Tail Height to Accommodate Larger Propeller for Rotax 912

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jonfilipa

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Jun 7, 2009
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Finishing up last welding steps on the fuselage, and another big decision to make is to pick a final tail height. Given that I'm 6'2" I anticipate having to raise the turtledeck an inch or two to accommodate torso height which per longstanding best practice also increases tail height by the same amount.

That said, my plan is to go with a Rotax engine and at least per my best initial estimate a 64 inch propeller. Per previous feeds, I'm pretty sure this will still give adequate ground clearance versus the typical 52-54" prop on a Sonerai. That said, still need to maintain yaw stability with a bigger prop. Agricultural engineering approach would say to increase tail height by the increase in propeller radius - 5 inches in this case - to maintain same height of tail in "clean" air above propeller slipstream. I know others have had to increase tail height to accommodate Jabirus and/or other engines, so am looking for a quick check on my thought process.
 

cosmic

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Aug 29, 2006
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Australia
While some people have increased tail height I wouldn't agree that it is necessarily longstanding best practice. That's just what people have done and I assume because it seems easier. I went the other way and moved the seat down and moved the elevator push rod to get more than adequate torso height for 6'2" maintaining the original Sonerai tail design. With a carbon fiber car racing seat bolted to the floor it is very comfortable and knees pass directly over the spar without contact.

My plane has a Jabiru 3300 and runs a 60" 3 bladed prop. When I had the undercarriage made by Grove (brake lines drilled inside the leg) I got them to make the gear leg 5" longer than standard. It works well and to my eye it looks about the right angle for a high performance taildragger. A bit like a small Harmon Rocket.
 

Flyguyeddy

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Jun 9, 2018
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Central illinois
While some people have increased tail height I wouldn't agree that it is necessarily longstanding best practice. That's just what people have done and I assume because it seems easier. I went the other way and moved the seat down and moved the elevator push rod to get more than adequate torso height for 6'2" maintaining the original Sonerai tail design. With a carbon fiber car racing seat bolted to the floor it is very comfortable and knees pass directly over the spar without contact.

My plane has a Jabiru 3300 and runs a 60" 3 bladed prop. When I had the undercarriage made by Grove (brake lines drilled inside the leg) I got them to make the gear leg 5" longer than standard. It works well and to my eye it looks about the right angle for a high performance taildragger. A bit like a small Harmon Rocket.
Can you post some photos of this setup cosmic?
 

jonfilipa

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Jun 7, 2009
Messages
25
Cosmic - nice setup. I'm guessing with 120 hp and variable pitch prop performance must be pretty outstanding. Do have a couple follow up questions:
- What propeller are you running?
- Regarding the 5 inch gear extension, were you just going for aesthetics (looks) or was your intent to be able to land slower with hitting tailwheel first?
- Any particular reason for going with the Grove gear? Ability to customize and have brake lines inside legs?
- Was your carbon fiber seat custom built or was it something purchased (i.e. Sparco model XYZ)?
 

cosmic

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Aug 29, 2006
Messages
44
Location
Australia
Cosmic - nice setup. I'm guessing with 120 hp and variable pitch prop performance must be pretty outstanding. Do have a couple follow up questions:
- What propeller are you running?
- Regarding the 5 inch gear extension, were you just going for aesthetics (looks) or was your intent to be able to land slower with hitting tailwheel first?
- Any particular reason for going with the Grove gear? Ability to customize and have brake lines inside legs?
- Was your carbon fiber seat custom built or was it something purchased (i.e. Sparco model XYZ)?
- The prop is a Bolly and ground adjustable pitch. Not in-flight variable pitch. Performance is outstanding anyway. Bolly is the manufacturer of the Scimitar prop for Jabiru.
- The 5 inch gear extension was decided after assessing the deck angle of several aerobatic taildraggers. My original plan was to get enough ground clearance to run a larger 2 bladed prop which I may yet do. Another factor was watching 2 different Sonerais landing with standard gear. After the tailwheel touched there appeared to be quite a bit of bouncing when the mains touched. Maybe pilot skill was a factor in what I saw but I have no regrets at all about extending the gear. My plane lands beautifully and although I think it looks better, aesthetics was not the driver.
- Grove was recommended to me. I bought wheels and brakes from Grove too. The gun-drilled brake lines was an option they had available and seeing I had already spent an arm and a leg, a bit more didn't matter. After all, it is aeroplane money which as you probably know is a bit like Monopoly money. The internal brake lines makes a clean leg so I may remove the fairings because they didn't seem to make much ( if any) difference to speed.
- The seat was well used when it was obtained and sorry I don't know the manufacturer.
 

