Greg, what you have sounds very similar to the problem we rectified on my friend's h36, which also has the springless tailwheel fork.
It has been a couple years and this greybeard's memory is flawed, but here is what I recall: What I found was that the tailwheel fork's axle (vertical, if that term is valid), was misshapen rather than round, and at its base, where it is welded into a larger tube that is a component of the fork, there was some wear. The wear meant that that edge was not perfectly perpendicular to the axle axis, but was in a plane a degree or two off. Most landings could shake you teeth out. We tried various tire pressures, etc. If it has ever been disassembled there is a chance that all the bushings and spacers were not reinstalled in proper sequence Michael On Jul 26, 2017 2:51 PM, "Greg Wilson" <[email protected]> wrote: > I haven't found propwash to be a problem but tailwheel shimmy is something > my H36 suffers from. I've tightened the tail wheel steering & rudder cables > as much as possible but is hasn't helped much. > > Mine is "A" version without tailwheel shock absorbers. I generally land on > grass & keep taxi speed down to avoid the shimmy. Not only uncomfortable > but also chews out tailwheels fast. > > Anyone have a solution? > > Thanks, > > Greg. > > > Greg Wilson > > > > > ---- On Wed, 26 Jul 2017 22:38:12 +1000 Michael Stockhill<[email protected]> > wrote ---- > > Thanks, Tom and Laurie, > > I live in Polson, Montana. I did fly another H36 and don't recall it > having that tendency, however it had its own problems, being very tail > heavy and with a tailwheel fork issue of its own that caused it to set up > an oscillation that would shake your teeth out. I was able to sort that out > for the owner. > > You have given me lots of ideas for some trouble shooting. It is > refreshing to know that this tendency may not be typical of the breed. > > M > > On Jul 26, 2017 1:00 AM, "Laurie Hoffman via dog" < > [email protected]> wrote: > > Thanks Tom, > I was thinking something along these lines. An issue between rudder and > tailwheel interplay perhaps. I know of instances of steering/rudder cables > being too tight that have caused Dimona operators over controlling problems > during the ground run. The comment of the previous owner of Michael's > aircraft and the faulty tailwheel repair seems to confirm the possibility. > I'm no engineer though and Rob, Nigel, Macca and others would know best. > I don't have the wide T/W experience that you have Michael, about 1000hrs > in SuperCubs, a few in Pawnees, Callair and some several hundreds in TMGs. > I've flown quite a few TMG types and I have to say that after something > like 15 years of operating, our Dimona is an absolute delight both in the > air and on the ground. > The other owners and myself have taken off and landed in what on occasions > were horrendous cross wind conditions and the Dimona has handled them all > wonderfully despite not having differential braking. > If possible i would strongly recommend that you fly in another H36 to see > if there is any difference to yours. Just remind me where you are located > pls. > I don't believe asymmetric blade effect to be of any real consequence with > the L2000 and doesn't appear to be noticeable with the L2400. > Compared with the other aircraft that you have flown the Dimona certainly > does need sensitive control input. Just a thought, but after your extensive > experience with US clockwise rotating engines and even though you are aware > of the difference, any chance that you may still be unconsciously applying > right rudder during rotation? Also wondering if you have any gliding > experience in FRP aircraft Michael with which you can compare the H36. > Best Regards > Laurie > > > > > > > ------------------------------ > On Wednesday, July 26, 2017, 12:17:05 PM GMT+10, <[email protected]> > wrote: > > > > > Dear all, > > My dimona S.n. 3506 had developed ovalized bolt holes on the tailwheel > steering horn over time (circled green in attached drawing from H36 parts > manual). Although I had previously adjusted the turnbuckles to align > the rudder and tailwheel, a subsequent off center touchdown would misalign > the rudder and wheel – resulting in a startling condition in which > straight rudder input yielded a strong turning output, ground loop imminent. > > The cause of the problem became apparent when I held the rudder firmly > while twisting the tailwheel – three degrees