Van's Air Force
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Emp ??
- Thread starter Jaypratt
- Start date
smokyray
Well Known Member
Can be done...
Jay, my buddy Arvil put an 8 tail on a -4 with a few mods, it can be done but looks out of proportion. However, I happen to have a partial RV4 kit with a completed empennage and another empennage kit. Also have a wing kit, canopy, fuselage kit etc. Let me know what you need...
Smokey
863-397-1657
PS: Parts trades are cool too...
Jay, my buddy Arvil put an 8 tail on a -4 with a few mods, it can be done but looks out of proportion. However, I happen to have a partial RV4 kit with a completed empennage and another empennage kit. Also have a wing kit, canopy, fuselage kit etc. Let me know what you need...
Smokey
863-397-1657
PS: Parts trades are cool too...
SportAvServ
Well Known Member
8 tail
I spoke to one of the engineers at Van's about this, he was less than enthusiastic. He said because of the size there would be no gain in performance, and because of the weight would not help the CG. Nothing but detrimental effects. Bummer too, wanted the pre punched thing.
RT
I spoke to one of the engineers at Van's about this, he was less than enthusiastic. He said because of the size there would be no gain in performance, and because of the weight would not help the CG. Nothing but detrimental effects. Bummer too, wanted the pre punched thing.
RT
rvbldr3170
Active Member
EMP ??
The RV-4 CAN be really tail heavy with an O-320 and a wood prop even with the stock empennage.
I would look at this mod with very scareful consideration
The RV-4 CAN be really tail heavy with an O-320 and a wood prop even with the stock empennage.
I would look at this mod with very scareful consideration
RV4
I bought a RV 4 that was a bute. It was tipped over there is damage to the empennage and canopy. I was thinking a prepunched 8 tail would be easier to build to replace. I see it will be too heavy. I am going to look at some pre built ones that are out there. My standards are high. I may have to build a new one my self. I am in Texas so if there are any 4 emps here I would like to see those first.
Thanks
I bought a RV 4 that was a bute. It was tipped over there is damage to the empennage and canopy. I was thinking a prepunched 8 tail would be easier to build to replace. I see it will be too heavy. I am going to look at some pre built ones that are out there. My standards are high. I may have to build a new one my self. I am in Texas so if there are any 4 emps here I would like to see those first.
Thanks
tikicarver
Well Known Member
Funny he would say there is no gain in performance. I need to replace the tail on the RV4 I bought. I have talked with a few local RV builders. They said the older RVs (mine is a 1986) had problems with yaw. They recommended the RV8 tail because it is bigger and it is pre-punched so would be easier to build. 0ne guy said at some point Van enlarged the tail, but he wasn't sure if the current -4 tail is larger than the original plans.
I would like to know what the weight and dimension difference is between the -4 and the -8 tails.
Tom Martin
Well Known Member
The RV8 tail will fit on a RV4 as I have used them on two HRIIs. The extra weight comes from the larger surfaces and the counterbalanced rudder. There is no reason that you could not cut some height off both the VS and rudder and eliminate the counterbalance. This would not be a difficult modification. This would also give it a more balanced "look" with the RV4. Compare the size of a RV4 rudder wiht that of a RV8 before you purchase as you would not want to have less rudder. I believe the 8 rudder may not have as much chord as the 4.
The C.G. the airplane is flying at has some effect of yaw stability. The further aft the C.G. is, the lower the pitch and yaw stability will be. The only reason someone might say that older RV-4's had a yaw stability problem was that most of the older airplanes had wood propellers. Couple that with a big size buddy in the back and the airplane is likely flying with a C.G. at the aft end of the C.G. range. It is not nearly as much of a problem with a fixed pitch metal or a constant speed prop. Add weight to the tail (with a heavier emp.) and the C.G. will move further aft, possibly negating any improvement gained by the larger vertical stab.
The RV-8 emp is heavier because the rudder and elevator skins are .020 thick instead of .016. Because the elevator counterweights are heavier for the thicker skins. Because the vertical and rudder is larger, and because the rudder has a counterweight.
The size of the vertical tail on the RV-4 has never been changed.
I don't know if anyone knows what the actual weight differences of the two emp kits is, but even if it is only 4 pounds or so, that is a significant moment value that should be taken lightly
Last edited by a moderator:
AZtailwind
Well Known Member
So now my questions: is the 4 vertical/rudder the same as the older 6? I see that vans has seperate parts for the 4 and 6?? Also the older non-Counter bal 6 is pre-punched just as the new 6/8 is according to the parts list:
R-601-1 RUDDER SKIN C'BAL 016 $118.08
R-601PP RUDDER SKIN NON-C'BAL $111.36
I have a fairly decent 6 vertical/rud but I would prefer to build a newer 6/8 Vert for my project.
Mike S
Senior Curmudgeon
I don't know if anyone knows what the actual weight differences of the two emp kits is, but even if it is only 4 pounds or so, that is a significant moment value that should be taken lightly
I think (Hope?) you mean "NOT taken lightly"
I don't know the exact dimensions of each but I think they are very close to the same surface areas. What I think is different is the spacing between the fwd and aft spars between the 4 & 6 (I would have to look at some plans to be sure). If they are close then they could probably be made to work though the fit of the emp. fairing is anybody's guess.
It was a little play on words (note the winky guy at end), I guess I didn't do a very good job...
