VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Model Specific > RV-4
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 03-15-2014, 03:41 PM
Pittsbuilder Pittsbuilder is offline
 
Join Date: Jul 2011
Location: Hampton, Ga (4A7)
Posts: 5
Default -8 Tail on my Fastback -4?

Hey guys, I'm thinking about putting the RV8 tail on my RV4. I have Several reasons for wanting to do this. I inherited the project partly complete, and am converting to Fastback (mod mostly complete.) The horizontal stab was built with several degrees twist at each tip. If the HS is inline with the axis of the aircraft, each tip is twisted down. Also, my 4 is an old kit, which has the thinner skins, and I fear that I will eventually have issues with cracking anyway. A friend of mine has an -8 tail mostly built that I can pick up for a decent price, thinking about pulling the trigger.

I know several members here have done this swap, and I would love to get some info from them. How hard was the conversion? Exactly what is involved to make it happen? Difference in flying qualities? I tried to message one of the aforementioned members, but to no avail. I also tried the search, and found a couple posts with some mention of it, but not really much helpful info. Any help/suggestions would be greatly appreciated.
Reply With Quote
  #2  
Old 03-15-2014, 03:58 PM
southtarnation's Avatar
southtarnation southtarnation is offline
 
Join Date: Oct 2008
Location: Punta Gorda, Fl
Posts: 325
Default

I am re doing a 89 -4 into a fast back and changed out the tail. i thought about using the -8 tail and it can be done pretty easily from what i understand but the determining factor for me was the -8 tail weighs more. About 10-15 pounds more if I recall. I got a second hand -4 tail section and was able to use just the feathers with my existing vert and horizontal stabs. The -8 rudder has a larger surface area too.
__________________
Jesse
'89 RV-4, N2626C - purchased flying
Converted to Fastback - Sliding Canopy - Tall Gear
Dynon Skyview w/ acc. & VP-x Sport
Catto 3-Blade (gen. 1)
Based: KPGD
Reply With Quote
  #3  
Old 03-15-2014, 05:18 PM
Pittsbuilder Pittsbuilder is offline
 
Join Date: Jul 2011
Location: Hampton, Ga (4A7)
Posts: 5
Default

10-15 lbs? Wow, that's a lot more than I would have thought. I might guess 5lbs more, but I wouldn't have thought 10+. I am not super concerned with tail weight as I am going to have an IO360 and CS prop up front that will help in that department.
Reply With Quote
  #4  
Old 03-15-2014, 07:15 PM
Michael Henning Michael Henning is offline
 
Join Date: Jun 2011
Location: Nashua, NH
Posts: 536
Default

The -4 tail is ez to build. The elevator & rudder skins are what are thin, and can be swapped out for thicker skin. I would do that and save the weight, especially if it is 10-15 pounds more(thats a whole lot of moment arm wayyy back there).
__________________
Mike
RV-4 #2750
N654ML
IO-360
WW150C Prop
1018 lbs
Flying
Reply With Quote
  #5  
Old 03-16-2014, 03:07 AM
WAM120RV WAM120RV is offline
 
Join Date: Dec 2006
Location: Coventry. England
Posts: 614
Default Digging yourself a hole?

Hi Michael,

I think you are digging yourself a hole. I love my 4 but if I am objective about it I would have built it lighter. In fact I am in weight saving mode at the moment.

The 'problem' with the 4 is that unless you build really light you are eating into both aerobatic and max weight limits. Also they tend to be tail heavy.

There is nothing wrong with the standard 4 tail, not all of them have cracking on the elevators and rudder. I suspect the larger 8 tail would leave it over finned and ruddered.

What would I do if I built another 4?

1. Fastback...... with you on this.
2. IO 340 or tuned 0-320 to keep the weight down.
3. Catto or light VP prop. ( they tend to need a heavy prop or weight at the front to balance the aeroplane. ( Another reason to avoid weight on the tail.)
4. Light weight battery.

Minimal panel weight, no strobes landing lights.

The 4 is a sports car, not a tourer!!!

Just my opinion!!
__________________
http://www.aerobuilder.blogspot.com


Steve Arnold
England

In completion stage of Loehle P5151
Built and now Flying G.BVLR Vans RV4
Rebuilt G.BDBD Tailwind
Rebuilt G BVTN Kitfox
Built G CDCD RV9A with WAM120
Riveted wings on Glastar G.LEZZ Now (G. SKUA)
Reply With Quote
  #6  
Old 03-16-2014, 08:12 AM
Tom Martin Tom Martin is offline
 
Join Date: Jan 2005
Location: Ontario, Canada
Posts: 1,544
Default

I built a RV4 with the standard tail. Then I built two HRIIs and used the RV8 tail rather then the RV4 tail.
The RV8 tail will bolt right on, the only modification is the need to raise the bottom forward tip rib of the VS. Depending on how high your fast back is you might not even have to do this.
In terms of flight quality, the larger counterbalanced rudder works very well with a HRII. It stopped that little tail wags the dog thing that sometimes happens with a RV4; YMMV. The elevators on the RV8 tail work on the HRII but would be better if they were a bit larger. I am sure that they would work just fine on a RV4.
The bad news, as others have mentioned, is added weight. OK for a HRII but no so good for a RV4 regardless of how big an engine you put on it. Weigh your RV4 tail and then weigh your buddies RV8 tail. Borrow some weight and balance records and run the numbers.
My advice would be to fix or replace your RV4 HS, fly with the control surfaces that came with it and if need be to build new control surfaces later with heavier skins.
If the HS is sound, and the "twist" is the same on both sides you could just fly with it and see how it behaves. Another complete tail can be built after you are flying your airplane and replace the original parts before final paint.

