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H700 and H800 gear legs

Started by JamesCaird, August 14, 2023, 07:45:39 AM

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Hi Guys-  Can we have a discussion about the H700 and H800 series main gear legs?  I am interested to learn what the design ideas were and why the  295 style gear legs were not used.  I have seen some H800 which have reverted back to the 295 design.  Was it a question of materials?  Why was the gear length/height altered?  I remember Louis has remarked how the shorter gear height reduced AOA and the consequences of that.  What have others with 700/800 Helios experienced?  Thoughts? Cheers/ JC


The legend about it, as told by M. Montgomery, was that the Helio at the time of the 700-800 was run by an ex-Cessna guy.  So instead of beefing up the 295 landing gear for the extra 400 pounds ( remember that a 295 original gross weight is 3400 pounds, and the 800, 3800 for landing, 4000 pounds for take0ff ) he did choose to use straight spring gear legs.   Like a Cessna.  Except it was made out of fiberglass.

Also, on these airframes, he did hope to convert them to tricycle gear.  So the airframes of the 800 were made with a provision to move the landing gear in the back, like a tricycle 295.  They didn't have the time, or didn't figure out how to make the front gear.  A 295 landing gear type with a shock absorber would have been difficult to design so it could had move in the back of the CG to make it a tricycle. It was easier done with a fix non-schoch absorber legs.

By removing the big travel of the landing gear of an Helio, you do lose on take-off the possibility of gaining some AOA as you accelerate.  And you surely lose some absorption when landing.

There was some concern that the fiberglass legs were delaminating  I don't think it is true.  The chain of events that brought that was a couple of landing gear collapse.  But i did have one of those collapse and the chain of events was not the failure of the legs.  It was the steel box on which the shaft of the wheels was attached.  This steel box was badly welded.  So it did bend an open up, and then the fiberglass legs would go into the ground and delaminate.  I am not sure it would have delaminated id there was still a tire attached to the leg.

Some kind of notice was issued by Transport canada about this welded box, but i never found it again to post it here.

There were of course that stronger aluminum legs as an STC to replace the fiberglass one. Less springly and more comfortable. 

What else to say ?  The shaft that held together the motor mount, the landing gear, and the airplane frame was a little different.  In a 295, the legs will rotate at this shaft.  So you need a way to grease it.  And the shaft is usually side bolted in place so the shaft won't turn inside the engine mount and airplane frame.  It will be the leg that will turn slide around the shaft.

In a 800, the legs do not turn on the shaft. The landing gear is fixed except for the deformation of the fiberglass.  Like a Cessna.  So the shaft has two bolts on each side, and you tighten them as strong as you can so it won't move on the shaft.  The dowel-shaft is not hollow. It is solid.  The shock absorber is replaced with a fix adjustable big turnbuckle-like bolt.

If you do replace on a 800 the fixed landing gear with a moveable 295 type, you have to consider to change also the shaft to make it work like a 295.  Not like a fixed non-rotating 800 legs.  So you do have something else to work on than just but back a shock absorber.


Thanks, Louis, for sending that.  As you know I had H22 which is an H800 from the factory.  I am not sure how it came off the production line gear-wise but eventually it got to David Maytag in Scottsdale who was using it as a test bed for a number of different engines.  Later it was sold to Pima County Sheriff's department and with an RR/Allison 250 B17c engine it was flown by them for 7000 hrs with a camera system.  Initially it had the 295 type main gear legs forward with the shock absorbers connected to the center structure.  What they told me was that the pilots could not keep it on the runway landing but I think they were landing it at 6o kts all the time.   They converted it to tri-gear with the Cessna spring gear legs and nose wheel like an HT-295.  I have a pair of those original fiberglass "Clubs"  but never tried them. I don't know why more tailwheel 700/800 owners don't go back to 295 gear.  FAA?  as you say, the 700 and 800's are built with the gear leg provisons for tail wheel or tri gear and the back end has the fixtures for the tailwheel assembly.  maybe not enough of them?  How many remain? 


Once i was touring with my flying Winnebago.  Sleeping in it at airports. And i was at that airport where your plane was flying.  Another one if i remember.  Both turbines ?  I don't recall. Maybe one was tri-gear and the other one was a tailwheel.  I wanted to go see them in the morning, at their hangar, but it was like a secret operation and i wasn't allowed to look at them. 

