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Thrust angle in an XL with a Jabiru 3300

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craig(at)craigandjean.com
Guest

Posted: Tue Jul 31, 2007 11:04 pm Post subject: Thrust angle in an XL with a Jabiru 3300

So I hung my engine for the first time tonight. The first thing I did was

stand off to the side and look at it. Hmm, nose looks low. The XL's plans

(page 6-JE-1, 12/04) indicate that the engine's crank should be parallel

with the upper longeron (basically the sill of the cockpit). According to my

digital level my thrust angle is off by about 4 degrees, prop hub low. The

same page in the plans says that the firewall should be canted back 13

degrees relative to a plumb line from the longerons while mine measures in

at 11. So that is 2 degrees of the difference, the rest must be in the motor

mount.



I see two places to attack the problem: where the motor mount bolts to the

firewall and where the engine hangs on the mount. I suspect I'll have to

shim both. Jabiru supplies 4 spacer washers with the FWF kit that can be

placed between the motor mount "pin" and the rear rubber bushing. On the

HomebuiltHELP FWF DVD Pete at Jabiru USA says you can add up to two. I'd be

adding mine at the bottom of course. What I don't like about these washers

is that without them the stepped shoulder of the front "T" washers pull down

tight against the motor mount "pins". So what happens when you add the

spacers? You have to compress the rubber bushings that much more which also

undoes some of the gain from the spacers. I may make some tubular spacers

the diameter of the mounting pins and the height of the spaces to prevent

this problem. Or I suppose I could trim the same thickness off of the front

bushing but I don't feel good about that. Either way I'm probably going to

need longer bolts.



Those are my thought on the problem. Have I missed anything? How much does

all this really matter? Somewhere I read a post quoting someone at the

Zenith factory saying that they didn't achieve the 13 degree firewall angle

all that often.



-- Craig

craig(at)craigandjean.com
Guest

Posted: Wed Aug 01, 2007 12:56 pm Post subject: Thrust angle in an XL with a Jabiru 3300

I called the Zenith factory about my nose-low engine and spoke with Caleb.

He said that the 4 degree down-angle is just the engine sagging on the

rubber mounts and not to worry about it. Says it will go away in the air

when the engine is pulling the plane through the air. Which begs the

question - how do you measure the thrust angle in the air? I guess it will

improve but by how much? He didn't seem to think it was worth worrying

about. I wonder how much clearance I have to leave on the cowl to prevent

contact in the air.



-- Craig

rpf(at)wi.rr.com
Guest

Posted: Wed Aug 01, 2007 2:23 pm Post subject: Thrust angle in an XL with a Jabiru 3300

Hi Craig,



My engine (3300 on a 601xl) is 3 degrees down at it fly's very nice.



Randy

---

craig(at)craigandjean.com
Guest

Posted: Wed Aug 01, 2007 2:49 pm Post subject: Thrust angle in an XL with a Jabiru 3300

 	  Quote: 	
		   My engine (3300 on a 601xl) is 3 degrees down and it fly's very nice.


	


Thanks. Who knows how much my plane will differ from others when all rigged?

I think that for a given plane the only way to prove it one way or the other

would be to test it with and without the droop. On the other hand I can't

see any reason not to conform to (or approach) the figure in the plans if

possible.



As soon as I can locate a hook scale I intend to test Caleb's theory by

providing some upward force at the hub with my engine hoist. I (and others)

are predicting the theory won't hold up. At least when new those rubber

mounts are HARD. And from what I have seen and heard most cowls don't have a

lot of clearance around the prop hub. At the same time I'll test to see how

much movement I'll need at the lower firewall mounts to take the droop out.



-- Craig

wjones(at)brazoriainet.co
Guest

Posted: Wed Aug 01, 2007 3:14 pm Post subject: Thrust angle in an XL with a Jabiru 3300

Hey Craig ,I bought a Big Game hook scale from academy sport stores for 

weighting my engines .It was not expensive

Wade Jones    South Texas

601XL plans building

Cont. 0200

---

joe(at)kfiz.com
Guest

Posted: Thu Aug 02, 2007 7:08 am Post subject: Thrust angle in an XL with a Jabiru 3300

Craig,



My engine measured 2.7 degrees down. I had Al Beyer from Oshkosh over to 

check it on the digital level. We decided to correct the problem. I sent my 

motor mount back to Jabaru and they brought a new one out to EAA for me. 

