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View Full Version : Eliminating the Pacer's humpback look



cook11
09-20-2018, 12:32 PM
Does anyone know how the humped back look was taken out of the Mystery Pacer?

Glen Geller
09-20-2018, 03:10 PM
Does anyone know how the humped back look was taken out of the Mystery Pacer?

I believe an enormous pile of money was used to smush it down.

GG

Vagabondblues
09-20-2018, 04:35 PM
I read that he cut down the standoffs on the frame that hold the wood longerons by 3 inches

Gilbert Pierce
09-20-2018, 06:24 PM
Look at Ms. Pearl, copied from Jim Younkin’s Mystery Pacer. He lowered the center spine lowering the headroom in the rear seat. i.e. like a Clipper.
http://miss-pearl.org/

Stephen
09-20-2018, 07:47 PM
Look at Ms. Pearl, copied from Jim Younkin’s Mystery Pacer. He lowered the center spine lowering the headroom in the rear seat. i.e. like a Clipper.
http://miss-pearl.org/

Is this a minor alteration, with a log book entry? Hmmmm.

Steve Pierce
09-21-2018, 06:37 AM
There is a vee created by Piper 3/8" channel that supports the top stringer. That was cut and lower I am sure.

Stephen
09-21-2018, 10:14 AM
There is a vee created by Piper 3/8" channel that supports the top stringer. That was cut and lower I am sure.

I've lowered that vee section on my plane but, it does not really change the hump much. To get the top flat would take the removal of rear upper tubing and changing it to go straight across. I looked at Miss Perky's (aka the Pearl) pictures and it did not look like the tubing was changed. I'm not sure how these tubes are in the Clipper.

Steve Pierce
09-21-2018, 10:22 AM
I was thinking it was taller but it is higher just above the rear seat cross tube on the Tri-Pacer fuselages I have here than it is on the Clipper. Also the Clipper center stringer lays on the horizontal tubes aft of the rear seat where the Tri-Pacer has a short cathedral.
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cook11
09-21-2018, 11:54 AM
My Pacer is down for a rebuild so I was looking at what would be involved we reducing the humpback appearance the Younkin mentioned. Here is what the airframe looks like:

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Vagabondblues
09-21-2018, 02:52 PM
Re-read the article. He lowered the front attach for the stringer and also raised it about an inch and a half at the vertical stab. My Pacer does not have a baggage compartment which allows the "V" brace to slope almost to the middle of the "D" windows. Yours has a baggage compartment which changes the structure to behind the windows, from what I can see in the pictures. Since the structure is behind the windows the height of the stringer is about 4" higher than a model without the baggage. Adding height to the rear stringer attach would be the best was to reduce the humpback.

Rick-CAS
09-21-2018, 06:42 PM
I did this to my project. You actually raise the stringer to get the hump out. Mine is up 2 1/2” at the rear.

wmvosburgh
09-22-2018, 06:26 AM
Is this a minor alteration, with a log book entry? Hmmmm.
So what's the consensus from folks? Minor alteration or...? If you're looking to keep certification.
Always though that reducing the hump would reduce the stubby look from a side profile.

Steve Pierce
09-22-2018, 07:38 AM
I'd leave it alone and spend my time on other aspects of completeing the project. They look fine to me and when you change one thing it has been my experience that it effects 2-3 other things.

Stephen
09-22-2018, 09:26 AM
So what's the consensus from folks? Minor alteration or...? If you're looking to keep certification.
Always though that reducing the hump would reduce the stubby look from a side profile.

Raising the Vee at the rear in my opinion is a minor alteration. This requires no structural changes.

dgapilot
09-22-2018, 02:39 PM
Generally any changes to the outer mold line are major alterations.


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Stephen
09-22-2018, 08:17 PM
Generally any changes to the outer mold line are major alterations.


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Explain. "Changes to the outer mold". This differs from my understanding.

dgapilot
09-23-2018, 04:53 PM
Part 1.1 major Alterations . . . Appreciably affect flight characteristics.

Part 43 Appendix A (a)(1)(iii) fuselage

AFS-300 job aid (D)(4) changes in basic dimension or aerodynamic contour . . .

AC 43-210a figure 3-2 “could the alteration or repair have an appreciable affect on . . . Flight characteristics”


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Stephen
09-23-2018, 08:06 PM
Part 1.1 major Alterations . . . Appreciably affect flight characteristics.

Part 43 Appendix A (a)(1)(iii) fuselage

AFS-300 job aid (D)(4) changes in basic dimension or aerodynamic contour . . .

AC 43-210a figure 3-2 “could the alteration or repair have an appreciable affect on . . . Flight characteristics”


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I don't see how changing the height of a "non-structural" fuselage stringer and inch or so, "appreciably affects flight characteristics". I can believe some IA's interpreting differently.

andya
09-23-2018, 08:26 PM
Have to believe that if a field approval were needed, there would be a split in the opinions
of PMI's

cook11
09-24-2018, 09:17 AM
What are your thoughts on tapering the fuselage by decreasing how far the side stringers stick out on the sides? My Pacer is experimental so I do not require STC's or 337's. This is an extreme alteration....

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I'd be curious to know how this Pacer flies......

dgapilot
09-24-2018, 09:32 AM
I don't see how changing the height of a "non-structural" fuselage stringer and inch or so, "appreciably affects flight characteristics". I can believe some IA's interpreting differently.

It is the installer that has the responsibility to make the minor/major determination. Likewise it it the next IA that has to sign that the Aircraft is Airworthy (1. Meets type design or properly altered state. 2. Is in condition for safe flight). As an IA, if the outer mold line is changed without a supporting 337, I would not sign an Airworthy annual. Just my opinion, but backed by about 50 years experience. You would be surprised what aerodynamic effects small changes can make.


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dgapilot
09-24-2018, 09:39 AM
Don’t get me wrong, if I were doing a Pacer, I’d do a lot of Younkin’s mods, including eliminating the hump. I’d just have paper to cover them.


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cook11
10-03-2018, 09:55 AM
Is there a rule of thumb on how far the side and bottom fuselage stringers should be from the fuselage tubing? I just got my aluminum stringer extrusion from Univair yesterday and I would like to start installing it.


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dgapilot
10-03-2018, 11:35 AM
How about what is shown on the fuselage assembly drawing, since that is part of the “Type Design”


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cook11
10-04-2018, 10:11 AM
I cannot seem to find dimensions on the drawings disc I have. Is there a drawing reference # that shows what the dimensions should be?

Thanks!

Stephen
10-04-2018, 12:47 PM
If the stand offs are still on, use them as your guide. On the bottom, I'll check but, if I remember correctly they attach directly to the frame. Or, find a plane you can look at. The drawings are a challenge to decipher sometimes.

Steve Pierce
10-05-2018, 06:23 AM
There is the fuselage tubing drawing with general dimensions and there is a fitting drawing which shows dimensions on things welded to the frame.