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jaydub
Joined: 07 Jan 2020
Posts: 74
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 Posted: Sat Apr 15, 2023 9:44 am Post subject: Rotax engine mount plate |
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I'll call the new owners of the Kolb company next week but since they are fairly new owners (they may not know of all the design changes from early to later models) I thought I'd throw this out on the list.
For a little back history I bought a FSII (7 ribs per wing and had the back seat) built around 1990 or so and it came with a 12.0 hour Rotax 447 (engine castings say 89 or 90 depending on the castings so this is how I'm dating the airplane) and ground adjustable Ivoprop. I overhauled the engine and it's ready to run. This plane included everything but most of the fuselage. The only fuselage that came with it was the engine mounts, mount plates and rear drag link spar and its u-joints. I'll call this plane #1. In my quest to find a fuselage I picked up an entire FSII that was picked up from Kolb in late 2014 or early 2015. I decided to finish building the kit (I'll call plane #2) because I have a paper trail and use the 447 from plane #1.
Plane #1 is a 1990 model (based on engine casting dates) with the 2 piece engine mounting plate with a gap in the middle under the engine. The drawings I have for plane #2 shows a one piece "hour glass" shaped plate. Last night I was looking over my 447 mounted on plane #2 using the mounts and mount plates from plane #1. I was comparing it to the chunk of fuselage/engine mount from plane #1 and I notice the rear engine mount pad (the upside down U shaped piece that the Lord mounts bolt onto) goes back further than the spar on plane #1 than it does on plane #2. It seems that means my engine is further forward with this setup but I don't know for sure. I also noticed there is some strapping welded onto the U shaped piece going down to structure below that the earlier one doesn't have. I assume this is so one can run a higher hp engine like a 582 or the higher powered Hirths on the newer FSIIs because the torque and vibration is better braced? I was surprised to find a difference of that magnitude.
Anyone familiar with the change in the Firestar II engine mounting for Rotax between 1990 and 2015? Does the hourglass shaped mount plate move the engine back further from the drag link u-joints like the earlier models?
I can try to get photos out in the next few days if that helps. I'm hoping someone here remembers why that was all changed and if I need to do something different.
Thanks,
Jay
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jaydub
Joined: 07 Jan 2020
Posts: 74
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| Posted: Sat Apr 15, 2023 12:11 pm Post subject: Re: Rotax engine mount plate |
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Here's some photos
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racerjerry
Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY
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| Posted: Sun Apr 16, 2023 5:33 am Post subject: Re: Rotax engine mount plate |
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I built my Firestar II around '94 - '96. The plans / instructions page 1 was copyrighted Dec, 1991.
Engine mount drawing (p15) is dated Jan 1993. This page shows two engine mount setups; one for the 447, other for 503. Both have two separate nearly identical mounting plates; but it says the 447 requires circular cutouts between the two plates to clear bottom of engine case. Otherwise, there is no difference between the two plates other than required hole spacing.
The "hourglass" shape mounting plate is NOT shown at all in my plans; but that is what I received in MY kit and it apparently accommodates BOTH engines. In other words; THERE IS NO DIFFERENCE in engine position.
In any event, don't be overly concerned with engine position / attitude as long as your prop clearance to boom tube is sufficient. INSTEAD, pay a lot of attention to WEIGHT an BALANCE calculations; with YOU seated in airplane. Someone else must read scales. THIS is what can KILL YOU; not a slight difference in engine position / attitude.
While I am on my soapbox, I need to caution you about first flights in draggy ultralights.
WITH a high mounted engine pusher type ultralight, when you suddenly chop power - TWO things IMMEDIATELY happen: Nose goes UP and airspeed goes DOWN, quickly stalling the airplane. You MUST be spring loaded to PUSH STICK FORWARD in order to maintain airspeed and prevent a stall.
Regardless of prior flight experience, it's best to have at least SOME instruction in a similar configuration two-place pusher type ultralight. A CUB, for example; reacts MUCH differently.
Jerry King
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jaydub
Joined: 07 Jan 2020
Posts: 74
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| Posted: Sun Apr 16, 2023 6:29 am Post subject: Rotax engine mount plate |
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Hi Jerry,
Thanks for the reply. So your plans engine plate must be different than the plates I have from about 1990. I don't know if you could see in the photos mine are just 2 plates. but the rear one has a bit of a notch machined out of it for the gearbox drain. Mine don't appear home-made at all nor do mine have any clearance holes. Plane #1 kit may be older than 1990 as I know when I built a CGS Hawk in 1991 I had bought the frame kit first, the fabric kit second, and the engine kit last. I don't know if Kolb also sold them that way too? If so my fuselage/engine mounts could be earlier than the engine.