Jabaru found the top tubes were cut one inch too long! I had a talk with the 

owner of the company in when he was at the Neenah airport. He told me there 

were some early mounts out there that were made by a subcontractor in 

Wisconsin that were built wrong! Jabaru replace the mount for free, and was 

very gracious about it. Top notch people! I'm putting my engine on this week 

and I will let you know if the problem has been fixed.



I would prefer to get as close to the plans as I can while shimming the 

engine down or neutral. Over the years the engine will compress the mounts 

and sink somewhat. Then I can shim it up over time. A heck of a lot better 

idea than to re-trim the cowl!



Joe in Oshkosh

sonar1(at)cox.net
Guest

Posted: Thu Aug 02, 2007 3:48 pm Post subject: Thrust angle in an XL with a Jabiru 3300

Hi  Craig:

I had an occasion to call Caleb at Zenith also.

I told him that the pre-drilled factory side skin 6-B-11-2 had the wing 

at 81.8 degrees instead of the plans 81 degrees. He said that it was 

close enough.

I told him that the bottom of the skin between the gear and the spar did 

not follow the plans. He said to force it.

We ended up remaking both forward skins to conform to the plans.

Your 4 degrees droop sounds like a lot to me.

I'm not sure that Caleb understands the seriousness of properly building 

and flying your own plane.

Just my opinion..................Fred Sanford............601XL riveting 

fuselage

JerryHey

Joined: 05 May 2007
Posts: 30

Posted: Thu Aug 02, 2007 4:09 pm Post subject: Thrust angle in an XL with a Jabiru 3300

I apologize for speaking about something I clearly am not qualified  

to speak about since I am  just starting a 701 and have no  knowledge  

of the Jibiru what so ever. However, I have been building engine  

mounts for a variety of aircraft for some time and I have never been  

asked to provide 4 degrees of down thrust.  The range is from ZERO  

down thrust to 1.2 degrees.  I can't recall any more than that.  If  

the isolation dampeners are that soft, then I wonder about how badly  

the engine must be vibrating.  Also, I don' t understand why a  

different engine would have a different thrust angle.  The thrust  

angle is determined by the designer and then it is adhered to by the  

builder regardless of the engine.    Just my opinion       Jerry

On Aug 2, 2007, at 7:47 PM, fred sanford wrote:



 	  Quote: 	
		   



 Hi  Craig:

 I had an occasion to call Caleb at Zenith also.

 I told him that the pre-drilled factory side skin 6-B-11-2 had the  

 wing at 81.8 degrees instead of the plans 81 degrees. He said that  

 it was close enough.

 I told him that the bottom of the skin between the gear and the  

 spar did not follow the plans. He said to force it.

 We ended up remaking both forward skins to conform to the plans.

 Your 4 degrees droop sounds like a lot to me.

 I'm not sure that Caleb understands the seriousness of properly  

 building and flying your own plane.

 Just my opinion..................Fred Sanford............601XL  

 riveting fuselage

Tim Juhl

Joined: 21 Mar 2006
Posts: 488
Location: "Thumb" of Michigan

Posted: Fri Aug 03, 2007 7:05 am Post subject: Re: Thrust angle in an XL with a Jabiru 3300

For Joe,

What is the correct length for the top tubes?  I bought a Jab FWF kit this year which I assume is up to date but I would like to confirm that I have the correct mount.



As far as the engine "rising" in flight - I suspect that is a possibility - indeed I have seen engines do a lot of wiggling on their mounts - I guess I would be concerned about clearance with the cowling both where the prop shaft passes through and in general.

Tim

_________________
______________
CFII
Champ L16A flying
Zodiac XL - Jabiru 3300A
Almost done! It'll fly in spring!

dredmoody(at)cox.net
Guest

Posted: Fri Aug 03, 2007 7:32 am Post subject: Thrust angle in an XL with a Jabiru 3300

It may be a big hassle at this point for some, but it seems that before the engine is attached to the motor mount, one could bolt the mount to the firewall and using a smart level, get some very accurate readings. The angle formed by the top and bottom mounts on the right side relative to the top longeron would be 90 degrees if the thrust line is zeroed out. The same is obviously true for the left side. Wouldn't this take the guesswork out of "how much is the engine weight causing the rubber dampeners to sag?"



