendations for trouble shooting please send them through.  Any help would be appreciated.



James



PS. I will send though a picture of th aircraft shortly but the owner has recently changed prop to see if that will fix the problem and has the spats (wheel fairings) on the aircraft. 



PPS. He also says that the sink rate is very high when practicing engine failures...any comments?

_________________
Cell +27 83 675 0815

steve.freeman(at)syntaxds
Guest

Posted: Mon Oct 18, 2010 6:23 am Post subject: HDS Speed Problem (lack of)

Hi James,



You should try contacting Don Honabach who monitors this list.  He has done

extensive work in this area. 



Thank you,

 

Steve Freeman



--

jonathan(at)entry.co.za
Guest

Posted: Mon Oct 18, 2010 6:34 am Post subject: HDS Speed Problem (lack of)

JAMES: Quick question to the list and especially for anyone with an HDS 

operating

on 100 hp.



JONATHAN: I am afraid you will never get to 135mph, I have a 601XL, with 

100hp (Thinner wing than the HDS) and I have never been able to get to 

135mph in the cruise.



Jonathan

jlatimer1(at)cox.net
Guest

Posted: Mon Oct 18, 2010 7:08 am Post subject: HDS Speed Problem (lack of)

James,



This was a hot topic in the days prior to the XL.  Zenith was overly 

optimistic on the published speeds of the HDS.



I have an HDS that I just completed my 40 hour test period.  I have a 

Rotax 912 100 hp with a warp drive prop set for a static rpm of 5400. My 

WOT top speed in level flight at 3000 ft 95 degree F was 118 mph 

(calibrated).  My plane is completely stock.  I have no wheel pants or 

any other aerodynamic enhancements.



I've been a passenger in Don Honabach's HDS and believe it is much 

faster than mine.  He has a Jab 3300 with 125 hp, wheel pants, fuselage 

to center wing fairing, his wing joints are blended in really nicely. He 

has been very meticulous about trying to get every mph he can.  When I 

was a passenger, I saw 130 kts on the gps.  I've never seen anywhere 130 

kts on my gps in my plane.



You may want to search the archives, this was a really hot topic pre-xl 

era.



Jerry

HDS 912 ULS 42.6 hrs

just happy to be finally flying

On Sun, Oct 17, 2010 at 10:35 PM, Scotsman wrote:



 	  Quote: 	
		   



 Quick question to the list and especially for anyone with an HDS 

 operating on 100 hp.



 A friend of mine in South Africa is having difficulties getting 

 anywhere near the advertised speeds for the HDS on the Zodiac website 

 (135 mph cruise).  Has anyone else had similar difficulties and if 

 not:



 - What prop are you running

 - What hp is your engine

 - What pitch is it set at

 - What is your empty weight

 - What speed to you achieve at sea level with full throttle - straight 

 and level



 And to anyone else on the list if you have any recommendations for 

 trouble shooting please send them through.  Any help would be 

 appreciated.



 James



 PS. I will send though a picture of th aircraft shortly but the owner 

 has recently changed prop to see if that will fix the problem and has 

 the spats (wheel fairings) on the aircraft.

 PPS. He also says that the sink rate is very high when practicing 

 engine failures...any comments?



 --------

 Cell   +27 83 675 0815





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=316128#316128

psm(at)att.net
Guest

Posted: Mon Oct 18, 2010 7:47 am Post subject: HDS Speed Problem (lack of)

Hi Jerry,



I've been flying a Tecnam Echo Super with Rotax 912-ULS and Sensenich ground adjustable propeller.  I found the best cruise speed setting for the propeller gives me less than 5500 rpm at full throttle in cruise.  This is a lot lower rpm than your 5400 static.  



Perhaps you would get higher cruise speed if you adjust the propeller for more pitch.



Paul

Camas, WA

--

larry(at)macsmachine.com
Guest

Posted: Mon Oct 18, 2010 10:21 am Post subject: HDS Speed Problem (lack of)

Hi James,

I fly a 601HDS tri-gear with a Stratus Subaru EA81 (100 hp) and get 133 mph

max and a comfortable cruise of 115 to 120.  The Warp Drive 70-inch 3-blade

Prop is set to 17-1/2 degrees pitch with an 11-inch spinner.  It has my own

wheel fairings over 3.5 x 8.0 tires and gearboxes, fairings on the step

struts and 

The fuselage to stabilizer gaps are closed.  The plane weighs  750 lb.

empty, is capable of a 1300 lb. max takeoff weight. Never lands at more than

1200 lbs.



