Horizontal Stabilizer

[JR_T]

In a genuine effort to minimize as much emotion as possible from the issue of a horizontal stabilizer on an RAF2000, let’s stipulate a decision to install a horizontal stabilizer on an RAF2000 that does not have a stabilator or lowered keel. Let’s NOT revisit how we arrived at the decision, but rather layout the technical case for the following:
1. What is the optimum size / aerodynamic shape? Why? Winglets or not?
2. What is the correct angle of incidence? As measured how / where?
3. Where and how should it be mounted?
4. Does a horizontal stabilizer currently exist that satisfies the criteria in 1 and 2 above?
5. If so, where can it be purchased?
6. Other salient issues?

I think it could be quite constructive to listen to the technical rationale, including various alternatives and the tradeoffs associated with those alternatives.

Looking forward to an interesting and enjoyable dialog.

- JR

[gyromike]

Good start Jerry.

But I think the first things that need to be nailed down is:

How much thrust is the prop generating?
What is the offset between thrustline and CG?

I have heard ~10 inches of offset, and thrust runs from ~500 lbs. on up with the modified EJ22's and EJ25's.

Using those numbers we get 416 lb.ft. of nosedown torque that needs to be compensated for. Since there are some with more powerful engines, we could consider 416 lb.ft. to be on the low side. Jonathan Weis's EJ22 pulled 700 lbs. of thrust! With a 10" offset that's 581 lb.ft. or torque.

Might as well split the difference and call it 500 lb.ft.

Now we'll need a moment arm from CG to 25% chord of the stabilizer, but I don't have a spare RAF handy to take any measurements.

Doug Riley took measurement of some h-stabs, but I don't recall what he came up with. Maybe he'll chime in.

[GyroRon]

JR, this looked like the best possible way to easily mount a stab to the RAF. This is Pat McNears ship, Stan Foster has Pat's phone number and could put you in touch with him if you wanted to call Pat about the angle of incidence and how he relocated the tailwheel.

Mounting the stab on the extension behind the rudder gives the stab a longer momment arm, making it more powerful, more stable.....


This stab was made by Don Parham, but he is out of the stab making business. It was made out of fiberglass.

You can buy a identical stab as Pats, but made out of carbon Fiber / Kevlar, from Aircommand international. It is somewhat pricey, but it is one of the best on the market.

The winglets on the stab help to stabilize the gyro in yaw, making for far less work on the rudder pedals to keep cordinated flight.

[Aviomania]

JR.

Ron?s picks show a good sized stab. Installing the stab so far back increases the moment arm, but it will only work at high airspeeds since it is located outside the prop wash. At very low airspeeds the stab will be ineffective to counter react torque the HTL of the RAF. Another problem of that configuration is that the stab can be easily damaged during landing ( or takeoff ) especially if the gyro is banked for any reason during touchdown (or liftoff).

Ideally the stab (or at least a big part of it) should be placed in the prop wash so that as soon as you apply power the stab will "fly" at hi airspeed regardless of the gyro?s actual airspeed.
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[StanFoster]

Pat Mcnears stab is the same one I had on my RAF. Pats of course is extended back...if I remember right...20 inches. Anyway...Pat is running around 200 horses and that machine flies nice. I have ridden in it and what a nice flying machine. I cant wait to ride in it again at Bensen days. Ol Pat already has my seat saved.:whoo:


Stan

[StanFoster]

JR: By the way....I love that paint scheme on your RAF in your avatar. That really looks sharp.


Stan

[Ga6riel]

good plan

you absolutely need a moment arm worked out
the notion of lengthening is a good one but, theres a but
you need to include how thats done,
merely lengthening should be out, new tail boom is the go

you also need to nail down the thrust
and the offset of thrust to CG

good luck, great plan

[C. Beaty]

Pat sawed out strips along the centerline of an aluminum tube and then welded it back together, creating a tube that would telescope inside of the standard RAF keel tube for his tail mounting extension. My recollection is that he used 2 x 2 square tube, converting it to 1¾” x 2” tube.

Using a wire feed welder will only anneal the material immediately adjacent to the weld, leaving the critical corners at normal strength.

[Ga6riel]

not sure i totally like the idea of that
i understand the utility of it can be useful
but, it would be difficult to be insure the weld totally penetrated
the inside being inaccessible, even to inspect

not only that, the tube size goes down, not up

[barnstorm2]

............will only work at high airspeeds since it is located outside the prop wash. At very low airspeeds the stab will be ineffective to counter react torque the HTL of the RAF. Another problem of that configuration is that the stab can be easily damaged during landing ( or takeoff ) especially if the gyro is banked for any reason during touchdown (or liftoff).........Ideally the stab (or at least a big part of it) should be placed in the prop wash so that as soon as you apply power the stab will "fly" at hi airspeed regardless of the gyro’s actual airspeed.