How about opinions form those on the list who have lots more experience? I'll be wrestling with this beast soon and would appreciate some advance advice from the old heads out there.



Dred

zodiacjeff(at)msn.com
Guest

Posted: Fri Aug 03, 2007 11:22 am Post subject: Thrust angle in an XL with a Jabiru 3300

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> >It may be a big hassle at this point for some, but it seems that before  the engine

 	  Quote: 	
		  is attached to the motor mount, one could bolt the mount to  the firewall and

using a smart level, get some very accurate readings.  The angle formed by the

top and bottom mounts on the right side relative  to the top longeron would

be 90 degrees if the thrust line is zeroed out.  The same is obviously true for

the left side. Wouldn't this take the  guesswork out of "how much is the engine

weight causing the rubber  dampeners to sag?"


	


 +++ Dr. Ed,

  

 If builders are concerned, this should be an avenue that might be  pursued.  Be alert that the mount, without the engine attached, is very  'plastic' and due to heat factors while welding the pads for the rubber mounts  (Jabiru calls them cushions) might be on four different planes.  Accurate  measurements might be impossible but even the old Mk I Eyeball will tell you if  closer investigation is needed.  Knowing the quality of parts out of the US  Jabiru distributors/dealers presently makes an aberration unlikely.

  

 I have in front of me a drawing "Jabiru 3300 Engine Mount W/Assy CH601  Zodiac" from Jamie Cook, Product Support Supervisor, along with an e-mail to  Fred Hulen about problems early 3300-into-601 builders were having with offsets  in the mount.  Fred and I, along with Stan Challgren, had three of the  first four FWF kits into the US (in my knowledge).  Fred was further ahead  in construction at the time and had tried a trial fit of the mount to his  fuselage when I received an urgent e-mail that the mount had some upthrust but  no right thrust.  What started was a dialogue that got Fred and me new  mounts.  This was at the time that Jabiru was removing the old west coast  distributor and turning to Pete Krotje to instill a new trust in the product  here in the States.  Though we had not purchased the engines (very early  serial numbers) from Pete he was more than helpful.

  

 The drawing shows dimensions that the 'new' factory welding jig was  designed to follow.  None of the tubes have dimensions on them but the one  overall measurement that you might be able to use to check would be to measure  from the top right firewall pad to a line that intersects a plane through the  top and bottom right engine pads at a 90 degree angle.  That dimension  should be ~ 244.5mm.  CAVEAT:  if Jab has changed the mount since the  11/12/2000 of the e-mail then all bets are off.

  

 We were told that the first mounts were outsourced and that led to the  quality control issue.  

  

 Joe in Oshkosh, were your mount top tubes really 25mm longer than  designed?  This would result in a downthrust angle the nature of 8 to 10  degrees.  Al Beyers, can you confirm?

  

 The new mounts we received had about 2 degrees of downthrust, and about 2  to 2.5 of right thrust which fit my old R/C modeling designing habits  nicely.

  

 BTW, Jerry Hey and others who have not seen Jabiru 'cushions' or  experienced a Jab running - be assured the mounts are quite firm (mine have  sagged with four years of use but then grandma says that too), and the 2200 and  3300 series motors do not vibrate, they purr.  My CFI during a flight  review last week simply could not believe we were flying behind a  non-certificated engine.  Jerry, don't take that personally, you were  honest enough to say you had little knowledge of Jabs and members who go through  opinions after opinions cloaked as facts applaud you.  I was just yankin'  your chain...

  

 ...and, who is this WW?  Walks on Water?  Willy Wonka?

  

 Craig, are you planning on anchoring your nose wheel to the garage  floor when you hoist the prop hub with scale attached?  If you don't then  won't the figures be misleading?  How much from 'give' in the cushions and  how much in lifting the front of the fuselage?