My big concern with the engine position is solely that it puts the prop much closer (2.5-3 inches) to the aileron tubes because the engine sits further forward in relation to the trailing edge of the wing. I did measure the distance between the main spar tang and the drag link mount on both my new wings and the old wings and that dimension didn't change nor does it appear to change from the drag link attachment to the trailing edge of the wing. That means the engine is further forward for sure putting the prop that much closer to the aileron tubes. If the prop hits the aileron tubes that could kill me that's what I am concerned with.
In my newer manual it does state that if you are using an ivoprop (which flex forward and aft) you must add the 2.5" prop spacer which I bought and installed with my ivoprop from plane #1. I didn't get a spacer with plane #1 so that might be why. I had thought maybe that had gotten lost but maybe the earlier models didn't need it.
I'm well aware of the importance of w&b and how to measure and calculate (tomorrow I'll be helping a buddy do his kitfox) as I have done them many times for new and altered homebuilts and have done hundreds of w&b calculations in my career as a professional bush pilot because I had to do them for every flight. I'm well aware of the differences between flying GA planes and light pushers as I also have over 450 hours in a 447 powered CGS Hawk which is very similar to the Firestar. I appreciate the heads up but I recall vividly how different they fly.
Jay
Sent: Sunday, April 16, 2023 at 7:33 AM
From: "racerjerry" <gnking2(at)verizon.net>
To: kolb-list(at)matronics.com
Subject: Re: Rotax engine mount plate
I built my Firestar II around '94 - '96. The plans / instructions page 1 was copyrighted Dec, 1991.
Engine mount drawing (p15) is dated Jan 1993. This page shows two engine mount setups; one for the 447, other for 503. Both have two separate nearly identical mounting plates; but it says the 447 requires circular cutouts between the two plates to clear bottom of engine case. Otherwise, there is no difference between the two plates other than required hole spacing.
The "hourglass" shape mounting plate is NOT shown at all in my plans; but that is what I received in MY kit and it apparently accommodates BOTH engines. In other words; THERE IS NO DIFFERENCE in engine position.
In any event, don't be overly concerned with engine position / attitude as long as your prop clearance to boom tube is sufficient. INSTEAD, pay a lot of attention to WEIGHT an BALANCE calculations; with YOU seated in airplane. Someone else must read scales. THIS is what can KILL YOU; not a slight difference in engine position / attitude.
While I am on my soapbox, I need to caution you about first flights in draggy ultralights.
WITH a high mounted engine pusher type ultralight, when you suddenly chop power - TWO things IMMEDIATELY happen: Nose goes UP and airspeed goes DOWN, quickly stalling the airplane. You MUST be spring loaded to PUSH STICK FORWARD in order to maintain airspeed and prevent a stall.
Regardless of prior flight experience, it's best to have at least SOME instruction in a similar configuration two-place pusher type ultralight. A CUB, for example; reacts MUCH differently.
Jerry King
--------
Jerry King
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510630#510630
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stuart(at)harnerfarm.net
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| Posted: Sun Apr 16, 2023 6:56 am Post subject: Rotax engine mount plate |
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I'll add a tiny bit to the prop spacer issue.
Bryan at Kolb told me that with the IVO prop the spacer was a must on a
2013 Firefly with a Rotax 447. The reason was the flex of the prop made
it at least slightly possible that the prop could hit the aileron tubes
and the spacer eliminated that possibility.
However, I went with the Warp Drive and it is is much stiffer. We had
quite a conversation about it and after a while Bryan recommended that I
use the spacer on the Warp Drive as well. His reasoning was that it will
help lower the pulsations of air on the trailing edge if the prop is a
little farther back. This should help with the longevity of the covering
and in general just put less stress on the plane and lower transmitted
noise as well.
I followed his advice and can say it all works better than I expected.
It does sound like somewhere along the line they did move the engine
forward, probably to help W&B, but that created the need for the spacer.
Tradeoffs, always tradeoffs....
Stuart
On 4/16/23 09:28, Jay Dub wrote:
| Quote: |
Hi Jerry,
Thanks for the reply. So your plans engine plate must be different than the plates I have from about 1990. I don't know if you could see in the photos mine are just 2 plates. but the rear one has a bit of a notch machined out of it for the gearbox drain. Mine don't appear home-made at all nor do mine have any clearance holes. Plane #1 kit may be older than 1990 as I know when I built a CGS Hawk in 1991 I had bought the frame kit first, the fabric kit second, and the engine kit last. I don't know if Kolb also sold them that way too? If so my fuselage/engine mounts could be earlier than the engine.