Aviomania,

I used that same stab on my AirCommand SxS.

I agree that a HS in the prop-stream is effective at any airspeed as long as the prop is generating force.

I am re-building the Air Command and placing the new HS in the prop-stream for that reason and because I felt that the landing gear was placing the HS in 'dirty air'.

However, I would like to say that although it looks close to the ground I would have to disagree that it would be a problem for landing. I landed and taxied in many a rough grass strip and I never had any problems with it. If you land at such an angle that you damage the HS you must be landing at such a screwed up attitude you would have to expect to damage a few things not just the HS. IMHO.

JR_T,

Excellent idea for a thread. Thank you.

[Doug Riley]

Mike's right. The first step is to measure the PPO moment. With most gyro props, static thrust is probably maximum thrust. Therefore, you can start with measured static thrust.

Here's a possible approach to sizing a HS to eliminate PPO moment. This is experimental, folks. Use at your own risk. It's YOUR life you are putting on the line.

__________________________________

You must know the distance (vertically) between the prop thrustline and the CG. You can take the numbers people toss around for the RAF (10, 12, 14 inches) or measure yourself. I'd do the latter. Thrust x height of thrustline above CG is PPO moment.

Next you must know the lever arm. It's the distance from the CG back to the 1/4 chord of your HS. (1/4 chord is a line 1/4 of the way back from the leading edge). I think it's around 7 feet for an unmodified RAF and a couple feet more for Pat's "stinger" that Chuck mentioned.

Next you must determine the speed and extent of the propwash. Chain the machine down safely. Run it up to full throttle. Wear earplugs, goggles and protective clothing. Poke an airspeed indicator pitot around in the propwash in the space where you propose to put your HS. Map out the speed of the wash at various points on your imaginary HS. Develop the best average you can of the airspeed.

I have posted a chart of lift-per-square-foot for HS's at various speeds and incidences here half a dozen times. Maybe Mike can post a link for those who refuse to search for it.

The math is just this:

Divide the PPO moment by the length of your tail lever arm. This number is the pounds of down-lift you need at WOT.

Use the chart and your known average propwash speed to pick a HS size and incidence. Keep the incidence low -- 2-4 degrees for an airfoil-shaped HS. The HS should make slightly more down-lift than is need to counter the PPO moment. I'd over-compensate by 10%-ish.

Verify that your tail structure (and stinger, if any) can carry the down-load you're going to put on it, with strength to spare. Get a book or an engineer if you don't know how to figure the strength of a beam.

Hang-test the gyro with the HS installed. It should hang at about 11 deg. nose-down on the keel. You may have to move the rotor head back a ways; don't fail to do this. Do not use a hang spec of less than 10 degrees or your gyro will be tail-heavy.

Test-fly carefully, and run the tests that Greg Gremminger has repeatedly described. Adjust the HS incidence so that airspeed changes with throttle change are within the range the tests specify (10%, I think).

[gyromike]

Here's a link to the chart Doug had posted.
The link will take you to thepost which has instructions on how to use the chart:

http://www.rotaryforum.com/forum/showpost.php?p=156341&postcount=13

[Aviomania]

Aviomania,


However, I would like to say that although it looks close to the ground I would have to disagree that it would be a problem for landing. I landed and taxied in many a rough grass strip and I never had any problems with it. If you land at such an angle that you damage the HS you must be landing at such a screwed up attitude you would have to expect to damage a few things not just the HS. IMHO.

JR_T,

Excellent idea for a thread. Thank you.

Barnstorm.
From what i can see on the pictures of the raf, the tail wheel is in front of the stab. On the contrary the tail wheel of your aircommand is behind it. As you can see on the simple sketch i am attaching the ground clearance on you stab tips ( at trailing edge) will be about 4-6 in. even if you land at 10 deg nose up. On the raf the clearance will be maybe 2 in. if it banks at 5 deg they will touch. I have seen pilots landing in those attitudes some times. Then again the assumptions are based on what i can see on the Pics.

i have build several similar stabs for aircomands and i am using some dihedral so that it will have better ground clearance. If you are interested to see how they look like go to http://www.rotaryforum.com/forum/showthread.php?t=11251&page=2.

The best option is as you are planning to rebuild your Aircommand. No dihedral stab in the prop wash. I wish you success in doing it.
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[GyroRon]

Nicolas, on the RAF that I posted pictures of, his tailwheel is much bigger than what you would see on a typical aircommand type gyro. Also it is mounted below the keel several inches and not onto the keel as many gyros mount them.