  

 To fine tune thrust measurements for you particular installation (not all  are going to get the magic 13 degree firewall tilt) you can use the shims  provided by Jabiru for that purpose.  After I had my engine mounted there  was talk on the JabbaChat Newsletter out of OZ about reversing the male/female  cushions which resulted in smoother running.  I think reversing them might  also make the use of shims a bit easier but don’t' hold me to it.  I make  adjustments for compression of lower mount cushions by making C-washers of .050,  093, or .125 stock and after loosening the bottom  through-firewall-from-longeron nut just slip them between mount pad and  firewall.  All you need is a friend to gently apply some upforce to the  prop hub.  Doing things this way you can really fine-tune thrust  adjustments if that's your bag.

  

 I have about 3/16 inch clearance between spinner backplate and cowl.   If the engine thrashed around too much I think the marks would be there to  confirm that but only bugs and a few stone chips are present after 300 +  hours.  And I do throw the old girl around a bit (the a/c, not  grandma).

  

 Pete Krotje, if you're monitoring and have a few minutes could you please  correct any misinformation so this thrust question can be laid to rest.

  

 In closing: Caleb.  I met Caleb at OSH last week.  Nice young  man, very polite and kind enough to entertain an old customer.  Now whether  he has an engineer's degree or not, I think we should give him a chance to learn  how to relate to customers who need reassurance on some construction  detail.  If his answer is not to your liking, ask to speak with  Roger.  Best yet, find a builder that you trust and has been flying a  while.  Get to know him real well.  Odds are that if his a/c is  working and you can sit in it and offer to buy some gas for a ride, then maybe  your Zenith engineer might become a lifelong friend.  And your questions  get answered over coffee or beer.

 

 	  Quote: 	
		  How about opinions form those on the list who have lots more  experience? I'll be

wrestling with this beast soon and would appreciate  some advance advice from

the old heads out there.

  
	


 Well, though I'm usually referred to as 'the old fart' I'll take Ed's  description as a compliment.  Hope a little bit of this helps Jab  builders.

  

 CAVU Jeff Small  N6322T  HDS/3300  

  

 "You're not building a jet fighter."  Chris Heintz

  

 



 

   [quote][b]

craig(at)craigandjean.com
Guest

Posted: Fri Aug 03, 2007 11:44 am Post subject: Thrust angle in an XL with a Jabiru 3300

>  ...and, who is this WW?  Walks  on Water?  Willy Wonka? 

  

 WW is William Wynne - the  Corvair aircraft guy 

  

  >   Craig, are you planning on anchoring your nose wheel to  the garage floor when you hoist the prop hub with scale attached?  If you  don't then won't the figures be misleading?  How much from 'give' in the  cushions and how much in lifting the front of the fuselage?

  

 I was going to measure the absolute angles of the engine's top and the  top longeron and calculate the relative difference. This is what I did with the  engine only supported by the mount. I suppose this may include some flex in the  fuselage but it sort of simulates what happens in flight. I suppose I'll "mike"  the supported and unsupported distance from the mount plate on the engine to the  pin's back on the mount (for all four positions). That would measure just the  rubber bushings' movement/compression/expansion. But I don't know if I will get  all this done before I leave for vacation in Norway.

  

 What is interesting to me is I have mentioned this issue on the Yahoo  Jabiru engines list and Pete from Jabiru USA (source of the mount) has had no  comment. I know he is "present" because he has responded to other posts on other  issues. I'll probably contact him direct when I have more  numbers.

  

 -- Craig

   [quote][b]

n801bh(at)netzero.com
Guest

Posted: Fri Aug 03, 2007 2:19 pm Post subject: Thrust angle in an XL with a Jabiru 3300

Just my two cents worth, this might and might not apply but since alot of the Zenith line uses a similar concept things might translate over. On my 801 the plans call for 2-3 degrees to the right to compansate for P factor, Zenith calls for the crank to be parallel to the fuselage reference line, ie, no down thrust. So, here I was left scratching my head as I was designing my engine mount for the V-8 Ford, and so I head over to the airport and measure every single engine plane on the ramp to see if there is common ground.  There is no standard because some planes cant the rudder, some set angle of incidence of the horizontal stab/ elevator differently, yada,yada,yada.  As I was measuring the last Cessna I found up drives the owner of the FBO, and politely asked my interest engine mounting offsets. I explain I am building a Zenith 801 with a rather large engine in it and was about to fabricate a mount and was rounding up as much data as I could. He first answer was " Oh, your the idiot that's gonna put a V-8 in an experimental" , his next comment was, hey, follow me back to my office and I will call a neighbor who might know the answer. Well, next thing I know I am speaking to Frank Christenson, who also lives here in Jackson Hole, This guy designed the Husky, Christen Eagle and alot of other planes. I explained my HP, prop size and weight of the plane, within about 5 seconds he said," try 1.5 degrees to the right and 1 degree down. Anyone of his caliber with that fast of a response was gospel to me. The right offset is perfect but I could have gone to 1.5 or maybe 2 degrees down cause the plane flies slightly nose up. About two degrees of flaps cures that though. In closing my gut feeling for the 601 would be 2-2.5 down and 2 to the right.  YMMV..... 