Normally, I fly at between 1100 to 1250 lbs. at 4200 to 4600 rpm and can

carry to 23 gallons fuel in the header and wing tanks. Also have a belly

mounted radiator 

with fairing and louvers.  The plane can be seen

http://www.macsmachine.com/images/completion/full/601ezfrontright.gif



Larry McFarland 601HDS at www.macsmachine.com



--

larry(at)macsmachine.com
Guest

Posted: Mon Oct 18, 2010 10:34 am Post subject: HDS Speed Problem (lack of)

James,

I forgot to mention forced landings in the HDS.  The effect of landing the

HDS without power is best practiced on a nice solitary airstrip. 

A real forced landing is akin to landing a well thrown manhole cover.  You

need lots of altitude and airspeed to be able to select your touchdown

spot.  I practice each time I'm out at least once, gliding from downwind at

85 mph thru the final at 70 to flare at 55 to get  within 10-20 feet beyond

the end of the 

runway. The HDS is a great little plane, joy to fly.   My journal, beginning

section 8 and again at 13  and 14 document recent flying experiences now, if

you're interested.



Larry McFarland 601DS 



--

don.honabach(at)pcperfect
Guest

Posted: Mon Oct 18, 2010 12:59 pm Post subject: HDS Speed Problem (lack of)

James,



One thing to consider is that all ZAC #s are given at sea level. As such, your ASI/IAS may show lower even though you are performing near published spec speeds. 



So for instance, let's say you are flying at 120MPH IAS at 6,000 feet. You need to convert this to your True Air Speed (i.e. TAS) to see what your IAS would effectively read at sea level and then compare that to the published ZAC #s.



In this case, here's how the math works:



  TAS Correction Factor = ~2% for each 1,000 feet or 12% when flying at 6,000 feet.



  TAS = IAS x TAS Correction Factor



  TAS = 120MPH * 1.12 = 134.4MPH



This is going off memory, so I apologize if this is 100%.



One of my pet peeves is that ZAC puts out #s at sea level which leads to unrealistic expectations. In contrast, Vans puts out performance #s at 7,500 feet. 



By the way, while I get close to published specs at high power settings, I'm still a little short even with a 120HP power plant. If someone has the secret recipe for getting faster speeds on the HDS - I'd love to know as well. With the extra HP, I can push up the throttle for faster speeds (and definitely really nice climbs), but the fuel burn rate gets out of control when doing so...



Don Honabach

Tempe, AZ 

601HDS - 150 Hours +

--

jlatimer1(at)cox.net
Guest

Posted: Mon Oct 18, 2010 1:27 pm Post subject: HDS Speed Problem (lack of)

One of the settings that I during phase I was a static rpm of 5200. 

This did not give me a significant increase in speed. My max inflight 

rpm with this setting was just less than 5400. It did seem to increase 

my oil temps.  My present setting seems to work for me.  Will probably 

try different settings in the future.  After all it is an experimental.



Jerry



On Mon, Oct 18, 2010 at 8:44 AM, Paul Mulwitz wrote:



[quote] 



 Hi Jerry,



 I've been flying a Tecnam Echo Super with Rotax 912-ULS and Sensenich 

 ground adjustable propeller.  I found the best cruise speed setting 

 for the propeller gives me less than 5500 rpm at full throttle in 

 cruise.  This is a lot lower rpm than your 5400 static.

 Perhaps you would get higher cruise speed if you adjust the propeller 

 for more pitch.



 Paul

 Camas, WA

 --

don.honabach(at)pcperfect
Guest

Posted: Mon Oct 18, 2010 1:56 pm Post subject: HDS Speed Problem (lack of)

 	  Quote: 	
		  > PPS. He also says that the sink rate is very high when practicing engine failures...any comments?


	


I believe this is fairly common on the HDS and I've read others indicate that glide rate during power off is high on this model. I'd be curious if those flying with HD wings have the same sink rates.



Thanks,

Don

--

psm(at)att.net
Guest

Posted: Mon Oct 18, 2010 3:43 pm Post subject: HDS Speed Problem (lack of)

Hi Jerry,



The way I found the "Best" setting for my plane was to make little changes and do a speed run (at 3000 feet?).  I plotted the indicated airspeed and RPM (over a range of RPMs) on a piece of graph paper.  This showed me the trend rather than the exact measurements (any measurement is subject to "Noise" but averaging them together tends to remove the measurement errors).