of play was then evident. > Disassembly of the tailwheel drive horn revealed the wear on the horn tube > where it is fixed to the tailwheel shaft with two M10 bolts. Repair was > accomplished by slightly reaming the oval holes until roundness was > restored, and then bushing the M10 bolts for a tight fit – no play even > before tightening the bolts. > > I now include visual tailwheel udder alignment check as part of my > positive control check before flight..even a little misalignment results in > nasty directional behavior right after the wheels leave the ground and > right after they touch down. > > Cheers, > > Tom > > > Sent from Windows Mail > > *From:* Michael Stockhill <[email protected]> > *Sent:* Tuesday, July 25, 2017 8:40 PM > *To:* [email protected], Laurie Hoffman <[email protected]> > > Thanks Laurie and Ian. > > I've owned my Dimona 16 years. I have about a thousand hours in > taildraggers up to a DC-3, owned a Cessna 180, and flew a dehavilland > Beaver for a few seasons before moving onto other things. I have flown > many different tailwheel types and must say that my Dimona's ground > handling is the most sensitive (to the point of occasionally being > seriously uncomfortable) of anything I recall having flown. (When I asked > the previous owner about crossword handling, he said to just go someplace > else.) > > There were at least a couple instances where I had PIO on the rudders > during landing before I determined that the tailwheel fork had been > repaired with zero degrees castor or rake. It was very squirrelly and easy > to over control on the ground before I reworked the tailwheel fork. That > made it much better, but it has always wanted to head for the weeds (to the > right) as the tail comes up for takeoff. (Perhaps when the tailwheel leaves > the surface.) > > Much of the time I attributed this to habitual taildragger habit patterns > of using right rudder during takeoff to compensate for P factor and > gyroscopic effects rather than left rudder on the Dimona. > > Inflight handling, trim, and rigging are fine, other than pretty heavy > ailerons in powered cruise flight. > > Although the book suggests a three point takeoff, I have always raised the > tail at thirty knots or so (I have never really noted that speed as it is > only when the airplane is ready, so don't hold me to that number). Wings > are level with no aileron input to cause adverse yaw, but there is a > significant yaw excursion. > > I seem pretty much used to this now, but have been working with a friend > so he can fly my bird. He was a Naval aviator--a Top Gun spin instructor > in F-18s etc. After a few takeoffs threatening a visit with the weeds he > said he's never flown anything before that he couldn't comfortably take > off. I have offered to come up with a way of providing him with a cat shot! > > This doesn't seem normal. It is like there is quarter right rudder as the > tailwheel leaves the ground, so we have lots of fun overcorrecting. > > I really want to revisit neutral rudder and tailwheel to see if there is > any deflection, but last time I looked I couldn't see anything out of the > ordinary. I will get into the service manual soon (after an engine repair > on my PIK-20E, with is another eventful story) and look into rigging. > > So anyway, what do you folks experience? This is way more than P factor. > It is always a challenge to stay anywhere near the runway centerline on > takeoff roll. I tend to let it find a line it likes rather than risk > overcontolling. None of this seems normal for an aircraft with a long tail > arm, although the maingear seems quite a bit forward of most designs and > configurations. > > Cheers, > > Michael > > On Jul 25, 2017 4:48 PM, "Laurie Hoffman via dog" < > [email protected]> wrote: > > I get the impression that Michael experiences the aircraft pulling to the > right on most/all of his take offs on rotation? > > Cross winds would explain only some of these. I can't recall ever noticing > it Michael. Is it yawing only or is there some initial roll there too? > > If you simulate the low speed flight in the air does that reproduce it? > Possibly a rigging or control deflection issue. > > Best Regards > Laurie > > > > > > > ------------------------------ > On Tuesday, July 25, 2017, 10:33:18 PM GMT+10, Ian Mc Phee < > [email protected]> wrote: > > > Yep RHS x winds are always an issue. Have a look at the bight of prop and > upward going prop and downward going prop. Big