do not archive



Ben Haas

N801BH

www.haaspowerair.com



-- <dredmoody(at)cox.net> wrote:

--> Zenith-List message posted by: <dredmoody(at)cox.net>



It may be a big hassle at this point for some, but it seems that before the engine is attached to the motor mount, one could bolt the mount to the firewall and using a smart level, get some very accurate readings. The angle formed by the top and bottom mounts on the right side relative to the top longeron would be 90 degrees if the thrust line is zeroed out. The same is obviously true for the left side. Wouldn't this take the guesswork out of "how much is the engine weight causing the rubber dampeners to sag?"



How about opinions form those on the list who have lots more experience? I'll be wrestling with this beast soon and would appreciate some advance advice from the old heads out there.



D========================sp;       - The Zenith-List;the many List utilities such as the ================================================         - NEW MAontent now also available via the Web&nbsp======================================

   [quote][b]

joe(at)kfiz.com
Guest

Posted: Sat Aug 04, 2007 7:48 am Post subject: Thrust angle in an XL with a Jabiru 3300

TO: Jeff Small, Everyone



Hi Jeff,



Yes I can confirm the motor mount issue. Al and I double checked the 

firewall angle with a digital angle. We measured the engine angle on the 

plane and it measured 2.7 degrees down. Al and I spent the afternoon 

shimming and playing around with it without success. We thought of shimming 

the lower motor mount attach points to the fuselage and we would of had to 

pull it back more than an inch.



I sent the mount back to Tennessee and the factory confirmed the problem. 

The people at Jabaru are first class! They said they would return my mount 

to Oshkosh (seeing that I live a mile or so from the airport). They used it 

in the Jabaru booth for display. I am putting the mount on this week and I 

will confirm with everyone when it's mounted.



If I had a welder here at home, and I was good enough to fix such a critical 

part, I would have. I thought it was better to have the factory take a look 

at it.



I did learn one thing! trial fit the mount first before you paint. I spent a 

lot of time priming and painting it before I fit it! Real bad move! I plan 

on building everything firewall forward first, then a complete disassembly, 

then paint and polish.



Joe in Oshkosh

dave.thompson(at)verizon.
Guest

Posted: Sun Aug 05, 2007 9:52 am Post subject: Thrust angle in an XL with a Jabiru 3300

Joe & list,  

   

I’m not building yet so take these statements accordingly…  

   

Joe wrote:  

    	  Quote: 	
		  “I plan on building everything firewall forward first, then a complete disassembly, then paint and polish.” 	
  

   

Back in the 80’s my Dad, Brother & I built a Quickie. We welded up an engine stand on a small $100.00 trailer. We then mounted an exact replica of the firewall, at the correct angle to the stand. Just for the fun of it we also built a plywood instrument panel on the stand, mounting all the engine instruments & controls. We then installed the complete firewall forward package, including the cowling.  We put about 15 hours on the engine on the stand, working through the various bugs. When we finally moved the FWF system to the airframe, we were very confident of the system. During first flights, the extra effort paid off with no engine bugs at all. By the way, at one point, we installed a heavy duty hunter’s scale between the trailer and our car. With a little math, we found that we were getting approximately 21 HP out of the little Onan engine. I know we DID have resistance from the trailer wheels & stuff so the readings were not too accurate. However, the engine WAS rated at 22 HP.  

   

Joe,   

   

If you plan to do it twice, you might build it on a stand and break in the engine too. You said that you were going to disassemble it anyway. If and when I build, I plan to do the same with my Corvair.  

   

Just my two cents worth.  

   

Dave Thompson  

Westminster, CA  

        [quote][b]

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