Jim Mockley
I'm New Here
RV4 Emp. Kit
I have an RV4 Emp. Kit which is taking up space in my garage. Make me an offer...It must be removed from my location in Portland, OR.
I have an RV4 Emp. Kit which is taking up space in my garage. Make me an offer...It must be removed from my location in Portland, OR.
Dean Pichon
Well Known Member
I know of a -4 with a -8 tail
There is a -4 with a -8 tail in Nashua, NH. It has been flying for some years this way and appears to do so without issue (IO-360 w C/S prop). To someone familiar with -4's, it appears to have a larger tail, though I doubt most would notice without a "normal" -4 available for reference. I actually like the larger tail, but I used to have a Citabria so I have a soft spot for big tails. I recently built a new rudder for my -4 and would have appreciated a pre-punched kit!
There is a -4 with a -8 tail in Nashua, NH. It has been flying for some years this way and appears to do so without issue (IO-360 w C/S prop). To someone familiar with -4's, it appears to have a larger tail, though I doubt most would notice without a "normal" -4 available for reference. I actually like the larger tail, but I used to have a Citabria so I have a soft spot for big tails. I recently built a new rudder for my -4 and would have appreciated a pre-punched kit!
tikicarver
Well Known Member
I went out an measured some airplanes this weekend.
I had access to a -6A, -8 and 9A and I have plans for the -4.
This is what I found:
The 9A is totally different than the others, it has a "hershey bar" shaped H-stab. So, I only compared measurements of the -4, -6, and -8.
The H-stab on the -6A and the -8 seem identical. the elevators also measure the same. On the -4, the only difference is the tip of the H-stab is a little narrower, but the root is the same and the length is the same. This results in the -4 having a little more sweep back to the leading edge. So that would mean a little less surface area.
On the rudder, the -4 and the 6 measure about the same. On the -8 rudder, the bottom is the same width but it is taller. it also has the counter weight on the top. It looks like they just extended the top enough to include the counter weight.
Again on the V-stab. the -4 and the -6 look the same. The -8 is has the same measurement on the bottom of the V-stab, but it is taller.
Keep in mind i just did quick measurements with a tape measure. it would be interesting to compare the distance between the actual ribs on the -8 plans.
If someone has a set of -8 plans, and they can send me some of those dimensions, I will compare them to the -4 plans.
Without more details, I would say in general, if you put an -8 tail on a -4, you would have about the same surface area on the elevator and a little more on the H-stab. If you mod the -8 rudder and V-stab to leave off the counter weight, then you would end up with about the same size V-stab and rudder as a standard -4 and you would have pretty close to the same weight since you removed the counter weight.
I had access to a -6A, -8 and 9A and I have plans for the -4.
This is what I found:
The 9A is totally different than the others, it has a "hershey bar" shaped H-stab. So, I only compared measurements of the -4, -6, and -8.
The H-stab on the -6A and the -8 seem identical. the elevators also measure the same. On the -4, the only difference is the tip of the H-stab is a little narrower, but the root is the same and the length is the same. This results in the -4 having a little more sweep back to the leading edge. So that would mean a little less surface area.
On the rudder, the -4 and the 6 measure about the same. On the -8 rudder, the bottom is the same width but it is taller. it also has the counter weight on the top. It looks like they just extended the top enough to include the counter weight.
Again on the V-stab. the -4 and the -6 look the same. The -8 is has the same measurement on the bottom of the V-stab, but it is taller.
Keep in mind i just did quick measurements with a tape measure. it would be interesting to compare the distance between the actual ribs on the -8 plans.
If someone has a set of -8 plans, and they can send me some of those dimensions, I will compare them to the -4 plans.
Without more details, I would say in general, if you put an -8 tail on a -4, you would have about the same surface area on the elevator and a little more on the H-stab. If you mod the -8 rudder and V-stab to leave off the counter weight, then you would end up with about the same size V-stab and rudder as a standard -4 and you would have pretty close to the same weight since you removed the counter weight.
Except for the RV-8 skins being thicker, (more weight) and the elevator counter balance weights being heavier (for two reasons; more weight required to balance the heavier skins, and the RV-4 elevator counter balance arms are longer which requires less weight to balance a given size elevator.
tikicarver
Well Known Member
true that the skins are a little heavier. However the elevator counter weights are probably not very different, with a longer arm you don't have to add weight to balance out a slightly heavier elevator. .016 skins weigh .23lbs/sq ft and .020 skins weigh .288 lbs/sq ft. Doing a little rough math and one side of the elevator in .020 skins would weigh about .5 lb heavier than a .016 one. So you could use the same counterweight and move it 3 inches forward. Interestingly, my measurement showed the -8 tip is 3 inches wider than the -4, so that moves the counterweight 3 inches forward.
So, without the rudder counterweight, the only remaining issue is that the -8 tail would be about 2.5 lbs heavier because of the skins.
That is not much difference considering there are several other things that effect the overall CG of the aircraft. The engine, prop and accessories you choose will have a big effect.
So, without the rudder counterweight, the only remaining issue is that the -8 tail would be about 2.5 lbs heavier because of the skins.
That is not much difference considering there are several other things that effect the overall CG of the aircraft. The engine, prop and accessories you choose will have a big effect.
Actually the counterweights are quite different.
The distance from the hinge line to the center (approx. C.G.) of the RV-4 elevator counter weight is about 10 inches, but on the RV-8 it is only about 7 inches.
Because of this, an RV-8 with .020" skins has counter weights that are more than 30 % heavier than those required on an RV-4.