Afterward, i met a sheriff that was explaining to me that it was full of some kind of cellular data grabber equipment.  A program across the state that would grab cellular connection.  Useful afterward for criminal investigation.  They were flying with some kind of exception certificate of airworthiness for police purposes, but then they were starting to have problem to get insurance for the person on board.  Flying 7000 hours starting to be not an exception.  At another airport, they was another plane, maybe a 207, doing the same mission.

FAA surely.  But also it isn't a simple task to switch a 800 landing gear for a 295.  With yours, with the lightness of the turbine, no problem.  But with that big 8-cylinder 800 engine in the nose, the 295 legs might be not strong enough.  You also have to equip your firewall with the bumps that the shock 295 shock absorbers need. They ar enot there on a 800 firewall.  I don't know how much a fiberglass landing gear weight against the 295, but if i remember when i was tossing them around, the 800 landing gear looks like double the weight.  It is probably stronger than a 295 gear.  It has to be .  This airplane was so nose heavy.

Here we use 210 i think for the cellular grabbing mission.  Two of them.  When there is a party of bikers, the fly over them all day.  I don't know if they push for IFR in bad weather.  But i am always scared something happens to them.  We had anti-poaching plane like that, and one night in bad weather, they died.  After that , it wasn't allowed anymore to fly IFR at night with a police exception paperwork.


Thank you again, Louis.  The two surveillance Helios were N613SD (#1709) and N400HE (H22).  #1709 came to Arizona as an HT 295 with a GO-480. After some demonstration of Camera systems from Bob Mickelson of (name escapes me- Sky Vision or something like that) they sent it to Steven Murray at Carlsbad, CA, to add the Camera system and others.  They operated mostly at night with regular missions tracking and /or following bad guys. They also had Lo-Jac which allowed them to follow a tagged vehicle.  After some time with the GO-480 they converted N613SD (1709) to the Allison 250 turbine.  After some time they acquired N400HE (H22) from David Maytag  and put the same Allison 250  on it. They hangared the airplanes during the day and most missions were at night and typically at 7000MSL, 70 knots for 5+ hours.
Eventually they had some insurance problems with lawyers getting in the way and these Experimental/Public Use certificates now had more that 10,000 hours between them.  The flight wing of the PIma County Sherriff's Departement seemed to have no end of  $$$$. (Drug busts, I presume?) So they had to let the trouble free Helios go and replaced by Cessna 206 with Soloy conversions.  I think they now also have Caravans.
After all that I can say that the Allison 250 in H22 was well done, looked good to my eye and was trouble free.  In cruise it would burn about 20GPH for 110-115 kts.  It liked it up around 10-12,000 ft. Take off was about 7 seconds- from non aggressive power in to 31kts/rotate I would climb out at 37-38 kts if necessary.  it also has Beta so can make for a very short landing roll. I liked to bring it down final at 45kts and let it slow at the numbers. Very sweet airplane and often a Show-Stopper at flyins, especially on the Amphibs because it was so tall.
   Landing gear-for the 295 shock absorbers on the fwd mains:  You just need to add the tabs on the center tube for attachment. Not sure about the firewall bumps.  I know what you mean.  Will look in #1709 today. H22 fit the shock absorbers and  all in there. For weight to Allison 250 is 206 # where the go-480 is something like 450#? Naturally the Allison is hung out ahead further to get the CG correct. 


What a beautifull and intelligent conversion to put an Allison there !!

Do you know why they only want now turbine airplane for those mission ?


You have the Beta ?!

Wow !

Change evrything.  The only thing i found on the Pilatus on floats, is that i have to wait until using the reverse.  The nose is long, and it was cartwheeling if i would put the reverse before the flaots have settle into the water.  A strange feeling.  Now i wait a little before using the reverse.  Anyway, i don't know why i use it.  I always have plenty of space in front.  Probably a case of , well, why not ?