Bil438

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Oct 17, 2007
Messages
802
Have you flown your Sonerai yet? May I ask whether the fin and rudder are adequate in reversing turns and say aerobatics?
Bill E
- The prop is a Bolly and ground adjustable pitch. Not in-flight variable pitch. Performance is outstanding anyway. Bolly is the manufacturer of the Scimitar prop for Jabiru.
- The 5 inch gear extension was decided after assessing the deck angle of several aerobatic taildraggers. My original plan was to get enough ground clearance to run a larger 2 bladed prop which I may yet do. Another factor was watching 2 different Sonerais landing with standard gear. After the tailwheel touched there appeared to be quite a bit of bouncing when the mains touched. Maybe pilot skill was a factor in what I saw but I have no regrets at all about extending the gear. My plane lands beautifully and although I think it looks better, aesthetics was not the driver.
- Grove was recommended to me. I bought wheels and brakes from Grove too. The gun-drilled brake lines was an option they had available and seeing I had already spent an arm and a leg, a bit more didn't matter. After all, it is aeroplane money which as you probably know is a bit like Monopoly money. The internal brake lines makes a clean leg so I may remove the fairings because they didn't seem to make much ( if any) difference to speed.
- The seat was well used when it was obtained and sorry I don't know the manufacturer.
 

Aviacs

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Mar 16, 2019
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97
Location
Elmira, NY
Cosmic - interesting (& attractive) canopy set up.
Is the front section fixed?
Are you sure it is not somewhat taller than plans?

I'm only 6'-0" & cannot close the canopy on my head while sitting on the seat pan, which is a thin sheet of aluminum down about level with the longerons. The amount to be gained (in mine) by lowering the control tube looks to be about 3/4" (less than 1" anyway) at the expense of a lot of work and fudging.

Anyway, the looks of your canopy is appealing. The photo angle makes it appear slightly taller than the turtle deck.
I've been considering that approach (taller canopy without raising existing turtledeck), with some added roll protection structure.

smt
 

cosmic

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Aug 29, 2006
Messages
44
Location
Australia
Have you flown your Sonerai yet? May I ask whether the fin and rudder are adequate in reversing turns and say aerobatics?
Bill E
Yes - first flight was 2 years ago and the plane currently has 42 hours. In my experience the general handling of the Sonerai is much like a Corby Starlet (very good handling). Rudder authority is powerful. Several experienced aerobatic pilots have flown it and no negative handling characteristics were noted. It is very straightforward to fly but it is not a Cessna or Cherokee.
 

cosmic

Active Member
Joined
Aug 29, 2006
Messages
44
Location
Australia
Cosmic - interesting (& attractive) canopy set up.
Is the front section fixed?
Are you sure it is not somewhat taller than plans?

I'm only 6'-0" & cannot close the canopy on my head while sitting on the seat pan, which is a thin sheet of aluminum down about level with the longerons. The amount to be gained (in mine) by lowering the control tube looks to be about 3/4" (less than 1" anyway) at the expense of a lot of work and fudging.

Anyway, the looks of your canopy is appealing. The photo angle makes it appear slightly taller than the turtle deck.
I've been considering that approach (taller canopy without raising existing turtledeck), with some added roll protection structure.

smt
Yes the front section of the (RV3) canopy is fixed. It is a long time (25 years) since the fuselage tubes were cut and welded but I can't remember any deviations. It is possible there may be slight differences between my plans and yours. Today I measured from the top of the floor tubes to the top of the turtledeck and it is 37 inches. The canopy as you mentioned sits above the turtledeck about 1 inch but has a slight curve up creating a faction more headroom. I would be surprised if you couldn't get more than an inch additional headroom from dropping the seat to the floor.
 

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Aviacs

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Mar 16, 2019
Messages
97
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Elmira, NY
Yes the front section of the (RV3) canopy is fixed.
Looking at the side view - is your S2 still 2 place?
Coincidentally, i have a RV3 canopy. Did you combine the -3 front with a Sonerai back? or???

Pics posted before show my seat area. there is not 1" to be gained between the bottom seat back rail, and the cross rail between the longerons.

