As we all know the -4 has a rear cg issue. Has anyone ever thought of doing a bungee system for the counter balance to keep the elevator's in trail? I know the Sonex is rigged in this way and was just wondering if it has been tried or is there something I am missing? If we could remove the lead out of the tail that would be huge!
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Bungee's for elevator counter balance?
- Thread starter Jstov
- Start date
Steve Barnes
Well Known Member
No issues
If the plane is flown within the design and CG limits there are no issues. I have over 1400 hours in an RV4.
If the plane is flown within the design and CG limits there are no issues. I have over 1400 hours in an RV4.
I agree...but
To put a full grown adult male in the back seat and then get low on fuel you can get close to the rear cg limit. I personally know people who have a 150 or less weight limit on back seat passengers. If you can remove a little weight off the tail it would help.
To put a full grown adult male in the back seat and then get low on fuel you can get close to the rear cg limit. I personally know people who have a 150 or less weight limit on back seat passengers. If you can remove a little weight off the tail it would help.
Kyle Boatright
Well Known Member
You can not trim out pitch instability due to an out of range CG.
Kyle Boatright
Well Known Member
Aah, gotcha. The counterbalance weights are to prevent flutter, not to keep the elevator in trail. I don't think bungees are an appropriate solution for flutter prevention.
One thing you can do is keep the moment arm on the elevator unchanged but at a reduced weight by 'packing' it into the front section; e.g., use depleted uranium, which is more dense than lead. I suspect the weight savings is pretty small, but if you just need a little bit....
David Paule
Well Known Member
Study up on something called a "downspring."
Dave
Dave
I just read this accident report and have abandoned the idea. It shows the importance of weight and balance on control surfaces!
http://www.vansairforce.net/safety/G-GNDY.pdf
http://www.vansairforce.net/safety/G-GNDY.pdf
grubbat
Well Known Member
Learning
It's a good thing that you asked the questions before making changes and gained some knowledge that altered your plans. Imagine the poor soul who said in their mind, "hey it's expermential, I can do what I want". Kudos to you!
Cj
It's a good thing that you asked the questions before making changes and gained some knowledge that altered your plans. Imagine the poor soul who said in their mind, "hey it's expermential, I can do what I want". Kudos to you!
Cj
Weight issues?
Hi
Whether you have rear c of g issues will depend on your engine/prop set up. An 0.320 with a wood prop may come into that catagory, but putting your battery on the firewall will help this.
The main issue I have found with weight in a 4 is the max all up weight.We are allowed 1550 in the UK and its easy to hit this with full fuel and two on board.
I am 170 and can carry 193 in the rear seat with full fuel an am at max weight but no where near rear c of g. That is with an 0-320 and a sensenich metal prop.
Personally I would never alter control surfaces from what has been proven to work. I have put diesels in RV's so am not adverse to experimentation but there are limits.
You are right to start planning but as I say C of G is not really an issue provided you have the right weight up front.
Hi
Whether you have rear c of g issues will depend on your engine/prop set up. An 0.320 with a wood prop may come into that catagory, but putting your battery on the firewall will help this.
The main issue I have found with weight in a 4 is the max all up weight.We are allowed 1550 in the UK and its easy to hit this with full fuel and two on board.
I am 170 and can carry 193 in the rear seat with full fuel an am at max weight but no where near rear c of g. That is with an 0-320 and a sensenich metal prop.
Personally I would never alter control surfaces from what has been proven to work. I have put diesels in RV's so am not adverse to experimentation but there are limits.
You are right to start planning but as I say C of G is not really an issue provided you have the right weight up front.
I am installing an O-320 so weight up forward is important to me. I also
Plan on installing the battery on the firewall to help this. Interesting to hear that you can put that much in the back seat of your -4. From what I have heard it can cause very lightweight controls especially in the flare. I am used to this so I am not worried about it. I flew a sonex for years and that is a very light weight, pitch sensitive aircraft. Arlie installed an oil tank for a smoke system in the original battery location. I think that will be a great useful a weight addition up front! Add inverted oil and now we are really talking!
Plan on installing the battery on the firewall to help this. Interesting to hear that you can put that much in the back seat of your -4. From what I have heard it can cause very lightweight controls especially in the flare. I am used to this so I am not worried about it. I flew a sonex for years and that is a very light weight, pitch sensitive aircraft. Arlie installed an oil tank for a smoke system in the original battery location. I think that will be a great useful a weight addition up front! Add inverted oil and now we are really talking!
That's for trim, not flutter. Bungees won't help either. The weights change the natural frequency of the elevator, they are not there to keep the elevator near 0 deflection. The only other thing that could be done is to fit some sort of damper but that is way too complicated and probably not that much lighter.
I have a friend with a Christian Eagle who used to fly airshows. At Media days all the journalists wanted rides. He just insisted that he had a 135 lb load limit in the frint seat, which was total bull, to make sure he always got the slim female media people.