difference > > Ian McPhee > 0428847642 > Box 657 Byron Bay NSW 2481 > > On 25 Jul 2017 10:03 am, "Michael Stockhill" <[email protected]> wrote: > > Have any Dimona operators found that their bird diverges to the right when > rotating for takeoff? Mine consistently does that as the tailwheel lifts > off. After 400 or so flights I think I am past adding right rudder for a > prop that turns contrary to all the taildraggers I have flown. > > Michael Stockhill > Polson MT > > On Jul 22, 2017 3:23 PM, "Laurie Hoffman via dog" < > [email protected]> wrote: > > Rob you forgot to mention that on two of those occasions when we had prop > work done, that there were other faults also. > The blades looked like they had been refinished by someone who had never > spray painted before. At least once there was an issue with seal > installation with grease being sprayed everywhere on use. > Laurie > > Sent from Yahoo7 Mail on Android > <https://overview.mail.yahoo.com/mobile/?.src=Android> > > On Sun, 23 Jul, 2017 at 6:16 am, Ian Williams > <[email protected]> wrote: > Hi Rob, > Can you explain the difference in TBO between the BT and T blades ? I > thought both were the same. > Best regards > Ian Williams > > Sent from my iPad > > On 22/07/2017, at 7:51 PM, Rob Thompson <[email protected]> wrote: > > I just heard that GFA has adopted the CASA rules on overhauling > propellers. See http://services.casa.gov.au/airworth/airwd/ADfiles/ > equip/prop/PROP-001.pdf > > This means that as soon as it is documented in the system there is no > longer a calendar time for overhauls. > > Ian McPhee has been dealing with Prop Care (www.propcare.com.au) in > Brisbane for Hoffman overhauls and hopefully they will be soon doing work > on Hoffman props. > > We are continuing to have a nightmare run with Eric at Australian Air > Props at Bankstown. 3 times in the past 2 years our prop has come back to > us with problems. Once *WAY* out of balance then next time set much too > coarse and only pulling 2000 at full power. Then recently he sent it back > to us with the counterweights set incorrectly and the rpm was fluctuating > on run up and early take off roll. > > Add to that he charges a fortune because he knows that the only other > option in Australia is to send the props to Germany. Up near $4000 now for > about 10-15 hours work. > > Fingers crossed that the Brisbane mob will be able to do them. > > Rob Thompson > 0429 493 828 > > > > > > ------------------------------ > *From:* [email protected] <[email protected]> on behalf > of Michael Stockhill <[email protected]> > *Sent:* Monday, 17 July 2017 4:23 AM > *To:* [email protected]; Laurie Hoffman > *Subject:* Re: [DOG mailing list] H36 Ignition Switch (and brakes) > > For what it is worth, the mag switches on my Aztec with similar magnetos > are rated at 6 amps 125V a.c./dc. The p lead grounds the primary coil. I > found one source that says the primary coil puts out about 150 volts. The > secondary coil puts out 10-15000 Volts. 40 amp or even 20 amp rated switch > looks like overkill for whatever reason. Maybe consevative because we only > get one of them. > > Michael > > On Jul 15, 2017 1:29 AM, "Laurie Hoffman via dog" < > [email protected]> wrote: > > Hi Tom and Mike, > > Rob and I have the wreck of an H36 from which we have salvaged many parts > for our functioning H36, especially the L2400 which we had top overhauled. > > Tom, I gritted my teeth and dived back into the wreck to recover the > ignition switch and a panel switch. The wreck is already well dismantled > however I still had a cow of a job getting access to the switches and > removing these. I dread to think how much time it would take to install a > new switch in the original position in a complete panel. My strong > recommendation is that if you have an ignition switch failure seriously > consider installing a new switch in another location on the panel, simply > reroute the wiring from the old to the new and then cover up the old switch > and placard the new. > > Although psychically the switch toggles and bodies appear the same, the > switches have a very different rating. The panel switch is rated 15A while > the ignition switch is rated 40A! > > The link that you posted to a new switch I just noticed is only rated 20A. > Maybe something like this one Tom.... > Longacre 45423 40 Amp Weatherproof Toggle switch #1731 | eBay > <http://www.ebay.com.au/itm/Longacre-45423-40-Amp-Weatherproof-Toggle-switch-1731-/272686767789?epid=708201179&hash=item3f7d65dead:g:4QcAAOSw~FJZJvde> > > $ 