Author Topic: Convert 391B to Same engine and prop as the H250?  (Read 406 times)

Flathorn

Convert 391B to Same engine and prop as the H250?
« on: July 01, 2021, 09:56:18 PM »
  Curious  if anyone has converted a 391 B to the same  engine/prop as used on the H250? Feasible? Possible with FAA with minimal difficulties?  Thanks

Doug Johnson 1

Re: Convert 391B to Same engine and prop as the H250?
« Reply #1 on: July 02, 2021, 04:36:06 AM »
There is a 'maybe it was done' on c/n 047

click on https://flyhelio.com/smf/index.php?topic=694.msg3664#msg3664

and there is a 'probably done' on c/n 073

click on https://flyhelio.com/smf/index.php?topic=721.msg3696#msg3696

There is no STCs of this mod or 337s of this because both were done outside the USA.

It might be approachable as a one time STC by getting all your facts together and presenting them to an FAA designated Engineer.

And even then probably best chance would be in Alaska region.

Plus 'Helio Alaska' is there and they would probably help you.
« Last Edit: July 02, 2021, 04:42:45 AM by Doug Johnson 1 »

Doug Johnson

Re: Convert 391B to Same engine and prop as the H250?
« Reply #2 on: July 03, 2021, 10:26:50 AM »
I was thinking about my previous post and realized i should have added more to that post because there would be some other modifications that would probably have to be done which is Helio mod #48 and #45 which were done on c/n 075, 086 and 087 by the  CIA to convert a H-395 with the higher horsepower and if you were going to convert to H-250 you might as well go with 300 hp IO-540

https://flyhelio.com/smf/index.php?topic=723.msg5527#msg5527

https://flyhelio.com/smf/index.php?topic=735.msg3718#msg3718

https://flyhelio.com/smf/index.php?topic=736.msg3719#msg3719

STCs for the 540 SA1643CE and SA1936CE

I will attach some photos that show what is involved in the 2 mods there is enough structural changes that you would need a lot of assistance from the owners of the type certificate.

so your original question. Feasible?  yes

Possible with FAA with minimal difficulties? unlikely even in Alaska.

Interesting topic though.

I believe the only way you could covert an H-391B to an H-395 or H-250 even though it has been done 5 times in the past would be with the assistance of the owners of the type certificate to develop an STC.

« Last Edit: July 04, 2021, 09:34:47 AM by Doug Johnson »
Doug

Doug Johnson

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« Reply #3 on: July 03, 2021, 10:28:32 AM »
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Doug

Flathorn

Re: Convert 391B to Same engine and prop as the H250?
« Reply #4 on: July 03, 2021, 10:26:14 PM »
Doug,

   My reasoning for the original question, was  not to change the airplane to an H250 but simply use the firewall forward from the H250 on the 391 B airframe.  It would be 10 less horsepower, so no additional stresses on the airframe. Would guess considerably lighter. No  changes in the gross weight. Readily available engine and prop components. Performance would hopefully be better than the H250 because of lesser empty weight. Just not the higher allowable gross weight of the  H250.  I am thinking it would be a pretty easy  bolt on application.   I chased the  300 hp  conversion STC for the H250 and came to a dead end with the FAA.  Can a person produce an "owner built STC" if the original STC is no longer available?

jmetzler

Re: Convert 391B to Same engine and prop as the H250?
« Reply #5 on: July 04, 2021, 07:36:53 AM »
You are correct in that the HP is less, so that wouldn't be a big issue. However, the engine mount is totally different as the 540 is a rear mount, not a bottom mount. The airbox, air intake, exhaust, baffles, engine instruments and Operating Handbook would be different. I'm not sure about the cowling, but I think there are some differences there too. If you had access to an H250 wreck you would be home free with the parts. The FAA issues are another story. I'm pretty sure it would require an STC and that is no easy task in today's world. It is an interesting direction to go though since the GO435 engines are getting very difficult to get overhaul parts for.

Flathorn

Re: Convert 391B to Same engine and prop as the H250?
« Reply #6 on: July 04, 2021, 09:02:11 AM »


     I do have an H250 we are putting back together, and in the process bought another H250 parts plane, fuselage only. Have a 391B major project also, and this idea crossed my mind, as the parts plane H250 would give me all the parts. Thanks for your input. Might be a way to keep more of the 391B planes in  the air. Probably a major problem with the FAA though , even though it seems a simple swap.

Doug Johnson

Re: Convert 391B to Same engine and prop as the H250?
« Reply #7 on: July 04, 2021, 09:25:34 AM »
Interesting after thinking about your question all day, I was hung up on increased horsepower and gross weight and was going to post about the fact that I had over looked c/n 010 a 6th Helio that had been converted to a prototype H-392 then reportedly an H-395, and another the H-291 prototype that became first the H-250 prototype then with almost no changes other than eng, the prototype for the H-295 and was later placed in the production line and became c/n 1231.

I was then going to bring up the fact you would still only have a 3000 lb gross weight and less thrust because of he eng prop combination and without the structural changes hat stringers in tail cone and an increase to .050 rear spar in wing, and heavier duty flaps and stabilator.

None of that really matters for what you are trying to accomplish Jim mentioned the 250 cowling and it is different, the eng mount is 6 inches longer to move the lighter eng forward and maintain CG limits, so of course you need a 6 inch longer cowling, no big thing make one out of fiberglass. The Helio O-540 motor mount there are a few around from wrecks and GO-480 eng conversions. Or go to Abe at 'Helio Alaska" and get a print and have one fabricated. I think going with the MT composite prop would be the way to go also, take some weight off the nose although it might be worth making the cowling a bit longer if fabricating the mount from scratch.

If you went for a one time STC using a DER assigned to you by the FAA and the Help of the guys at 'Helio Alaska' it might turnout to be relatively easy, You are just doing what the Factory did once before, just not going for the increased gross. The difficulty I see is writing the manuals both pilots and maintenance for the new model of Helio. Will it be an H-391C eng variant or would it be an H-250B four place variant. I think you might spend a lot of hours finding the a/c limitations, maybe not.

As jim said it is an interesting direction to take, and might put some life back into Helio and be an affordable option with probably more performance than the straight H-250.

I think it is well worth researching with the right people. And with all those H-250 parts in your possession it makes it even easier. For what its worth that's my opinion.
« Last Edit: July 04, 2021, 09:58:43 AM by Doug Johnson »
Doug

Flathorn

Re: Convert 391B to Same engine and prop as the H250?
« Reply #8 on: July 04, 2021, 09:58:50 AM »

    Thanks  Jim and Doug.  This all brings up the other related subject which is the prop.  I will be needing a prop for the 250 .  Any info  around about an MT prop for the H250?  Who to contact?   One more step , glass panels engine and flight in Helios?

Flathorn

Re: Convert 391B to Same engine and prop as the H250?
« Reply #9 on: July 04, 2021, 10:04:29 AM »


   Forgot one of my earlier questions.  Can an unsupported STC  be " owner produced"?  If no longer available and no other source if you have all the original information?

Flathorn

Re: Convert 391B to Same engine and prop as the H250?
« Reply #10 on: July 04, 2021, 10:58:33 AM »


Another  question out of my ignorance.  I was looking through the book  " The  Helio Courier  Ultra C/STOL  Aircraft "  by  Frank  Rowe.   Under the 391B there is shown a gross  weight,  Gross, Agricultural  3500 lbs.   What is that all about?  Spray plane?   On page  74 in the book.

Doug Johnson

Re: Convert 391B to Same engine and prop as the H250?
« Reply #11 on: July 04, 2021, 11:11:22 AM »
I think you can find your prop info on who to conact here
https://flyhelio.com/smf/index.php?topic=1433.msg6832#msg6832

I think you can basically repeat the requirements for the previous unsupported STC
as a one time stc, but I think you need to talk to a designated engineering rep
on how it works.

I thing your 3500 gross is actually restricted category 8 check out this link about H-391B, c/n 099.

https://flyhelio.com/smf/index.php?topic=475.msg2481#msg2481

But what it doesn't say is that you can put your aircraft into and remove it from cat 8 with a log book endorsement. But if exceed any of the cautions you are required to do an inspection of the aircraft not sure what category of inspection. I suggest you read the category 8 rule.

« Last Edit: July 08, 2021, 09:51:52 AM by Doug Johnson »
Doug