I chose the final setting based on operating issues rather than speed, but I got close to the best speed in cruise anyway.  I decided I wanted to be able to run the engine at full throttle in level flight without going over the red line.



Good luck,



Paul



--

larry(at)macsmachine.com
Guest

Posted: Mon Oct 18, 2010 4:26 pm Post subject: HDS Speed Problem (lack of)

Hi Don,

I've flown an HDS just like mine with full HD wings and the climb and glide

are far better, although the cruise speeds are also a bit slower, by 15 - 20

mph.



Larry McFarland 



--

jlatimer1(at)cox.net
Guest

Posted: Mon Oct 18, 2010 5:24 pm Post subject: HDS Speed Problem (lack of)

Paul

I did something similar, but my goal wasn't to maximize the speed.  I 

plan on operating my plane at Flagstaff Arizona (part time), which has 

an altitude of 7K ft and in the summer time the density altitude can go 

over 10K ft.  So I had to compromise some speed for rate of climb. 

Right now I'm happy with where I have the prop set.  That could change 

in the future.

Jerry

On Mon, Oct 18, 2010 at 4:40 PM, Paul Mulwitz wrote:



[quote] 



 Hi Jerry,



 The way I found the "Best" setting for my plane was to make little 

 changes and do a speed run (at 3000 feet?).  I plotted the indicated 

 airspeed and RPM (over a range of RPMs) on a piece of graph paper. 

 This showed me the trend rather than the exact measurements (any 

 measurement is subject to "Noise" but averaging them together tends to 

 remove the measurement errors).



 I chose the final setting based on operating issues rather than speed, 

 but I got close to the best speed in cruise anyway.  I decided I 

 wanted to be able to run the engine at full throttle in level flight 

 without going over the red line.



 Good luck,



 Paul



 --

Z601d(at)anemicaardvark.c
Guest

Posted: Tue Oct 19, 2010 5:35 am Post subject: HDS Speed Problem (lack of)

This is what you'd expect, I think. As I recall, the HDS used smaller, less 

draggy wings, to increase airspeed. That means less lift, and less glide.



On Monday 18 October 2010 19:22:35 you wrote:

[quote] 

 <larry(at)macsmachine.com>

 

 Hi Don,

 I've flown an HDS just like mine with full HD wings and the climb and glide

 are far better, although the cruise speeds are also a bit slower, by 15 -

 20 mph.

 

 Larry McFarland

 

 --

flyadive(at)gmail.com
Guest

Posted: Tue Oct 19, 2010 2:23 pm Post subject: HDS Speed Problem (lack of)

Jerry, Paul & Gaggle: 



I am learning about ROTAX & Jab engines, I do have a lot of experience with Lycoming.

So when I read about the Static RPM being 5200 & 5400 RPM my ears perked up.

 



Question:  Is there a Static reading required by the manufacture?

Question: What is the Red Line?

With Lycoming the static for an O-320 is 2100 to 2250 RPM.

 Red Line in flight is 2700 RPM.

With a two blade aluminum prop the rule of thumb is:  Every inch (1") of pitch your Static will be reduced by 50 RPM.

So, to get the MAX CRUSE you would want the MAX PITCH.  YET!  You MUST stay within the "Approved" Static range.  And Approved pitch of the GA prop - DANG the FAA

 



An example:  Let's say you are getting 2350 RPM Static.

By doing the math... 2350 - 2100 [Min Static] = 250 RPM

250 RPM divided by 50  = 5

That means you can increase your Pitch by 5 inches.  And still be able to pass the Min Static Requirement for Annual... OK, I know you guys don't do an Annual.

 Now some say the RPM per Inch is 100 

So 250 divided by 100 = 2.5 or an increase of 2.5 Inches.

I like a safety margin - Especially if you are starting with a NEW engine.  Over time the compressions get low and it becomes harder to reach the required Static.

 Some split the difference and use 75 RPM per inch.

Next step:

If you continue with the math there is a percentage difference between Red Line and Min Static.

For 2100 Static it is: 2100 divided by 2700 = 22.2% lower than Red Line

 For 2250 Static it is: 2250 divided by 2700 = 16.6% Lower than Red Line

Can you guess where I am going with this?

Continuing with the math there is a percentage difference between Red Line and Min Static, that I would like to apply to your engines.

 For 5200 Static it is: 5200 divided by 5400 = 3.8% lower than Red Line <-- 5400 is that  Red Line?

For 5400 Static it is: 5400 divided by 5500 = 1.8% Lower than Red Line <-- 55000 is that Red Line?

