Author Topic: The H-391B model Helio as of 01/19  (Read 559 times)

Doug Johnson 1

The H-391B model Helio as of 01/19
« on: January 23, 2019, 11:29:44 AM »
I intend to do this with each category of the airplane and we can start here

                                        H-391B and those converted to H-395A
Don’t write off the H-391B yet. There are 23 H-391Bs still around which is 22.55% of 102 built, 18 in the US, 5 in Canada, 6 of them are projects and one of those is an experimental made from Helio parts see c/n 103, and 4 other possible projects are around 1 in Canada, 1 in the R/Philippines, and 2 in the US.

The "H-391B Model" was the first model to continue to a production run and with its  Controled/STOL, crash-cage/fuselage and all aluminum fuselage the template for all Helios. 102 built

All but 6 have been converted to H-395A configuration with removal of the exhaust augmentor and installation of larger cowl flaps (Helio mod #48). This removal of the augmentor makes the Helio considerably louder my understanding is that the 6 that still have the augmentor the perforated aluminum has been replaced with stainless steel which doesn’t erode and cuts done on maintenance. They are also considerably quieter a/c.

The first H-391 that the exhaust augmentor was removed on and the cowl flaps removed was c/n 044

C/n 032 and up, gross wt increased from 2800 to 3000 lbs (Type Certificate was amended) previous c/ns require Helio Mod # 21 to replace all landing gear, and some structural modifications to increase gross wt.
Of those left only 001, 011, 028, and 029 are affected.

Helio mod #45 was basically a conversion of the fuselage/crash cage to H-395 configuration which was done to c/n 075, 086, 087 and experimental 103 and one H-391 was also converted to H-250 configuration. This is only practicable on a total disassembly type upgrade, and if doing that you might as well upgrade to 3800 lb gross at the same time, by putting heavier wall diagonal tubing in the upper and lower fuselage bays as was done on the 7/800 models, this is actually lighter than the 3800lb upgross STC, by this time you have entered the experimental configuration area or at the very least the onetime STC area.

Actually, the Helio is quite strong so why not place yourself in category 8 and fly overgross which is legal it mostly means that you use caution and reduce your maneuvering speed if you encounter turbulence you slow down. It also requires you to inspect the aircraft and landing gear if you land a little hard. But you do that anyway don’t you.

The factory options included an easily removable 25-gal fuel bladder for extended range to be hung in the baggage area. The extra fuel bladders in the outer bays of the wing didn’t come along until the H-395 which also required a heavier rear spar in the wing. Another factory option was mufflers to be installed inside the cowling alongside the engine my understanding was that this quieted the aircraft even more than the exhaust augmentor alone and removed the annoying rumble vibration in the floor caused by the exhaust augmentor.

Another thing that can be done with all the Helios is pull out all the old glass wool type insulation and replace it with sound proofing insulation the easiest is ¾” on the underside of the headliner and 1’’ under the floor covering. next at least ¾’’ behind the cargo area, then 2’’ replacing the covering on the firewall. The hardest is gluing ¾’’ inside the doors and all the other surface on the sidewalls. It is amazing how much quieter and warmer the a/c becomes.

below are the history paragraphs of the H-391s still in service

« Last Edit: February 03, 2019, 08:18:26 PM by Doug Johnson 1 »


Re: The H-391B
« Reply #1 on: January 23, 2019, 01:51:08 PM »
There are 4 H-391B's currently in residence in the US.

N100HC, N4121D, N4138D, and N4139D respectively.

The big issue with 391B is the dinosaur of "geared" Lycoming's the ill-fated GO-435-C2B2-6, try to find an overhaul facility to work on these is nearly impossible. One place might be Central Cylinder in Omaha, NE

The hubs and gear boxes are essentially very life limited, as well as the AD's on the Hartzell 101" 2-blade



Re: The H-391B
« Reply #2 on: January 23, 2019, 03:12:40 PM »
The FAA Registry shows 18 H391B's registered in the US. Most will have the replacement prop that Hartzell offered installed that does not have the AD on it.

Doug Johnson 1

Re: The H-391B model Helio as of 01/19
« Reply #3 on: January 23, 2019, 03:57:42 PM »
There are 18 H-391Bs registered in the US, 5 registered in Canada, 6 projects and the one experimental being assembled from parts. there are 4 other possible projects around 1 in Canada, 1 in the R/Philippines, and 2 in the US.

I don't think the prop will be an issue because of the Hartzell 101'' HC-A2MV20-1A/V10133N prop being available. I also think their is an MT option at least a person I was talking to that was fairly knowledgeable believed there was or could be by going the one time STC route.

I also believe there are more GO-435s around they are just hard to find. Just do an E-bay search for the Lycoming GO-435. They are a fairly popular engine for Air Boats here in Nebraska more Airboats here than Florida. Probably why they are still being rebuilt at Central Cylinder in Omaha, NE

If the engines become impossible to find, I would imagine the H-391 becomes really cheap and it becomes affordable to turn them into H-395s using Helio Factory mod no. 45.

« Last Edit: February 01, 2019, 02:10:41 PM by Doug Johnson 1 »


Re: The H-391B model Helio
« Reply #4 on: January 24, 2019, 03:01:48 PM »
My H-391B is still in service. Serial #28 N12620. It has the prop with the AD and I would love to get rid of it as well as the GO-435 (I love the engine but would like a more practical and long lived solution). Can I (legally) modify mine to a 395?

Tim McNamara MD


Re: The H-391B model Helio
« Reply #5 on: January 24, 2019, 03:29:54 PM »

I believe Helio mod 45 lets you upgrade to a GO-480 but no increase in gross weight, you are still @ 3000 LBS.

« Last Edit: January 24, 2019, 03:33:48 PM by tailhook »

Doug Johnson 1

Re: The H-391B model Helio as of 01/19
« Reply #6 on: January 24, 2019, 03:52:40 PM »
Tim, I apologize for overlooking you good thing I have edit privileges for my own posts. I went back and made the correction.
according to the FAA records your Helio has been converted to a H-395A which happens when remove the exhaust augmentor and install larger cowl flaps. But.....

To convert to just H-395 and install a GO-395 is a big project and the Helio Factory is the only one that can legally do that using Helio mod #45 which requires lots of strengthening to the crash-cage/fuselage and a bit to the tail cone. There was never a STC to do this./

The only way you could do it now is go experimental and completely disassemble the airplane.

look at this previous post
« Last Edit: February 01, 2019, 02:11:19 PM by Doug Johnson 1 »


Re: The H-391B model Helio
« Reply #7 on: January 24, 2019, 05:37:34 PM »
Thanks guys (Stephen and Doug),

Yes the exhaust has been modified but I'm still at 2800lbs gross I believe. At the light weight it performs really well and is a joy to fly. What's required to get the 3000lbs increase?



Re: The H-391B model Helio
« Reply #8 on: January 24, 2019, 05:52:24 PM »
You answered my own question (read about my airplane above) without me digging out the logbooks. It does have the 3000#  increase. BTW, I really appreciate the effort you put into keeping this information out there and sorted!


Doug Johnson 1

Re: The H-391B model Helio as of 01/19
« Reply #9 on: February 03, 2019, 08:21:59 PM »
edited the list above and the count is 23 are left 18 in the US and 5 in Canada. I think I am still missing  a history file.

I had left 045 out in the previous list.