I have seen this RAF fly and seen it take off and land on uneven strips, and land sideways, and the stab still has plenty of clearance.

You could still extend the keel past the rudder, and for clearance you could mount the stab on top of the extension, or even on a raised extension off the lengthened extension

[barnstorm2]

Ahhh.

I see what you mean. I did not realize the tail wheel was not at the end of the keel.

I see what you mean and I agree.

I like the V HStab in the pictures of your AirCommand.

I still don't think you would be having the problem illistrated in #3.

The graphic does not show the tail wheel. If the tailwheel is in the same postition as #2 and #1 well then I guess it might be a problem. Even so if you imagine the attidtude of the rest of the craft you are making a landing on one mail wheel and are looking to bend up more then the HStab.

If the tailwheel is at the end of the keel and you are scraping the HStab you are dam lucky you are only scraped the HStab!

If you want to be able to make that kind of landing without doing damage in my opinion you should build a Monarch with the G-Force gear..... ;)

[Aviomania]

Nicolas, on the RAF that I posted pictures of, his tailwheel is much bigger than what you would see on a typical aircommand type gyro. Also it is mounted below the keel several inches and not onto the keel as many gyros mount them.

I have seen this RAF fly and seen it take off and land on uneven strips, and land sideways, and the stab still has plenty of clearance.

You could still extend the keel past the rudder, and for clearance you could mount the stab on top of the extension, or even on a raised extension off the lengthened extension

.Yes Ron,
It can land with out problems in runways and grass strips and it will improve the raf. If you try to land thought in some of the places we have to land here in Cyprus.....then it is another story!!! We must have grater clearance.

Anyway I am just making suggestions on were is best to mount the stab and not to criticize. This threat is about were is the best position for an HS and i simply stated the negatives of such installation.
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[GyroRon]

It is just better to mount the stab as far back as possible, it makes it more powerful. Doing it the way it is shown on the black RAF in my pictures is the cheapest and easiest way to do it.

Hey Steve, look... it is a miracle!..... a RAF thread with no negative comments!!! See they aren't ALL the same ole same ole! :)

[cgmg]

One additional comment on Pat's setup.

His tailwheel is mounted in the original location on the keel, but offset to the side of the keel. This places the HS much closer to the ground than the majority of other McNear conversions I've seen done since Pat's.

In all of the pictures I remember seeing of others who have done the 20" extension, they have also moved the tailwheel back to the end of the keel. This would raise the ground clearance compared to Pat's setup, in my estimation, from 2-3 more inches.

Mark Knight has finished my keel extension parts, so once I mount the extension, I'll be able to let you know what the actual ground clearance is.

[Steve Osborne]

It is just better to mount the stab as far back as possible, it makes it more powerful. Doing it the way it is shown on the black RAF in my pictures is the cheapest and easiest way to do it.

Hey Steve, look... it is a miracle!..... a RAF thread with no negative comments!!! See they aren't ALL the same ole same ole! :)

Yes Ron, it is. Would be nice if it stays this way. I am not sure if Pats is the easiest way. This one only takes about 1/2 hr to install. Might be less expensive though, mine was a little pricey around $1000.00. I can not say further back is necessary with this Stab, since it has passed the stability tests solo. Still waiting for a nice day to check at max gross. I will be posting the results then.... Wait.... I do not want to give anyone the wrong idea, so I am not saying it would not be better to move it back, Just may not be necessary.

[JR_T]

Hey Steve, look... it is a miracle!..... a RAF thread with no negative comments!!! See they aren't ALL the same ole same ole! :)



That's been my hope since my first posting on this forum.

Also value and appreciate the technical responses to my h/s questions.

THANKS!

- Jerry

[Doug Riley]

There are at least two more advantages to a longer tail tube.

First, the damping power (added dynamic stability) of a HS increases as the square of the length of the tube. Long-coupled aircraft handle nicer than short-coupled ones, even if neither one is truly statically UNstable.

Second, the performance "hit" that you take for a complete balancing-out of PPO torque is less with a longer tail. This "hit" is caused by down-load; the rotor feels down-load as just extra weight. If you use a long lever arm, you can have fewer pounds of down-load, hence fewer pounds of phantom weight for the rotor to overcome.

Example: Aa typical RAF 200 has about 600 foot-lb. of PPO torque at WOT. To cancel out this torque with a HS on a 6-foot lever arm requires 100 lb. of down-load. Go to a ten-foot arm and the down-load is 60 lb. 15-ft. tail means 40 lb., etc.