My big concern with the engine position is solely that it puts the prop much closer (2.5-3 inches) to the aileron tubes because the engine sits further forward in relation to the trailing edge of the wing. I did measure the distance between the main spar tang and the drag link mount on both my new wings and the old wings and that dimension didn't change nor does it appear to change from the drag link attachment to the trailing edge of the wing. That means the engine is further forward for sure putting the prop that much closer to the aileron tubes. If the prop hits the aileron tubes that could kill me that's what I am concerned with.
In my newer manual it does state that if you are using an ivoprop (which flex forward and aft) you must add the 2.5" prop spacer which I bought and installed with my ivoprop from plane #1. I didn't get a spacer with plane #1 so that might be why. I had thought maybe that had gotten lost but maybe the earlier models didn't need it.
I'm well aware of the importance of w&b and how to measure and calculate (tomorrow I'll be helping a buddy do his kitfox) as I have done them many times for new and altered homebuilts and have done hundreds of w&b calculations in my career as a professional bush pilot because I had to do them for every flight. I'm well aware of the differences between flying GA planes and light pushers as I also have over 450 hours in a 447 powered CGS Hawk which is very similar to the Firestar. I appreciate the heads up but I recall vividly how different they fly.
Jay
Sent: Sunday, April 16, 2023 at 7:33 AM
From: "racerjerry" <gnking2(at)verizon.net>
To: kolb-list(at)matronics.com
Subject: Re: Rotax engine mount plate
I built my Firestar II around '94 - '96. The plans / instructions page 1 was copyrighted Dec, 1991.
Engine mount drawing (p15) is dated Jan 1993. This page shows two engine mount setups; one for the 447, other for 503. Both have two separate nearly identical mounting plates; but it says the 447 requires circular cutouts between the two plates to clear bottom of engine case. Otherwise, there is no difference between the two plates other than required hole spacing.
The "hourglass" shape mounting plate is NOT shown at all in my plans; but that is what I received in MY kit and it apparently accommodates BOTH engines. In other words; THERE IS NO DIFFERENCE in engine position.
In any event, don't be overly concerned with engine position / attitude as long as your prop clearance to boom tube is sufficient. INSTEAD, pay a lot of attention to WEIGHT an BALANCE calculations; with YOU seated in airplane. Someone else must read scales. THIS is what can KILL YOU; not a slight difference in engine position / attitude.
While I am on my soapbox, I need to caution you about first flights in draggy ultralights.
WITH a high mounted engine pusher type ultralight, when you suddenly chop power - TWO things IMMEDIATELY happen: Nose goes UP and airspeed goes DOWN, quickly stalling the airplane. You MUST be spring loaded to PUSH STICK FORWARD in order to maintain airspeed and prevent a stall.
Regardless of prior flight experience, it's best to have at least SOME instruction in a similar configuration two-place pusher type ultralight. A CUB, for example; reacts MUCH differently.
Jerry King
--------
Jerry King
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=510630#510630
|
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worrybear(at)verizon.net
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| Posted: Sun Apr 16, 2023 7:19 am Post subject: Rotax engine mount plate |
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Jay, I got an email meant for Jerry. Just thought you should know. Dan
Kolb Mark ll
--
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jaydub
Joined: 07 Jan 2020
Posts: 74
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| Posted: Sun Apr 16, 2023 3:26 pm Post subject: Re: Rotax engine mount plate |
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Thanks Stuart,
From looking at the bracing differences on the rear engine mount U channel, I'm guessing they moved the engine forward so they could better brace the U channel for the rear mounts.
I remember reading something in the archives that people added bracing to that channel down to the boom tube/fuselage bolt on both sides when using a higher powered engine. I'm thinking maybe the factory moved it so it could be better braced.
You can see how it's braced on my plane #2 vs no extra bracing on plane #1 in the photos.
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Tue Apr 25, 2023 7:27 pm Post subject: Re: Rotax engine mount plate |
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FWIW: helped build a FSII that has the extra braces from the rear spar carry through up to the motor mounts, wanted to put a 582 on it and the Kolb people got unhappy with us. So we modded it.
Here is the illustrated story:
http://oh2fly.net/oldpoops/582%20Mods.html
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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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