To answer your original question again. Yes, the RV8 tail will fit. It is your plane, recognize the options, and built it as you wish.
__________________
Tom Martin RV1 pilot 4.6hours!
CPL & IFR rated
EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
RV14 Tail dragger

Fairlea Field
St.Thomas, Ontario Canada, CYQS
fairleafield@gmail.com
Reply With Quote
  #7  
Old 03-17-2014, 06:10 AM
WAM120RV WAM120RV is offline
 
Join Date: Dec 2006
Location: Coventry. England
Posts: 614
Default Gain v loss

Hi

Another way of looking at this is gain v loss.

Purely in terms of aircraft performance you gain nothing by fitting an 8 tail but you loose useful load, aerobatic load.

Ok you will not have to build a new stab but if you search these threads a lot of people are struggling with the weight limits on a 4 trying to push a quart into a pint pot!!

The closer to 900lbs you can get your 4 the better, 1000 is acceptable but will put a 100lb reduction on what you can carry. I am lucky I am not a heavy guy 165lbs and my wife is light too. I can carry a 200lb person in the back seat and with full fuel I am at gross 1550 lbs in the UK.

I took a friend up for a flight yesterday and he summed it up just like me....a 4 is a sports car, build it and fly it that way.
__________________
http://www.aerobuilder.blogspot.com


Steve Arnold
England

In completion stage of Loehle P5151
Built and now Flying G.BVLR Vans RV4
Rebuilt G.BDBD Tailwind
Rebuilt G BVTN Kitfox
Built G CDCD RV9A with WAM120
Riveted wings on Glastar G.LEZZ Now (G. SKUA)
Reply With Quote
  #8  
Old 03-17-2014, 10:28 AM
Michael White's Avatar
Michael White Michael White is offline
 
Join Date: Jan 2005
Location: Cartersville, Georgia KVPC
Posts: 945
Default

Quote:
Originally Posted by WAM120RV View Post
....a 4 is a sports car, build it and fly it that way.
Perfectly put, Steve!
__________________
Moose
VAF #136
Reply With Quote
  #9  
Old 03-17-2014, 03:09 PM
AX-O's Avatar
AX-O AX-O is offline
 
Join Date: Jun 2005
Location: SoCal
Posts: 2,452
Default Don't do it.

RV-8 tail
Rudder = 8.5 lbs
V-stab = 8.5 lbs
H-stab = 17.5 lbs
L elevator = 8.5 lbs
R elevator = 8.5 lbs
Total = 51.5 lbs

RV-4
Rudder = 4.5 lbs
V-stab = 7 lbs
H-stab = 19 lbs
L elevator = 4.5 lbs
R elevator = 4.5 lbs
Total = 39.5 lbs

Difference of 12 lbs (the wrong direction). Part were not painted however, primed inside.
__________________
Axel
RV-4 fastback thread and Pics
VAF 2020 paid VAF 704
The information that I post is just that; information and my own personal experiences. You need to weight out the pros and cons and make up your own mind/decisions. The pictures posted may not show the final stage or configuration. Build at your own risk.
Reply With Quote
  #10  
Old 03-18-2014, 07:40 PM
nkd4flyr nkd4flyr is offline
 
Join Date: Jan 2005
Posts: 12
Default

I did it and it worked great!

Seems every few years this topic comes up.

I converted to the RV-8 tail about 4 years ago. Net gain on the T/W 3#.

After seeing the post from Axel I decided to confirm what I remembered from the conversion. So I dug out of storage my old RV-4 tail (built in 1995) weighed in at 44#, .016 skins on control surfaces, zinc chromate primer - no paint.

The 8 tail weighed 50#, epoxy primer! elevators balanced! farings on.

I used one of the pads from the digital scales that we use to weigh airplanes. They round to the nearest #. I came up with a difference of 6#, 7# worst scenario.

My 4 is equipped with an O/360 & Hartzell CS.

A friend of mine converted the same time. His 4 has an IO 320 with wood prop. He likes the conversion.

The most significant difference is: much more stable flight. I don't need any more down trim with a backseat passenger. I do 3 point landings - the flare is more like the 8. No loss in top speed.

The advantage of the 8 tail is easy to build compared to the 4 & it's going to be straighter than the 4.

Axel, it is a mystery to me if the elevators you weighed were balanced how they can weigh the same. Both the 4 & 8 elevators that I have weighed, there is a noticeable difference in weight between the right & left elevators. I used a bathroom scale to weigh the elevators individually.

Would I do it again. Yes.

We have 2 RV-4's in the shop being built with RV-8 tails.

Loyd
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 05:25 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.