 

Those percentages are quite low.  There does not seem to be much of a load on the prop due to pitch.  So, next question:

Has anyone EXPERIMENTED with obtaining a MAX Pitch for the Min Static RPM?

 That would give you MAX CRUSE.

Of course Altitude / Density Altitude has a bit to do with it also.  Those at high elevation airports or in hot areas and both, have more of a problem and a less range to play in.

 



I'm interested in hearing your comments and learning the WHY of those numbers posted.

Barry





  [quote][b]

psm(at)att.net
Guest

Posted: Tue Oct 19, 2010 3:53 pm Post subject: HDS Speed Problem (lack of)

Hi Barry,  

   

I think I have a headache from all those numbers . . .   

   

The Rotax world and ground adjustable propellers is apparently quite different from the lycosaurus world with fixed metal propellers.  

   

The Rotax 912-ULS is essentially an automotive technology engine with a gearbox (and liquid cooling, and dual carburetors, dry sump).  The critical numbers are 5800 RPM redline with 5500 maximum continuous power.  I don't remember the definition of how long you can run between 5500 and 5800 but it is something like a few minutes for takeoff and initial climb.  The RPM numbers refer to the crankshaft rather than the propeller.  I think the gearbox is something in the neighborhood of 2.5 to 1.  

   

The Sensenich ground adjustable propeller I have on the Tecnam Echo doesn't tell you anything about pitch in inches.  It has index marks numbered from 1 to 5.  Each is only about a millimeter from the next one so it is very difficult to get a reading more accurate than 1/2 or maybe 1/4 of an index mark.  You loosen the clamping bolts and rotate the blades (which are kept at similar angles by some mechanical arrangement) to your desired index mark and then tighten the clamping bolts and torque them.  The nominal setting is 3.5.  I simply don't have a clue how this might translate to inches of pitch.  

   

The gear box changes all the torque issues about minimum static RPM and maximum pitch.  I think in all cases the issue here is whether or not your engine can produce enough torque with a given pitch to get the plane off the ground and climbing.  This depends not only on the engine and pitch but also on the weight and wing loading of the plane.  If you set the pitch too high you might get a great cruise speed but crash into the trees at the end of the runway on takeoff.  Also, if the pitch is too high the engine can't turn it fast enough, because of torque load, to achieve the suggested airspeed.  You just don't get a linear response from pitch changes to cruise speed.  

   

The Jabiru 3300 engine is more like a Lycosaurus engine - direct drive, air cooled, single carb.  Its max. RPM is 3300.  I am not aware of a well defined maximum continuous power setting but there might be one specified by Jabiru or any given airframe manufacturer.  Maximum continuous power might be set by cooling issues rather than the tendency of the engine to fall apart due to internal forces.  

   

My experience with the Rotax says the propeller setting can be varied only a very small amount.  Too small a pitch and it gets way too easy to exceed maximum RPM.  Too steep and you can't get the plane off the ground.  I started at the nominal setting of 3.5 and was able to get a full range of performance choices with only 1/2 to 1 index mark in each direction.   

   

 I haven't tried any of this with the Jabiru.  My XL with Jabiru has a wood fixed prop, and I haven't yet started the engine.  

   

I wish I could tell you more, but  I'm afraid we just aren't speaking the same language.  

   

Paul  

Camas, Wa  

     

From: owner-zenith-list-server(at)matronics.com [mailto:owner-zenith-list-server(at)matronics.com] On Behalf Of FLYaDIVE

 Sent: Tuesday, October 19, 2010 3:20 PM

 To: zenith-list(at)matronics.com

 Subject: Re: HDS Speed Problem (lack of)  

  

   

Jerry, Paul & Gaggle:     

   

    

I am learning about ROTAX & Jab engines, I do have a lot of experience with Lycoming.  

    

   

    

So when I read about the Static RPM being 5200 & 5400 RPM my ears perked up.  

    

   

    

Question:  Is there a Static reading required by the manufacture?  

    

Question: What is the Red Line?  

    

   

    

With Lycoming the static for an O-320 is 2100 to 2250 RPM.  

    

Red Line in flight is 2700 RPM.  

    

   

    

With a two blade aluminum prop the rule of thumb is:  Every inch (1") of pitch your Static will be reduced by 50 RPM.  

    

   

    

So, to get the MAX CRUSE you would want the MAX PITCH.  YET!  You MUST stay within the "Approved" Static range.  And Approved pitch of the GA prop - DANG the FAA  

    

   

    

An example:  Let's say you are getting 2350 RPM Static.  