This is why tractor gyros have few stability problems and pleasant handling; their frame layout provides a long tail arm for the HS to work with. It's harder to fit a long tail arm on a pusher, but, as with other things, longer is often better.

[gwilliams38]

JR:

Given your stipulation to install a HS that does not include the "Stabilator" nor a lowered keel, would you consider in this forum the possibility of the "SparrowHawk" conversion? Probably not. I was considering the latter, but am now considering the more conventional HS being discussed here.

JR-Are you considering a HS? The last I knew, you flew without one.

I am looking forward to (hopefully) some consensus and conclusions in this thread.

G. Williams

[JR_T]

My intent for stipulating a h/s was to elicit technical rationale in terms of "what" and "how" for members, given a decision on "why." In other words, I was looking for the same thing as you "... consensus and conclusions ..." based on facts and technical data. You are correct, I am quite comfortable flying my RAF in the stock configuration, but as a fellow pilot and gyro enthusiast, I am also interested and open to discussions relating to stability and various modifications to improve stability.

- Jerry

[Aussie_Paul]

You are correct, I am quite comfortable flying my RAF in the stock configuration, but as a fellow pilot and gyro enthusiast, I am also interested and open to discussions relating to stability and various modifications to improve stability.
- Jerry

Great personal attitude Jerry.

Aussie Paul. :)

[LARRYEBOYER]

As a previous owner of a RAF in the standard keel mode with the Stab shown above, I was very happy with the flying stability. Larry martin thought the design out very carefully and the issues of the RAF. The RAF needs a downward force to counter the HTL. Larry cambered the airfoil to produce a downward pull.He knew that the farther back the stab was the more effective. Larry added 10 inches of additional chord to give the effect of a stab mounted further back.He also angled the outer parts to allow for the stab to not contact the ground abd also built dyhedral into it to allow a good flair potential. Also winglets to give the RAF better directional stability especially when doors are on.I don't know what more you could ask your stab to do.
When I did my Boyer Mod on the keel, The stab became a problem in several ways. First, I had changed the keel legnth to 10 inches longer and the stab got emersed in the prop wash. That, coupled with the increased chord worked so well that the RAF wants to fly nose high in the original mast forward position. The reduced thrust line and the increased effectiveness of the stab plus weight further back are to blame. I had to move the mast back to the #2 position to get the nose to fly at a lower attack to the relative air.That created another problem. Ground handling. The nose doesn't want to stay planted on the ground when you taxi. I had to add 15 lbs of lead shot and place it in a bag up front when I fly solo. No biggie. I have to take the time to move my axel back.
Steve O and I want to produce the LM stab but also are considering a change. We want to change the winglets to 90 degree positions versus the 45 degree position as it is now. It should offer even better directional stability for the RAF with doors and also shorten the overall width.

[JR_T]

EXCELLENT post (#26), Larry! Practical, usable, actionable.

Jerry

[LARRYEBOYER]

I wanted to post a couple pictures of the LM Ultimate stab mounted on the boyer mod.The first picture showes the negative lift of the airfoil.It is flat on top and concave underneith. The second shows the wide chord. The third shows how far back the stab is from the cabin alowing for a very effective moment arm. Also with a little imagination you can see that the stab is in the bottom part of the prop blast. Also a very attractive stab that goes quit well with the vertical stab.I reshaped my vertical to fit the stab.If you look at the attatchment point in picture 2, that was about the original width of the LM "bad" stab. You can see how Larry redesigned it and added the additional chord width. This makes for lots of surface to counter the downward force of cabin and HTL.

You have to admit " a very attractive and easy conversion from some of the other proposed fixes for the high thrust line RAF."

[JR_T]

I wanted to post a couple pictures of the LM Ultimate stab mounted on the boyer mod.



Thanks for sharing the pictures! Much appreciated by all, I'm sure.

Jerry

[gwilliams38]

Hello Fellow RAF Pilots!:wave:

I'm afraid this forum had died due to the author's requirement for specific tests/measurements/results/conclusions by non-scientists. The "scientific method" can only be conducted in controlled environments with a control group and an experimental group (or subject).

His experiments have no control or experimental group. Therefore, he does not conform to the experimental method. You must do these flight tests in two aircraft of twins(@least similar structure).

JR: Get REAL. Most pilots are not physics majors. You have much expertise and experience, but I don't think you are an aeronautical engineer, are you?

Does anyone else have these thoughts? If not, I'll get lost.

I think we need real communication by experts in physics, aeronautical design, etc. Otherwise, this is just pissin' in the wind.

:violin: