Questions About Ballast

[kestrel]

The prototype 5 is built very light. The battery is a lithium super light thing mounted near the firewall inside the plane.

[...]

If you were to build with an IO-540 300hp and put a concorde battery in the tail, just aft of the baggage area, you would likely not need much ballast if any. If I was to build a 5 I would just put a concorde in the back it.

The cables to that Concord battery in the back may weigh more than the EarthX ETX-900. They will also cause voltage drop between the battery and starter. Put an EarthX up front. You can still also put a Concord in the back when you need the ballast and skip the long cables. ;-)

[zkelley2]

I would be very surprised if you could get even close to using all that useful load without the need for ballast when empty... and have stability in line with FAR requirements.(yes, I know as an experimental we can put our aft CG where it shouldn't be and "fly better", but that's not best practice.) Cessna, Piper and Beech can't do it with airplanes that size.

That is to say you could get the empty CG to a place where you don't need ballast solo, but you'll never be able to get 1500lbs in it without going well aft of where the aft CG limit should be with respect to longitudinal static stability. Unless you're carrying gold bars in forward locations.

[Collin Campbell]

Another thing I might add is that in refining the plans, Bob tells me he is going to tilt the firewall back (2 1/2") the same as the 4-place. (The prototype firewall is vertical) So this change will allow moving the engine back a bit...at least 1 1/2" or maybe 2". As it is now the engine is as close to the firewall as we could get it and still get the mags out. I am thinking most people will use the IO-540, which as Rollie mentioned is a bit lighter than the IO-580, so the need for any ballast will be lessened if not required at all. Having a tool box just aft of the baggage area for essentials would make a difference too. Speaking of the battery...we used the Earth X ETX 900, weighs only 5 lbs and that thing cranks the engine like you would not believe! 900 cold cranking amps...think it would crank my diesel tractor!

[way_up_north]

The empty weight does not include ballast.

The ballast in the model 5 was put there as a starting point to ensure the aircraft would stay inside cg limits that were set conservatively before flight testing began. Jared ended up removing half the ballast and the plane still flew fine without running out of elevator in the flare, which was a concern with a forward cg.

The prototype 5 is built very light. The battery is a lithium super light thing mounted near the firewall inside the plane. Also it has the IO-580, which is a bit heavier than the 540 I suspect most builders will use. If you were to build with an IO-540 300hp and put a concorde battery in the tail, just aft of the baggage area, you would likely not need much ballast if any. If I was to build a 5 I would just put a concorde in the back and also add a compartment for tiedowns and tool kit, also just aft of the baggage area since those are things I always have in the plane and don't want them taking up space in the baggage area anyway. Concorde batteries weigh around 30 lb, the setup I have in my Patrol for the tiedowns and tool kit weighs 5 lb, plus the 19 lb of tiedowns, tools and spare quart of oil brings it to 24 lb. Add a battery box and you are looking at close to 60 lb back there. The lightest the 5 has been tested was with 84 lb of ballast, if I remember correctly. The center of the battery would be a foot aft of where the center of the ballast box is, so that puts it very close to the same cg.

That's just how I would do it, I have no need to haul almost 1200 lbs of stuff with full fuel, if I were building a 4 or 5, it would be for the space, not for the payload. The ballast set up allows you to build light and maximize payload by working whatever ballast system you want to use. You could use jugs of water and dump the water out when you pick up a load, you could shift the ballast forward when you load cargo, but then you are still hauling the ballast so you really don't have the extra payload capability in that scenario.

As far as putting less weight further back in the tail, I asked Bob about that. I'm not an engineer but he is. He said adding any significant amount way back in the tail could make the plane unsafe, as in spin recovery might not be possible and some other good reasons that I can't remember but it made good sense not to try it.

I appreciate you posting and clearing up some questions..

A project like this operates on a lot of good will, I wanted to thank you for your time and effort with this...for myself and future builders. You're making possible a dream that just would not be possible without people like yourself and Colin Campbell. Also Mark Goldberg was instrumental in this planes development, he and Bob didn't have to offer plans...they could have had this as a factory only kit...and it would still sell like hot cakes..I really appreciate that they are willing to sell plans for this. I think its unique...I don't know of any other time a 6 place experimental thats scratch buildable...


so for myself and other future builders ...a big Thank you...Bob, Colin, Mark, Jared and yourself are the MVPs of the experimental world.

[Rollie]

The empty weight does not include ballast.

The ballast in the model 5 was put there as a starting point to ensure the aircraft would stay inside cg limits that were set conservatively before flight testing began. Jared ended up removing half the ballast and the plane still flew fine without running out of elevator in the flare, which was a concern with a forward cg.

The prototype 5 is built very light. The battery is a lithium super light thing mounted near the firewall inside the plane. Also it has the IO-580, which is a bit heavier than the 540 I suspect most builders will use. If you were to build with an IO-540 300hp and put a concorde battery in the tail, just aft of the baggage area, you would likely not need much ballast if any. If I was to build a 5 I would just put a concorde in the back and also add a compartment for tiedowns and tool kit, also just aft of the baggage area since those are things I always have in the plane and don't want them taking up space in the baggage area anyway. Concorde batteries weigh around 30 lb, the setup I have in my Patrol for the tiedowns and tool kit weighs 5 lb, plus the 19 lb of tiedowns, tools and spare quart of oil brings it to 24 lb. Add a battery box and you are looking at close to 60 lb back there. The lightest the 5 has been tested was with 84 lb of ballast, if I remember correctly. The center of the battery would be a foot aft of where the center of the ballast box is, so that puts it very close to the same cg.

That's just how I would do it, I have no need to haul almost 1200 lbs of stuff with full fuel, if I were building a 4 or 5, it would be for the space, not for the payload. The ballast set up allows you to build light and maximize payload by working whatever ballast system you want to use. You could use jugs of water and dump the water out when you pick up a load, you could shift the ballast forward when you load cargo, but then you are still hauling the ballast so you really don't have the extra payload capability in that scenario.

As far as putting less weight further back in the tail, I asked Bob about that. I'm not an engineer but he is. He said adding any significant amount way back in the tail could make the plane unsafe, as in spin recovery might not be possible and some other good reasons that I can't remember but it made good sense not to try it.

[auburntsts]

I'm not a Bearhawk builder (yet) or owner, but I'll give my $.02 as an RV-10 builder/owner.

-- Empty weight generally does not include temporary ballast, so you have to subtract out any added ballast from your useful load

-- If you change load configurations from one flight to the next (IOW add/subtract passengers, fuel, and/or cargo) you need to compilate a new weight & balance calculation for that particular flight and that would determine where you place any ballast or whether you would need any ballast at all.

-- Putting temporary weight in the tail is usually impractical for access reasons. The only time I've seen that was for permanent ballast to offset a particular engine installation, and even then that was the result of going beyond the original aircraft design.

-- IMO a water tank would add unnecessary weight and complexity to a build. What I do is use a 5 gal plastic collapsible water cube used for camping. Empty it weighs almost nothing but it allows me to add from 0 to 40 lbs in the baggage area on a whim. The beauty is I can fly out with it full and dump the water if I need to pick up passengers and/or stuff (or vice versa). At home base I don't leave it stored on the plane although I keep it filled in the hangar so I can use it as needed which is typically when I'm solo or with a co-pilot.

[way_up_north]

While we wait for the official numbers to be released

I had a few questions about ballast on planes that need to do that.

Keep in mind I`m a guy with just ground school and a few hrs in the air so feel free to educate me

The Bearhawk 5 prototype has ballast weight at the back of the passenger cabin (this may change....just using this as an example)

Questions:

-does the empty weight of 1512 lbs include the ballast as shown in the video

-as it is I guess you have to carry the ballast with you if youre not using it...if you flew with 6 people one direction and back with just you the pilot....you would need forward(near the CG) ballast storage area to keep these weights stored.

-could you put weights further back in the tail ....further away from the CG to equal that so you could use less weight(transfer weights from the back to front as needed) or is the fuselage/tail not strong enough to have weight back there

-or a water ballast tank in the tail ...filled up or emptied as needed...hopefully not frozen

Thanks
Way_up_north