Wich bring me to ask you if you have a propeller lock.  To be able to start the turbine without eating the plane in front of you on the dock.  You probably saw that youtube with a caravan eating a Otter in front of him.  And how you do manage to close the turbine at the dock.  Took me some time to undestand how i could use the turbine to park at the dock and shutting it down without eating the plane in front of me.  But may be the Allison is different than a PT6


Allison 250 in the Helio?  Not sure-  maybe David Maytag gave them some advice as he had tried a number of engines, recip. radials and turbines. The guy who orchestrated the Helios and the Turbines for Pima County was Rick Pearson, an officer there  but also a knowlegeable Helio guy.  I think he had a friendly relationship with David Maytag. The Allison 250  does not overdo it, I don't think but some folks might always want more power. Some variants are rated to 450HP. Helio actually did an Allison 250 B15 way back in the 60's.  It ended up in S. America but brought back to USA  and may be with the Perrys now.
   The Beta range:  I never tried very much to back up but was quite natural to pull beta to stop on landing.
As you know when you close the fuel to shut down, the pitch control goes to max so you have to be ready with brakes or dock lines or enough room to handle it when on floats. It will shoot ahead 20 ft. When you start you have to be headed in the clear like any float plane.  Can't put a brake on the prop.  Don't think that would go well.


On the PT6, when docked, you can just put the prop at zero thrust and shutdown the fuel.  The prop will turn a long time but you will not have that pushing forward movement.  Then many are equipped with prop start lock that will engage by itself at that position.  When starting the engine, there in no forward thrust.  You have to put it in reverse a little, and then the lock pin will disengage and the prop will be able to pitch for forward thrust.  On a Caravan, i think it is by STC.


Back to the gear legs:   on Helio #1709, which is a factory tri-gear, the firewall has the bumps to give room for the hydraulic shock absorbers.  The center tube at the bottom of the firewall is there but it does not have the attachment tabs for the bottom end of the shocks.  Back aft, the after most bulkhead is not re-enforced and does not have the attach points for the tailwheel shock.  Just forward of that on the tailcone sides there is no re-enforcement for the A-frome bolts.   Those are rather small details in the overall construction.  I guess I am surprised they did not allow for a fairly easy gear swap in the future.


What is the prop on your turbine conversion ?


96" Hartzell.  Don't remember the model.  They go from almost flat pitch in Ground Idle,(or actual flat pitch when you work at it.)  But when you shut down or flame out the prop governor runs it to full feather.  So on shutting down, say, going from flat to full feather the prop goes all the way from fine pitch to highest pitch which is why it tries to yank you ahead.


Then this is the big difference with mines on the Pilatus.  When shutting down the engine, the POH also ask to pull the prop lever.  Thus going from flat pitch to coarse.  With the forward surge. Something about changing the oil in the prop governor.

But when on floats, the power lever is put to flat pitch, and the prop lever is left untouched.  When shutting down the turbine by the fuel lever, you don't touch either the prop or the power lever.  Then the prop hold itself at flat pitch and there is no forward surge movement to the plane.  Handy on a dock because instead of shutting down the engine before the dock, you can use forward and backward to park like a car.  After an hour of the shutting down, the prop loose the oil pressure and go back slowly to coarse feathered.

Caravan and turbine modified Beaver and Oter are like that too.  At least the ones with Pratt PT-6

After that, for starting it depends if you have the prop lock or not.  Stc by Harztell for some planes.  The way it works is that there are three pins with spring that pushes them to lock the prop at zero thrust. The springs push them in place when the prop will turn slowly enough.  It is the centrifugal force that holds them outside of the lock.   So when you will start the turbine, the prop will be already flat, so there is no surge forward movement when passing from feathered to zero thrust.  To remove the lock, a small beta position of the power lever  once the prop is turning and the centrifugal force will slide the pins out of the locks hole. 

To park at the dock, it is perfect.

To start the engine at the dock, you have to look at the blades to know if the lock was locked. ( Shut down at zero trust.) If they are already at zero, you can take a chance of starting the turbine with the nose pointing at another plane. Because this is an indication that the locks are in place.   I prefer not to.  To stressful and so easy to turn the nose toward free space.  I would do it just for flashing and leave the dock in reverse.  I will try it when i will be younger. 

After that, you really have to unlock it by putting the power lever to beta.  Because if you apply power with the pin in place in their lock holes, you simply sheer them.  They will break and the lock won't work anymore. 

Here is what Hartzell say about it.  They call it start-lock:

PIQUA, Ohio – February 18, 2004 – Hartzell Propeller Inc. announced today that its increasingly popular high performance three-bladed Top Prop™ propeller kits for the 208, 208A Caravan and 208B Grand Caravan are available with optional start locks. This option was developed in response to requests received from several seaplane operators.  Start locks prevent the blades from entering feathered condition after shut down. On start up, this feature allows for the elimination of thrust and any unwanted aircraft movement ... which is particularly desirable and helpful for aircraft operating on floats.  This is the only propeller available for the Caravan with factory installed start locks.