    

By doing the math... 2350 - 2100 [Min Static] = 250 RPM  

    

250 RPM divided by 50  = 5  

    

That means you can increase your Pitch by 5 inches.  And still be able to pass the Min Static Requirement for Annual... OK, I know you guys don't do an Annual.  

    

Now some say the RPM per Inch is 100   

    

So 250 divided by 100 = 2.5 or an increase of 2.5 Inches.  

    

I like a safety margin - Especially if you are starting with a NEW engine.  Over time the compressions get low and it becomes harder to reach the required Static.  

    

Some split the difference and use 75 RPM per inch.  

    

   

    

Next step:  

    

If you continue with the math there is a percentage difference between Red Line and Min Static.  

    

For 2100 Static it is: 2100 divided by 2700 = 22.2% lower than Red Line  

    

For 2250 Static it is: 2250 divided by 2700 = 16.6% Lower than Red Line  

    

Can you guess where I am going with this?  

      

Continuing with the math there is a percentage difference between Red Line and Min Static, that I would like to apply to your engines.  

    

For 5200 Static it is: 5200 divided by 5400 = 3.8% lower than Red Line <-- 5400 is that  Red Line?  

    

For 5400 Static it is: 5400 divided by 5500 = 1.8% Lower than Red Line <-- 55000 is that Red Line?  

  

    

   

    

Those percentages are quite low.  There does not seem to be much of a load on the prop due to pitch.  So, next question:  

    

Has anyone EXPERIMENTED with obtaining a MAX Pitch for the Min Static RPM?  

    

That would give you MAX CRUSE.  

    

Of course Altitude / Density Altitude has a bit to do with it also.  Those at high elevation airports or in hot areas and both, have more of a problem and a less range to play in.  

    

   

    

I'm interested in hearing your comments and learning the WHY of those numbers posted.  

    

   

    

Barry  

    

   

    

   

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jlatimer1(at)cox.net
Guest

Posted: Tue Oct 19, 2010 6:44 pm Post subject: HDS Speed Problem (lack of)

Barry,



I have a Warp Drive 3 blade carbon fiber ground adjustable 72 inch prop.  



Like Paul posted the redline on the Rotax is 5800 rpm.  The Rotax is also not to be operated wide open throttle for more than 5 mins.  It is also not to be operated above 5500 rpm.  The gear reduction is 2.47:1.



My prop is now set at 14.5 degrees of pitch measured at the tip of the prop.  This gives me 5400 rpm static.  I also found that 1 degree change of pitch makes roughly a 100 rpm in static rpm in the narrow range we are interested in.  This was a number that has been posted on the Rotax Matronic forum in the past.  This rpm means you do not hit redline as the prop unloads during the takeoff roll, so you don't have to monitor the tach closely.  Also at 5400 rpm I also achieve 5650 rpm WOT at 3000 ft.  



I was also a little uncomfortable with the high rpm, but the Rotax is designed to run in 5000 to 5500 rpm range.  At 5000 rpm the Rotax published fuel burn is 4 gal/hr and at 5500 rpm it goes to 5 gal/hr  at 5800 it is 6.1 gal/ hr.  I climb at 5400 rpm and usually cruise at 5000rpm.  I could cruise a little faster if I ran the Rotax at 5500 rpm, but I like the 4 gal/hr fuel burn.  I also run on auto gas my cost of operation is really nice when compared to traditional aircraft motors.  This is important to me since I'm retired.  



Jerry

On Tue, Oct 19, 2010 at 3:19 PM, FLYaDIVE wrote:



 Jerry, Paul & Gaggle: 



I am learning about ROTAX & Jab engines, I do have a lot ofÂ experienceÂ with Lycoming. 

So when I read about the Static RPM being 5200 & 5400 RPM my ears perked up. 

Question: Â Is there a Static reading required by the manufacture? 

Question: What is the Red Line? 

 [quote][b]

klaus(at)utdallas.edu
Guest

Posted: Wed Oct 20, 2010 5:07 am Post subject: HDS Speed Problem (lack of)

Hi,



The cruise speed of the HDS is below the advertised 135 mph, 

and it seems impossible to change the plane to get there.

At least that's what I concluded after a lot of improvements.

With a good propeller such as the 2-blase Sensenich,

a cruise of 100kts at 4 gph is possible with the Rotax 912.

I cruise at 90 kts at 3.5 gph when not in a hurry.