Batten shows aprox shape that would just about fit my head. Going to the effort, will probably go a little higher for comfort & headset.
 

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Czr7s1

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Mar 30, 2013
Messages
11
Cosmic - As others mentioned, this is a good looking airplane! I had to look at this on my computer to make sure it was indeed a Sonerai. Only way I can really tell in my eyes is the tiny rudder. What's some specs? Gross weight, Takeoff/landing roll, your climb must be through the roof, stall, etc...

To make sure I know what I'm looking at here, few questions:
  • Sonerai II with front seat capped? Any fuselage length mods?
  • Is that a Sonerai cowl that's been modified or something you made or adapted to fit around the Jab?
  • Don't know what the weight difference is but skinning in alum looks great! I could be wrong but there's no way the skin is riveted straight to the fuselage tube - Do you have pictures of the "bulkheads" attaching to the tubes, etc?
If you have more pictures of this "rocket" and have time to share, please do!

Chris
 

Czr7s1

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Joined
Mar 30, 2013
Messages
11
A screenshot of the stock Sonerai II fuselage (wireframe) in Solidworks with an Edge 540 in the background for reference ;)...I was playing around with lines and rudder yesterday. Also have a VW in there that would be flywheel dive. (All reports on the stock rudder size say its does great - this is was just for smiles) The line and circle are 38" from the bottom longeron centerline. At 5'11, my butt to top of head height is every bit of 36" so I figured 38" and the elevator pushrod will still have to go under and through some of the bottom fuselage members with bottom part of fuselage in that area extended down.
SoneraiII_mod.png

Still in the planning phase as all I have is a Sonerai I I'm working on at the house to actually sit in - raising turtledeck now.
 

jonfilipa

Active Member
Joined
Jun 7, 2009
Messages
25
Aviacs - From the pic of your seat, is the thumbwheel/all thread assembly with the wire wrapped around it for flaperon control?

Jon
 

cosmic

Active Member
Joined
Aug 29, 2006
Messages
44
Location
Australia
Looking at the side view - is your S2 still 2 place?
Coincidentally, i have a RV3 canopy. Did you combine the -3 front with a Sonerai back? or???

Pics posted before show my seat area. there is not 1" to be gained between the bottom seat back rail, and the cross rail between the longerons.

Batten shows aprox shape that would just about fit my head. Going to the effort, will probably go a little higher for comfort & headset.
It is a Sonerai 1 with low wing and no canopy parts for a Sonerai were used.
 

Aviacs

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Joined
Mar 16, 2019
Messages
97
Location
Elmira, NY
Aviacs - From the pic of your seat, is the thumbwheel/all thread assembly with the wire wrapped around it for flaperon control?
It is elevator trim. It biases the spring load to one end or the other.
As far as details, i did not build the airplane, and have not yet flown it.
As i learned after joining the forum last year, it is the former GXPD. So there is a lot of info about it over the years on this site.

Need to resolve the height and canopy issue in order to fit. Hope to accomplish that this year....

smt
 

cosmic

Active Member
Joined
Aug 29, 2006
Messages
44
Location
Australia
Cosmic - As others mentioned, this is a good looking airplane! I had to look at this on my computer to make sure it was indeed a Sonerai. Only way I can really tell in my eyes is the tiny rudder. What's some specs? Gross weight, Takeoff/landing roll, your climb must be through the roof, stall, etc...

To make sure I know what I'm looking at here, few questions:
  • Sonerai II with front seat capped? Any fuselage length mods?
  • Is that a Sonerai cowl that's been modified or something you made or adapted to fit around the Jab?
  • Don't know what the weight difference is but skinning in alum looks great! I could be wrong but there's no way the skin is riveted straight to the fuselage tube - Do you have pictures of the "bulkheads" attaching to the tubes, etc?
If you have more pictures of this "rocket" and have time to share, please do!

Chris
- No it is a Sonerai 1 with low wing. No change to fuselage length.
- The cowl was made to fit the plane.
- Empty weight is 588 pounds. The aluminium skins are riveted to shallow steel "u" shaped channels welded to the longerons. Have attached a picture showing a couple of channels and also shows 3 small tube braces welded into the last station at the tail. The braces added significantly to the torsional rigidity of the fuse but perhaps a fabric covered fuse would have been stiffer. Also a link to a short video.
 

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