22.95 > Longacre 45423 40 Amp Weatherproof Toggle switch #1731 | eBay > Longacre 45423 40 Amp Weatherproof Toggle switch #1731 in | eBay! > > <http://www.ebay.com.au/itm/Longacre-45423-40-Amp-Weatherproof-Toggle-switch-1731-/272686767789?epid=708201179&hash=item3f7d65dead:g:4QcAAOSw~FJZJvde> > > > In Oz I have found Narva (driving light manufacturers) switches which look > suitable. Heavy duty and this one rated at 50A for 12v. > > Heavy Duty - Products - Narva > <http://www.narva.com.au/products/browse/heavy-duty-2> > > Heavy Duty - Products - Narva > <http://www.narva.com.au/products/browse/heavy-duty-2> > > > The wreck is a Mk2 by the way while our operational H36 is a Mk1 so if > anyone needs a good Mk2 wing or two, let us know! > > > > Re hydraulic fluid, we use only OM16 which I gather is equivalent to 5606. > > Best Regards > Laurie > > > > > ------------------------------ > *From:* Michael Stockhill <[email protected]> > *To:* [email protected] > *Sent:* Saturday, 15 July 2017, 10:13 > *Subject:* Re: [DOG mailing list] H36 Ignition Switch (and brakes) > > Hi Tom et al > > I think I found that the MS O rings are okay. Mine were fine through two > rebuilds (preventative maintenance each time I put on new tires) over 16 > years. > > Mike > > > On Jul 14, 2017 10:01 AM, "Tom Preisser" <[email protected]> wrote: > > Hi Laurie, > > I have what I believe to be an ignition switch in my spares. Can't be > positive without digging behind the panel to look at my installed switch, > but you can check your removed switch against it. The spec is MS 35058-22 > http://www.bandc.aero/ > toggleswitch-MS35058-22.aspx > <http://www.bandc.aero/toggleswitch-MS35058-22.aspx> > > And I think it could be a different spec to the other fuel pump, etc > switches (beefier), given that it has a separate entry than the 15A > switches in the old H36 parts manual (with part numbers no longer valid for > Diamond)... > > BTW on brakes (and thanks Mike for your advice)... just now installing a > new caliper piston which makes the O ring fit much better in the > cylinder (seems I had to take off too much corroded material from the > groove of the original installed one, so it no longer sealed tightly)... > > For those of you running DOT3 fluid, I have obtained some EPDM O-rings to > use rather than the BNR (nitrile) MS-28775-218 O-rings supplied to me by > Diamond (which they may have sent probably because the HK36 and DA20 use > 5606 aviation brake fluid). See this RAS thread for the details on why BNR > is not suitable for DOT3... > https://groups.google.com/ forum/#!topic/rec.aviation. soaring/4MiwHrkryFg > <https://groups.google.com/forum/#%21topic/rec.aviation.soaring/4MiwHrkryFg> > > And I talked to a lady who has worked at Cleveland Brakes for decades, and > she gasped!! when I said that Hoffmann used DOT3. She says Cleveland only > recommends aviation brake fluid - but I'm sticking with DOT3 as per the US > type certificate! > > Cheers, > > Tom > > > On Thu, Jul 13, 2017 at 7:26 PM, Laurie Hoffman via dog < > [email protected]> wrote: > > Hi All, > > After extensive investigation into intermittent electrical problems > eventually developing into a situation where the motor had to be shut down > in flight due to rough running, it appears that the culprit is the ignition > switch. > > Physically, the switch appears identical to the other original panel > toggle switches operating fuel pump, avionics, strobe etc. > > Does anyone know if they are the same switch and also is there anyone out > there in DOG land who might have specs for the switches? > > Best Regards > Laurie > > > > > > ------------------------------ > *From:* Greg Wilson <[email protected]> > *To:* [email protected] > *Sent:* Sunday, 18 June 2017, 8:10 > *Subject:* [DOG mailing list] Easy fit ADSB > > These are a very easy install and cheap too. > > https://www.recreationalflying.com/threads/wow-these-are-good- > looking-gadjets.161803/ > > > Greg Wilson > > > > > > > > > > ------------------------------ ------------------------------ --------- > You are subscribed to the Dimona Owners Group mailing list. > To unsubscribe, send email to: dog-unsubscribe@lists. riverland.net.au > <[email protected]> > > > > > > --------------------------------------------------------------------- > You are subscribed to the Dimona Owners Group mailing list. > To unsubscribe, send email to: [email protected] > >