The high sink rate can be fixed with wing root fairings, see



http://utdallas.edu/~klaus/Airplane/wing_root_fairing.html



This change is particularly effective when the engine has a

heavy engine. A builder with Jabiru 3300 got significant

improvements with the fairings. On my plane, the sink rate

is like a Cessna 150: 650 fpm at 65 kts with 1020 lbs total weight.

There are more stats on the website



http://utdallas.edu/~klaus/Airplane



Happy flying,



Klaus



[url=http://www.utdallas.edu/%7Eklaus][/url]



 [quote][b]

flyadive(at)gmail.com
Guest

Posted: Wed Oct 20, 2010 9:52 am Post subject: HDS Speed Problem (lack of)

Jerry, Paul & Gaggle: 



It seams that I did not present my synopsis clear enough.

I do understand the Rotax engine RPM's as for Max RPM and Cruse RPM but what I did not see from your responses was the STATIC RPM.

 



From the number you posted we are looking at ONLY 1.3 to 1.8% difference between YOUR numbers.

It really does not matter what RPM the Lycoming is doing in comparison to the Rotax... ONLY the percentage of difference.

 



With 22.2% & 16.6% for the Lycoming - Your Rotax MIGHT have a static RPM around: 

5400 x 22.2% = 1198 RPM lower (5400 - 1198 =  4202 RPM) 4202 RPM as the Static

5400 x 16.6% = 1896 RPM lower (5400 - 896 =  4504 RPM) 4504 RPM as the Static

 So your static range would be: 4202 to 4504 RPM

And How do you achieve that Static RPM?

By Increasing the Pitch.

This would increase your Cruse Speed.

Of course as with all planes with a fixed pitch prop, when you increase the pitch you decrease the climb performance.

 



SOooooo, does Rotax post a Static Range?

Barry

  [quote][b]

psm(at)att.net
Guest

Posted: Wed Oct 20, 2010 11:08 am Post subject: HDS Speed Problem (lack of)

Hi Barry,  

   

Sorry about the confusion.  

   

I didn't quote a static rpm for the Rotax because I have never seen or heard the concept applied to that engine.  In my own testing I did not do static testing.  This might be important for a new installation, but I was trying to optimize a setup that was already flying.  

   

Your focus on all the mathematics to predict what setting is the right one seems important when dealing with fixed metal propellers.  You can't repitch them too many times or the metal will fail.  This is not a problem with the ground adjustable propellers since there is no damage done by resetting the pitch.  

   

I don't think your proposed rule about the percent of rpm for static testing applies the same when a gearbox is used.  It would be a totally different situation since the engine doesn't see the torque effects of changing propeller pitch in the same way as a direct drive engine.  Also, the mechanics of the Lycoming are quite different from the automotive style Rotax.  

   

To make this discussion even more complicated, let me add the problem I hope to face in a couple of years.  I want to install an electric power plant in a Buttercup I am currently building.  Selecting a propeller for that - or even deciding on an initial pitch on an adjustable propeller - could wind up being quite a challenge.  

   

Paul  

Camas, WA  

     

From: owner-zenith-list-server(at)matronics.com [mailto:owner-zenith-list-server(at)matronics.com] On Behalf Of FLYaDIVE

 Sent: Wednesday, October 20, 2010 10:49 AM

 To: zenith-list(at)matronics.com

 Subject: Re: HDS Speed Problem (lack of)  

  

   

Jerry, Paul & Gaggle:     

   

    

It seams that I did not present my synopsis clear enough.  

    

   

    

I do understand the Rotax engine RPM's as for Max RPM and Cruse RPM but what I did not see from your responses was the STATIC RPM.  

    

   

    

From the number you posted we are looking at ONLY 1.3 to 1.8% difference between YOUR numbers.  

    

   

    

It really does not matter what RPM the Lycoming is doing in comparison to the Rotax... ONLY the percentage of difference.  

    

   

    

With 22.2% & 16.6% for the Lycoming - Your Rotax MIGHT have a static RPM around:   

    

5400 x 22.2% = 1198 RPM lower (5400 - 1198 =  4202 RPM) 4202 RPM as the Static  

    

5400 x 16.6% = 1896 RPM lower (5400 - 896 =  4504 RPM) 4504 RPM as the Static  

    

So your static range would be: 4202 to 4504 RPM  

    

And How do you achieve that Static RPM?  

    

By Increasing the Pitch.  

    

This would increase your Cruse Speed.  

    

Of course as with all planes with a fixed pitch prop, when you increase the pitch you decrease the climb performance.  

    

   

    

SOooooo, does Rotax post a Static Range?  

    

   

    

Barry  

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