Today's Message Index:
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1. 06:07 AM - Re: HDS Speed Problem (lack of) (Klaus Truemper)
2. 10:52 AM - Re: HDS Speed Problem (lack of) (FLYaDIVE)
3. 12:08 PM - Re: HDS Speed Problem (lack of) (Paul Mulwitz)
4. 01:53 PM - 701 Beefed up specs (Keith Burris)
5. 02:40 PM - Re: HDS Speed Problem (lack of) (Jerry)
6. 04:16 PM - Re: 701 Beefed up specs (FLYaDIVE)
7. 10:20 PM - Re: HDS Speed Problem (lack of) (Scotsman)
Message 1
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| Subject: | Re: 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
Message 2
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| 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
Message 3
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| 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@matronics.com
[mailto:owner-zenith-list-server@matronics.com] On Behalf Of FLYaDIVE
Sent: Wednesday, October 20, 2010 10:49 AM
Subject: Re: Zenith-List: 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
Message 4
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| Subject: | 701 Beefed up specs |
Folks;
I am told that there is a way to beef up the 701 to hold an engine as heavy
as the 750 will.
Questions:
Is this true?
Is this a Zenith supported mod?
Are plans available showing how it's done?
Thanks in advance.
-- Keith
Message 5
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| Subject: | HDS Speed Problem (lack of) |
Barry.
Rotax does not post a static rpm They just post the max rpm limits and the idle
rpm limits.
Like Paul stated, I was using the static rpm to setup a new installation. If the
plane is already flying, you can change the pitch of the prop to maximize whatever
performance factor is important to you and the way you fly your airplane.
I may have confused you by using static rpm. I was using static rpm as my baseline
to compare different pitch settings of the prop. The Warp drive prop I'm using
doesn't have the reference marks that the prop that Paul is using. To set
the pitch on the Warp takes about an hour. I feel that the time-to-time variation
in measuring the pitch of the prop is higher than the variation in static
rpm. That is why I use it as a baseline.
During phase I flight testing, I tested 4 different settings before settling on
the one I'm presently using.
Sorry for the confusion.
Jerry
Message 6
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| Subject: | Re: 701 Beefed up specs |
Keith:
You can always add gussets and braces OR build a mount of thicker and larger
tubing.
BUT! What will happen to the W&B?
Barry
Message 7
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| Subject: | Re: HDS Speed Problem (lack of) |
Wow list thanks for all the replies I will forward them to the owner of the HDS
and hopefully he can report back when he finds a workable solution to increase
his cruise speed.
Larry - I particularly enjoyed the "landing a well thrown manhole cover" comment...very
apt!
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Cell +27 83 675 0815
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